Environmental influence on Hg and 137Cs levels in perch (Perca fluviatilis L.) and roach (Rutilus rutilus L.) from circumneutral lakes

Sammanfattning: Mercury and radioactive caesium have received immense attention in Sweden during the past decades, as common contaminants in fish. This thesis examines how the Hg and 137Cs levels in fish from 79 circumneutral lakes are affected by various environmental factors. In addition, the observed contaminant levels in the fish are compared to observations from more acidiclakes.Partial least square regression models (PLS) were used to assess the influence of 46-53 environmental predictors on Hg and 137Cs levels in perch (Perca fluviatilis L.) and roach (Rutilus rutilus L.). Linear regression intercepts of contaminant concentration vs. fish size were used as estimates of lake specific contaminant level in fish, in the cases when the contaminant content had a clear size-dependency.Differences in land use in the catchment areas were found to be a good predictor of both Hg and 137Cs levels in the fish. Lowest levels were found in lakes draining arable land. High Hg levels in both species were predominantly found in forest lakes, whereas high 137Cs levels were observed in wetland lakes.The Hg and 137Cs levels in the fish were negatively correlated to the cation concentration in lake water, but had a positive relationship to the amount of humic matter, i.e. low contaminant levels in hard-water lakes and high levels in brown-water lakes. No effect of lake pH was found on Hg or 137Cs levels in either species. The Hg contents in perch and roach were of the same magnitude as in fish from more acidic lakes. The radiocaesium deposition in the close vicinity of lakes had a more profound effect on the 137Cs levels in fish than more distantdeposition.