Lean retired as a professor from University of Ottawa in 2009 where he held an NSERC Industrial Chair in Ecotoxicology. He developed and served as Director of the Joint Ecotoxicology Program for Ottawa and Carleton Universities. He now runs his consulting firm (Lean Environmental) with current projects in Costa Rica and Cambodia. He is a visiting professor at the Universidad National in Heredia, CR. Prior to 1996, he spent 24 years as a scientist and project leader at Environment Canada’s National Water Research Institute in Burlington, Ontario, Canada where he was principal investigator for projects on the influence of nutrients on eutrophication in the Great Lakes Ecosystem. His work included studies on ozone depletion in the Arctic and Antarctic regions. Lean has published 285 peer-reviewed scientific papers and 24 book chapters. In 1993, he received the Chandler-Misener Award for excellence in Great Lakes research; in 2003 the Frank Rigler Award for outstanding freshwater research and the Miroslaw Romanowski Medal given by the Royal Society of Canada for his research in environmental toxicology. The current work is on mercury sources and its role as a toxic chemical in food webs leading to humans. It includes mass balance calculations of industrial mercury sources and global sinks, the role of UV radiation, nutrients and fish population dynamics. His first degree was in Chemical Engineering but he recognized the potential impact of chemical pollutants on ecosystem processes so he returned to University of Toronto for his PhD in Biology with a focus on limnology on the role of phosphorus in lake eutrophication. He also served on the Science Advisory Panel for the International Joint Commission, was coauthor of Ontario Government’s Far North Report for Northern Ontario and was a contributing author to the Canadian position document for submission to the United Nations as part of the binding international agreement for mercury emission control.