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(T/MF162) Identifying Uncertainty in the Exposure Assessment of New Substances in Canada and Recent Developments to Address Exposure Uncertainty. Hammond, Greg2, Atkinson, Andy2, Postlethwaite, Emma2, Bonnell, Mark 1, 2 1 ABSTRACT- In 1999 the New Substances Division (NSD) of Environment Canada undertook an examination of uncertainties associated with the exposure assessment process used to estimate environmental concentrations of new substances in the Canadian environment. The purpose of this study was to identify specific components of the exposure assessment process that contribute a high degree of uncertainty due to large extrapolations, assumptions or data gaps. These components were targeted for further development within the bounds of a screening level of assessment in order to reduce the overall uncertainty in the exposure assessment. By undertaking a qualitative assessment of the current practices used to conduct an aquatic exposure assessment for new substances, uncertainties were identified with (1) the scenarios used to calculate the release of substances from industrial plants for specific and default uses, (2) the partitioning and removal of substances in wastewater treatment plants, (3) the dilution approaches used to calculate aquatic concentrations of new substances, and (4) the lack of exposure assessment procedures for media other than the water column. The results of the uncertainty examination resulted in the development of a strategy for improved exposure assessment of new substances. Under this strategy, the NSD has begun the Canadian validation of available chemical plant release scenarios, has begun adapting the USEPAs PDM4 model for Canada, has initiated the updating of the widely used fugacity based STP model and has initiated the development of a screening level multi-media exposure assessment approach. Key words: exposure assessment, new substances, uncertainty, model development |
