Consultations on the CEPA New Substances Notification Regulations and New Substances Program - Final Report of the Multistakeholder Consultations

Appendix 7: Additional Information on the Assessment of Degradation Products

The exposure assessment of a substance includes the evaluation of the overall environmental persistence of a substance and its degradation products. In the context of the NS Program, biodegradation and hydrolysis are key elements in determining the half-life of a substance in various environmental media (air, water, soil and sediment). However, depending upon the circumstances, other degradation/disposal processes may be considered, such as photodegradation, thermolysis and incineration.

The biodegradation/hydrolysis half-lives of a substance are evaluated using experimental, surrogate or predicted data. Substances with shorter half-lives and not released on a continuous basis may not reside in a medium for a sufficient period of time to allow for chronic exposure of organisms. Also, biotic and hydrolytic degradation products are considered on an equal basis with the parent compound during the assessment, in order to determine the long-term potential toxicity of the breakdown products, as well as the potential toxicity of the parent compound. In general, these breakdown products tend to be less toxic, more water-soluble and, hence, more bioavailable to organisms; however, in some circumstances, degradation products possess greater toxicity than the parent compound.

This appendix examines four cases of previously notified polymers and chemicals and summarizes Environment Canada's concerns with degradation products. It also draws attention to the type of additional information that was requested by the department to ensure a comprehensive risk assessment of the notified substance and its degradation product(s) and the respective evaluation decisions.

Case Studies

1. A polymer was notified and assessed by the departments. The substance was initially notified as a low concern polymer, but has subsequently been reclassified as not low concern, based on the fact that it is expected to degrade or decompose. It was determined that microbial degradation of the polymer in anaerobic sediments would lead to release of a potentially toxic degradation product. To address these concerns, the notifier was contacted to conduct an anaerobic degradation test to ascertain the substance's stability under anaerobic conditions. To date, the information has not been received. A Schedule VIII notification will be required, including hydrolysis and ready biodegradation data.
   
   
2. In another example, a polymer and its degradation products were of moderate (bordering high) toxicity in the aquatic environment. Information supplied in the notification package indicated that acid treatment (i.e., hydrolysis under acidic conditions) of the polymer alleviated environmental concerns by preventing aqueous discharge of the oil layer containing the hydrophobic (toxic) degradation product. The notifier was requested to provide additional information with respect to the effectiveness of the sewage treatment plant to degrade the notified polymer. The environmental risk assessment focused on the toxicity, release and fate of the parent compound, as well as of the toxic degradation product. The substance was subject to a Ministerial condition; restrictions included that the substance be hydrolyzed prior to disposal, with the requirement that hydrolysis efficiency remove at least 90% of the substance from the aqueous discharge. The above actions ensured that the substance would not be released at levels resulting in a risk to humans or the environment.
   
   
3. For an alkyltin notification, the impurities and degradation products were determined to be more inherently toxic than the parent compound. The toxicity of the notified substance and its degradation products was investigated using toxicity data for shorter alkyl chain structural analogues (i.e., the expected worst-case degradation product of the notified alkyltin), as well as available data from the scientific literature. The environmental risk assessment focused on the potential release of the substance to the environment. Additional information was obtained from the notifier with respect to handling, processing and use of the substance. Toxicity concerns were alleviated by imposing a condition on the import and manufacture of the substance, including a restriction on the substance being released into the environment, and a condition requiring that handling, processing and use of the substance occur only in a fully contained process; any unreacted substance would have to be recovered and reprocessed.
   
   
4. A brominated flame retardant was notified and assessed by the departments. Three potential routes of degradation were identified, using experimental data and available data in the scientific literature for structural analogues. These were as follows: 1) degradation of the linear carbon chain; 2) dehalogenation in water and sediment; and 3) hydrolysis, although the latter was determined to be limited and not of concern due to the substance's lack of appreciable water solubility. Sediment species were exposed to degradation products; once transformation occurred in the sediment, the more soluble degraded substances could be transported back into the water column from interstitial waters. Ecotoxicity of the notified substance and degradation products was examined in the 1) water column for the parent compound, 2) sediment for degradation products and 3) water column for reflux of degradation products. Sediment toxicity data were available in the literature for a surrogate degradation product. A suspicion of toxic was determined on the basis of release of the substance in liquid form, resulting in a risk to the aquatic environment, and on the basis of highly toxic degradation products. A condition was imposed by Environment Canada, limiting importation of the substance to instances where it is encapsulated in plastic pellets or flakes.

In the above cases, the notifier was contacted for additional information, and/or supporting documentation/surrogate data were available to the evaluator to assess the potential risk of the notified substance and its degradation product(s).

It is recommended that examples of the type of additional information requests with respect to degradation products be provided in the Guidelines rather than in the Regulations, since the information described above would be required only on a case-by-case basis. The NS Program will continue to address toxicity of degradation products in the risk assessment, without compromising risk to the environment and human health. The Program will respond with requests for additional information and/or impose conditions, when warranted.