Exposure and Risk Assessment Modeling to Screen and Prioritize Commercial Chemical Inventories

Abstract

National and international regulatory programs seek to evaluate the exposures, hazards and risks chemicals may pose to humans and the environment. There are many chemicals of commerce requiring assessment and few measured data available thus requiring the application of models for screening level assessments. Current methods for priority setting use “bright line” cut-off criteria in multiple categories such as persistence (P), bioaccumulation (B), toxicity (T), and quantity (Q). The present study illustrates the application of a novel holistic mass balance modelling method to screen and prioritize chemical inventories for exposures and risks to ecological receptors and humans. The RAIDAR model is used to combine P and B information into an exposure assessment factor (EAF), and P, B, T and Q into a risk assessment factor (RAF) providing single values for transparent comparisons and rankings based on exposure and risk objectives. The present study also includes estimates of biotransformation in food webs in the screening level calculations. The method is illustrated as a case study using 30 organic chemicals selected from the Canadian Domestic Substances List. The priority setting results of the cut-off based categorization are largely inconsistent with the proposed holistic mass balance modelling method. Current “bright line” category based methods are shown to be largely ineffective at prioritizing those chemicals that pose the greatest risks to humans and the environment. It is suggested that in order to minimize potential errors in preliminary stages of chemical assessments, complementary holistic methods for priority setting such as those proposed in the present study should be considered.