Follow the Mercury


This month, an international team of scientists from the United States and Canada will start adding minute quantities of three different stable (i.e., non-radioactive) isotopes of mercury to a 128-acre watershed in the Experimental Lakes Area of northwestern Ontario, Canada. DOE’s Office of Biological and Environmental Research supports one of the U.S. scientists. The purpose of the study referred to as METAALICUS, or Mercury Experiment To Assess Atmospheric Loading in Canada and the U.S., is to find out what happens to the concentration of methylmercury in fish when the atmospheric deposition of mercury increases. Agencies involved in the study include Fisheries and Oceans Canada, EPA, the U.S. Geological Survey, DOE, the Electric Power Research Institute. It also includes a host of collaborating universities and institutions from both the U.S. and Canada. DOE’s Office of Biological and Environmental Research sponsors one of the U.S. scientists involved in the study. The reason for the study is concern about mercury loading and its effect on mercury in fish. Mercury is a neurotoxin and is known to be detrimental to humans, especially growing children. It is also the most common cause of fish advisories in North America. Although mercury is a naturally occurring heavy metal, it is also released into the environment by human activities, including the combustion of coal. Mercury enters most ecosystems through atmospheric deposition. In the U.S., coal-fired power plants are the single greatest source. The study will consist of adding the three stable isotopes with different atomic mass (mercury-199, mercury-200 and mercury-202)) to three different portions of the watershed in a region where atmospheric mercury deposition is low. The total amount added will be about 37 grams over a 3-year period. The diluted mercury-200 will be sprayed by plane across the upland area of the watershed when it is raining, mercury-199 will be sprayed from the ground on wetland areas, and mercury-202 will be added directly to the surface of a lake by injection from a small boat at a depth of about 1.5 meters. Because it is possible to measure the amount of each mercury isotope in environmental samples, such as of water, fish, soils, and vegetation, each isotope will be traced through the complex pathways that link the atmosphere with fish in the lake. The study will help answer the question about the plausible link between atmospheric emissions of mercury and methylmercury in fish and whether the concentration of mercury in fish would change if the atmospheric deposition of mercury increased or decreased. It will also address other questions such as where the mercury comes from that bioaccumulates in fish, over what time scales the deposited mercury will be observed in fish, and what the fate is of new mercury in the system.