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Final Screening Assessment
Petroleum Sector Stream Approach
Chemical Abstracts Service Registry Numbers
(PDF Version - 473 KB)
Table of contents
- Substance Identity
- Physical and Chemical Properties
- Releases to the Environment
- Environmental Fate
- Persistence and Bioaccumulation Potential
- Potential to Cause Ecological Harm
- Potential to Cause Harm to Human Health
The Ministers of the Environment and of Health have conducted a screening assessment of the following industry-restricted gas oils:
|CAS RN[a]||DSL[b] name|
|64741-59-9||Distillates (petroleum), light catalytic cracked|
|64741-82-8||Distillates (petroleum), light thermal cracked|
[a] The Chemical Abstracts Service Registry Number (CAS RN) is the property of the American Chemical Society, and any use or redistribution, except as required in supporting regulatory requirements and/or for reports to the government when the information and the reports are required by law or administrative policy, is not permitted without the prior written permission of the American Chemical Society.
[b] DSL, Domestic Substances List
These substances were identified as high priorities for action during the categorization of substances on the Domestic Substances List (DSL), as they were determined to present greatest potential for exposure of individuals in Canada, and were considered to present a high hazard to human health. These substances met the ecological categorization criteria for persistence or bioaccumulation potential and inherent toxicity to aquatic organisms. These substances were included in the Petroleum Sector Stream Approach (PSSA) because they are related to the petroleum sector and are considered to be of Unknown or Variable composition, Complex reaction products or Biological materials (UVCBs).
These gas oils are a group of complex combinations of petroleum hydrocarbons that serve as blending stocks in the production of fuels that are used in diesel engines and for both industrial and domestic heating. Some of the blended products may also be used as solvents. The composition and physical-chemical properties of gas oils vary with the sources of the crude oil or bitumen and the processing steps involved. Chemical Abstracts Service Registry Number (CAS RN) 64741-59-9 is a light, catalytically cracked petroleum distillate with a typical boiling point range of 179–382°C and is a complex combination of aromatic and aliphatic hydrocarbons, mainly in the carbon range of C9–C25. CAS RN 64741-82-8 is a complex combination of aromatic, aliphatic and cycloalkane hydrocarbons, mainly in the carbon range of C10–C22, with a typical boiling point range from 160–370°C. In order to predict the overall behaviour of these complex substances for the purposes of assessing the potential for ecological effects, representative structures have been selected from each chemical class in the substances.
Both substances considered in this screening assessment have been identified as industry restricted (i.e., they are a subset of gas oils that may leave a petroleum-sector facility and may be transported to other industrial facilities). According to information submitted under section 71 of the Canadian Environmental Protection Act, 1999 (CEPA 1999), and other sources of information, these gas oils are transported from petroleum facilities to other industrial facilities by ship and by truck; therefore, exposure of the environment is possible.
Based on comparison of levels expected to cause harm to organisms with estimated exposure levels and other information, these gas oils have a low risk of harm to aquatic life due to spills in the relatively confined waters around a loading wharf. The estimated frequency of spills of sufficient volume to be of concern to the environment during ship loading is less than 1 incident per year; for truck loading, close to zero incidents of concern per year are expected, given the low volumes transported.
Based on the information presented in this screening assessment on the frequency and magnitude of spills, there is low risk of harm to organisms or the broader integrity of the environment from these substances. It is concluded that the industry-restricted gas oils (CAS RN 64741-59-9 and 64741-82-8) do not meet the criteria under paragraphs 64(a) or 64(b) of the Canadian Environmental Protection Act, 1999 (CEPA 1999) as they are not entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity or that constitute or may constitute a danger to the environment on which life depends.
A critical effect for the initial categorization of industry-restricted gas oil substances was carcinogenicity, based primarily on classifications by international agencies. Several cancer studies conducted in laboratory animals resulted in the development of skin tumours following repeated dermal application of CAS RN 64741-59-9. Industry-restricted gas oils demonstrated genotoxicity in in vivo and in vitro assays but do not appear to affect reproduction or development in laboratory animals when applied dermally. There are no carcinogenicity studies by the inhalation route to inform the carcinogenic potential of these substances in the general population following inhalation exposure. Information on additional gas oil substances in the PSSA that are similar from a processing and physical-chemical perspective was considered for characterization of human health effects.
There is potential limited general population exposure via inhalation of ambient air containing gas oil vapours due to evaporative emissions during transportation. A comparison of critical inhalation effect levels and upper-bounding estimates of exposure by the inhalation route results in margins of exposure which are considered adequate to address uncertainties related to health effects and exposure. General population exposure to industry-restricted gas oils via the dermal and oral routes is not expected; therefore, risk to human health from these routes of exposure is not expected.
Based on the information presented in this screening assessment, it is concluded that the industry-restricted gas oils (CAS RNs 64741-59-9 and 64741-82-8) do not meet the criteria under paragraph 64(c) of the Canadian Environmental Protection Act, 1999 (CEPA 1999) as they are not entering the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health.
It is therefore concluded that the industry-restricted gas oils listed under CAS RNs 64741-59-9 and 64741-82-8 do not meet any of the criteria set out in section 64 of CEPA 1999.
The Canadian Environmental Protection Act, 1999 (CEPA 1999) (Canada 1999) requires the Minister of the Environment and the Minister of Health to conduct screening assessments of substances that have met the categorization criteria set out in the Act to determine whether these substances present or may present a risk to the environment or to human health.
Based on the information obtained through the categorization process, the Ministers identified a number of substances as high priorities for action. These include substances that
- met all of the ecological categorization criteria, including persistence (P), bioaccumulation potential (B) and inherent toxicity to aquatic organisms (iT), and were believed to be in commerce in Canada; and/or
- met the categorization criteria for greatest potential for exposure (GPE) or intermediate potential for exposure (IPE) and had been identified as posing a high hazard to human health based on classifications by other national or international agencies for carcinogenicity, genotoxicity, developmental toxicity or reproductive toxicity.
A key element of the Government of Canada’s Chemicals Management Plan is the Petroleum Sector Stream Approach (PSSA), which involves the assessment of approximately 160 petroleum substances that are considered high priorities for action. These substances are primarily related to the petroleum sector and are considered to be of Unknown or Variable composition, Complex reaction products or Biological materials (UVCBs).
Screening assessments focus on information critical to determining whether a substance meets the criteria set out in section 64 of CEPA 1999. Screening assessments examine scientific information and develop conclusions by incorporating a weight-of-evidence approach and precaution.
Grouping of Petroleum Substances
The high priority petroleum substances fall into nine groups of substances based on similarities in production, toxicity and physical-chemical properties (Table A1.1 in Appendix 1). In order to conduct the screening assessments, each high priority petroleum substance was placed into one of five categories (or “streams”) depending on its production and uses in Canada:
Stream 0: substances not produced by the petroleum sector and/or not in commerce;
Stream 1: site-restricted substances, which are substances that are not expected to be transported off refinery, upgrader or natural gas processing facility sites;
Stream 2: industry-restricted substances, which are substances that may leave a petroleum sector facility and be transported to other industrial facilities (e.g., for use as a feedstock, fuel or blending component), but do not reach the public market in the form originally acquired;
Stream 3: substances that are primarily used by industries and consumers as fuels;
Stream 4: substances that may be present in products available to the consumer.
An analysis of the available data determined that 16 petroleum substances are evaluated under Stream 2, as described above. These occur within five of the nine substance groupings: heavy fuel oils, gas oils, petroleum and refinery gases, low boiling point naphthas and crude oils.
This screening assessment addresses two industry-restricted gas oil substances described under Chemical Abstracts Service Registry Numbers (CAS RNs) 64741-59-9 and 64741-82-8. These substances were identified as GPE during the categorization exercise, and were considered to present a high hazard to human health. These substances met the ecological categorization criteria for persistence or bioaccumulation potential and inherent toxicity to aquatic organisms. According to information submitted under section 71 of CEPA 1999 (Environment Canada 2008, 2009) and other sources of information, these substances can be consumed on-site or transported from petroleum facilities to other industrial facilities, but they are not sold directly to consumers.
One site-restricted gas oil was previously assessed under Stream 1, and an additional eleven gas oils are being assessed separately as they belong to Streams 3 and 4 (as described above). The health effects of the industry-restricted gas oils were assessed primarily using data specific to the two CAS RNs (64741-59-9 and 64741-82-8), but also considered health effects data on additional gas oil substances (i.e., a “pooled” approach).
Included in this screening assessment is the consideration of information on chemical properties, uses, exposure and effects, including additional information submitted under section 71 of CEPA 1999. Data relevant to the screening assessment of these substances were identified in original literature, review and assessment documents and stakeholder research reports and from recent literature searches, up to September 2011 for the environmental, human exposure and health effects sections of the document. Key studies were critically evaluated and used, when available, with modelling results to reach conclusions.
Characterization of risk to the environment involves consideration of data relevant to environmental behaviour, persistence, bioaccumulation and toxicity, combined with an estimation of exposure of potentially affected non-human organisms from the major sources of release to the environment. To predict the overall environmental behaviour and properties of complex substances such as these industry-restricted gas oils, representative structures were selected from each chemical class contained within the substances. Conclusions regarding risk to the environment are based on an estimation of environmental concentrations resulting from releases and the potential for these concentrations to have harmful effects on non-human organisms. As well, other lines of evidence including fate, temporal/spatial presence in the environment, and hazardous properties of the substance are taken into account. The ecological portion of the screening assessment summarizes the most pertinent data on environmental behaviour and effects and does not represent an exhaustive or critical review of all available data. The industry-restricted gas oils are complex and variable, and any approach or model will not fully represent the range of variables found in these substances. Environmental models and comparisons with similar petroleum substances may have assisted in the assessment.
Evaluation of risk to human health involves consideration of data relevant to estimation of exposure (non-occupational) of the general population, as well as information on health effects. Health effects were assessed using toxicological data pooled across high priority gas oil substances. Decisions for risk to human health are based on the nature of the critical effect and margins between conservative effect levels and estimates of exposure, taking into account confidence in the completeness of the identified databases on both exposure and effects, within a screening context. The screening assessment does not represent an exhaustive or critical review of all available data. Rather, it presents a summary of the critical information upon which the final conclusion is based.
This screening assessment was prepared by staff in the Existing Substances Programs at Health Canada and Environment Canada and incorporates input from other programs within these departments. The human health and ecological portions of this assessment have undergone external written peer review and consultation. Comments on the technical portions relevant to human health were received from scientific experts selected and directed by Toxicology Excellence for Risk Assessment (TERA), including Dr. Thomas Booze (California Environmental Protection Agency, Department of Toxic Substances Control), Dr. Michael Dourson (TERA), Dr. Stephen Embso-Mattingly (NewFields Environmental Forensics Practice, LLC) and Dr. Michael Jayjock (The LifeLine Group). Although external comments were taken into consideration, the final content and outcome of the screening assessment remain the responsibility of Health Canada and Environment Canada.
The critical information and considerations upon which the draft screening assessment is based are summarized below.
These gas oils are a category of petroleum substances that are used primarily in the production of fuels used in diesel engines and for both industrial and domestic heating. Some of the blended products may also be used as solvents (CONCAWE 1996). CAS RN 64741-59-9 is a complex combination of petroleum hydrocarbons that boils between 179°C and 382°C with a carbon range of C9–C25 (CONCAWE 1996; ECB 2000; API 2003a) (see Table A2.1 in Appendix 2). CAS RN 64741-59-9 is typically composed largely of aromatic compounds (60–72%), with the remainder being varying proportions of alkanes, cycloalkanes and alkenes. CAS RN 64741-82-8 consists predominantly of unsaturated hydrocarbons (aromatics) in the range of C10–C22, with a boiling point range from 160–370°C (CONCAWE 1996; Shell 2011).
These UVCB substances are complex combinations of hydrocarbon molecules that originate in nature or are the result of chemical reactions and processes that take place during the upgrading and refining process. Given their complex and variable compositions, they could not practicably be formed by simply combining individual constituents.
Physical and Chemical Properties
The composition and physical-chemical properties of gas oils vary, depending on the source of the crude oil or bitumen and the processing steps involved (CONCAWE 1996). The general physical-chemical properties of the industry-restricted gas oils are presented in Table 1.
|Boiling point (ºC)||Experimental||160–382||CONCAWE 1996; ECB 2000; |
|Density (kg/L)||Experimental||0.84–0.97||15||CONCAWE 1996|
|Vapour pressure (Pa)||Experimental||400||40||CONCAWE 1996|
|Log Kow |
|Experimental||3.9 - greater than 6.0||CONCAWE 1996|
Typically, gas oils contain C9–C25 straight and branched alkanes, cycloalkanes, aromatic hydrocarbons and mixed aromatic cycloalkanes. Those that undergo cracking processes (processes that break long-chain hydrocarbons into shorter chains), such as those in this report, generally contain some unsaturated alkene hydrocarbons (CONCAWE 1996), although the proportions of these alkenes in these particular CAS RNs typically represent less than 4% of the substances overall. As well, the boiling point range reflects the size and type of hydrocarbons in the substances.
To predict the environmental behaviour and fate of complex substances such as these industry-restricted gas oils, representative structures were selected from each chemical class contained within the substances. Twenty-seven representative structures were selected (see Table A2.2 in Appendix 2) from the database in PETROTOX (2009). In choosing representative structures, the amount of available data, boiling point ranges and carbon ranges were considered. Structures with a CAS RN were preferred. As the compositions of these gas oils are not well defined and are indeed variable, representative structures are not considered to be proportional with respect to actual concentrations in the substances. The selection process resulted in representative structures for alkanes, isoalkanes, one-ring and two-ring cycloalkanes, polycycloalkanes, cycloalkane monoaromatics and diaromatics, and one- to four-ring aromatics, ranging from C9–C20 (see Table A2.2 in Appendix 2). Physical-chemical data for each representative structure were assembled from scientific literature and from the group of environmental models included in the United States Environmental Protection Agency’s (U.S. EPA) Estimation Programs Interface Suite (EPI Suite 2008) (see Table A2.2 in Appendix 2). This process was used to enable the assessment of all gas oils (and other petroleum substances) within the context of the PSSA.
The industry-restricted gas oils considered in this screening assessment are produced in Canadian refineries and upgraders. The CAS RN descriptions (NCI 2006) and typical process flow diagrams (Hopkinson 2008) indicate the origin of these gas oils. Information submitted under section 71 of CEPA 1999, and other sources of information, indicates that the substances can be intermediate streams consumed within a facility or transported off-site (Environment Canada 2008, 2009).
CAS RN 64741-59-9 is formed from the catalytic cracking of substances from a variety of distillation and extraction (e.g., solvent deasphalting or visbreaking) processes within a refinery.
CAS RN 64741-82-8 refers to a distillate obtained from a thermal cracking unit (e.g., coking or visbreaking process) fed with vacuum distillation residues or bitumen coking and hydrocracking residues.
According to the information collected through the Notice with respect to certain high priority petroleum substances (Environment Canada 2008) and the Notice with respect to potentially industry-limited high priority petroleum substances (Environment Canada 2009) published under section 71 of CEPA 1999, as well as other sources of information, the industry-restricted gas oils considered in this screening assessment have been identified as being consumed at the facility, blended into substances leaving the site under a different CAS RN or transported to another industrial facility. Although these substances were identified by multiple use codes established during the development of the Domestic Substances List (DSL), it has been determined from information submitted under section 71 of CEPA 1999, voluntary submissions from industry, an in-depth literature review and a search of material safety data sheets that the industry-restricted gas oils identified as CAS RNs 64741-59-9 and 64741-82-8 may leave the petroleum facility and be transported to another industrial facility for use as a feedstock, but do not reach the public market in the form originally acquired.
Releases to the Environment
Potential releases of the industry-restricted gas oils include releases within facilities from activities associated with processing, as well as releases related to transportation of the substances between industrial facilities.
Due to the complex nature of the petroleum industry and transportation industry, as well as the ambiguity in the literature in the use of the terminology that is critical to the understanding of the Stream 2 PSSA assessments, it is important that the definitions specific to the assessment of the industry-restricted petroleum substances are well understood. Table 2 lists the terminology specific to the present assessment.
Table 2. Definitions of terms specific to the PSSA assessments of industry-restricted petroleum substances
- A generic term to define a leak, spill, vent or other release of a gaseous or liquid substance, including controlled release and unintentional release, as defined below, but not including catastrophic events.
- Controlled release
- Any planned release for safety, maintenance or other purposes that is considered part of routine operations and occurs under controlled conditions.
- Unintentional release
- Any unplanned release of a petroleum substance. Causes can include equipment failure, poor maintenance, lack of proper operating practices, adverse weather-related events or other unforeseen factors, but can also be a routine part of normal operations. The following two categories are included under unintentional releases: (1) unintentional leaks or spills that occur from processing, handling and transport of a petroleum substance--such leaks or spills can be reduced or controlled by the industry; and (2) accidental releases that may not be controllable by the industry. Only unintentional leaks or spills (category 1, defined above) are considered in the assessment of the potential of industry-restricted petroleum substances to cause ecological harm.
- Fugitive release
- A specific type of unintentional release. It refers to an unintentional release, which occurs under normal operating conditions, of a gaseous substance into ambient air and which may occur on a routine basis. Fugitive releases can be reduced but may not be entirely preventable due to the substance’s physical-chemical properties, equipment design and operating conditions. Evaporative emission during the transportation of petroleum substances is a fugitive release and is considered in the human exposure analysis for purposes of assessing the potential of the substance to cause harm to human health.
Potential On-site Releases
Potential releases of gas oil substances from refineries or upgraders can be characterized as either controlled or unintentional releases. Controlled releases are planned releases from pressure relief valves, venting valves and drain systems for safety purposes or maintenance. Unintentional releases are typically characterized as spills or leaks from various equipment, valves, piping or flanges. Refinery and upgrader operations are highly regulated, and regulatory requirements are established under various jurisdictions. As well, voluntary non-regulatory measures implemented by the petroleum industry are in place to manage these releases (SENES 2009).
The industry-restricted gas oils considered in this screening assessment originate from a distillation column as a distillate. Thus, the potential locations at the facility for the controlled release of these substances include relief and venting valves or drain valves on the piping or vessels where these streams are generated.
Under typical operating conditions, controlled releases of these gas oil substances would be captured in a closed system , according to defined procedures, and returned to the processing facility or to the facility’s wastewater treatment plant. In both cases, exposure of the general population or the environment to these industry-restricted gas oils is not expected.
Unintentional releases (including fugitive releases) occur from equipment (e.g., pumps, storage tanks), valves, piping, flanges, etc. during the processing and handling of petroleum substances and can be greater in situations of poor maintenance or operating practices. Regulatory and non-regulatory measures are in place to reduce these events at petroleum refineries and upgraders (see Appendix 3) (SENES 2009). Rather than being specific to one substance, these measures are developed to be more generic to limit non-routine releases of all substances in the petroleum sector.
Conclusion for Potential On-site Releases
Based on the information presented in this screening assessment and in the screening assessment of the Stream 1 (site-restricted) gas oils, exposure of the general population or the environment to the on-site releases (controlled or unintentional) of industry-restricted gas oils is not expected.
Potential Releases from Transportation
As these industry-restricted gas oils can be transported between facilities, releases may also occur during transportation. In general, the three operating procedures involved during the process of transportation of petroleum substances are loading, transit and unloading. The transportation modes identified in the information submitted under section 71 of CEPA 1999 (Environment Canada 2009) and other sources of information were ship and truck; however, the volumes transported by truck are so small as to not warrant a release estimation to soil.
The on-site handling of petroleum substances for transportation is often regulated at the federal and provincial/territorial levels through legislation covering loading and unloading (see Appendix 3).
Storage of industry-restricted gas oils may be required before they are transported off-site. However, the general population near the storage area would not be exposed to industry-restricted gas oil vapours per se, but rather a complex combination of volatile compounds from all hydrocarbon substances present in the storage area or even in the whole petroleum facility. All relevant releases from storage (e.g., leaks, spills and breathing loss [expulsion of vapour due to changes in temperature and pressure]) are similar to potential on-site releases and are not further addressed in this screening assessment.
Tanks or containers for transferring petroleum substances are typically dedicated vessels; thus, washing or cleaning is not required on a routine basis (U.S. EPA 2008; OECD 2009). As such, the exposure of the general population and the environment around cleaning facilities is expected to be negligible with respect to the industry-restricted gas oils considered in this screening assessment. Cleaning facilities require processing of grey-water to meet local and provincial release standards.
Information on transportation quantities and relevant transportation modes was collected under section 71 of CEPA 1999 (Environment Canada 2009) and from other sources of information. Ship transportation was the only relevant mode identified, as truck transport was used only for very small volumes.
Two types of releases can potentially occur during transportation and are considered in this screening assessment. These are evaporative emissions and unintentional releases (e.g., spills or leaks) during the handling and transit processes.
Evaporative emissions are similar to breathing loss of organic substances from storage tanks. The quantity lost depends on the volatility of the substances, temperature or pressure changes that occur during transportation and the air-tightness of transport vessels and settings of valves. Ambient air is the receiving medium for the evaporative emissions.
Unintentional releases of gas oil substances due to spills generally enter water or soil, depending on the modes of transportation involved. Due to the relatively low volatility of gas oil substances, as defined by their physical-chemical properties, evaporative emissions into the air from spills would be proportionally less than releases into water and/or soil.
Potential releases associated with ship transport of these gas oils were assessed through analysis of historical spill data (2000–2009) from the Environment Canada Spill Line database (Environment Canada 2011). There are no reported spills of “gas oils” in the database, but there are reported releases of diesel fuel (reported as “diesel” or “diesel fuel”), light fuel or petroleum distillate that could include spills of these industry-restricted gas oils due to their similarity. The extracted data were analyzed to remove duplicate entries, where it was a known diesel fuel or an environmental emergencies training exercise. Spills of less than 10 L were not included in release estimations due to the likelihood that these spills were related to the commercial use of diesel fuel rather than the shipment of gas oils. Spills where collisions, poor road conditions and/or adverse weather-related events were listed as a source or cause of or reason for the spills were not included in the release estimate, as they are not considered preventable with regard to loading/unloading and transport of these gas oils.
Spills data with known volumes were collected from across Canada by the Environment Canada Spill Line database between 2000 and 2009; spills of approximately 2000 litres of light oil, diesel fuel and petroleum distillates in 36 incidents to the marine areas of interest were documented (Environment Canada 2011). Many other reports in the database had no estimate of the volume released into the environment. In order to account for the underestimation of the volume released, the estimated total volume was extrapolated by assuming that the distribution of reported volumes released was representative of all releases (Table A4.1 in Appendix 4). From 2000–2009, the extrapolated total volume of spills of light oil, diesel fuel and petroleum distillates to salt water was 5200 litres from 36 spills.
The Spill Line database did not contain information on releases of light oil, diesel fuel and petroleum distillates to salt water during ship transportation for the marine areas of interest, hence releases during ship transport were not considered for a marine release scenario.
Also, since there is no distinction in the database as to whether the spills occurred during loading, transport or unloading, the average spill volume was used for the loading and unloading scenarios. In the case of ship loading and unloading, the extrapolated total volume spilled of 5168 litres/36 spills = 144 L/spill (122 kg, given an average density of 0.85 kg/L) (CONCAWE 1996) is expected in marine waters.
These numbers of diesel fuel, light oil, and petroleum distillates releases are considered to be a low estimate of actual releases, as not all provinces and territories were reporting their spills to Environment Canada for all years, and some provinces and territories have minimum reportable spill quantities (Table A4.2 in Appendix 4). However, these data would also include spills of petroleum substances other than the two CAS RNs under assessment in this report.
The majority of diesel fuel, light oil, and petroleum distillates releases to marine waters occurred from motor vehicles of unknown kind, representing 85% of the total volume spilled. Industrial plants and other watercraft accounted for the source of 9% of the volume (see Table A4.2a). Unknown spills accounted for the remaining 6% of the volume spilled. Other spill sources included marine terminals, pipelines, tank trucks, marine tankers and others.
The Environment Canada Spill Line data were also analyzed for causes of diesel fuel, light oil, and petroleum distillates spills (Table A4.2b in Appendix 4); it was found that “unknown” and “other” spills accounted for 87% of the volume released, whereas container leaks, discharges and valves accounted for the remaining 13% of the volume.
Analyzing the data on reasons for diesel fuel, light oil, and petroleum distillates spills (Table A4.2c in Appendix 4) identified that the majority of releases had “unknown” or “other” reasons accounting for 90% of spills. Human error and vandalism were responsible for 10% of the volume. Equipment and material failure, corrosion and subsidence were also reasons identified for spills, but represented a small portion of overall volume.
For purposes of assessing the potential exposure of the environment from the transportation of industry-restricted gas oils, the ecological assessment focuses on unintentional releases to water. In comparison, assessment of potential exposure of the general population from transportation of industry-restricted gas oils focuses on evaporative emissions, which occur during regular operating activities. Although spills occur during transit and in loading or unloading operations, such releases are considered to occur on a non-routine or unpredictable basis in distinct locations and are therefore not considered in the assessment of exposure of the general population.
In addition, due to the relatively low volatility of the industry-restricted gas oils (see Table 1), as well as relevant legislation and best practices currently in place for on-site handling of these industry-restricted gas oils (Appendix 3), non-occupational human exposure as a result of loading and unloading is not expected and is not considered in the human exposure assessment.
When petroleum substances are released into the environment, four major fate processes will take place, i.e., dissolution in water, volatilization, biodegradation and adsorption. These processes will cause changes in the composition of these UVCB substances. In the case of spills on land or water surfaces, photodegradation can also be significant.
The rates of dissolution in water or volatilization of individual petroleum components are retarded by the complex nature of these petroleum mixtures. The solubility and volatility of individual components in mixtures are proportional to the solubility or volatility of the components in its pure state and its concentration in the mixture. Solubility and volatility of a component decrease when the component is present in a mixture (Banerjee 1984; Potter and Simmons 1998).
Each of the fate processes affects hydrocarbon families differently. Aromatics tend to be more water soluble than aliphatics of the same carbon number, whereas aliphatics tend to be more volatile (Gustafson et al. 1997). Thus, when a petroleum mixture is released into the environment, the principal water contaminants are likely to be aromatics, while aliphatics will be the principal air contaminants (Potter and Simmons 1998). The trend in volatility by compound class is as follows: alkenes ≈ alkanes greater than aromatics ≈ cycloalkanes. The most soluble and volatile compounds have the lowest molecular weight; thus, there is a general shift to higher molecular weight compounds in residual materials.
Biodegradation is almost always operative when petroleum mixtures are released into the environment. It has been widely demonstrated that nearly all soils and sediments have populations of bacteria and other organisms capable of degrading petroleum hydrocarbons (Pancirov and Brown 1975). Two key factors that determine degradation rates are oxygen supply and molecular structure. Although degradation occurs both in the presence and absence of oxygen, degradation is more rapid under aerobic conditions. Decreasing trends in degradation rates according to structure are as follows (Potter and Simmons 1998):
- n-alkanes (especially in the C10–C25 range which are degraded readily);
- benzene, toluene, ethylbenzene and xylenes (BTEX) (when present in concentrations that are not toxic to the microorganisms);
- polynuclear (polycyclic) aromatic hydrocarbons (PAHs); and
- higher molecular weight cycloalkanes (which may degrade very slowly (Pancirov and Brown 1975)).
Level III fugacity modelling of representative structures contained in the gas oils group of substances was performed using EQC (2003) (see Table A5.1 in Appendix 5) based on physical-chemical properties given in Table A2.2 (Appendix 2).
If released solely to air, the majority of C9–C15 representative structures of gas oils will remain in air. Some C18–C20 components will also remain primarily in air, except alkanes, two-ring cycloalkanes, polycycloalkanes and cycloalkane monoaromatics. The low volatile C20 representative structures will partition primarily to soil and sediments.
If released solely to water, the majority of C10 representative structures are expected to remain mostly in water, with minor amounts evaporating. The C10 n-alkanes will partition evenly between water and sediments (Table A5.1 in Appendix 5). The majority of the C15–C20 representative structures are expected to partition mainly to sediments based on their higher range of log Koc values (Table A5.1 in Appendix 5). The exceptions are the C15 cycloalkane diaromatics and the two-ring and three-ring aromatics, which will partition evenly between water and sediments if released solely to water (Table A5.1 in Appendix 5). The EQC model predicts little loss from water to air despite the high Henry’s Law constants for many of the representative structures.
CAS RN 64741-59-9 is similar to diesel fuel with respect to physical-chemical properties. Fingas (2001) estimated that 60% of a diesel fuel would evaporate from water in 48 hours at 15°C, and this likely approximates the extent of evaporation of CAS RN 64741-59-9 from water.
If released to soil, all components of gas oils are expected to remain primarily in soil. Such behaviour in soil is expected due to high sorption to the point of being relatively immobile for the largest structures, based on the estimated range of log Koc values (Table A2.2 in Appendix 2). Volatilization from moist soil surfaces should be an important fate process for many components, based upon estimated Henry’s Law constant values greater than 100 Pa·m3/mol (Table A2.2 in Appendix 2); however, the results of the EQC (2003) Level III fugacity estimations indicate that this process does not readily occur for many gas oil components. This is due to the competitive processes of sorption and volatilization.
Fugacity estimations in soil do not take into account situations where large quantities of a hydrocarbon mixture enter the soil compartment. When soil organic matter and other sorption sites in soil are fully saturated, the hydrocarbons will begin to form a separate phase (a non-aqueous phase liquid or NAPL) in the soil. At concentrations below the retention capacity for the hydrocarbon in the soil (Arthurs et al. 1995), the NAPL will be immobile; this is referred to as residual NAPL (Brost and DeVaull 2000). Above the retention capacity, the NAPL becomes mobile and will move within the soil (Arthurs et al. 1995; Brost and DeVaull 2000). According to a study by Brost and DeVaull (2000), the NAPLs of fuel products in the density range of diesel fuel, such as gas oils, will become mobile in the range of 7700–34 000 mg/kg dw depending on the type of soil. Above this range, they can move through the soil due to gravity.
Persistence and Bioaccumulation
In water, hydrolysis half-lives could not be predicted for hydrocarbons with the HYDROWIN (2008) model. Alkanes, alkenes, benzenes, biphenyls, PAHs and heterocyclic PAHs are all known to be resistant to hydrolysis (Lyman et al. 1990).
Since no empirical data were available on the degradation of these gas oils, a QSAR-based weight-of-evidence approach (Environment Canada 2007) was applied using the BioHCWin (2008), BIOWIN 3, 4, 5, and 6 (2009), CATABOL (c2004–2008) and TOPKAT (2004) biodegradation models (Table A5.2 in Appendix 5).
Primary biodegradation (estimated with BIOWIN 4 and BioHCWin) is the transformation of a parent compound to an initial metabolite. Ultimate biodegradation (estimated with BIOWIN 3, 5 and 6, CATABOL and TOPKAT) is the transformation of a parent compound to carbon dioxide and water, mineral oxides of any other elements present in the test compound and new cell material (EPI Suite 2008). BioHCWin (2008) is a biodegradation model specific for petroleum hydrocarbons. Model results are in domain for all MITI-based models (BIOWIN 5 and 6). Modelled results that were out-of-domain were not considered when determining the persistence of components.
For many of the C9–C20 components, both the primary and ultimate biodegradation models agree that these compounds would degrade quickly and would not likely be persistent (Table A5.2 in Appendix 5). The following show persistence in water (half-life = 182 days) based on the Persistence and Bioaccumulation Regulations (Canada 2000): C15–C20 two-ring cycloalkanes, C14–C22 polycycloalkanes, C15–C20 cycloalkane monoaromatics, C15 two-ring aromatics, C12 cycloalkane diaromatics and C16 four ring aromatics.
Using an extrapolation ratio of 1:1:4 for a water : soil : sediment biodegradation half-life (Boethling et al. 1995), the half-life in soil for most heavy ( greater than C12) representative structures is also greater than or equal to 182 days and the half-life in sediments is greater than or equal to 365 days.
The proportion of these gas oils that would be expected to be persistent cannot be accurately determined, as compositional details on these CAS RNs are not available. The limited compositional information on these two CAS RNs indicates that aromatics can account for up to 80% by weight of CAS RN 64741-59-9 and up to 43% by weight of CAS RN 64741-82-8 (API 1987, 2003a). As well, a typical gas oil has a total cycloalkane content of 8–10%.
AOPWIN (2008) is a model that calculates atmospheric oxidation half-lives of compounds in contact with hydroxyl radicals in the troposphere under the influence of sunlight. Atmospheric oxidation rates were calculated for all of the representative structures. According to this model, the components of gas oils will degrade readily by interactions with hydroxyl radicals in air (half-lives less than 1 day) (Table A5.3 in Appendix 5).
Based on results from AOPWIN (2008), there would be a relatively rapid removal process if these gas oils are introduced into the atmosphere, with oxidation half-lives of less than 1 day. With regard to the primary and ultimate biodegradation modelling, the C15–C20 two-ring cycloalkanes, C14–C22 polycycloalkanes, C15–C20 cycloalkane monoaromatics, C15 two-ring aromatics, C12 cycloalkane diaromatics and C16 four-ring aromatics in these gas oils meet the persistence criteria in water, soil and sediment (half-life in soil and water greater than or equal to 182 days and half-life in sediment greater than or equal to 365 days). Cycloalkanes represent a relatively small fraction (8–10%) of gas oils. There is no detailed information on the specific aromatic content of these gas oils; however, CAS RN 64741-59-9 may include up to 80% aromatics. Thus, these gas oils are expected to contain an unknown proportion of components that meet the persistence criteria as defined in the Persistence and Bioaccumulation Regulations (Canada 2000).
Potential for Bioaccumulation
Bioconcentration Factors (BCF) and Bioaccumulation Factors (BAF)
Since no empirical data on the bioaccumulation of gas oils or its components were found, empirical data on the bioaccumulation of components of diesel fuel and Fuel Oil No. 2 were used in a read-across approach. A predictive approach using a bioconcentration/bioaccumulation factor (BAF) model was also applied (Arnot and Gobas 2003, 2004). According to the Persistence and Bioaccumulation Regulations (Canada 2000) a substance is bioaccumulative if its BCF or BAF is greater than or equal to 5000; however, measures of BAF are the preferred metric for assessing bioaccumulation potential of substances. This is because BCF may not adequately account for the bioaccumulation potential of substances via the diet, which predominates for substances with log Kow greater than ~4.5 (Arnot and Gobas 2003).
Neff et al. (1976) exposed clams (Rangia cuneata), oysters (Crassostrea virginica) and fish (Fundulus similus) to the water-soluble fraction of Fuel Oil No. 2 (0.41 kg/L [2 ppm] total naphthalenes) for 2 hours, followed by depuration of hydrocarbons for 366 hours. All organs examined showed rapid accumulation of naphthalenes within the 2-hour exposure period, with the gall bladder and brain of fish accumulating the highest concentrations. BAFs of naphthalenes in clams ranged from 2.3–26.7 L/kg wet weight (ww) (Table A5.4 in Appendix 5). Release of naphthalenes by fish began immediately following transfer to fresh water, reaching undetectable levels after 366 hours (~15 days).
Peterson and Kristensen (1998) exposed eggs and larvae of zebrafish (Brachydanio rerio) and larvae of cod (Gadus morhua), herring (Clupea harengus), and turbot (Scophthalmus maximus) to 14C-labeled PAHs (naphthalene and phenanthrene). The experiments were performed in a semistatic test system and steady-state was not reached during the embryonic stage except for naphthalene. High BCFs were found in all cases, indicating that bioaccumulation can occur during early life stages, as fish larvae have higher lipid contents and lower metabolic capabilities than juvenile or adult fish.
Burkhard and Lukasewycz (2000) compiled data on tissue (lake trout Salvelinus namaycush), and water and sediment concentrations of PAHs from three published works and used the data to derive BAFs. Bioaccumulation factors for PAHs in these fish were 87 and 1550 L/kg ww for phenanthreneand fluoranthene, respectively (Table A5.4 in Appendix 5). Burkhard and Lukasewycz (2000) note that there is significant uncertainty in the BAFs for phenanthrene and fluoranthene, as both chemicals were present in the tissues at concentrations just greater than the method detection limit.
Hardy et al. (1974) carried out an experiment giving cod (Gadus morhua) single doses of hexadecane (a C16 n-alkane) in the diet and tracked metabolites. Entirely unchanged hexadecane was found in the liver. Hardy et al. (1974) suggest that such findings do not support high metabolic conversion of hexadecane in the liver of cod; n-alkanes were preferentially deposited in liver over flesh of cod. However, the liver is the major site of chemical biotransformation, so higher concentrations in liver would be expected. Cravedi and Tulliez (1981) dosed rainbow trout with dodecyl cyclohexane (a C18 alkyl cycloalkane) and studied its elimination and metabolism from the fish. Approximately 75% of the dose was absorbed. A major source of unmodified substance elimination was through the gills. Considerable amounts were also metabolized to a fatty acid and distributed throughout the body and 14% was excreted in urine (Cravedi and Tulliez 1981).
Cravedi and Tulliez (1983) also studied the dietary uptake of 1% C13–C22 n-alkanes in rainbow trout for 7 months. Trout were dosed with 10 000 ppm total n-alkanes in feed, and showed preferential fixation of C13–C14 n-alkanes in the adipose tissue. The mean accumulated mass of n-alkanes was 958 ppm per fish, so that a calculated BCF (diet) was 0.1. Alkanes longer than C16 were well retained (over 60% of accumulated n-alkanes remained after 8 weeks of depuration), while short-chain ( less than C16) n-alkane concentrations decreased more rapidly (20–50% remained after 8 weeks of depuration).
Colombo et al. (2007) studied the bioaccumulation dynamics of C12–C25 n-alkanes and aliphatic unresolved complex hydrocarbons (UCM) in a detritivorous fish (Prochilodus lineatus) collected from the sewage-impacted Buenos Aires coastal area. Fish muscles contained large amounts of C12–C25 n-alkanes and aliphatic UCM, reflecting the chronic bioaccumulation of fossil fuels from sewage particulates. The hydrocarbon composition in fish muscles was enriched in C15–C17 n-alkanes relative to a fresh crude oil and settling particulates. The bioaccumulation factors plotted (BAFs: 0.4–6.4 dry weight or 0.07–0.94 lipid-organic carbon) against Kow showed a parabolic pattern maximizing at C14–C18.
McCain et al. (1978) reported that 1- and 2-methylnaphthalene and 1,2,3,4-tetramethylbenzene were accumulated to a greater extent than other oil components in English sole (Parophrys vetulus) from oil-contaminated sediments. Tissue burdens of hydrocarbons decreased with increasing exposure time, such that after 27 days of exposure, only the liver had a detectable hydrocarbon burden. McCain et al. (1978) suggested that induction of the aryl hydrocarbon hydroxylase (AHH) enzyme system eventually resulted in hydrocarbon removal.
Weinstein and Oris (1999) found that 4-day-old fathead minnows (Pimephales promelas) bioconcentrated fluoranthene (BCF 9054 L/kg) with only 24 hours exposure and steady-state was reached. They observed that the age of the fish likely impacted the ability to depurate fluoranthene and that older, more mature fish would be unlikely to bioacumulate PAHs. Weinstein and Oris (1999) used a static renewal system which is less preferable to flow-through designs where consistent exposures can be maintained, thus this study was considered to be of low reliability. However, the study does show that bioaccumulation is important for toxicity in the early life stages (Weinstein and Oris 1999). In contrast, De Maagd (1996) found a BCF of 3388 L/kg ww for fluoranthene in adult fathead minnows.
Guppies (Poecilia reticulata) bioconcentrated pyrene, with BCFs in the range of 4786–11 300 L/kg ww (depending on the type of test) after 48 hours of exposure, while lighter-weight PAHs had lower BCFs (1050–2238 L/kg ww for fluorene and 4550–7244 L/kg ww for anthracene) (De Voogt et al. 1991). For fish, only 70% of anthracene depurated within 200 hours and only 20% of fluorene was depurated within 200 hours. The BCF result for anthracene by De Voogt et al. (1991) was not considered reliable in determining the bioconcentration potential of this substance due the lack of evidence that a steady-state had been reached within the 48 hours of exposure.
Mollusc studies have typically found high potentials for the bioconcentration of PAHs. This may be caused by the relatively slow rates of depuration when compared to fish studies coupled with fairly rapid uptake. Other works have shown that BCFs for PAHs in molluscs and some crustaceans are considerably higher than in fish (Table A5.5 in Appendix 5). Unlike fish and some crustaceans, molluscs are unable to rapidly metabolize aromatic hydrocarbons, and accumulation can occur in stable tissue compartments with low hydrocarbon turnover and are not readily exchangeable (Stegeman and Teal 1973; Neff et al. 1976).
McLeese and Burridge (1987) studied the bioaccumulation potential of PAHs by a number of saltwater invertebrates using PAH-seawater solutions or PAH-contaminated sediments. When PAHs were dissolved in water, fluoranthene produced relatively high BCF values in mussels (Mytilus edulis) (BCF of 5920 L/kg ww) and clams (Mya arenaria) (BCF of 4120 L/kg ww) after short 96-hour exposures. However, when PAHs are present in the sediment, only mussels have a high potential for bioconcentration (BCF of 5950 L/kg ww). Fluoranthene can be depurated from molluscs given time, depuratating faster than heavier PAHs that were also studied (triphenylene and perylene). Shrimps and polychaetes did not readily bioaccumulate PAHs.
Other invertebrates have also been shown to bioaccumulate petroleum hydrocarbons. Muijs and Jonker (2010) studied the bioaccumulation of petroleum hydrocarbons (total and divided into three different carbon ranges) over 49 days by the aquatic worm, Lumbriculus variegatus, after exposure to a series of 14 field-contaminated sediments with a known history of oil pollution. A maximum tissue concentration was reached for the C11–C16 fraction after 14 days of exposure but then decreased; other fractions did not show any decrease in tissue concentration once a maximum was achieved. After 28 days of exposure, it was estimated that 70–90% of equilibrium was reached, although it was noted that it may take greater than 90 days for hydrocarbons greater than C34 to reach equilibrium. Characterization of the accumulated hydrocarbons was not determined, however, alkanes from C10–C34 were identified in the aquatic worms. The accumulation of higher molecular weight alkanes may be due to ingestion of organic matter to which the chemicals are sorbed. Depuration was not studied.
Overall, BCF values determined for various PAHs (Table A5.5 in Appendix 5) were highly variable, ranging from 180 to over 9000 L/kg ww. The majority of BCF studies on PAHs have found that bioconcentration can occur after short exposure times but that the majority of organisms also exhibit rapid depuration once the contaminant is removed..
Three studies on BAFs of PAHs in aquatic organisms (fish and clams) were found. Hence, experimental values of BAFs from the work of Neff et al. (1976), Zhou et al. (1997) and Burkhard and Lukasewyez (2000) were compiled for comparison with modelled data (Arnot and Gobas 2003) (Table A5.4 in Appendix 5). In general, the modelled values approximate those measured (Table A5.6 in Appendix 5) for the selected PAHs. None of the measured and modelled values were shown to be bioaccumulative according to the BAF criterion (BAF greater than or equal to 5000) in the Persistence and Bioaccumulation Regulations (Canada 2000) with the exception of the substituted PAH, isoheptylfluorene (see Table A5.6 in Appendix 5).
In characterizing bioaccumulation, the derivation of a BAF is preferred over a BCF since chemical exposure through the diet is not accounted for in the latter (Barron 1990). BCFs are typically derived under laboratory controlled conditions. According to Arnot and Gobas (2006), the BCF is a poor descriptor of biomagnification in food webs because it is derived from laboratory experiments and does not include dietary exposure. Thus, BCFs have been shown to underestimate bioaccumulation potential or biomagnification of chemicals in the food web, as predators consume prey containing lipophilic compounds (U.S. EPA 1995). As hydrophobicity increases, dietary uptake is likely to be more important than absorption from water (Arnot and Gobas 2003). Further, laboratory BCFs have been shown to overestimate bioaccumulation potential when a chemical is bound or strongly sorbed to sediment (i.e., less bioavailable).
Due to the scarcity of measured BAF values (Table A5.4 in Appendix 5), BCFs from various published work were compiled (Table A5.7a in Appendix 5) and used to help verify measured and modelled BAF values. In contrast to the few available experimental BAFs on PAHs, a suite of BCFs for components of gas oils were found, including alkanes, isoalkanes, two-ring cycloalkanes, one-ring aromatics, cycloalkane monoaromatics, cycloalkane diaromatics and polyaromatics (Table A5.7a in Appendix 5). Model estimates of these BCFs were also produced using a kinetic mass-balance model (Arnot and Gobas 2003) to fit the model kinetic elimination constants to agree with the observed BCF data in order to generate BAF predictions that reflect the known elimination rates.
A kinetic mass-balance model is, in principle, considered to provide the most reliable prediction method for determining bioaccumulation potential because it allows for correction of the kinetic rate constants and bioavailability parameters, when possible. BCF and BAF model predictions are considered “in domain” for this hydrocarbon assessment because it is based on first principles. As long as the mechanistic domain (passive diffusion), global parameter domain (range of empirical log Kow and molecular weight), as well as metabolism domain (corrected metabolic rate [kM]) are satisfied, predictions are considered valid (Arnot and Gobas 2003, 2006). The kinetic mass-balance model developed by Arnot and Gobas (2003, 2004) was employed using metabolic rate constants normalized to both conditions of the study and a representative middle trophic level fish as outlined in Arnot et al. (2008a,b) when a BCF or growth corrected elimination rate constant is known. Both BCF and biomagnifications factor (BMF) empirical data were used to correct default model uptake and elimination parameters, which are summarized in Table A5.7b (Appendix 5).
In Table A5.7b (Appendix 5), some metabolic rate constants calculated from the empirical BCF data were negative, suggesting that the metabolic rate is essentially zero and that other routes of elimination are more important. Accordingly, no metabolic rate correction was used when predicting the BCF and BAF for these structures. Gut and tissue metabolism is generally not regarded as an important elimination process for chemicals with log Kow less than ~4.5 (Arnot et al. 2008a,b; Arnot and Gobas 2006), but this can depend on the size and lipid content of fish used in testing.
In Table A5.7a (Appendix 5), only the C15 isoalkane (2,6,10-trimethyldodecane), C8 one-ring cycloalkane (ethylcyclohexane), and C13 two-ring aromatic (2-isopropylnaphthalene) had measured and/or modelled BCFs or BAFs greater than or equal to 5000. However, the measured diaromatic (2-isopropylnaphthalene) that was found to be highly bioaccumulative contains the isopropyl functional group that is considered atypical in petroleum and requires a more thorough appraisal of reasonableness of model predictions based on available experimental information (Lampi et al. 2010). As well, Neff et al. (1976) found that the C12 and C13 diaromatics (alkylated naphthalenes and biphenyls) were not highly bioaccumulative in clams upon exposure to an oil-in-water dispersion of Fuel Oil No. 2. Thus, the combined weight of evidence suggests that these C12 and C13 diaromatics are not likely to be highly bioaccumulative. For the C8 cyclohexane (ethyl cyclohexane), the predicted BAF (Arnot and Gobas 2004) for the middle trophic level fish is 5495 L/kg ww, which just exceeds the criterion (BAF greater than or equal to 5000), suggesting that it is bioaccumulative when all routes of uptake are considered. This prediction, however, was generated with a metabolic rate equal to zero because of the potential error associated with the estimate of metabolism rates (see Table A5.7b in Appendix 5). Factoring in metabolism, it is expected that the BAF would be lower and likely below 5000. As well, the experimental BCF suggests this C8 cycloalkane is not highly bioaccumulative (Table A5.7a in Appendix 5). Combining these lines of reasoning suggests that this C8 cycloalkane is also not likely to be bioaccumulative according to the Canadian criteria. For the C15 isoalkane (2,6,10-trimethyldodecane), two predicted BAFs are presented (575 and 47 863 L/kg ww). The latter BAF of 47 863 L/kg ww is preferred, as the depuration rate constant from the study was available to calculate the metabolic rate constant. This higher predicted BAF value is also in agreement with the slow rate of metabolism. Combining these lines of reasoning suggests that this C15 isoalkane is likely bioaccumulative according to the Canadian criteria.
Most components greater than C20 have an estimated log Kow greater than 8 and were excluded from the modelling, as predictions may be highly uncertain due to limitations of the model (Arnot and Gobas 2003). In Arnot and Gobas (2006), at a log Kow of 8.0, the empirical distribution of “acceptable” fish BCF data shows that there are very few chemicals with fish BCFs exceeding the Canadian criterion of BCF greater than or equal to 5000. Examination of Environment Canada’s empirical BCF/BAF database for DSL and non-DSL chemicals developed by Arnot and Gobas (2003) and further by Arnot (2005, 2006) shows that these are all highly chlorinated substances (i.e., decachlorobiphenyl, nonachlorobiphenyl, heptachlorobiphenyl), which have BCFs in the 105 range, noting that octachloronaphthalene has a measured BCF of less than 1000 L/kg ww (Fox et al. 1994; Gobas et al. 1989; Oliver and Niimi 1988), and all have log Kow values less than 8. Therefore, the predicted BCF and BAF values with log Kow greater than 8 were considered out of the parametric domain of the Arnot-Gobas model (2003) and considered highly uncertain and not reliable.
BCF and BAF model estimates were also generated for an additional 26 C9–C22 linear and cyclic representative structures using the modified Arnot-Gobas three trophic level model (2004) (Table A5.6 in Appendix 5), as no empirical bioaccumulation data were identified for these substances. Metabolism and dietary assimilation efficiency kinetics were corrected for these predictions based on analogue BCF and BMF test data. From this analysis, only the C14 polycycloalkane was predicted to have a BCF suggesting a high bioconcentration potential. However, one isoalkane, one one-ring cycloalkane, one two-ring cycloalkane, two polycycloalkanes, one one-ring aromatic, two cycloalkane monoaromatics, and one cycloalkane diaromatic were found to have high BAFs; the log Kow for these structures suggests that dietary uptake can predominate (up to 87% of total uptake) but will not be the sole route of exposure, as some substances are expected to have 90% bioavailable fraction in the water column. BAF is, therefore, considered the most appropriate metric to assess the bioaccumulation potential of these structures and represents a comparison of whole body burdens compared with concentrations in water. The BCF and BAF predictions for these fractions are within the parametric, mechanistic and metabolic domains of the model and so are considered reliable.
Biomagnification Factors (BMF) and Trophic Magnification Factors (TMFs)
BMF values from ExxonMobil Biomedical Sciences Inc. (EMBSI), used to derive kinetic information for 15 substances, are included in Table A5.7a (Appendix 5) (Lampi et al. 2010). None of these analogues have BMFs greater than 1, suggesting that these hydrocarbons will not biomagnify when compared to the concentrations expected in food items. A combination of metabolism, low dietary assimilation efficiency and growth dilution appear to limit the biomagnification potential of these compounds (see Tables A5.7a and A5.7b in Appendix 5).
Lampi et al. (2010) also summarized TMFs for PAHs from three field studies. The TMFs for various PAHs are summarized in Table A5.8 (Appendix 5).
Field-based TMFs for the PAHs studied are mostly less than 1, except fluorene and acenaphthene, which are approximately 1. A combination of metabolism, low dietary assimilation efficiency and growth dilution appear to limit the trophic magnification potential of these compounds as well. Therefore, it is not likely that the linear, cyclic and aromatic components of these gas oils will undergo biomagnification or trophic magnification.
Biota-sediment Accumulation Factors (BSAFs)
Lampi et al. (2010) also summarized the available BSAF data for several PAHs from a database compiled by the U.S. EPA (2008a). Median field-based fish BSAF values for PAHs expected to be found in gas oils (acenaphthylene, acenaphthene, fluoranthene, fluorene, naphthalene and phenanthrene) ranged from 0.001–0.1. Ninetieth percentile BSAF values ranged from 10-4 to just less than one, with naphthalene being the only PAH with a BSAF close to but below one. None of the PAHs have fish BSAFs greater than one. This is expected, given the same rationale for low BMF and TMF values. However, data were not extracted for invertebrate BSAFs from the U.S. EPA database. In the case of invertebrates, these factors can be much greater than one, because invertebrates do not have the same metabolic competency as fish (e.g., B[a]P) (Muijs and Jonker 2010; Stegeman and Teal 1973; Neff et al. 1976).
As previously noted, Muijs and Jonker (2010) studied the bioaccumulation of oil in the aquatic worm, L. variegatus. Resulting BSAFs varied from 0.01–2.3. The wide range is likely related to the differences in oil weathering status. The BSAF values for separate hydrocarbon blocks appeared to be relatively constant up to C22, indicating that L. variegatus proportionally accumulated these fractions from sediment. Beyond C22, BSAFs decreased for all sediments studied, likely due to the reduced bioavailability of the higher boiling point fractions such as PAHs. Likewise, there may be enhanced sorption of PAHs to sediment and in some cases the nonaqueous phase liquid (NAPL). Muijs and Jonker (2010) also suggest that the studied aquatic worm may even avoid NAPLs, which may also limit the bioaccumulation of the very hydrophobic fractions.
As noted previously, of the parameters that have prescribed Canadian regulatory criteria, BAF values are preferred over BCF values because they represent the potential accumulation in biota from all exposure sources and thus represent a more complete picture of the total body burden of chemicals. Biomagnification (BMF), trophic or foodweb magnification (TMF) and biota-sediment accumulation factors (BSAF) are also considered very important for understanding the pattern of bioaccumulation and are used in a weight of evidence for the overall bioaccumulation potential of a chemical.
In general, the C10–C15 alkanes, C10 one-ring cycloalkanes, C9 one-ring aromatics and C10 cycloalkane monoaromatics were not found to meet the bioaccumulation criterion as defined in the Persistence and Bioaccumulation Regulations (Canada 2000). This conclusion is based on consistencies found between available BCF and BAF experimental data, BCF and BAF kinetic mass-balance model predictions (Arnot and Gobas 2003) and modelled results using the Arnot-Gobas three trophic level model (2004).
The majority of components greater than C20 (alkanes, isoalkanes, two-ring cycloalkanes and one-ring aromatics) have estimated log Kows greater than 8 and were therefore excluded from modelling, as predictions may be highly uncertain due to limitations of the model (Arnot and Gobas 2003). Likewise, for these greater than C20 components, no experimental measured BCFs were found.
In terms of the polycycloalkanes, the C18 polycycloalkane (hydrochrysene) did not meet the criteria of BCF or BAF greater than or equal to 5000 for its modelled BAF prediction using the modified Arnot-Gobas three trophic level model (2004) (Table A5.6 in Appendix 5), whereas the C14 and C22 polycycloalkanes were found to meet the criteria based on the same model. The metabolic rate constant (0.45/day) for hydrochrysene suggests a rapid rate of metabolism in comparison to the lower metabolic rate constants (0.01/day and 0.04/day) for the C14 and C22 polycycloalkanes. Study details from experimental evidence for a similar polycycloalkane could not be obtained to determine predicted BCFs and BAFs, thus the available evidence suggests that the C18 polycycloalkane (hydrochrysene) is not bioaccumulative based on modelled results alone.
The C14 and C22 polycycloalkanes, C15 one-ring aromatics, C15–C20 cycloalkane monoaromatics and C20 cycloalkane diaromatics were found to meet the bioaccumulation criterion based on modelled results from the Arnot-Gobas three trophic level model (2004). For these particular components, the metabolic rate constants (normalized to a 184 g fish at 10°C) range from 0.01–0.13 (day-1), suggesting a slow rate of metabolism. In the case of C14 and C22 polycycloalkanes, the C15 one-ring aromatic and the C20 cycloalkane monoaromatic, only experimental BMFs for comparative analogues were available. The BMFs were all less than 1, suggesting that these components will not biomagnify. In the case of the C15 cycloalkane monoaromatic, only an experimental BCF (3418 L/kg ww) for a similar component (octahydro-phenanthrene) was found. However, considering the slow rate of metabolism of 0.197 (day-1) for octahydrophenanthrene, there is the potential that predicted BCFs and BAFs for the C15 cycloalkane monoaromatic could exceed the Canadian criteria, although this cannot be determined due to the lack of details from the relevant study. Lastly, the only analogue similar to the C20 cycloalkane diaromatic (isoheptylfluorene) is fluorene, which has an experimental BCF of 1030 L/kg ww. However, the presence of an isoheptyl group may affect the bioaccumulation potential of fluorene and the low kM value suggests a slow rate of metabolism. Overall, the available evidence suggests that these components are likely to bioaccumulate based on available modelled and experimental results.
BMF values for 19 substances comprising some isoalkanes, one- and two-ring cycloalkanes, polycycloalkanes, one-ring aromatics, cycloalkane monoaromatics, cycloalkane diaromatics, and three- and four-ring aromatics (see Table A5.7a in Appendix 5) show that no components have BMFs greater than 1. This suggests that these particular hydrocarbons will not biomagnify when tissue concentrations are compared to concentrations in food items. Thus, the available evidence suggests that there is limited biomagnification of petroleum hydrocarbons. It is possible that BSAFs will be greater than 1 for invertebrates (up to 2.3 for total petroleum hydrocarbons in L. variegatus (Mujis and Jonker 2010) as they do not have the same metabolic competency as fish, but BSAFs will likely decrease beyond C22 due to reduced bioavailability of the higher boiling point fractions (Muijs and Jonker 2010).
Overall, there is consistent empirical and predicted evidence to suggest that nine representative structures (C15 isoalkane, C15 one-ring cycloalkane, C15 two-ring cycloalkane, C14 and C22 polycycloalkanes, C15 one-ring aromatic and C15–C20 cycloalkane monoaromatics) meet the bioaccumulation criteria as defined in the Persistence and Bioaccumulation Regulations (Canada 2000). These components are associated with a slow rate of metabolism and are highly lipophilic. Exposures from water and the diet, when combined, suggest that the rate of uptake would exceed that of the total elimination rate. However, these components are not expected to biomagnify in aquatic food webs, largely because a combination of metabolism, low dietary assimilation efficiency and growth dilution allows the elimination rate to exceed the total uptake rate from the diet.
In general, the C12–C15 cycloalkane diaromatics and C15 three-ring aromatics were not found to meet the bioaccumulation criteria as defined in the Persistence and Bioaccumulation Regulations (Canada 2000). This conclusion is based on consistencies found between available BCF and BAF experimental data, BCF and BAF kinetic mass-balance model predictions (Arnot and Gobas 2003) and modelled results using the Arnot-Gobas three trophic level model (2004).
Experimental BAFs and BCFs suggest that PAHs, as a whole, have low bioaccumulation potential in fish. This is due in part to the metabolism of PAHs by fish, resulting in low or nondetectable concentrations of the parent PAHs in fish tissues (Varanasi et al. 1989). Regarding BAF, none of the measured or modelled values were shown to meet the bioaccumulation criterion (BAF greater than or equal to 5000) as defined in the Persistence and Bioaccumulation Regulations (Canada 2000) with the exception of modelled BAF values for isoheptyl fluorene (see Table A5.6 in Appendix 5). Lampi et al. (2010) found that isopropyl functional groups increased the bioaccumulation potential of naphthalene although isopropyl groups are considered atypical in petroleum. Thus highly alkylated PAHs, especially those with iso- groups, likely have a greater potential to bioaccumulate simply from increased partitioning to lipophillic tissues in biota and possibly some hindrance of biotransformation. With regards to the modelled BAF value for isoheptyl fluorene, the only similar analogue (fluorene) has an experimental BCF of 1030 L/kg ww which is slightly higher than the predicted BCF using the mass-balance kinetic model (Table A5.6 in Appendix 5). However, there is some uncertainty surrounding the kinetic rate constants used to model BCFs and BAFs for these two compounds (e.g., the metabolic rate constants were either estimated from QSARs or based on analogue data) as well as the degree of trophic magnification within the foodweb used by the model), suggesting that the BAFs may be overestimated. However, given that the log Kow of this compound is 7.4, the optimal range for high bioaccumulation from the diet and water coupled with a possible slow rate of metabolism and that a TMF for fluorene is approximately one (Table A5.8 in Appendix 5), a high bioaccumulation potential may still be likely.
None of the modelled BCF values for representative PAHs were shown to meet the bioconcentration criterion (BCF greater than or equal to 5000) as defined in the Persistence and Bioaccumulation Regulations (Canada 2000) (see Table A5.6 in Appendix 5). This is largely due to the lower contribution of chemical uptake from water from highly hydrophobic substances, but also because PAHs such as naphthalene and phenanthrene are metabolized by fish resulting in very low or nondetectable concentrations of the parent PAHs in fish tissues (Varanasi et al. 1989). However, measured BCFs in fish for phenanthrene exceed the bioaccumulation criterion (Table A5.5 in Appendix 5). For fluoranthene, Weinstein and Oris (1999) reported a BCF of 9054 L/kg ww in fathead minnows, Burkhard and Lukasewycz (2000) determined a BAF of 1550 L/kg ww in trout and De Maagd (1996) determined a BCF of 3388 L/kg ww in fathead minnows. As previously mentioned, the Weinstein and Oris (1999) and De Voogt et al. (1991), as well as the Peterson and Kristensen (1998) studies reporting high BCF values contain sufficient levels of uncertainty or the early life stage results cannot easily be interpreted versus other studies or regulatory criteria for bioaccumulation. The findings of these studies were thus considered equivocal and received a lower weighting for determining bioaccumulation potential according to criteria. The high laboratory BCFs are also not consistent with field measured BAFs in fish. Consequently there is greater evidence weight and consistency from kinetic data, modelled BCF and BAF values, laboratory and field evidence for vertebrates (i.e., fish) to suggest that vertebrates possess sufficient metabolic capacities and other elimination processes to mitigate body burdens of PAHs below levels considered by criteria to be high leels of bioaccumulation.
Empirical BCF data for invertebrates, namely molluscs (fluoranthene) have been shown to be relatively high. In the case of blue mussels, a 96-hour study with fluoranthene resulted in a BCF value of 5920 L/kg ww which exceeds the bioaccumulation criterion (Table A5.5 in Appendix 5). This indicates that there is significant potential for body burdens to reach toxic levels in these lower trophic level organisms as they lack the metabolic capability to eliminate PAHs in comparison to fish. Thus, high accumulation patterns are found in both the lab and field. There is also potential for these body burdens to exceed the internal narcotic thresholds, assuming PAH exposure is constant and continuous. However, the majority of BCF studies on PAHs have found that bioconcentration by invertebrates can occur quickly but that the majority of organisms also exhibit rapid depuration once the contaminant is removed. Therefore, exposure duration is critical to bioaccumulation and toxicity.
Field-based TMFs for PAHs were mostly less than 1, with the exception of fluorene and acenaphthene which are approximately one (Table A5.8 in Appendix 5). It appears that biomagnification and trophic magnification are mitigated by a combination of metabolism, low dietary assimilation efficiency and growth dilution through the food-chain. Thus, the available evidence suggests that there is limited biomagnification and trophic magnification for PAHs.
As PAHs tend to accumulate in sediments, benthic organisms may be continuously exposed to the contaminants. Because invertebrates do not have the same metabolic competency as fish (Muijs and Jonker 2010; Stegeman and Teal 1973; Neff et al. 1976), the bioaccumulation potential in invertebrates is expected to be higher than in fish. While only BSAFs for fish were found for some PAHs and were below one, it is possible that BSAFs will be greater than 1 for invertebrates as they have lower metabolic competencies than fish. However, BSAFs will likely decrease beyond C22 due to reduced bioavailability of the higher boiling point fractions (Muijs and Jonker 2010).
Overall, there is consistent empirical and predicted evidence to suggest that one PAH representative structure (C20 cycloalkane diaromatic) meets the bioaccumulation criteria as defined in the Persistence and Bioaccumulation Regulations (Canada 2000).
Proportion of Bioaccumulative Components in Gas Oils
There is a lack of detailed compositional information for these gas oils. As such, the proportion of bioaccumulative structures in these gas oils cannot be determined with certainty. However, it can be compared to the compositional analyses of diesel fuel from Canadian sources. This analysis, based on the empirical and predicted analysis of BCF and BAFs, indicates that the total potentially bioaccumulative fraction based on diesel ranges from 20–25% by weight (Yang 2001). The majority of this fraction is composed of dicycloalkanes and alkylated monoaromatics.
Based on the combined evidence of empirical and predicated analysis of BCF and BAFs, the gas oils assessed in this report may contain components that meet the bioaccumulation criteria defined in the Persistence and Bioaccumulation Regulations (Canada 2000).
Potential to Cause Ecological Harm
Ecological Effects Assessment
Information relevant to the toxicity of gas oils to various organisms is provided below. As well, PAHs are components of gas oils and have been considered in a previous risk assessment. PAHs are on the List of Toxic Substances under Schedule 1 of CEPA 1999 (Environment Canada 2010).
Evidence from field and laboratory studies using field samples indicates that biota are adversely affected at various Canadian sites contaminated by PAHs of different industrial origins (Canada 1994).
There are potential hazards associated with the metabolism of PAHs such as B[a]P. This process may create metabolites that are potent mutagens. Under laboratory conditions, neoplastic and genotoxic effects have been associated with exposure to PAHs for both terrestrial and aquatic organisms. In field studies, preliminary stages of chemically induced carcinogenesis have been shown (Canada 1994).
Shell (2011) provides a numerical score for acute and chronic aquatic toxicity indicating that 64741-82-8 is very toxic to aquatic life (Hazard Statement H400 under the Globally Harmonized System of Classification and Labelling of Chemicals [UNECE 2011] and a classification value of 1), and very toxic to aquatic life with long-lasting effects (Hazard Statement H410 and a classification value of 1). Under this schema, a classification value of 1 for acute aquatic toxicity means a median lethal concentration (LC50) or median effect concentration (EC50) less than or equal to 1 mg/L in either a 96-hour L(E)C50 test for fish, 48-hour L(E)D50 for invertebrates or 72- to 96-hour ErC50 for algae. For chronic toxicity to aquatic life, a classification value of 1 means that for substances that are non-rapidly biodegradable (assumed), a no-observed-effect concentration (NOEC) less than or equal to 0.1 mg/L or, if absent, an L(E)C50 less than or equal to 1 mg/L.
However, no experimental data were available for the aquatic toxicity of these gas oils; therefore, data from similar diesel fuels and Fuel Oil No. 2, as well as modelled data were used to estimate the potential for aquatic toxicity.
CONCAWE developed an aquatic toxicity model specific for petroleum hydrocarbon mixtures called PETROTOX (2009). This model assumes chemical action via narcosis and therefore accounts for additive effects according to the toxic unit approach. It can model petroleum hydrocarbon toxicity for C4–C41 compounds dissolved in the water fraction. Substances smaller than C4 are considered too volatile to impart any significant toxicity and compounds larger than C41 to be too hydrophobic and immobile to impart any significant aquatic toxicity. PETROTOX (2009) generates estimates of toxicity with a median lethal loading (LL50) rather than a LC50 due to the insolubility of petroleum substances in water. The LL50 value is the amount of petroleum substance needed to generate a water-accommodated fraction (WAF) that is toxic to 50% of the test organisms. It is not a measure of the concentration of the petroleum components in the water-accommodated fraction.
The modelled ecotoxicological data in Table A5.9 (Appendix 5) with different aromatic to aliphatic ratios were restricted to marine organisms since the only significant route of transportation of these industry-restricted gas oils is by marine tanker. The data indicate that these gas oils have a high potential to cause harm to most aquatic organisms at relatively low concentrations (majority less than or equal to 1 mg/L). The likelihood of harm is largely related to the aromatic content, as the 80:20 (aromatic/aliphatic content) ratio used in modelling is more toxic to marine organisms than the 61:39 ratio or the 50:50 ratio.
To determine whether the modelling data from PETROTOX are suitable to use, a read-across approach was also conducted to compare the modelled toxicity of these gas oils with Fuel Oil No. 2 and diesel fuel oil. Fuel Oil No. 2 is a distillate light fuel oil, also referred to as home heating oil, with a boiling point range of 160–360°C (IARC 1989a). Diesel fuels are petroleum distillate fractions consisting primarily of C9–C20 hydrocarbons and have a typical boiling point range of 282–338°C (Coast Guard 1985). The acute aquatic toxicity values of Fuel Oil No. 2 and diesel fuel are presented in Tables A5.10 and A5.11 (Appendix 5).
Aquatic LC50 values for Fuel Oil No.2 and diesel fuel range from 0.9–23.7 mg/L. The modelled aquatic LL50s from PETROTOX (0.1–9.8 mg/L) fall within this range, although the LL50 is not a direct measurement of the concentration of the dissolved fraction that would cause toxicity (Table A5.9 in Appendix 5). Therefore, the modelled data from PETROTOX are within the appropriate range of measured toxicity values for similar commercial products.
The LC50 from Fuel Oil No. 2 is 0.9 mg/L, based on exposure of mysid shrimp to the water-soluble fraction over 48 hours (Anderson et al. 1974). The aromatic content of Fuel Oil No. 2 is usually 25%, while the gas oil 64741-59-9 has a much higher aromatic content of 61–80% by volume. The lowest modelled data for the water-accommodated fractions of gas oil 64741-59-9 are 0.06–0.08 mg/L, based on acute exposures of a marine amphipod (Rhepoxynius abronius). Such a difference could be explained by the high proportion (up to 80%) of aromatics in this gas oil. The modelled ecotoxicological data in Table A5.9 (Appendix 5) indicate that this industry-restricted gas oil has the potential to cause harm to many marine organisms at relatively low concentrations ( less than or equal to 1 mg/L). Unfortunately, compositional data for 64741-82-8 were insufficient to run PETROTOX; however, statements from the European manufacturer confirm a range of toxicity values, generally less than or equal to 1 mg/L. Thus, the average of the modelled data for WAFs for CAS RN 64741-59-9 (0.07 mg/L) was used to represent the critical toxicity value (CTV) for these industry-restricted gas oils.
The acute oral median lethal dose (LD50) to rats was 3200 mg/kg-bw (API 1982, 1985a). As there were no inhalation studies for industry-restricted gas oils beyond acute durations, a read-across to other gas oils, including fuels, was considered. Acute inhalation toxicity in rats was 3350–5400 mg/m3 air (API 1986a, b). At necropsy, the main effects observed were marked inflammation both of the respiratory tract and lungs (CONCAWE 1996). It is expected that wild animals would react in a similar manner if exposed to these levels of these substances; therefore, 3350 mg/m3 will be used for the CTV for inhalation by non-human mammals.
Ecological Exposure Assessment
Estimations of releases of these gas oils were made using information on volumes transported by each mode identified in submissions under section 71 of CEPA 1999 (Environment Canada 2009). Estimations of losses to the sea were determined based on information from Canada’s east coast developed by the Risk Management Research Institute (RMRI 2007) in addition to spill data fromEnvironment Canada’s Spill Line database (Environment Canada 2011).
Release scenarios were developed for ship to water for loading only since it is likely the predominant source based on confidential information received in response to section 71 of CEPA 1999 (Environment Canada 2009). There were no other transportation methods or releases to water examined.
To determine the predicted environmental concentration (PEC) in water, the volume of water predicted to be in contact with spilled oil was provided by a report prepared by the Risk Management Research Institute (RMRI 2007). This work estimated the risk of oil spills in Hazard Zones around the southern coast of Newfoundland and Labrador based on the nature of the water (open or partially constricted), the type of vessels travelling through the zones, and the quantities of oil transported. The estimated volume of water in contact with spilled oil was dependent on the volume of oil spilled during the event and the Hazard Zone of the spill.
For the ship loading scenarios, the volume of water in contact with oil is from Hazard Zone 1, as this region includes loading operations at Whiffen Head and Come By Chance refinery in Newfoundland and Labrador (RMRI 2007). The area of a slick created within Hazard Zones around Newfoundland was estimated for specific volume ranges of oil using ocean spill dispersion models, and then the volume of contacted water was estimated by multiplying the area by 10 to represent the top 10 meters of water. This estimate assumes that all of the water is equally contacted by the petroleum substance spilled. This work was originally developed for crude oil, but it can be applied to gas oils as they have a similar density.
In the case of the loading of gas oils onto ships, an estimated 144 L (122 kg) of gas oil could be lost in an average event. This is approximately equivalent to 1 barrel (U.S.), and is therefore expected to be in contact with 40×106 m3 of water (Table A5.12 in Appendix 5). The resulting concentration in water would be 0.003 mg/L (i.e., 1.22×108 mg in 4.0×1010 L), which is considered the PEC for ship loading.
The quantities of these gas oils transported by truck were too minor to warrant an exposure assessment.
Characterization of Ecological Risk
The approach taken in this ecological screening assessment was to examine available scientific information and develop conclusions based on a weight-of-evidence approach as required under CEPA 1999. For each endpoint organism, an estimate of the potential to cause adverse effects, or predicted no-effect concentration (PNEC), was determined. The PNEC is the lowest CTV for the organism of interest divided by an appropriate assessment factor. An assessment factor of 100 was used to account for the extrapolation of modelled acute toxicity data to chronic effects in the field. Also, a PEC was determined. A risk quotient (RQ = PEC/PNEC; Table 3) was calculated for each endpoint organism and is an important line of evidence in evaluating the potential risk to the environment. In the case of the loading of gas oils onto ships, the PEC for an average spill, as calculated above, is 0.003 mg/L; the average modelled value for WAF was used as the CTV..
|Medium||Organism||PEC||CTV||Assessment factor||PNEC||Risk quotient|
|Marine water (ship loading)||Rhepoxynius abronius||0.003 mg/L||0.07 mg/L||100||0.0007 mg/L||4.3|
To yield a risk quotient of 1, a marine spill during loading would need to be greater than 33 L given the scenario presented here. Only four marine spills recorded in Canada from 2000–2009 were of that volume or greater, therefore less than 1 spill per year is expected to be potentially harmful.
This critical spill volume was calculated based on models developed by RMRI (2007) relating the volume spilled and concentration of petroleum substance in the water. These models take into consideration dispersion of the petroleum substance spilled and, therefore, the calculated spill volume relating to a risk quotient of 1 is not for the acute, initial exposure to the spilled material. It is recognized that local, acute effects may occur during the inital phase of a spill before significant dispersion occurs.
The physical-chemical properties of gas oils may increase the potential risk of gas oils to the aquatic environment. Light refined products, such as diesel fuel and Fuel Oil No. 2 (and these gas oils), are narrow-cut fractions that have low viscosity and spread rapidly into thin sheens. As low-viscosity, moderately persistent oils, light distillates tend to disperse readily into the water column by gentle wave action. Thus, they have the highest potential of any oil type for vertical mixing, which in turn causes a greater potential for dissolution to occur--from both surface sheens and droplets dispersed in the water column. The water-soluble fractions are dominated by two- and three-ring PAHs, which may affect aquatic life. Thus, spills of light distillates have the greatest potential to affect water-column resources (NRC 2003). A major difference between CAS RN 64741-59-9 and both Fuel Oil No. 2 and diesel fuel is that it has a higher aromatic content ranging from 61–80%, while Fuel Oil No. 2 has an aromatic content around 25% and diesel fuel can range up to 37%. This can have a major impact on the toxicity of this gas oil compared to finished, blended fuels as toxicity increases as the aromatic fraction increases (Table A2.1 in Appendix 2).
Based on results from AOPWIN (2008), all components of gas oils will degrade readily by interactions with hydroxyl radicals in air. Based on the primary and ultimate biodegradation modelling, the C15–C20 two-ring cycloalkanes, C14–C22 polycycloalkanes, C10–C20 cycloalkane monoaromatics, C15 two-ring aromatics and C12–C15 cycloalkane diaromatics in these gas oils meet the persistence criteria in water, soil and sediment (half-lives in soil and water greater than or equal to 182 days and half-life in sediment greater than or equal to 365 days). The cycloalkanes represent a relatively small fraction (8–10%) of gas oils. There is no detailed information on the specific aromatic content of these gas oils; however, CAS RN 64741-59-9 may include up to 80% aromatics (by volume), which would include the persistent aromatics listed here. Thus, these gas oils are expected to contain an unknown proportion of components that meet the persistence criteria in soil, water and sediment as defined in the Persistence and Bioaccumulation Regulations (Canada 2000).
Based on the combined evidence of empirical and predicted analysis of BCFs, BAFs, BMFs, TMFs and BSAFs, the gas oils assessed in this report may contain components (up to approximately 25% by weight) that meet the criteria for bioaccumulation as defined in the Persistence and Bioaccumulation Regulations (Canada 2000), but are not likely biomagnified in food webs. Both empirical and predicted BCF and predicted BAFs are greater than or equal to 5000 for isoalkane, cycloalkane and some aromatic substances. There is consistent steady-state and kinetic evidence to suggest that these components do not metabolize very quickly and have sufficient dietary assimilation efficiency, that when tissue levels are compared with the bioavailable fraction in water, accumulation factors are expected to be high.
In general, fish can efficiently metabolize aromatic compounds. Of the aromatic representative structures of gas oils with high bioaccumulation potential, only a C20 cycloalkane diaromatic was bioaccumulative (i.e., BCF or BAF greater than 5000). This structure contains an isoalkyl functional group which may hinder biotransformation. There is some evidence that alkylation increases bioaccumulation of naphthalene (Neff et al. 1976, Lampi et al. 2010) but it is not known if this can be generalized to larger PAHs or if any potential increase in bioaccumulation due to alkylation will be sufficient to exceed the Canadian criteria.
Bioaccumulation of aromatic compounds might be lower in natural environments than what is observed in the laboratory. PAHs may sorb to organic material suspended in the water column (dissolved humic material) which decreases their overall bioavailability primarily due to an increase in size. This has been observed with fish (Weinstein and Oris 1999) and Daphnia (McCarthy et al. 1985).
In general, fish can efficiently metabolize aromatic compounds. However, there is evidence that fluoranthene is highly bioconcentrated in molluscs. There is potential for such bioaccumulative components to reach toxic levels in organisms if exposure is constant, continuous and of sufficient magnitude; however, this is unlikely in the water column following a spill scenario due to relatively rapid dispersal.
As shown in Table A5.13 (Appendix 5), some components may meet both the persistence and bioaccumulation criteria in the Persistence and Bioaccumulation Regulations. These include the C15 dicycloalkanes, C14 and C22 polycycloalkanes, and C15–C20 cycloalkane monoaromatics.
With regard to invertebrates, fluoranthene, which has high bioaccumulation potenetial in molluscs, is also persistent in sediments which could lead to exposure of longer duration. Based on the Level III fugacity modelling of this substance (Table A5.1), fluoranthene is expected to partition to sediments when released to water where it might accumulate in benthic invertebrates species with low metabolic capacities. However, the proportion of fluoranthten in these gas oils is low. In addition, given that there are on average approximately 4 spills per year of diesel, light oil, and petroleum distillate between 2000 and 2009, of which only a fraction would be the two gas oils under assessment in this report, it is expected that spills of gas oils in water during loading are likely not harmful to aquatic organisms.
Based on the information presented in this screening assessment on the frequency and magnitude of spills, there is low risk of harm to organisms or the broader integrity of the environment from these substances. It is concluded that the industry-restricted gas oils (CAS RNs 64741-59-9 and 64741-82-8) do not meet the criteria under paragraph 64(a) or 64(b) of the Canadian Environmental Protection Act, 1999 (CEPA 1999) as they are not entering the environment in a quantity or concentration or under conditions that may have an immediate or long-term harmful effect on the environment or its biological diversity or that constitute or may constitute a danger to the environment on which life depends.
Uncertainties in Evaluation of Ecological Risk
This analysis addresses uncertainty associated with each component of the current assessment, including but not limited to representative structures selection and quantification, exposure estimation, effects estimation, and risk characterization.
All modelling of the substances’ physical-chemical properties, and persistence, bioaccumulation and toxicity characteristics is based on chemical structures. As these gas oils are complex UVCBs, they cannot be represented by a single, discrete chemical structure. The specific chemical composition of the substances falling under CAS RNs 64741-59-9 and 64741-82-8 are variable and not well defined. Gas oil streams under the same CAS RNs can vary significantly in the number, identity and proportion of components, depending on operating conditions, feedstocks and processing units. Therefore, for the purposes of modelling, a suite of representative structures that provide estimates for the entire range of components likely present was identified. Specifically, these structures were used to assess the fate and hazard properties of gas oils. Given that more than one representative structure may be used for the same carbon range and type of component, it is recognized that structure-related uncertainties exist for this substance. The physical-chemical properties of 24 representative structures were used to estimate the overall behaviour of these gas oils, in order to represent the expected range in physical-chemical characteristics. Given the large number of potential permutations of the type and percentages of the structures in gas oils, there is uncertainty in the results associated with modelling.
Uncertainty arises from the variability of spill data. The available data on spills generally do not report values for each specific substance by CAS RN. For marine transportation, Environment Canada reported spills data for substances similar to these gas oils, specifically fuel oils, gasoline, diesel fuel and jet fuel. Spill data specific to these industry-restricted gas oils are not available for each mode of transportation.
This assessment involves the prediction of effects on biota using measured inputs and modelled accumulation or exposures, which typically relies on modelled exposures for organisms at higher trophic levels. However, all models are simplifications of natural systems or processes, and therefore rely on a number of assumptions. These, in turn, create uncertainties in the outcomes.
The BAF model calculations were derived from a large database of measured BAF values from the Great Lakes for chemicals that are poorly metabolized (e.g., PCBs). With metabolic biotransformation, the BAF model predictions are in general agreement with measured BAFs in fish. Many petroleum hydrocarbons are readily metabolized, somewhat by invertebrates and at much higher levels in fish (Arnot and Gobas 2003; Arnot et al. 2008a, b). There is some uncertainty when estimating the biotransformation used by the model at the first trophic level. Thus, the BAF model predictions may be an overestimate in consideration of these factors.
The significance and impact of bioaccumulation is species-specific and is dependent on a range of factors such as species, size and the environmental conditions. At present, there are no field data on the study of bioaccumulation of gas oils as a class; therefore, predicting effects is based on modelling BAFs of representative structures based on laboratory-acquired partitioning data.
Potential to Cause Harm to Human Health
The exposure characterization for industry-restricted petroleum substances focuses on fugitive releases. This includes evaporative emissions during the various modes of transportation of petroleum substances. The unintentional release (leaks or spills) data used in the ecological assessment are, for the purposes of assessing the potential to cause harm to human health, considered to be releases that occur on a non-routine or unpredictable basis in specific geographical locations. These unintentional releases typically do not contribute to the potential for exposure of the general population in Canada.
Due to the relatively low volatility of the industry-restricted gas oils (see Table 1), as well as relevant regulations that limit potential releases during the handling of petroleum substances (see Appendix 3), non-occupational exposure of the general population as a result of loading or unloading is not expected. Despite relatively low volatility, evaporative emissions of the industry-restricted gas oils during transit (i.e., during transport by ships between facilities), as well as during loading and unloading stops in port, will enter ambient air. As such, inhalation is the primary route of potential exposure for the general population in the vicinity of such transporation corridors.
As monitoring data on gas oils in the environment are not available, gas oil vapour concentrations in ambient air were estimated using SCREEN3 (1996), a screening-level Gaussian air dispersion model based on the Industrial Source Complex (ISC) model (for assessing pollutant concentrations from various sources in an industry complex). The driver for air dispersion in the SCREEN3 model is wind. The maximum calculated exposure concentration is selected based on a built-in meteorological data matrix of different combinations of meteorological conditions, including wind speed, turbulence and humidity. This model directly predicts concentrations resulting from point, area and volume source releases. SCREEN3 gives the maximum concentrations of a chemical at chosen receptor heights and at various distances from a release source for a given population in the vicinity of the release source in the direction downwind from the prevalent wind one hour after a given release event. During a 24-hour period, for point emission sources, the maximum 1-hour exposure (as assessed by the ISC Version 3) is multiplied by a factor of 0.4 to account for variable wind directions. This gives an estimate of the air concentration over a 24-hour exposure (U.S. EPA 1992). Similarly, for exposure events happening over the span of a year, it can be expected that the direction of the prevalent winds will be more variable and not correlated with the wind direction for a single event. Thus, the maximum amortized exposure concentration for one year is determined by multiplying the maximum 1-hour exposure by a factor of 0.08. Such scaling factors are not used for non-point source emissions. However, to prevent overestimation of the exposures originating from area sources, a scaling factor of 0.2 was used to obtain the yearly amortized concentration from the value of the maximum 1-hour exposure concentration determined by SCREEN3. Detailed input parameters for SCREEN3 are listed in Table A6.1 (Appendix 6). It should be noted that the estimated exposure concentrations are considered to be conservative, as SCREEN3 is, by design, a conservative screening-level tool used as a rapid approach to estimate the air dispersion of various chemicals.
As a conservative estimate, the regular evaporative emissions determined for one day of the port stop process are assumed to originate from a defined area rather than a moving source (i.e., the 1-day exposure scenario used to represent all 7 days of the typical port stop process is the worst-case scenario, whereby the ship is in port and stationary); as such, actual levels are expected to be lower, considering that the release source is moving for a portion of the 7-day port stop process (i.e., when the ship is coming into and leaving port). Estimated regular evaporative emissions of industry-restricted gas oils to air during ship transit (including time during which the ship is in port) are approximately 1100 kg/year or 3.2 kg/day (Table A6.2 in Appendix 6). The emission rate (7.4×10-5 g/s·m2) is derived based on the emission of 3.2 kg/day and the estimated emission area of 50 m × 10 m. This emission rate (7.4×10-5 g/s·m2) is used in SCREEN3 for determining the concentration of the gas oil vapours in ambient air (SCREEN3 1996). Exposure to the evaporated gas oils will occur over a typical port stop of one week.
The estimated maximum concentration of ambient gas oil vapours during 24 hours is presented in Table A6.3 (Appendix 6). For a conservative estimate of exposure to the general population in the vicinity of these transportation corridors, the concentration at 1000 m was used for ambient air concentrations of gas oil vapours from evaporative emissions during the 7-day port stop process. The maximum concentration in ambient air at 1000 m was estimated to be 1.0 µg/m3.
Due to the use of an evaporative emissions value from a point source rather than a moving vessel, the placement of the receptor at 1000 m from the release source, and the conservative nature of SCREEN3 modelling, the estimated exposure concentration to the general population is considered to be conservative.
Health Effects Assessment
Health effects of the two industry-restricted gas oils (CAS RNs 64741-59-9 and 64741-82-8) were assessed primarily using data specific to these two CAS RNs. However, given the limited number of studies available that specifically evaluate the health effects of the industry-restricted gas oil substances for certain endpoints and/or routes of exposure, additional gas oils in the PSSA that are similar from both a process and a physical-chemical perspective were also considered. Because both the industry-restricted and additional gas oil substances have similar physical-chemical properties, their toxicological properties are likely similar. The health effects data were therefore pooled and used to construct a toxicological profile to represent all gas oils. Accordingly, the health effects of gas oils are represented as a group, not by individual CAS RNs.
Appendix 7 contains a summary of the available health effects information for CAS RNs 64741-59-9 and 64741-82-8 in laboratory animals. A summary of key studies is presented below. The health effects literature has referred to different stream samples of CAS RN 64741-59-9 as API 83-07, API 83-08, MD-7 light cycle oil (LCO), Mobil LCO and light catalytic cracked distillate (LCCD). Different stream samples of CAS RN 64741-82-8 have been referred to as Mobil coker light gas oil (CLGO), DGMK No. 8 and light thermal cracked distillate.
Gas oils have low acute toxicity. API 83-07 exhibited an oral LD50 of 3200 mg/kg-bw in female rats and an inhalation LC50 of 3350 mg/m3 in male rats (API 1982, 1985a, 1986a). API 83-07 and 83-08 exhibited a dermal LD50 of greater than 2000 mg/kg-bw in rabbits (API 1982, 1985a,b). Slight to severe skin irritation was observed in all cases of acute dermal exposure. Acute studies were not identified for CAS RN 64741-82-8.
In short-term and subchronic dermal studies of CAS RNs 64741-59-9 and 64741-82-8, moderate to severe skin irritation and inflammation were observed in laboratory animals at all doses tested. In a short-term study that exposed pregnant Sprague-Dawley rats to Mobil LCO from gestation days 0–19 or 6–15, a lowest-observed-adverse-effect level (LOAEL) of 50 mg/kg-bw per day was established based on decreased maternal body weight gain and body weight (likely due to reduced feed consumption), as well as skin irritation (Mobil 1988a). In a subchronic study that exposed male and female Sprague-Dawley rats to CAS RN 64741-82-8, 5 days/week for 13 weeks, a LOAEL of 30 mg/kg-bw per day was established based on increased lymphocytes in females and a 10% decrease in thymus weight in males (Mobil 1991). Four further short-term and subchronic dermal studies were identified for CAS RN 64741-59-9. These studies found decreased thymus weights and increased liver weights in rats, as well as varying degrees of skin irritation in rats and rabbits (API 1985c,d; Mobil 1985; Feuston et al. 1994). Two further short-term and subchronic dermal studies were reported for CAS RN 64741-82-8. Light thermal cracked distillate was applied to the skin of pregnant Sprague-Dawley rats at doses of 15, 60, 250 or 500 mg/kg-bw per day on gestation days 0–19. Maternal effects such as moderate to severe skin irritation, erythema, flaking, scabbing and thickening of the skin were observed at an unspecified dose (Mobil 1988b). In the second study, doses of 30, 125, 500 or 2000 mg/kg-bw per day were applied to male and female Sprague-Dawley rats, 5 days/week for 13 weeks. Increased relative liver weights were observed at 125 mg/kg-bw per day (Feuston et al. 1994).
Repeated-exposure studies assessing the health effects due to inhalation of the industry-restricted gas oils were not identified. Thus, critical effect levels were derived from health effects studies on related gas oil substances (as mentioned above). In a short-term (4 week) repeated-exposure study of male and female Sprague-Dawley rats exposed to CAS RN 64742-80-9 (hydrodesulfurized middle distillates), 25 mg/m3 was identified as a lowest-observed-adverse-effect concentration (LOAEC) based on microscopic changes in nasal tissue and subacute inflammation of the respiratory mucosa (API 1986c). An increased leukocyte count (~30%) was also noted, but no corresponding macroscopic changes were observed at necropsy. In a repeated-exposure subchronic inhalation study of another gas oil (CAS RN 68334-30-5; diesel fuel), 250 mg/m3 was identified as a LOAEC based on decreased body weight and increased response time in an acoustic startle reflex assay at all exposure levels tested in both male and female Sprague-Dawley rats exposed 2 days/week for 13 weeks; however, no corresponding histological changes in the nervous system were noted (Lock et al. 1984). Therefore, 25 and 250 mg/m3 were considered the short-term and subchronic inhalation critical effect levels, respectively, for the industry-restricted gas oils.
CAS RNs 64741-59-9 and 64741-82-8 have been evaluated in a limited number of in vitro and in vivo genotoxicity assays. In vivo, API 83-07 and API 83-08 did not affect the mitotic index of rat bone marrow cells in two cytogenetic assays (API 1985e, 1986d), but API 83-07 was positive for sister chromatid exchange in mice (API 1989a). In vivo studies for CAS RN 64741-82-8 were not identified. In vitro,MD-7 LCO exhibited a mutagenicity index of 14 in a modified Ames assay and was found to contain 8.7% polycyclic aromatic compounds (Nessel et al. 1998). Positive results for both API 83-07 (with metabolic activation) and API 83-08 (with and without metabolic activation) were also observed in the mouse lymphoma assay (API 1985f,g). Equivocal results for one sister chromatid exchange assay were observed for API 83-07, both with and without metabolic activation (API 1988). CAS RN 64741-82-8 exhibited positive results in a modified Ames assay in two different studies (Blackburn et al. 1984, 1986; Conaway et al. 1984; DGMK 1991).
Thus, the industry-restricted gas oils demonstrate genotoxic potential, as evidenced by positive in vivo and in vitro results for the sister chromatid exchange, mouse lymphoma and Ames assays. However, given the limited number of experiments conducted for the two industry-restricted CAS RNs, other PSSA high priority gas oils were also considered. The potential genotoxicity of the two industry-restricted gas oils is supported by the overall genotoxicity database for additional gas oil substances, although it is recognized that the results were variable depending on the substance tested and the assay used. Overall, gas oils, including CAS RNs 64741-59-9 and 64741-82-8, demonstrate genotoxic potential.
Regarding the carcinogenic potential of the industry-restricted gas oils, CAS RNs 64741 59-9 and 64741-82-8 were classified as Category 2 carcinogens (R45: may cause cancer) by the European Commission (ESIS 2008). The United Nations’ Globally Harmonized System of Classification and Labelling of Chemicals has classified these substances as Category 1B carcinogens (H350: may cause cancer) (European Commission 2008a). The International Agency for Research on Cancer (IARC) has also indicated that CAS RN 64741-59-9 exhibits sufficient evidence in experimental animals for carcinogenicity (consistent with a Group 2A probably carcinogenic to humans classification). The data supporting this conclusion were considered when they classified “occupational exposures in petroleum refining” as Group 2A (probably carcinogenic to humans), although CAS RN 64741-59-9 was not directly assigned to an IARC carcinogen group per se (IARC 1989a). Other gas oils have been classified by IARC as Group 3 carcinogens (not classifiable as to their carcinogenicity to humans) (IARC 1989b,c).
The dermal carcinogenic potential of CAS RN 64741-59-9 has been investigated in multiple skin painting studies in mice. A statistically significant increase in the number of mice with skin tumours occurred after mice were chronically exposed to MD-7 LCO at 343 mg/kg-bw per day, the lowest test dose applied (Nessel et al. 1998). Tumour types and relative incidences were consistent across different studies, with squamous cell carcinomas exhibiting the highest incidence, followed by fibrosarcomas and papillomas (Skisak et al. 1994; Broddle et al. 1996; Nessel et al. 1998). One study investigated the tumour initiating and promoting activity of LCCD (Skisak et al. 1994). Skin tumours formed in 93% of mice when LCCD was used as a tumour growth promoter, but only 30% of mice developed tumours when it was used as a tumour initiator. Together, the results indicate that CAS RN 64741-59-9 may exhibit significant tumour promoting and carcinogenic activity when applied chronically to the skin of mice.
The dermal carcinogenic potential of CAS RN 64741-82-8 was assessed as a test substance blend with three other gas oil substances. Mice were dermally exposed to 1389 mg/kg-bw of the blended substance twice per week for 80 weeks. At 80 weeks, 98% of exposed mice had developed skin tumours (ARCO 1980a,b, 1981). It is difficult to ascribe a carcinogenic effect to CAS RN 64741-82-8 based on this study, however, given that the substance was administered in combination with three other substances.
Regarding the tumourigenicity of gas oils, it is recognized that these substances may contain appreciable concentrations of components that are tumourigenic, such as PAHs, and the quantity of this fraction can vary depending on the nature and amount of diluent fractions and whether the residue component is cracked or uncracked. The Government of Canada has previously completed a human health risk assessment of five PAHs, including a critical review of relevant data, under the Priority Substances Program. Based primarily on the results of carcinogenicity bioassays in animal models, these PAHs were classified as probably carcinogenic to humans: substances for which there is believed to be some chance of adverse effects at any level of exposure (Canada 1994). Due to the lack of exposure to gas oils, evaluating the contribution of gas oil components to carcinogenic activity is beyond the scope of the current assessment.
The potential for CAS RNs 64741-59-9 and 64741-82-8 to affect reproduction and development has also been evaluated. The only reproductive or developmental LOAELs available for any gas oil substance were identified for CAS RN 64741-59-9 and were observed only at the highest dose tested. Mobil LCO exhibited a reproductive LOAEL of 1000 mg/kg-bw per day based on an increased incidence of resorptions after the substance was applied dermally to rats on gestation days 6–15 (Feuston et al. 1994). In a similar study, a LOAEL of 1000 mg/kg-bw per day was established for developmental toxicity based on statistically significant decreased fetal body weights after pregnant rats were dermally exposed to the substance on gestation days 0–6 and 6–15 (fetal body weights also trended lower in the group exposed to 500 mg/kg-bw per day on gestation days 0–19) (Mobil 1988a). Three studies assessing CAS RN 64741-82-8 found no developmental or reproductive effects when it was tested dermally in rats. Doses ranged from 15–2000 mg/kg-bw per day (Mobil 1988b, 1991; Feuston et al. 1994). All studies identified for other PSSA high priority gas oils administered dermally or via inhalation were noted to have negative results at all doses/concentrations tested. The available data indicate that, when applied dermally or via inhalation to laboratory animals during gestation, the industry-restricted gas oils do not exhibit significant reproductive or developmental toxicity.
No human epidemiological literature specific to the industry-restricted gas oils was identified. However, examination of studies that evaluated other gas oils revealed a case report involving repeated dermal exposure to diesel oil, resulting in adverse health effects, including renal failure (Crisp et al. 1979). Additionally, a case-control study of male cancer patients revealed a correlation between prostate cancer and occupational exposures to diesel fuels; however, there was no evidence for a positive dose-response relationship (Siemiatycki et al. 1987). Due to confounding variables and limited data, the evidence gathered from these studies is considered to be inadequate for a conclusion to be drawn on the effects of human exposure to gas oils.
Characterization of Risk to Human Health
Industry-restricted gas oils were identified as high priorities for action during categorization of the DSL because they were determined to present greatest potential for exposure of individuals in Canada, and were considered to present a high hazard to human health. A critical effect for the initial categorization of industry-restricted gas oil substances was carcinogenicity, based primarily on classifications by international agencies. These substances are classified as Category 2 carcinogens by the European Commission (ESIS 2008), Category 1B carcinogens using the Globally Harmonized System (European Commission 2008a) and Group 2A or 3 carcinogens by IARC (IARC 1989a,b,c). Several cancer studies conducted in laboratory animals reported the development of skin tumours following repeated dermal application of CAS RN 64741-59-9 (Skisak et al. 1994; Broddle et al. 1996; Nessel et al. 1998). Gas oils demonstrated genotoxicity in in vivo and in vitro assays. There are no carcinogenicity studies by the inhalation route to inform the carcinogenic potential of these substances in the general population following inhalation exposure.
The long-term health effects of the gas oils have primarily been examined through the dermal route of exposure; this is likely due in part to their relatively low volatility (Table 1). The rodent health effects studies from which the short-term and subchronic LOAECs were selected (as representative data for the industry-restricted gas oils) both used artificial methods (atomizer and heat) to generate aerosols and increase the concentrations of the substances in ambient air, thus underscoring the low volatility of gas oil substances in general and indicating that under normal conditions, the volatilization of the industry-restricted gas oils would be minimal (i.e., would not lead to significant vapour concentrations in ambient air).
Given that the potential for general population exposure to the industry-restricted gas oils results primarily from inhalation of ambient air containing gas oil vapours due to evaporative emissions during transportation and that the estimate of maximum air concentration (1.0 µg/m3) is considered to be low, the risk to human health is likewise considered to be low. The ambient air concentration estimate is very conservative and highlighted by the assumption of total daily evaporative emissions occurring within a defined geographic area from a stationary point source (under normal operating conditions, evaporative emissions occur predominantly from a moving source; thus, the releases are diluted across a large geographic area).
General population exposure to industry-restricted gas oils via the dermal and oral routes is not expected; therefore, risk to human health from these routes of exposure is not expected.
No data were available that were specific to the industry-restricted gas oils with respect to non-cancer effects (identified in laboratory animals) following inhalation exposures. Therefore, the lowest concentrations causing health effects due to inhalation, identified from the pooled toxicological dataset for gas oil substances, were used as representative data for CAS RNs 64741-59-9 and 64741-82-8. The short-term LOAEC identified from the pooled data on gas oil substances was 25 mg/m3, based on inflammation of the respiratory mucosa in Sprague-Dawley rats following 4 weeks of repeated daily exposure to CAS RN 64742-80-9. The subchronic LOAEC identified was 250 mg/m3, based on decreased rat body weights and increased response time in the acoustic startle reflex assay following 13 weeks of exposure to CAS RN 68334-30-5. Comparison of these non-cancer effect levels for inhalation exposure in rodents with the estimated maximum ambient air concentration of 1.0 µg/m3 (based on the vapour concentration in air at 1000 m from a stationary release source) results in MOEs of 25 000 and 250 000 for short-term and subchronic effects, respectively. These margins are considered adequate to address uncertainties in the exposure and cancer and non-cancer health effects databases, especially in light of the highly conservative nature of the maximum air concentration estimate and the use of the lowest critical effect levels from the pooled toxicological dataset for gas oil substances.
Uncertainties in Evaluation of Human Health Risk
The PSSA screening assessments evaluate substances that are UVCBs composed of a number of substances in various proportions due to the source of the crude oil or bitumen and its subsequent processing. Monitoring information or provincial and territorial release limits from petroleum facilities target broad releases, such as oils and grease to water or total volatile organic compounds to air. These release categories are too broad to allow specific UVCB substances to be identified as the source. As such, the monitoring of broad releases cannot provide sufficient data to associate a detected release with a specific substance identified by a CAS RN, nor can the proportion of releases attributed to individual CAS RNs be defined.
There is uncertainty regarding the magnitude of the conservatism built into the estimation of human exposure because, in the absence of ambient air monitoring data for gas oils, SCREEN3 modelling was used to profile gas oil vapour dispersion. Assumptions made in SCREEN3 (see Tables A6.1 and A6.2 in Appendix 6) also contribute uncertainty.
Uncertainty also exists in the equations used for estimating evaporative emissions. It is noted that transit evaporative emissions can vary with the tightness of transport vessels, valve settings, loading modes at terminals (e.g., submerge, splash or bottom) and use of a vapour balance system. The estimation of evaporative emissions does not account for these variables.
The specific chemical compositions of the streams falling under CAS RNs 64741-59-9 and 64741-82-8 are not well defined given that gas oils are UVCBs. Gas oil streams under the same CAS RN can vary significantly in the number, identity and proportions of components, depending on feedstocks and operating conditions of processing units. Consequently, the toxicological dataset reflects this variability. For this reason, there is some uncertainty in the characterization of risk to human health given that health effects data derived from studies of a particular stream may not be entirely representative of the spectrum of streams falling under the same CAS RN. More research by the scientific community and/or the petroleum sector to elucidate the exact compositions of petroleum substances would support more robust characterization of the potential health risks associated with potential exposure to these substances.
Uncertainty in the evaluation of risk also exists due to the fact that studies assessing repeated oral and inhalation exposures to CAS RNs 64741-59-9 and 64741-82-8 were generally not available, and studies assessing other gas oil substances were occasionally used for the purpose of the health effects assessment. As such, to derive margins of exposure for inhalation exposure to these substances, representative data from other gas oils were used, which introduced additional uncertainty. However, in each case where appropriate, conservative assumptions were made regarding exposure and health effects.
A full mode of action analysis regarding tumourigenesis was not conducted for this screening assessment of gas oils. Inherent differences of sensitivity between laboratory animals and humans were also not considered.
Based on a comparison of levels expected to cause harm to organisms with estimated exposure levels, the gas oils identified in this report have the potential to harm aquatic life in the relatively confined waters around a loading wharf. However, given the low frequency of gas oil spills to marine water during ship loading (on average less than 1 per year), spills of these industry-restricted gas oile are not expected to result in harm to the environment.
Based on the information presented in this screening assessment on the frequency and magnitude of spills, there is low risk of harm to organisms or the broader integrity of the environment from these substances. It is concluded that the industry-restricted gas oils (CAS RN 64741-59-9 and 64741-82-8) do not meet the criteria under paragraph 64(a) or 64(b) of the Canadian Environmental Protection Act, 1999 (CEPA 1999) as they are not entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity or that constitute or may constitute a danger to the environment on which life depends.
Based on adequate margins of exposure between critical effect levels and upper-bounding estimates of general population exposure, it is concluded that the industry-restricted gas oils (CAS RNs 64741-59-9 and 64741-82-8) do not meet the criteria under paragraph 64(c) of CEPA 1999 as they are not entering the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health.
It is therefore concluded that the industry-restricted gas oils (CAS RNs 64741-59-9 and 64741-82-8) do not meet any of the criteria set out in section 64 of CEPA 1999.
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- Appendix 1: Petroleum substance grouping
- Appendix 2: Physical and chemical data tables for industry-restricted gas oils
- Appendix 3: Measures designed to prevent, reduce or manage unintentional releases
- Appendix 4: Unintentional release estimation of diesel fuel spills to the marine environment
- Appendix 5: Modelling results for environmental properties of industry restricted gas oils
- Appendix 6: Modelling results for human exposure to industry restricted gas oils
- Appendix 7: Summary of health effects information for the industry restricted gas oils
 For the purposes of the screening assessment of PSSA substances, a site is defined as the boundaries of the property where a facility is located. In these cases, facilities are petroleum refineries, upgraders or gas plants.
 For the purposes of the screening assessment of PSSA substances, a closed system is defined as a system within a facility that does not have any releases to the environment and where losses are collected and recirculated, reused or destroyed.
 This category is used most commonly for agents, mixtures and exposure circumstances for which the evidence of carcinogenicity is inadequate in humans and inadequate or limited in experimental animals.
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