Modifying factors of toxicant impacts on biota

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The long-term objectives of my laboratory's program in environmental toxicology are: 1) to understand the environmental factors that modify the impacts of toxic chemicals on biota and, 2) to develop methods to assess contaminant impacts on free-living organisms.  An understanding of modifying factors is crucial for the application of laboratory toxicology data to the field, or the application of field data collected at one site to another, during site-specific quantitative environmental risk assessment (QERA) of contaminants to protect the environment.  While looking at the effects of various modifying factors over my career, it has become evident that what we are really looking at is how environmental factors modify the bioavailability of a chemical; how exposure concentration, time and assimilation/depuration kinetics interact to achieve a critical (threshold of toxicity) chemical concentration in the organism.  Models developed using this approach provide a deterministic link between hypothesis formulation and testing in environmental toxicology.  We have used this approach to characterize the kinetics of mercury in Lake Victoria, the toxicity of Cd in sediment to benthic invertebrates in both the laboratory and the field, the toxicity of tributyl tin oxide to aquatic invertebrates in freshwater, and the toxicity of metals in sediments from metal-impacted lakes.  In the future we will examine dietary vs. waterborne toxicity of metals to invertebrates, the ability to predict acute and chronic toxicity of copper to aquatic invertebrates, the toxicity of nanoparticles to aquatic biota and the interactive toxicity of ultraviolet light, products of combustion and metals to fish.  Overall, the work contributes to our basic understanding of the impact of environmental contaminants, and to sound scientifically-based Canadian environmental regulations.