Chemistry of Selenium in Life and Interplay with Toxic Elements

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BACKGROUND Selenium is an enigmatic element. Essential in organisms from all kingdoms and three domains of life, selenium is the rarest required element in the Earth's crust. Worldwide, availability is uneven; while some areas such as the Canadian prairies have soils rich in selenium, globally selenium deficiency is often a challenge. Indeed, selenium has perhaps the most delicate balance between insufficiency and toxicity of any essential element. Even slightly elevated environmental selenium from human activities is of concern due to biomagnification in the food web. Selenium is long known for complex interrelationship with certain toxic elements, especially with mercury, an element of global concern whose levels are rising due to human activities. While selenium is often thought to decrease mercury's toxicity, selenium can also greatly amplify mercury's toxicity, depending on their chemical forms and order of exposure. NATURE OF THE WORK This program seeks a holistic view of selenium's molecular level function and interaction with toxic elements from environment through human health, building on a career-long interest in selenium and synchrotron technologies. Short term objectives start from structural studies of newly available selenium-containing enzymes and their interactions with mercury, probing facets of potential mechanisms of mercury poisoning. These link to organism-level imaging of zebrafish as a model vertebrate and tissues from high environmental exposure, to probe molecular impacts of mercury poisoning, especially the role of mercury-selenium nanoparticles. Synchrotron X-ray methods underpin the program. The potential of high energy resolution methods to provide next-level speciation detail along with improved trace limits is only just being realized; such methods combined with microscopic mapping currently are in commissioning at synchrotron facilities. This program will help define best practices in these new directions for trace elements in complex systems. NOVELTY AND SIGNIFICANCE Selenium as a trace element is both a burden and a benefit to Canada. Slightly elevated selenium from anthropogenic activity can cause problems through ecosystem biomagnification. Conversely, selenium-rich soils across Canada's prairies lead to fortified agricultural products, with potential health and economic benefit. Fundamental studies on selenoenzymes connect to preeminent health concerns of our time such as cancer and diabetes. Selenium's complex relationship with mercury, an element of concern especially in Canada's Arctic, contributes to the question of risk associated with mercury in food such as fish as well as in traditional diets. Synchrotron developments will broadly benefit other researchers engaged across the lifecycle of trace elements, from geochemistry and microbiology, through soil and plant sciences, to ecosystem and human health.