Screening assessment on MBMBP phenols: chapter 1


Synopsis

Under the Canadian Environmental Protection Act, 1999 (CEPA 1999), the Ministers of the Environment and of Health have conducted a screening assessment of Phenol, 2,2'-methylenebis[6-(1,1-dimethylethyl)-4-methyl- (MBMBP), Chemical Abstracts Service Registry Number 119-47-1, which was selected as one of 123 substances on the Domestic Substances List for a pilot project for screening assessments.

MBMBP is used in industry as an antioxidant (in acrylonitrile-butadiene-styrene copolymer, polypropylene, polyacetal, rubber, latex and adhesives) and as a stabilizer (in styrenic and olefin polymers and polyoxymethylene homopolymers and copolymers). Results from the Notice with Respect to Certain Substances on the Domestic Substances List (DSL) conducted under the authority of section 71 of CEPA 1999 for the year 2000 indicated that MBMBP was not manufactured in Canada, although 10 to 100 tonnes of MBMBP were imported into Canada.

Based on its sources and use patterns, MBMBP is expected to be released mostly to water. Current Canadian releases to the aquatic environment could occur as a result of losses arising during the processing of plastics containing MBMBP. There are no natural sources of MBMBP in the environment. Data concerning measured levels of MBMBP in air, water, soil and sediment in Canada were not found.

When released to water, MBMBP partitions to water and sediment. In water, MBMBP undergoes slow biodegradation. MBMBP should not bioaccumulate to a high degree in the tissues of freshwater organisms, as the highest experimental bioconcentration factor identified was 125. MBMBP is therefore considered to be persistent in water but not bioaccumulative, according to the criteria specified in the Persistence and Bioaccumulation Regulations under CEPA 1999. No experimental data were found on the half-lives of MBMBP in soil or sediment. MBMBP is quickly removed from the troposphere, with an estimated atmospheric half-life of less than 7 hours.

According to experimental results, MBMBP has the potential to harm aquatic organisms. No experimental toxicity data were found for sediment-dwelling organisms. There is also a lack of data on the toxicity of MBMBP to terrestrial organisms. A risk quotient analysis, integrating potential exposure with known adverse environmental effects, was performed for aquatic and soil media. The predicted exposure concentration of MBMBP in surface water (based on conservative environmental modelling of current potential releases) was lower than the adverse effect threshold predicted for sensitive aquatic organisms. The predicted exposure concentration of MBMBP in soil (based on conservative environmental modelling of MBMBP-amended sewage treatment plant sludge) was lower than the adverse effect threshold predicted for sensitive soil-dwelling organisms.

Based on the available information and the weight of evidence, it is concluded that MBMBP is not entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term effect on the environment or its biological diversity or that constitute or may constitute a danger to the environment on which life depends. Therefore, it is concluded that MBMBP does not meet the criteria set out in paragraphs 64(a) and 64(b) of the Canadian Environmental Protection Act, 1999.

Comparison of a conservative critical effect level (i.e., 6 mg/kg-bw per day) for slight changes in biochemical parameters in a 90-day study in dogs with the highest of the upper-bounding estimates of exposure for all age groups in the population living in the vicinity of a point source (i.e., 0.037 µg/kg-bw per day) for the 0- to 6-month age group (based on conservative modelling of potential releases to the environment) resulted in a margin of exposure of approximately 160 000. This margin is considered adequate to address elements of uncertainty associated with limitations of the databases for population exposure and health effects (including intraspecies and interspecies variations in sensitivity, as well as the biological adversity or severity of the effects deemed critical), in which confidence is low and moderate, respectively.

Although no information was identified on the presence of MBMBP in consumer products, the nature of the physical and chemical properties is such that consumer products are not expected to contribute significantly to the exposure of the general population in Canada.

The outcome of this screening health assessment is that MBMBP does not meet the criterion set out under paragraph 64(c) of CEPA 1999--i.e., it is 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. This determination is based on the adequacy of the sufficiently health-protective margin between a conservatively selected lowest effect level and upper-bounding estimates of exposure of individuals in the general population.

Based on the information available for environmental and human health considerations, it is concluded that MBMBP does not meet any of the criteria set out in section 64 of the Canadian Environmental Protection Act, 1999.

 

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