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 factors (environmental and physiological) that modify the impacts of toxic chemicals on biota, 2) to develop methods to assess contaminant impacts on free-living organisms, and 3) to develop and test models predictive of the toxicity of toxicant mixtures to aquatic 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 to protect the environment. While looking at the effects of various modifying factors over my career, it has become evident that what we are 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 toxicity and bioavailability of single metals from sediments to benthic invertebrates in both the laboratory and the field, the relative contributions of dietary versus waterborne metals to toxicity in benthic invertebrates, and the acute and chronic toxicity of several waterborne metals to aquatic biota (largely through the use of the principles of the Biotic Ligand Model). In the next cycle we will look at refining and testing a model which we have developed to predict the toxicity to Hyalella azteca of up to ten metals in a mixture. In a second area of research, we will look at the interaction of selected metals and alkylated polycyclic aromatic hydrocarbons in mixture toxicity experiments with Daphnia magna. We will also assess the effect of genetic background on tolerance to metal exposure within the amphipod genus Hyalella. Overall, the work contributes to our basic understanding of the impact of environmental contaminants, and to sound scientifically-based Canadian environmental regulations.