The effects of solar radiation and dissolved organic matter on contaminant fate in freshwater ecosystems

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It is currently unclear why some lakes in Canada have fish and animals with high levels of contaminants while other similar lakes do not. The speciation of contaminants (or chemical form) is known to be a key factor controlling their movement in ecosystems and uptake by organisms. Speciation in turn is controlled by photochemical reactions which respond in different ways to changes in solar radiation, and interactions with dissolved organic matter (DOM) (the decay products of plant and animal matter). However, the exact relationships between these variables are poorly understood. The general goal of my research program is to determine the effects of solar radiation and DOM on contaminant fate in freshwaters. More specifically, I will collect water samples from a range of lakes and characterize differences in DOM structure. I will then use controlled laboratory experiments to test the effects of DOM structure and different wavebands of radiation on the photochemical reactions that control the fate and speciation of contaminants. The initial focus will be on mercury, which has a wide range of organic and inorganic properties, and is therefore useful as a model system for other contaminants. Mercury is also a highly toxic contaminant and due to its wide dispersion it is both a regional and a global concern. I anticipate that this research will result in predictive models that describe key factors controlling contaminant speciation and fate in ecosystems. This will increase our ability to predict which freshwater ecosystems are most likely to have significant contaminant accumulations in organisms. This in turn will benefit Canada by supporting effective regulatory policies and mitigative measures to protect the health of sensitive freshwater ecosystems and the human and wildlife populations that they sustain.