JEROME O. NRIAGU is Professor in the Department of Environmental and Industrial Health, School of Public Health, the University of Michigan, and an adjunct professor at the University of Waterloo. For many years he was a research scientist with the National Water Research Institute, Burlington, Ontario. He is the editor of the Wiley Series in Advances in Environmental Science and Technology and has edited, among many other volumes, Nickel and Human Health, Arsenic in the Environment, and Thallium in the Environment. Dr. Nriagu received BSc and DSc degrees from the University of Ibadan, Nigeria, an MS from the University of Wisconsin, Madison, and a PhD in geochemistry from the University of Toronto. He has published extensively in leading geochemical and environmental science journals and has received a number of awards for his work. He is a Fellow of the Royal Society of Canada. John B. Sprague is former professor at the University of Guelph, Canada, and president of J.B. Sprague Associates, Ltd. For 12 years, he was Scientist-in-Charge for pollution studies in the Atlantic Provinces, working with the Fisheries Research Board of Canada. He was a University of Guelph faculty member for more than 20 years.