MERCURY IN FISH MUSCLE IN ACIDIFIED AND LIMED LAKES

The concentration of Hg in muscle was monitored during 10 to 12 years in different size and age groups of pike (Esox lucius) and perch (Perca fluviatilis). The study was performed in one reference and five lime treated lakes. Before liming, the highest levels of Hg in fish were measured in a lake with an annual mean pH just above 5.0. Lower levels were obtained both in lakes which were more acidified and in those which were less acidified. After the start of liming, the fastest and largest changes were obtained in the lakes which were moderately acid before liming (mean pH 5.4-5.8). In small perch, the Hg-concentration was markedly reduced in two years and showed an 80 % decrease in ten years. A slower response was registered in the lakes originally having about 0.5 units lower pH. In the most acidified lake (pH 4.9) the concentrations even increased the first years after liming, but decreased again later on. The possible mechanisms involved are discussed.