Screening Assessment

Petroleum Sector Stream Approach

Petroleum and Refinery Gases
[Site-Restricted]

Chemical Abstracts Service Registry Numbers

68307-99-3, 68476-26-6, 68476-49-3, 68477-69-0, 68477-71-4, 68477-72-5, 68477-73-6, 68477-75-8, 68477-76-9, 68477-77-0, 68477-86-1, 68477-87-2, 68477-93-0, 68477-97-4, 68478-00-2, 68478-01-3, 68478-05-7, 68478-25-1, 68478-29-5, 68478-32-0, 68512-91-4, 68513-16-6, 68513-17-7, 68513-18-8, 68514-31-8, 68514-36-3, 68527-16-2, 68602-83-5, 68602-84-6, 68606-27-9, 68607-11-4, 68814-67-5, 68911-58-0, 68918-99-0, 68919-02-8, 68919-04-0, 68919-08-4, 68919-10-8 and 68952-79-4

Environment Canada
Health Canada
June 2013

(PDF Format - 529 KB)

Table of Contents

• Synopsis
• Introduction
• Substance Identity
• Physical and Chemical Properties
• Sources
• Uses
• Releases to the Environment
• Environmental Fate
• Persistence and Bioaccumulation
• Potential to Cause Ecological Harm
• Potential to Cause Harm to Human Health
• Conclusion
• References
• Appendices

Synopsis

The Ministers of the Environment and Health have conducted a screening assessment of the following site-restricted petroleum and refinery gases:

These substances were identified as high priorities for action during the categorization of the Domestic Substances List, as they were determined to present greatest potential or intermediate potential for exposure of individuals in Canada and were considered to present a high hazard to human health. Although they met the categorization criteria for persistence in the environment, they did not meet the ecological categorization criteria for bioaccumulation or inherent toxicity to non-human organisms. These substances were included in the Petroleum Sector Stream Approach because they are related to the petroleum sector and are all complex combinations of petroleum hydrocarbons.

Petroleum and refinery gases, produced from petroleum facilities (i.e., refining, upgrading or natural gas processing facilities), are a category of saturated and unsaturated light hydrocarbons. The compositions of petroleum and refinery gases vary depending on the source of the crude oil, bitumen, or natural gas as well as the process operating conditions and processing units used. As such, petroleum and refinery gases are considered to be of Unknown or Variable composition, Complex reaction products or Biological materials (UVCBs). In order to predict overall behaviour of these complex substances for purposes of assessing the potential for ecological effects, representative structures have been selected from each chemical class in the substance.

Site-restricted petroleum and refinery gases can serve as fuels, as intermediates for further separation of components, or as feedstocks for chemical transformation processes within a facility.

The petroleum and refinery gases considered in this screening assessment have been identified as site-restricted (i.e., they are a subset of petroleum and refinery gases that are not expected to be transported off the petroleum facility sites). According to information reported under section 71 of the Canadian Environmental Protection Act, 1999 (CEPA 1999), and other sources of information, these 40 site-restricted petroleum and refinery gases are consumed on site or are blended into substances leaving the site under different CAS RNs. However, it has been recognized that given the physical-chemical properties of these gases (e.g., high vapour pressures), releases of the petroleum and refinery gases into the atmosphere can occur. Dispersion modelling results show that unintentional releases of these site-restricted petroleum and refinery gases contribute to ambient background levels of 1,3-butadiene in the vicinity of petroleum facilities.

Based on the current available information, none of these CAS RNs contain components that meet the bioaccumulation criteria as defined in the Persistence and Bioaccumulation Regulations. However, many of the components of site-restricted petroleum and refinery gases persist in the atmosphere and meet the persistence criteria in the Regulations.

A number of regulatory and non-regulatory measures are already in place in Canada, which limit releases of site-restricted petroleum substances, including provincial/territorial operating permit requirements, and best practices and guidelines put in place by the petroleum industry at refinery, upgrader and natural gas processing facilities. Based on results of dispersion modelling, concentrations of components of petroleum and refinery gases in air surrounding petroleum facilities are not expected to be at levels that could result in harm to the environment.

Based on the information available, it is concluded that the 40 site-restricted petroleum and refinery gases included in this screening assessment do not meet the criteria under paragraphs 64(a) and (b) of 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.

One component of petroleum and refinery gases, ethene, is being assessed in a separate assessment and its potential to cause harm is not considered in this assessment. This will allow consideration of ethene releases from industrial operations generally, rather than attempting to link its release to the specific substances that are the subject of the current assessment.

Site-restricted petroleum and refinery gases were identified as a high priority for action as they were considered to present high hazard to human health. A critical effect for categorization of human health for petroleum and refinery gases was carcinogenicity, as another jurisdiction (the European Union) has identified petroleum and refinery gases containing 1,3-butadiene at concentrations greater than 0.1% by weight as carcinogens. Additionally, 1,3-butadiene has been identified by Health Canada and several international regulatory agencies as a carcinogen and was added to the List of Toxic Substances in Schedule 1 of CEPA 1999. 1,3-Butadiene was found to be a multi-site carcinogen in rodents, increasing the incidence of tumours at all inhalation concentrations tested. 1,3-Butadiene also exhibits genotoxicity in vitro and in vivo,and aplausible mode of action for induction of tumours involves direct interaction with genetic material.

1,3-Butadiene was selected as a high hazard component to characterize potential exposure to the general population as it is considered, based on available information, to be present in these petroleum and refinery gases. While limited, it is recognized that a small portion of the general population may be exposed to these petroleum and refinery gases in the vicinity of petroleum facilities. Furthermore, margins between high end estimates of exposure to 1,3-butadiene and estimates of cancer potency are considered potentially inadequate to address uncertainties related to health effects and exposure.

Based on the information available, it is concluded that the 40 site-restricted petroleum and refinery gases meet the criteria in paragraph 64(c) of CEPA 1999, as they are entering or may enter the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health.

Based on the information available, it is concluded that the 40 site-restricted petroleum and refinery gases listed under CAS RNs 68307-99-3, 68476-26-6, 68476-49-3, 68477-69-0, 68477-71-4, 68477-72-5, 68477-73-6, 68477-75-8, 68477-76-9, 68477-77-0, 68477-86-1, 68477-87-2, 68477-93-0, 68477-97-4, 68478-00-2, 68478-01-3, 68478-05-7, 68478-25-1, 68478-29-5, 68478-32-0, 68478-34-2, 68512-91-4, 68513-16-6, 68513-17-7, 68513-18-8, 68514-31-8, 68514-36-3, 68527-16-2, 68602-83-5, 68602-84-6, 68606-27-9, 68607-11-4, 68814-67-5, 68911-58-0, 68918-99-0, 68919-02-8, 68919-04-0, 68919-08-4, 68919-10-8 and 68952-79-4 meet one or more of the criteria set out in section 64 of CEPA 1999.

Introduction

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 presented an 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 (CMP) 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 as 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.^[1]

Grouping of Petroleum Substances

The high-priority petroleum substances fall into nine groups of substances based on similarities in production, toxicity and physicochemical properties (Appendix 1). In order to conduct the screening assessment, each high-priority petroleum substance was placed into one of five categories (“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^[2];

Stream 2: industry-restricted substances, which are substances that may leave a petroleum-sector facility and may be transported to other industrial facilities (for example, for use as a feedstock, fuel or blending component), but that 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 resulted in the determination that approximately 70 high-priority petroleum substances are site-restricted under Stream 1. Site-restricted substances are a subset of substances that are not expected to be transported off refinery, upgrader or natural gas processing facility sites as described above. These occur within four groupings: heavy fuel oils, gas oils, petroleum and refinery gases, and low-boiling- point naphthas.

These site-restricted substances were identified as having GPE or IPE during the categorization exercise based on their production volumes reported in the Domestic Substances List (DSL). Although they were considered persistent in the environment, they did not meet the ecological categorization criteria for bioaccumulation or inherent toxicity to non-human organisms. These substances were included in the Petroleum Sector Stream Approach because they are related to the petroleum sector and are all complex combinations of petroleum hydrocarbons. According to information submitted under section 71 of CEPA 1999, voluntary industry submissions, an in-depth literature review, and a search of material safety data sheets, these substances are consumed on-site or are blended into substances leaving the site under different Chemical Abstracts Service Registry Numbers (CAS RNs), which will also be addressed under the CMP.

This final screening assessment addresses 40 site-restricted petroleum and refinery gases captured under CAS RNs 68307-99-3, 68476-26-6, 68476-49-3, 68477-69-0, 68477-71-4, 68477-72-5, 68477-73-6, 68477-75-8, 68477-76-9, 68477-77-0, 68477-86-1, 68477-87-2, 68477-93-0, 68477-97-4, 68478-00-2, 68478-01-3, 68478-05-7, 68478-25-1, 68478-29-5, 68478-32-0, 68478-34-2, 68512-91-4, 68513-16-6, 68513-17-7, 68513-18-8, 68514-31-8, 68514-36-3, 68527-16-2, 68602-83-5, 68602-84-6, 68606-27-9, 68607-11-4, 68814-67-5, 68911-58-0, 68918-99-0, 68919-02-8, 68919-04-0, 68919-08-4, 68919-10-8 and 68952-79-4. The remaining high-priority petroleum and refinery gases (under six different CAS RNs) are being assessed separately, as they belong to Streams 2 or 4 (as described above).

Included in this final screening assessment is the consideration of information on chemical properties, hazards, uses and exposure, including the 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, stakeholder research reports and from recent literature searches, up to December 2009 for the environmental fate and effects sections, up to September 2011 for the exposure sections and up to December 2011 for the health effects section. Key studies were critically evaluated; modelling results were used to reach conclusions.

Characterizing risk to the environment involves consideration of data relevant to environmental behaviour, persistence, bioaccumulation and toxicity combined with an estimation of exposure to potentially affected non-human organisms from the major sources of release to the environment. Conclusions regarding risk to the environment are based in part on an estimation of environmental concentrations resulting from releases and the potential for these concentrations to have a negative impact on non-human organisms. As well, other lines of evidence of environmental hazard 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. Environmental models and comparisons with similar petroleum substances may assist 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 (based principally on the weight of evidence assessments of other agencies that were used for prioritization of the substance). Decisions for risk to human health are based on the nature of the critical effect and/or 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 final 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 conclusion is based.

This final 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/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 Patricia Nance (TERA), Dr. Bob Benson (United States Environmental Protection Agency [US EPA]), Dr. Stephen Embso-Mattingly (NewFields Environmental Forensics Practice, LLC), Dr. Michael Jayjock (The Lifeline Group) and Dr. Donna Vorhees (Science Collaborative).

Additionally, the draft of this screening assessment was subject to a 60-day public comment period. While 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 assessment is based are summarized below.

Substance Identity

Petroleum and refinery gases are a category of saturated and unsaturated petroleum light hydrocarbons produced by natural gas processing, petroleum refining and upgrader facilities (API 2001a). 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.

Some petroleum and refinery gases may also contain inorganic components, such as hydrogen, nitrogen, hydrogen sulphide, carbon monoxide and carbon dioxide. The compositions of petroleum and refinery gases vary depending on the source of the crude oil, bitumen, or natural gas, as well as the process operating conditions and processing units involved (Speight 2007). The potential components of petroleum and refinery gases are presented in Table 1.

The CAS RN descriptions are not useful in determining the exact composition of any specific petroleum and refinery gas substance, as they are written in broad, general terms with no quantitative analytical information on compositions. Because of the qualitative nature of these CAS RN descriptions, there may be significant compositional overlap between two petroleum and refinery gas substances with different CAS RNs (API 2001b).

1,3-Butadiene is a component of particular interest because of its physical-chemcial properties (e.g. volatility) and toxicological properties (e.g. carcinogenicity). There are limited data on the 1,3-butadiene content of site-restricted petroleum and refinery gases. Only two recent reports were identified (API 2009a, 2009b). These reports on category analysis and hazard characterization of petroleum hydrocarbon gases and refinery gases present compositional data on the 1,3-butadiene content in selected petroleum and refinery gas substances based on limited historical data from several US refineries from 1992 through 2002. Thirty-nine of the 40 CAS RNs identified in this screening assessment were analyzed for the potential presence of 1,3-butadiene. A compositional range for 1,3-butadiene of approximately less than 0.1–4% by weight was observed in 15 of the 39 CAS RNs that were analyzed. Detection limits of the study were not reported. The compositional ranges of specific gas components may vary significantly depending on the source of crude oil, bitumen, or natural gas, operating conditions, seasonal process issues and economic cycles. Substances containing C₄ through C₆ hydrocarbons may contain potentially carcinogenic hydrocarbon components including 1,3-butadiene and benzene at concentrations exceeding 0.1 wt% (API 2009a, 2009b). Therefore the site-restricted petroleum and refinery gases in the current assessment (which are predominately C₁ to C₅₎, are considered, based on available information, to contain 1,3-butadiene.

General descriptions of the 40 site-restricted petroleum and refinery gases are presented in Table A2.1 in Appendix 2.

Physical and Chemical Properties

Table 2 contains physical and chemical properties of petroleum and refinery gases that are relevant to their environmental fate. These were estimated based on modelled and experimental data available for a set of representative chemical structures. Based on the number of discrete substances and the types of petroleum hydrocarbons found in petroleum and refinery gases, the choice of representative structures was fairly straightforward. Petroleum and refinery gases are mainly composed of C₁–C₅hydrocarbons, which can be alkanes, isoalkanes, alkenes, cycloalkanes, cycloalkenes, dienes and cyclodienes. These components are all well-understood simple structures. The proportion of each component for a particular CAS RN can be highly variable within a facility or among different facilities; this makes prediction of the physical and chemical properties of such mixtures inexact. Information on the representative structures selected and their detailed physical and chemical properties is given in Table A2.2 in Appendix 2.

The components of petroleum and refinery gases are gaseous at environmentally relevant temperatures. If they are released to the environment, they will quickly disperse and separate. The C₅ alkane, alkene and cyclic components that are liquids at ambient temperatures have high vapour pressures, so they will also evaporate quite readily from soil or water.

Sources

Site-restricted petroleum and refinery gases are produced in Canadian refineries, upgraders and natural gas processing facilities. The CAS RN descriptions (NCI 2006), typical process flow diagrams (Hopkinson 2008), and information collected under section 71 of CEPA 1999 (Environment Canada 2008, 2009), indicate that these substances are either fuel gases consumed on-site or intermediates produced and consumed within a facility, and are not transported off-site. These site-restricted petroleum and refinery gases can be present in three types of petroleum facilities: petroleum refineries (where crude oils are converted into finished petroleum products, such as gasoline, jet fuel or base oils for lubricants); natural gas processing facilities (where crude natural gases are processed into clean natural gas and other C₂–C₅ hydrocarbons); and upgraders (where oil sand derived bitumen is converted into synthetic crude oil for further processing at a refinery).

CAS RN 68476-26-6 represents a fractionation mixture of light gases predominantly with hydrogenand C₁–C₂produced from a gas separation unit in a refinery or a bitumen upgrader after acidic compounds (hydrogen sulphide, carbon dioxide) are removed. This substance is usually consumed on-site as a fuel gas.

CAS RN 68476-49-3 represents a light hydrocarbon gas mixture treated by a Merox process (i.e., sweetening process) to remove sulphide compounds in a refinery, upgrader or natural gas processing plant. The gas mixture leaves a caustic washing and goes into an extractor to remove any mercaptan compounds.

CAS RN 68477-69-0 refers to an overhead substance stripped out of a butane splitter. It can be present in a gas separation unit of a refinery or a natural gas processing plant and may enter an alkylation unit as a feedstock.

CAS RN 68477-71-4 refers to a mixture of C₃–C₅ from the bottom of a depropanizer distillation column treated with a catalytic cracking effluent. The gas mixture normally enters a refinery gas plant for further separation or is further processed in an isomerization unit to produce isomers for the subsequent alkylation unit.

CAS RN 68477-72-5 represents an overhead gas mixture produced from a distillation column to stabilize catalytic cracked naphtha. The gas substance can either go into a refinery gas plant for further separation or enter an isomerization unit.

CAS 68477-73-6 represents an overhead substance from a distillation column to remove C₃ or lighter hydrocarbons from catalytic cracked naphthas. The overhead goes into a gas separation unit for further recovery.

CAS RN 68477-75-8 refers to a mixture of light components discharged from the top of a catalytic cracking fractionation column. The mixture goes directly into a gas separation unit.

Both CAS RN 68307-99-3 and CAS RN 68477-76-9 represent a mixture of overhead light hydrocarbons discharged from a stabilization column for polymerized naphtha. CAS RN 68307-99-3 is predominantly C₁ to C₄ whereas CAS RN 68477-76-9 is predominantly C₂ to C₃. The overhead substance normally undergoes further purification before being used as a final product (e.g., liquefied petroleum gas).

CAS RN 68477-77-0 represents an overhead light hydrocarbon from a stabilization column for reformed naphtha. The overhead goes into a gas separation unit for further recovery.

CAS RN 68477-86-1 refers to an overhead substance discharged from a deethanizer column. It usually undergoes further treatment for separating ethene and ethane.

Similar to CAS RN 68477-69-0, CAS RN 68477-87-2 refers to an overhead substance from a butane splitter in a refinery facility or a natural gas processing plant. It will enter an alkylation unit as a feedstock.

CAS RN 68477-93-0 refers to a gaseous substance discharged from the top of a stripping column. It usually returns to a gas absorber to remove any remaining acidic compounds (hydrogen sulphide and carbon dioxide) in an amine treatment process.

CAS RN 68477-97-4, CAS RN 68478-00-2 and CAS RN 68607-11-4 are generic descriptions of hydrogen-rich gaseous substances in a hydrotreating, catalytic reforming, hydrocracking or isomerization unit. CAS RN 68477-97-4 refers to a gaseous stream flashed from a separator following the reactor and recycled to the reactor after removal of any acid compounds. CAS RN 68478-00-2 refers to a hydrogen-rich light hydrocarbon gas effluent from the reactor that contains trace acidic compounds (e.g., hydrogen sulphide and carbon dioxide). CAS RN 68607-11-4 refers to a gaseous stream similar to CAS RN 68477-97-4 in a hydrotreating, catalytic reforming, hydrocracking or isomerization unit that is normally recycled and reused in the process.

Both CAS RN 68478-01-3 and CAS RN 68513-18-8 refer to substances in a catalytic reforming process. CAS RN 68478-01-3 refers to a reactor effluent that goes into a heat exchanger to be cooled down before being flashed off in the flash tank. CAS RN 68513-18-8 represents an off-gas stream flashed from a high-pressure flash drum where light compounds are removed and will be recycled to the reactor.

CAS RN 68478-05-7 represents an overhead gas mixture produced from a fractionation column in a thermal cracking reactor (coker or visbreaker) that will go directly into a gas separation unit for further recovery.

CAS RN 68478-25-1 represents a tail gas effluent from an absorber where acid compounds are removed from the fractionation effluents in a catalytic cracking reactor. The substance is normally used as a fuel within the facility.

CAS RN 68478-29-5 represents an overhead gas discharged from a stabilization column fed with hydrotreated cracking products. The substance mainly consists of C₁–C₅ and normally enters a gas separation unit for recovery.

CAS RN 68478-32-0 is a generic description of tail gas effluents from a distillation column to stabilize naphtha products, such as straight-run and catalytic reformed naphthas. The substance consists of C₃–C₆ and normally enters a gas separation unit for recovery.

CAS RN 68478-34-2 represents a mixture of light overhead hydrocarbons discharged from a fractionation column in a coking or visbreaking unit. It normally goes into a gas separation unit for further treatment.

Both CAS RN 68512-91-4 and CAS RN 68918-99-0 refer to an overhead gas effluent discharged from fractionation of crude oils. The substance consists of C₅ and lighter hydrocarbons and will enter a gas separation unit for further treatment.

CAS RN 68513-16-6 represents an overhead gas substance leaving a fractionation column treated with a hydrocracking effluent in a refinery or an upgrader. It will normally enter a gas separation unit for further processing.

CAS RN 68513-17-7 refers to a light hydrocarbon overhead discharged from a stabilization column for straight-run naphtha prior to gasoline blending. The gaseous substance goes into a gas separation unit for further processing.

CAS RN 68514-31-8 is a generic description of a light hydrocarbon gas mixture discharged from a fractionation column in a thermal cracking process (coking or visbreaking) or from atmospheric distillation of crude oils. The gas mixture is further processed in a gas separation unit for further purification.

CAS RN 68514-36-3 is a generic description of gaseous C₁–C₄ hydrocarbons after the removal of mercaptan or other acidic components. It will require further removal of caustic residues or gas purification.

CAS RN 68527-16-2 is a generic description of a light hydrocarbon mixture discharged from the top of a debutanizer column. It will enter a gas separation unit for further recovery.

CAS RN 68602-83-5 is a generic description of a gaseous mixture leaving atmospheric distillation of crude oils or a fractionation column in a cracking process (catalytic cracking or hydrocracking) of gas oils. It is normally discharged into a gas separation unit for further processing.

CAS RN 68602-84-6 represents an off-gas substance from a secondary absorber in a fluidized catalytic cracking unit. It will often be used as a fuel gas consumed on-site.

CAS RN 68606-27-9 refers to a hydrocarbon gas mixture discharged from a debutanizer treated with products of catalytic cracking of gas oils. The overhead substance mainly contains C₃–C₄ and is further processed in an alkylation unit to form iso-naphtha for gasoline blending.

CAS RN 68814-67-5 is a generic description of an off-gas stream produced from various refining units, such as hydrotreating, hydrocracking, hydroreforming and cracking (catalytic and thermal). The gas mixture mainly consists of hydrogen and C₁–C₃ and normally enters a gas separation unit for purification and recovery.

CAS RN 68911-58-0 represents an off-gas substance from a stabilization column for straight-run or cracked kerosene. It will enter a gas separation unit for recovery.

CAS RN 68919-02-8 refers to an overhead gas mixture discharged from a fractionation column in a fluidized catalytic cracking unit. It will go directly into a gas separation unit for further treatment.

CAS RN 68919-04-0 represents an off-gas mixture discharged from a distillation column following a hydrotreating process on a heavy distillate. It will normally be delivered into a gas separation unit for further processing.

CAS RN 68919-08-4 represents an off-gas mixture produced from a pre-flashed column or first distillation column of crude oils. It will go directly into a gas separation unit for further processing.

CAS RN 68919-10-8 refers to an overhead gas produced from a fractionation column following the first distillation of crude oils. It will enter a gas separation unit for further treatment.

CAS RN 68952-79-4 refers to an overhead gas substance from a stabilization column for hydrotreated naphtha. The gaseous mixture will enter a gas separation unit for further treatment.

Uses

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, the substances listed in this screening assessment were identified as either being consumed at the refinery, upgrader or natural gas processing facility or blended into substances leaving the site under a different CAS RN. The site-restricted petroleum and refinery gases discussed in this screening assessment are normally consumed on-site as fuel gas or require further processing to recover each valuable component in the mixture before leaving the facility. Although these substances were identified by multiple use codes established during the development of the DSL, it has been determined from information submitted under section 71 of CEPA 1999, voluntary industry submissions, an in-depth literature review and a search of material safety data sheets that these site-restricted petroleum and refinery gases are not expected to be transported off petroleum facility sites.

Releases to the Environment

Potential releases of petroleum and refinery gases from petroleum facilities can be characterized as either controlled or unintentional releases. Controlled releases are planned releases from pressure relief valves and venting valves, for safety purposes or maintenance, and are considered part of routine operations and occur under controlled conditions. Unintentional releases are typically characterized as unplanned releases due to spills or leaks from various equipment, valves, piping, flanges, etc., and may result from equipment failure, poor maintenance, lack of proper operating practices, adverse weather conditions or other unforeseen factors. Petroleum facilities are highly regulated and regulatory requirements established under various jurisdictions, as well as voluntary non-regulatory measures implemented by the petroleum industry, are in place to manage potential releases (SENES 2009).

Controlled Releases

The site-restricted petroleum and refinery gas CAS RNs in this screening assessment originate as overhead emissions from distillation columns, absorbers, flash tanks and reactors in a petroleum facility. The potential locations for the controlled releases of these gases are the safety valves or venting systems located on the piping or the vessels (e.g., reflux vessels, flash tanks, reactors, towers) where the gas streams are generated.

Under typical operating conditions, controlled releases of site-restricted petroleum and refinery gases are normally collected into a closed system,^[3] according to defined procedures, and usually go to a flare system for combustion. However, in some instances (e.g., to relieve pressure) they may be vented directly to the atmosphere. Exposure of the general population or the environment to releases that are controlled and only occur under typical operating conditions as described above is thus expected to be minimal for the petroleum and refinery gases under the CAS RNs identified in this screening assessment.

Unintentional Releases

Unintentional releases (including fugitive releases) occur from equipment seals (e.g., compressors and storage tanks), valves, piping, flanges, etc. during processing and handling of petroleum substances and can be higher in situations of poor maintenance or operating practice. Regulatory and non-regulatory measures are in place to reduce these events at petroleum refineries and upgraders (SENES 2009). Measures have also recently been applied to natural gas processing facilities (CAPP 2007). Rather than being specific to one substance, these measures are developed in a more generic way in order to limit unintentional releases of all substances in the petroleum sector.

For the Canadian petroleum industry, requirements at the provincial/territorial level typically prevent or manage the unintentional releases of petroleum substances within a facility through the use of operating permits (SENES 2009).

Additionally, existing occupational health and safety legislation specifies measures to reduce occupational exposures of employees, and some of these measures also serve to limit unintentional releases to the environment (CanLII 2009).

Non-regulatory measures (e.g., guidelines, best practices) to reduce unintentional releases are also in place at petroleum sector facilities. Such control measures include appropriate material selection during the setup and design process, regular inspection and maintenance of storage tanks, piping and other process equipment, the implementation of leak detection and repair or other equivalent programs, the use of floating roofs in above-ground storage tanks to reduce the internal gaseous zone, and the minimal use of underground tanks, which can lead to undetected leaks (SENES 2009).

Despite the fact that some measures and practices are in place to reduce the releases of petroleum substances within the facility, it has been recognized that fugitive releases of the petroleum and refinery gases into the atmosphere can occur due to their much higher volatility, (lower boiling point) and higher mobility as compared to liquid substances (US EPA 1995; CPPI 2005; CAPP 2007). In general, the common sources of fugitive releases from a petroleum sector facility are compressor seals, processing valves, flanges, pressure relief valve seals, storage tanks, loading operations, sample lines and open-ended lines (CCME 1993; CPPI 2005). Fugitive releases tend to occur more frequently when processing equipment is not properly maintained or operated, and could go undetected or unfixed for periods of time ranging from days to months (CCME 1993; CAPP 2007). Once released, gases disperse more readily into larger volumes than liquids. Although general population exposure is not typically expected from site-restricted petroleum substances, physical-chemical properties (e.g., higher volatility and vapour pressures) of the petroleum and refinery gases indicate that there is a limited potential for general population and environmental exposure in the vicinity of refinery, upgrader and/or natural gas processing facility sites. Accordingly, it is considered appropriate to quantify potential exposure to the general population from the unintentional releases of petroleum and refinery gases identified by the 40 CAS RNs considered in this screening assessment. Detailed analysis of human exposure was conducted using gas dispersion modelling (see Potential to Cause Harm to Human Health section).

Ethene has previously been identified as a potentially hazardous component to terrestrial plants in some of these petroleum and refinery gases. A comprehensive risk assessment of ethene is ongoing, and thus it is not considered here.

Environmental Fate

Although these site-restricted petroleum and refinery gases are not expected to be transported from the facility, their physical-chemical properties (e.g., high volatility) dictate that any release of them within a facility may lead to their escape to the environment. Therefore, fugacity modelling was used to estimate their environmental fate.

As noted previously, the atmosphere is expected to be the primary environmental compartment into which petroleum and refinery gases are released. When released to air, all components in petroleum and refinery gases are expected to remain in air as they are highly volatile (vapour pressures are 4 × 10⁴ – 7 × 10⁷ Pa) (Table A2.2 in Appendix 2). Therefore, when released, petroleum and refinery gases are expected to remain in the atmosphere (EQC 2003) (Table A2.3 in Appendix 2). Releases to water and soil are not expected.

Persistence and Bioaccumulation Potential

Environmental Persistence

The C₁–C₄ alkanes are relatively inert, non-polar, hydrophobic substances that do not react with water or hydroxide ions (Lyman et al. 1990). Empirical aerobic biodegradation data (API 2001a) show 66–76% biodegradation over 35 days for methane and ethane in water, but it is unlikely that these two gases would remain dissolved in water for that long under natural conditions.

As there are no experimental data on the degradation of these petroleum and refinery gases as complex mixtures, a quantitative structure-activity relationship (QSAR)-based weight-of-evidence approach (Environment Canada 2007) was applied using results from the BIOHCWIN (2008), BIOWIN (2009) and AOPWIN (2008) models. Modelled data for primary and ultimate biodegradation obtained with BIOHCWIN (2008) and BIOWIN (2009), respectively, indicate that none of the representative structures is persistent in water or soil environments (Table A2.4 in Appendix 2). The average atmospheric half-lives for photo-oxidation of 1,3-butadiene are 0.24–10 hours, however, the half-lives of 1,3-butadiene can vary significantly, from hours up to months, under different conditions (e.g., different seasons, clear or cloudy skies) (Canada 2000a). Predicted oxidation half-lives in air for petroleum and refinery gas components were 0.08–1559 days (Table A2.5 in Appendix 2). This is supported by calculated photodegradation values for alkanes (i.e., methane) based on equations from Atkinson (1990) that suggest half-lives of 3.2–960 days for degradation of some alkane components in contact with hydroxyl radicals in sunlight. These substances are not expected to react with other photo-oxidative species in the atmosphere, such as ozone; therefore, it is expected that reactions with hydroxyl radicals will be the most important fate process in the atmosphere for petroleum and refinery gases.

Many petroleum and refinery gas components are predicted to have atmospheric half-lives ranging from 2.4 to 1559 days, and are considered to be persistent in air (half-life in air ≥ 2 days), as set out in the Persistence and Bioaccumulation Regulations under CEPA 1999 (Canada 2000b).

Potential for Bioaccumulation

As no experimental bioaccumulation factor (BAF) or bioconcentration factor (BCF) data for petroleum and refinery gases as complex mixtures were available, a predictive approach was applied to the representative structures using available BAF and BCF models. The modified Gobas model for fish (BCFBAF 2008) predicted middle-trophic-level BAFs of 2.6–182 L/kg and BCFs of 1.7 – 55 L/kg, indicating that none of the representative structures for petroleum and refinery gases have the potential to bioaccumulate significantly in fish.

Based on the available kinetic-based modelled values, none of the components in petroleum and refinery gases meet the bioaccumulation criterion (BCF or BAF ≥ 5000) as set out in the Persistence and Bioaccumulation Regulations (Canada 2000b).

Potential to Cause Ecological Harm

Ecological Effects Assessment

Aquatic Compartment

A range of aquatic toxicity predictions for representative structures was obtained from the ECOSAR (2009) model. Predicted acute toxicity values (median lethal concentrations [LC₅₀s]) were moderate, ranging from 10 to 167 mg/L for fish, from 11 to 164 mg/L for daphnids and from 1 to 96 mg/L for algae. Some components are not sufficiently soluble in water to reach the predicted LC₅₀ concentrations, such as the simple alkanes and alkenes that likely make up the bulk of petroleum and refinery gases. These results indicate that, in general, these substances are not highly hazardous to aquatic organisms.

Terrestrial Compartment

Experimental data available for acute effects via inhalation in laboratory animals indicate that few of the representative structures are acutely toxic to mammals (ACGIH 2001, 2005; Canada 2000a). Methane is biologically inert (Rom 1992); iso-butane is toxic to rats at a concentration of 570 000 parts per million (ppm) over 15 minutes (ESIS 2007); an LC₅₀ was noted at 620 000 mg/m³ in rats for isobutylene (Shugaev 1969; BG Chemie 1991; ESIS 2000; OECD 2005); and inhalation exposure to 600 000 ppm of ethene continuously for 90 days in rats had only minor effects (Bingham et al. 2001; OECD 1998; ACGIH 2001). Propylene at 112 000 mg/m³ over four hours did not produce mortality (Conolly and Osimitz 1981), and at 40% (688 000 mg/m³) produces only light anaesthesia in rats (Bingham et al. 2001).

In addition, ovarian atrophy was observed following a 2-year chronic inhalation exposure of mice to 6.25 ppm (13.8 mg/m³) of another representative structure, 1,3-butadiene, while testicular atrophy was observed following exposure to 200 ppm (442 mg/m³) (ATSDR 2009).

Ecological Exposure Assessment

Although the petroleum and refinery gases in this screening assessment have been identified as site-restricted, there is limited potential for release to the ecosystem, as they are all gases that can unintentionally be released at a petroleum facility. Resulting concentrations of the components of petroleum and refinery gases in air surrounding petroleum facilities are expected to be minimal (e.g., in the low µg/m³ range for 1,3-butadiene), as indicated by results of air dispersion modelling described in the exposure section of the human health portion of this assessment.

Characterization of Ecological Risk

The major representative structures in petroleum and refinery gases have a very low acute and chronic toxicity to mammals (400 000 – 700 000 mg/m³ and 13.8 – 442 mg/m³, respectively), such that it is highly unlikely that mammals would be exposed to concentrations causing an effect.

It is also not expected that there would be significant contamination of watercourses from gaseous fugitive release from petroleum facilities. Therefore, no exposure assessment and risk quotient estimation for aquatic organisms has been conducted.

The significance of releases of ethene to the environment will be assessed in a separate report that considers all sources of release.

None of the components in these petroleum and refinery gases meet the bioaccumulation criteria set out in the Persistence and Bioaccumulation Regulations, but many of their principal components meet the atmospheric persistence criteria in the Regulations.

Based on the available evidence, it is not expected that the fugitive emissions of these petroleum and refinery gases are causing environmental harm.

Uncertainties in Evaluation of Ecological Risk

The proportions of each component in a specific petroleum and refinery gas CAS RN are generally not known. However, the low ecological toxicity of most of the components makes this information gap relatively unimportant for the assessment of ecological risk.

Potential to Cause Harm to Human Health

Exposure Assessment

The general physical and chemical properties of the petroleum and refinery gases indicate that when these gaseous substances are released, they will rapidly disperse in the environment in the vicinity of refinery, upgrader and/or natural gas processing facilities. Furthermore, when these gases are released into the air, the component chemicals will separate and partition in accordance with their own physical-chemical properties (API 2009a). As such, inhalation would be the primary potential route of exposure and is therefore the focus of the current exposure assessment.

Site-restricted petroleum and refinery gases may disperse into the air around a facility via unintentional releases from, for example, process equipment, valves and flanges. Due to limited information on emissions associated with these complex mixtures as a whole, it was considered appropriate to characterize the emissions of a specific component of the mixtures. 1,3-Butadiene was selected from the list of components (Table 1) that confer a broad range of potential toxicities as it is a high-hazard component representing the potential effects on human health of the petroleum and refinery gases. Furthermore, it is a component that is found in many of the site-restricted petroleum and refinery gases and was the basis for their classification as carcinogens by the European Union (European Commission 2004; ESIS 2008).

Potential Exposure to Unintentional On-site Releases

The annual average concentrations of 1,3-butadiene in ambient air have been reported by various sources to range from below 0.05 µg/m³ to 0.4 µg/m³, depending on location. In general, automotive emissions are a major contributor to 1,3-butadiene levels in ambient air (Canada 2000a). Curren et al. (2006) reported that the average annual 1,3-butadiene concentration at urban sites in Canada over 1995–2003 was 0.22 µg/m³. Additional monitoring data for 1990–2007 were collected from the Clean Air Strategic Alliance data warehouse in Alberta (CASA 2007), indicating that the average annual concentrations in central Edmonton, east Edmonton and central Calgary were 0.34 µg/m³, 0.18 µg/m³ and 0.32 µg/m³, respectively. The annual average concentration of 1,3-butadiene in ambient air ranged from below 0.05 to 0.2 µg/m³ in 2005 based on 49 monitoring sites across Canada (NAPS 2008), from below 0.05 µg/m³ to 0.05 - 0.1 µg/m³ in 2006 based on 47 monitoring sites (NAPS 2008), and from 0.01 to 0.4 µg/m³ in 2008/2009 based on 58 monitoring sites across Canada (NAPS 2010). For this assessment, 0.22 µg/m³ was selected to represent ambient background for comparison to modelled emissions.

No measured, and limited estimated quantitative data on emissions of 1,3-butadiene from Canadian petroleum facilities were identified. Therefore, potential human exposure to petroleum and refinery gases was estimated based on measured benzene emission data and the ratio of 1,3-butadiene to benzene in total refinery releases (NPRI 2000–2007; TRI 2007). Benzene emission is taken to be a measure of substance throughput in refinery facilities. To relate the substance throughput in a facility to the total 1,3-butadiene lost, it is assumed that a constant ratio holds between the total amount of 1,3-butadiene lost in the petroleum refinery gas production streams through fugitive emissions and the measured amount of benzene lost in all production streams of the facility through fugitive emissions. Thus the ratio of 1,3-butadiene to benzene in fugitive emissions was used as a scaling factor and applied to known emissions data. In general, fugitive releases of benzene in processing areas originate from processing units handling liquid substances. In comparison, fugitive releases of 1,3-butadiene in processing areas primarily originate from processing units handling gas substances. Compared with 1,3-butadiene, the amount of benzene released due to the fugitive releases in gas processing units which produce petroleum and refinery gases is considered minor. Furthermore, based on the carbon ranges reported in the CAS RN descriptions for the site-restricted petroleum and refinery gases, which are predominantly hydrocarbons ranging from C₁–C₄ (NCI 2006), only six of the 40 CAS RNs in this assessment may potentially contain benzene.

Data from the National Pollutant Release Inventory in Canada (NPRI 2000–2007) and the US Toxics Release Inventory (TRI 2007) were used to define the ratio of 1,3-butadiene to benzene in fugitive emissions from a petroleum facility. These ratios were used to generate a range of emission rates for estimating potential 1,3-butadiene exposure concentrations. The median ratio (50th percentile of the data set) from the NPRI data (1:216) was used for estimating the low end of the emission range. However, only three to six Canadian refineries and upgraders reported fugitive emissions of 1,3-butadiene in a given year over the period 2000–2007. The median ratio from the TRI data (1:85) was used for estimating the high end of the emission range. The TRI data came from 65 US refineries and are considered representative and robust due to the reporting requirements and the large reporting base.

Monitoring data on benzene emissions from a Canadian refinery were reported by Chambers et al. (2008) using a differential absorption light detection and ranging (DIAL) method. DIAL technology has been referenced as one of the best available methodologies for quantitative on-site monitoring of benzene in both refineries and storage facilities by the European Commission (EIPPCB 2003, 2006). The DIAL method has been cited as being able to provide reliable short-term emission estimates (CONCAWE 2008; US EPA 2010). When short-term emission estimates are extrapolated to project annual inventory values, high estimations may occur as compared to API emission algorithms based on standardized assumptions (CONCAWE 2008). Regardless of discrepancy between DIAL and API emission estimates, DIAL measurements, based on quantitative measurements, are considered to be a reliable estimation method and have been used to assess fugitive emissions in European refineries for over 20 years, and are accepted by the US EPA (CONCAWE 2008; US EPA 2006, 2010).

1,3-butadiene emissions were estimated based on benzene DIAL emission data (Chambers et al. 2008) and the ratios of 1,3-butadiene to benzene in the fugitive emissions of a facility (NPRI 2000-2007; TRI 2007), generating a range of emission values. The dispersion of 1,3-butadiene in air, for increasing distances from the release source, was modelled using SCREEN3 (1996) (developed by the US EPA), thereby generating a range of exposure concentrations at each distance.

SCREEN3 is 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 substance at chosen receptor heights and at various distances from a 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 direction. This gives an estimate of the air concentration over a 24-hour exposure (US 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 uncorrelated to 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 are listed in Table A3.1 of Appendix 3.

The modelling results from this approach are presented in Table A3.2 of Appendix 3. The results of the modelled dispersion profile of 1,3-butadiene, based on distance from the release source, demonstrate that fugitive emissions of petroleum and refinery gases from these facilities result in 1,3-butadiene concentrations in ambient air of approximately 0.44 µg/m³ at 200 m for the high end of the emission range and approximately 0.17 µg/m³ at 200 m for the low end of the range (Table A3.2 in Appendix 3). It is estimated that for the high end of the range (0.44 µg/m³, based on an emissions ratio of 1:85), the contribution of 1,3-butadiene associated with unintentional releases of petroleum and refinery gases will be equivalent to the average annual Canadian ambient air concentration of 0.22 µg/m³ at a distance of 500 m from the release source. For the low end of the range (0.17 µg/m³, based on an emissions ratio of 1:216), the contribution of 1,3-butadiene due to the unintentional release of petroleum and refinery gases decreases to 0.088 µg/m³ at 500 m from the release source.

Overall, the SCREEN3 air dispersion modelling suggests that the unintentional release of petroleum and refinery gases results in a contribution to ambient air concentrations of 1,3-butadiene in the vicinity of the release source. The estimated 1,3-butadiene concentrations from petroleum and refinery gases decline with increasing distance from the release source and, in conservative estimates at 500 m from the centre of the processing facility, are considered to reach values associated with the average Canadian background concentration.

A supplementary analysis of the estimated emissions data was conducted to assess the sensitivity of the exposure modelling outputs to the input parameters (as listed in Table A3.1 of Appendix 3) used in the SCREEN3 modelling. Of particular interest, an increase in the rate of release of emissions for a given site area in units of grams per second per metre squared (g/s·m²), or release intensity, can reflect either an increase in the rate of release (g/s) for a constant release area or release from a more localized area (m²), demonstrating production-volume changes that can have a significant impact on the maximum exposure estimations. Consequently, any increase in process volume at a refinery, upgrader and/or natural gas processing facility would result in increased levels, and thus exposures above the Canadian average annual ambient air concentration for greater distances from the release sources. Details of the effect of emission intensity on the estimated maximum annual exposures are shown in Figure A3.1 of Appendix 3.

An alternate approach for exposure characterization, based on application of standardized emission factors and components as described by the Canadian Chemical Producers’ Association and the Canadian Petroleum Products Institute (CCPA 2008; CPPI 2007), resulted in similar outputs. Overall, available information shows that there is a contribution to ambient background levels of the component 1,3-butadiene associated with the unintentional releases of petroleum and refinery gases. Accordingly, there may be limited general population exposure to petroleum and refinery gases in the vicinity of refinery, upgrader and/or natural gas processing facilities.

Atmospheric degradation of 1,3-butadiene is not considered in the exposure modelling. Although the average atmospheric half-lives for photo-oxidation of 1,3-butadiene are reported to range from 0.24–10 hours, the half-lives of 1,3-butadiene can vary significantly, from hours up to months, under different conditions (e.g., different seasons, clear or cloudy skies) (Canada 2000a). Therefore, as a conservative approach, losses due to photo-degradation of 1,3-butadiene are not considered in the estimation of the concentration profile of 1,3-butadiene in this screening assessment.

Health Effects Assessment

Health effects information for the 40 site-restricted petroleum and refinery gas substances was not available. Toxicological information for additional petroleum and refinery gas substances in the Petroleum Sector Stream Approach that are similar from both a process and physical-chemical perspective was also not found. Therefore, in order to characterize the toxicity of these site-restricted substances, US EPA High Production Volume Information System (HPVIS) read-across substances and petroleum and refinery gas component classes, including alkanes, alkenes, alkadienes, alkynes, aromatics, mercaptans and inorganics, were considered. Available literature relevant to petroleum and refinery gases and their individual components was considered in the preparation of the screening assessment, as a wide range of chemical species constitute these gas substances; however, only a summary of the critical information upon which the conclusion is based is presented here.

Gases (petroleum), light steam-cracked, butadiene concentrate (CAS RN 68955-28-2), was identified as a substance similar to hydrocarbons, C₃–C₄ rich, petroleum distillates (CAS RN 68512-91-4), a site-restricted substance, for the acute and genetic toxicity endpoints. An LC₅₀ value of ≥ 5300 mg/m³ was reported in rats for CAS RN 68955-28-2.

An increased frequency of micronuclei in erythrocytes was observed in the bone marrow of male and female CD1 mice exposed to CAS RN 68955-28-2 by inhalation for 2 days. In vitrogenotoxicity results for CAS RN 68955-28-2 were mixed: an increased mutation frequency was noted in mouse lymphoma cells without activation, and an increase in unscheduled deoxyribonucleic acid (DNA) synthesis was observed in mammalian cells, but negative results were reported for reverse mutation (Ames assay) and cell transformation (US EPA 2008a). CAS RN 68476-52-8, or hydrocarbons, C₄, ethylene-manuf.-by-product (C₄ crude butadiene; 10% butadiene), was also identified through HPVIS read-across analysis as a substance similar to CAS RN 68512-91-4 for repeated-dose, reproductive and developmental toxicity endpoints. In a study in which male and female Sprague-Dawley rats were exposed by inhalation to up to 20 000 mg/m³ prior to breeding, during breeding and up to gestational day 19, for a total of approximately 36–37 days (US EPA 2008a), a no-observed-adverse-effect concentration (NOAEC) of 20 000 mg/m³ was identified specifically for reproductive and developmental toxicity while a no-observed-effect concentration (NOEC) of 20 mg/L (20 000 mg/m³) was identified for repeated-dose toxicity due to lack of effects observed in a variety of endpoints.

As indicated above, there were no reports in the published literature of toxicological studies on any of the petroleum and refinery gases administered as a mixture. The petroleum and refinery gases have been previously evaluated for mammalian health hazards based on the assessment of individual components of the gas substances (API 2001b, 2009a, 2009b; CONCAWE 2005). The results of the component evaluation are useful in characterizing potential hazards associated with the mixtures. Generally, there are multiple potentially hazardous components in a petroleum and refinery gas substance (listed in Table 1); therefore, the component that is the most highly hazardous for a particular endpoint is used to characterize the hazard associated with the mixture (API 2009a, 2009b). International agencies and organizations have prepared hazard profiles of the various components of the petroleum and refinery gases (API 2001a, 2001b, 2009a, 2009c; CONCAWE 2005).

A brief summary of the toxicological effects of the component classes is presented in Appendix 4; however, a critical review of all hazard data on the numerous components was not undertaken. Rather, the current screening assessment of the site-restricted petroleum and refinery gas substances focuses on a specific component considered to conservatively represent the hazard posed by these substances as a group to human health. The alkadiene 1,3-butadiene (CAS RN 106-99-0) was selected as the high-hazard component to represent the critical health effects of the site-restricted petroleum and refinery gases, as it may be present in the 40 CAS RNs considered in this screening assessment and its critical health effects are well documented (Canada 2000a).

Extensive literature is available regarding the toxicokinetics and effects of 1,3-butadiene following acute, short-term and long-term exposures, primarily via the inhalation route. Recent assessments by the Government of Canada and other organizations have thoroughly characterized the hazard data (Canada 2000a; EURAR 2002; US EPA 2002; Grant 2008; ATSDR 2009). As relevant to the current screening assessment, the critical literature for characterizing the human health effects for 1,3-butadiene as a high-hazard component for the site-restricted petroleum and refinery gases is summarized.

Appendix 5 contains a summary of the critical health effects information on 1,3-butadiene. A review of the human health effects of 1,3-butadiene was previously done under the Priority Substances List (PSL) 2 assessment (Canada 2000a) This substance was subsequently added to the List of Toxic Substances - Schedule 1 of CEPA 1999.

Petroleum and refinery gases have been classified by the European Commission as a carcinogen when the concentration of 1,3-butadiene in the substance is greater than 0.1% by weight (European Commission 2004; ESIS 2008). As a component of petroleum and refinery gases, 1,3-butadiene has been classified as a carcinogen by numerous national and international agencies. Under the Priority Substances Assessment Program, the Government of Canada concluded that 1,3-butadiene met the criteria under section 64c of CEPA 1999 on the basis of a plausible mode of action for induction of tumours involving direct interaction with genetic material (Canada 2000a). The International Agency for Research on Cancer (IARC 2008) has also classified 1,3-butadiene as carcinogenic to humans(Group 1); the US EPA (2002) concluded that 1,3-butadiene is carcinogenic to humans by inhalation; the US National Toxicology Program (NTP 2005) has classified 1,3-butadiene as a known human carcinogendue to sufficient evidence of carcinogenicity in humans; and the European Commission has classified 1,3-butadiene as a carcinogen (Category 1:May cause cancer; substances known to be carcinogenic to humans), but also as a mutagen (Category 2: May cause heritable genetic damage; substances which should be regarded as if they are mutagenic to man) (EURAR 2002; ESIS 2008).

The carcinogenic potential of inhaled 1,3-butadiene has been clearly demonstrated in a two-year inhalation study in B6C3F1 mice exposed to 1,3-butadiene at concentrations of 0 to 625 ppm (0 to 1380 mg/m³) in a 103-week study. 1,3-Butadiene was found to be a potent carcinogen, inducing common and rare tumours at a variety of sites in mice. In most cases, there was evidence of an exposure–response relationship in the tumour incidence and the involvement of a genotoxic mechanism. A statistically significant increase in the incidence of alveolar/bronchiolar adenocarcinomas or carcinomas in females was observed at 6.25 ppm (13.8 mg/m³) (NTP 1993; EURAR 2002; US EPA 2002). As tumour induction was observed at all concentrations examined, it is likely that exposures lower than 6.25 ppm (13.8 mg/m³) would also cause cancer in mice (US EPA 2002).

The single long-term inhalation study in rats suggests that 1,3-butadiene is also a multi-site carcinogen in the rat; however, the effects were observed at air concentrations that were 2–3 orders of magnitude higher than in the mouse. In contrast to the mouse, the rat tumour profile suggests a possible non-genotoxic mechanism occurring indirectly via the endocrine system rather than directly by reactive metabolites (Owen 1981; Owen and Glaister 1990; Owen et al. 1987).

Although there are differences in species sensitivity to the carcinogenic properties of 1,3-butadiene, the available data provide unequivocal evidence that 1,3-butadiene is a multi-site carcinogen in rodents (US EPA 2002).

Several epidemiological investigations of the carcinogenicity of 1,3-butadiene have been conducted and have served as the basis for assessment of the weight of evidence for causality of associations based on traditional criteria (Canada 2000a; EURAR 2002; US EPA 2002). The investigation by Delzell et al. (1995, 1996), which was a large, good-quality cohort mortality study, portrays a clear association between exposure to 1,3-butadiene in the styrene-butadiene rubber industry and leukemia in humans. On the basis of this evidence, various international agencies have concluded that there is “sufficient evidence to consider 1,3-butadiene carcinogenic to occupationally exposed populations” (US EPA 2002) and that “butadiene should be regarded as carcinogenic in humans” (EURAR 2002).

Overall, on the basis of the available rodent and human evidence, it can be considered that 1,3-butadiene has the potential to induce tumours via a mode of action involving direct interaction with genetic material (Canada 2000a; EURAR 2002; US EPA 2002).

The Government of Canada has previously developed estimates of carcinogenic potency associated with inhalation exposure to 1,3-butadiene. A tumourigenic concentration (TC ₀₁) of 1.7 mg/m³ was derived from the epidemiological investigation of Delzell et al. (1995), and the quantitative estimate of carcinogenic potency (TC₀₅) derived on the basis of data in experimental animals was 2.3 mg/m³ for the most sensitive tumour site in mice (Canada 2000a).

The US EPA (2002) derived a cancer potency from inhalation exposure using the linear relative-rate model based on the same data as reported by the Government of Canada. An inhalation unit risk of 3×10^-5 (µg/m³)^-1 was calculated based on the Delzell et al. (1995) retrospective cohort study (US EPA 2002). More recently, an inhalation unit risk factor of 5×10^-7(µg/m³)^-1 has been calculated by the Texas Commission on Environmental Quality (TCEQ) based on updated human leukemia data (Grant 2008). The value derived by Grant (2008) used updated exposure estimates from the same study population that was selected as the best published exposure estimates by the US EPA (2002) to evaluate human cancer risk.

An extensive database exists on the genotoxicity of 1,3-butadiene investigated in a range of in vitro and in vivo studies encompassing a variety of biological systems ranging from bacteria to humans (EURAR 2002). Detailed examinations of this database can be found in a number of recent assessments conducted by the Government of Canada (Canada 2000a), the US EPA (2002), the European Commission (EURAR 2002) and ATSDR (2009). Consequently, this information was not included in Appendix 5.

To date, the studies evaluating the genotoxic potential of 1,3-butadiene in humans have produced equivocal results; however, 1,3-butadiene is clearly genotoxic in mice. The human data are too limited to allow the genotoxic potential of 1,3-butadiene in exposed humans to be dismissed (EURAR 2002; ATSDR 2009). Overall, 1,3-butadiene is considered a likely human somatic and germ cell toxicant (Canada 2000a). Also, based on the experimental animal data, it is in the highest category described in the weight-of-evidence scheme in the Guidelines for Mutagenicity Risk Assessment (US EPA 1986).

The reproductive organs have been identified as critical targets for 1,3-butadiene-induced non-carcinogenic effects in mice and rats (Canada 2000a; EURAR 2002; US EPA 2002; Grant 2008). The most sensitive reproductive effects identified consistently across various assessments of 1,3-butadiene were observed in a two-year chronic inhalation exposure study in B6C3F1 mice; mice were exposed to concentrations of 0 to 625 ppm (0 to 1380 mg/m³). Ovarian atrophy was observed following exposure to the lowest 1,3-butadiene concentration tested, 6.25 ppm (13.8 mg/m³), while testicular atrophy was observed following exposure to 200 ppm (442 mg/m³) (NTP 1993; EURAR 2002; US EPA 2002; Grant 2008; ATSDR 2009). Based on the proposed mode of action, specifically the involvement of the diepoxide metabolite in the induction of ovarian atrophy and a decrease in serum progesterone levels, these effects observed in mice are considered to have a threshold and to be concentration- and duration-dependent (US EPA 2002; Grant 2008).

No studies were identified in the available literature regarding the effects of inhalation exposure to 1,3-butadiene on reproduction or development in humans. However, it was noted that when considering the implications of the gonadal effects observed in mice for human health, there is no indication that humans respond in a quantitatively similar manner (EURAR 2002).

Characterization of Risk to Human Health

A critical health effect for the initial categorization of site-restricted petroleum and refinery gas substances is carcinogenicity, based primarily on classifications by international agencies. The European Union has identified petroleum and refinery gases containing 1,3-butadiene at concentrations greater than 0.1% by weight as carcinogens. Additionally, 1,3-butadiene has been identified by Health Canada and several international regulatory agencies as a carcinogen, and was added to the List of Toxic Substances in Schedule 1 of CEPA 1999.

1,3-Butadiene was found to be a multi-site carcinogen in rodents, increasing the incidence of tumours at all concentrations tested. Epidemiological studies provide further evidence for an association between exposure to 1,3-butadiene in an occupational environment and leukemia in humans. 1,3-Butadiene also exhibits genotoxicity in vitro and in vivo and aplausible mode of action for induction of tumours involves direct interaction with genetic material.

Both air dispersion modelling and calculations based on the application of emission factors indicates that unintentional releases of petroleum and refinery gases contribute to the overall 1,3-butadiene concentration in ambient air in the vicinity of refinery, upgrader and/or natural gas processing facilities. Consistent with refinery, upgrader and/or natural gas processing facilities being the primary point sources of emissions, the estimated 1,3-butadiene concentrations decline with increasing distance and are estimated to be comparable to or below Canadian average concentrations at distances of more than 500 m from the release source. Using the estimates of carcinogenic potency previously developed by the Government of Canada (Canada 2000a), together with the range of annual estimates of exposure derived from dispersion modelling of 1,3-butadiene as a high-hazard component of the petroleum and refinery gases, margins of exposure were derived for increasing distances from the release source (a single distance is illustrated in Table 3).

At a distance of 200 m from the release source, and using the high end of the exposure range, the margin of exposure is 5300 while at 500 m from the release source exposure approximates the Canadian average annual ambient air concentration of 0.22 µg/m³, with a corresponding margin of exposure of 10 500. Although the magnitude of risk would vary with the cancer potency metrics selected (e.g., TC₀₅; unit risks derived by US EPA and Texas Commission on Environmental Quality based on linear low-dose extrapolation models), use of a conservative cancer potency metric is considered appropriate given the uncertainties in the health effects database. The above-noted margin of exposure (5300) at 200 m from the release source for the high end of the exposure range is considered potentially inadequate to address uncertainties in the health effects and exposure databases for site-restricted petroleum and refinery gases. Uncertainties with respect to the exposure database are reflected in the model sensitivity analysis, which demonstrates that an increase in the process volume would increase the magnitude of exposure, as well as the distance from the release source before levels reached ambient levels (Figure A3.1 in Appendix 3).

With respect to non-cancer effects, reproductive toxicity was observed to be the critical endpoint. The lowest-observed-adverse-effect concentration (LOAEC) for inhalation exposure (the principal route of exposure for the general population) was 6.25 ppm (13.8 mg/m³), based on ovarian atrophy characterized by the lack of oocytes, follicles and corpora lutea in mice in a two-year chronic bioassay. Comparison of this LOAEC with the maximum annual high-end and low-end concentrations of the exposure range for 1,3-butadiene results in margins of exposure of approximately 31 000 and 81 000, respectively. These margins are considered adequate to address uncertainties in the non-cancer health effects and exposure databases for site-restricted petroleum and refinery gases.

Uncertainties in Evaluation of Human Health Risk

Uncertainty exists regarding exposure of the general population and the environment to site-restricted petroleum and refinery gases. Currently, no Canadian monitoring data are available for petroleum and refinery gases as a whole. Therefore, 1,3-butadiene was selected as a high-hazard component, and the potential unintentional releases of these gases were estimated by modelling the contribution of 1,3-butadiene emissions from refinery, upgrader, and natural gas processing facilities to concentrations in ambient air.

Uncertainties arose from utilizing NPRI and TRI data to calculate the ratio of 1,3-butadiene to benzene, and from utilizing DIAL measurements of benzene emissions at a Canadian refinery to estimate potential emissions from petroleum facilities.

There is uncertainty regarding the potential for exposure to 1,3-butadiene from natural gas processing facilities, as exposures were modelled based on data from petroleum refineries. Uncertainty exists in the possible differences in the composition of the petroleum and refinery gases between refineries or upgraders and natural gas processing facilities arising from differences in equipment between facilities.

It is assumed that all the estimated releases of 1,3-butadiene are attributed to the petroleum and refinery gases in this assessment.

There is uncertainty regarding the modelling of the concentration profile of 1,3-butadiene using SCREEN3 (1996). SCREEN3 requires limited input parameters and non-site-specific meteorological data which introduced uncertainty. All the assumptions made in the exposure analysis are listed in Appendix 3.

The petroleum and refinery gases assessed may each contain multiple inorganic and organic components that contribute to the overall hazard of the category substances. The compositional ranges of specific gas components may vary significantly depending on the source of crude oil, bitumen, or natural gas, operating conditions, seasonal process issues and economic cycles. Health effects have been characterized by the health effects associated with 1,3-butadiene emitted or released to the atmosphere; however, there is uncertainty regarding the concentration of this component in each specific petroleum and refinery gas substance as identified by their CAS RN.

Use of a single high hazard component to characterize hazard may not reflect all hazards associated with the mixture. Uncertainties with respect to health effects include limitations of a component approach, as other hazardous components in the petroleum and refinery gases (see Table 1) are not considered in the hazard and risk characterization.

Additional uncertainties relevant to the health effects evaluation of 1,3-butadiene are described in the earlier Government of Canada Priority Substances List assessment for this substance (Canada 2000a).

Conclusion

Based on the current available information, none of the 40 CAS RNs considered in this assessment contain components that meet the bioaccumulation criteria as defined in the Persistence and Bioaccumulation Regulations. Many of the components of site-restricted petroleum and refinery gases do meet the atmospheric persistence criteria defined in the Regulations.

Based on the information presented in this report, it is concluded that these petroleum and refinery gases do not meet the criteria under paragraphs 64(a) and (b) of 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.

On the basis of the available data, it is concluded that the site-restricted petroleum and refinery gases meet the criteria in paragraph 64(c) of CEPA 1999, as they are entering or may enter 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 site-restricted petroleum and refinery gases (CAS RNs 68307-99-3, 68476-26-6, 68476-49-3, 68477-69-0, 68477-71-4, 68477-72-5, 68477-73-6, 68477-75-8, 68477-76-9, 68477-77-0, 68477-86-1, 68477-87-2, 68477-93-0, 68477-97-4, 68478-00-2, 68478-01-3, 68478-05-7, 68478-25-1, 68478-29-5, 68478-32-0, 68478-34-2, 68512-91-4, 68513-16-6, 68513-17-7, 68513-18-8, 68514-31-8, 68514-36-3, 68527-16-2, 68602-83-5, 68602-84-6, 68606-27-9, 68607-11-4, 68814-67-5, 68911-58-0, 68918-99-0, 68919-02-8, 68919-04-0, 68919-08-4, 68919-10-8 and 68952-79-4) meet one or more of the criteria set out in section 64 of CEPA 1999.

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Appendices

Appendices of the Screening Assessment

• Appendix 1: Description of the nine groups of petroleum substances
• Appendix 2: Data tables for site-restricted petroleum and refinery gases
• Appendix 3: Exposure estimate modelling data and results
• Appendix 4: Summary of the toxicological effects of the component classes of petroleum and refinery gases
• Appendix 5: Summary of the critical health effects information on 1,3-butadiene
• Appendix 6: Revisions to Domestic Substances List (DSL) names of site-restricted petroleum and refinery gases

Footnotes

Date modified:

2013-10-01