T10 PM Advances in Bioaccumulation Assessment
Tuesday, 15 November 2005: 1:50 PM - 5:30 PM in 341-342

(BON-1116-519513) Addressing PBT program needs for new and existing substances in Canada.

Bonnell, M¹, Morin, D¹, ¹ Environment Canada, Gatineau, Quebec, Canada

ABSTRACT- The assessment of persistence, bioaccumulation and inherent toxicity (PBiT) is currently being performed in Canada for new and existing substances. Categorization of 23,000 existing substances on the Canadian Domestic Substances List (DSL) for PBiT is nearing completion, but further examination of PBiT properties will be performed at the risk assessment stage for those substances meeting the criteria, as is done for new substances. The criteria in the Persistence and Bioaccumulation Regulations (Canada Gazette 2000) are used by both programs to identify very persistent and very bioaccumulative substances. Inherent toxicity criteria are defined within each program, but are consistent. Obtaining reliable and accurate estimates of these three hazard properties presents challenges to regulators and non-regulators alike. Regarding ′B′, practical and scientific difficulties can arise when examining inventories of chemicals given the large number of substances to be examined, limitations of QSAR training set domains and the general lack of experimental data. Consequently, modeled values of bioaccumulation are often used as BCF testing is often cost prohibitive, requires animal testing and may not result in reliable results (e.g., poorly soluble, highly sorptive substances). However, QSAR models for ′B ′are driven by logKow input and most currently do not account for absorbtion, distribution, metabolism, and excretion (ADME) process, although some models are moving in that direction (e.g., Mekenyan′s POPs model, Gobas mass-balance BCF/BAF model). A tiered approach to bioaccumulation assessment, that includes ADME considerations, has been proposed by the ILSI-HESI (Health and Environmental Sciences Institute) Emerging Issues Committee for Bioaccumulation to help improve bioaccumulation assessment. Accurate assessment of bioaccumulation values, whether they are modeled or experimental, are needed by risk assessors for the examination of′B′ as it relates to the benchmark criteria as well as for determining the potential trophic transfer of contaminants in aquatic and terrestrial systems using food web and exposure based models. This presentation will discuss how the ILSI-HESI tiered approach may be applied in risk assessment of new and existing substances in Canada.

Key words: bioaccumulation, PBT, assessment