Organic and inorganic mercury in the food chain of some lakes and reservoirs in Finland

Abstract

Contents of organic and inorganic mercury in food chain specimens, as well as sedimentation in two natural Finnish lakes and three impounded reservoirs, were studied. The proportion of organic mercury of total mercury varied in individual specimens from 32.7 to 100 %. Sedimentation (settleable solid) with very high contents of organic matter had ratios of organic to total mercury ranging from 2.4 to 87.3 %. These variations were similar in each of five water ecosystems studied. Benthic invertebrates had higher ratios of organic to total mercury than reported earlier. Total mercury concentrations in fish, zoobenthos and zooplankton of young impounded reservoirs were significantly higher than those of natural lakes. To explain this it is suggested that humic materials transfer mercury to the water and thence into the food chain.