Use of Path Analysis to Investigate Mercury Accumulation in Brown Trout (Salmo trutta) in Norway and the Influence of Environmental Factors

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Abstract
We studied relationships between environmental factors and mercury accumulation in resident brown trout (Salmo trutta) in 25 lakes in Norway. Our survey showed that mercury concentrations in fish are elevated in areas receiving high atmospheric depositions of mercury. A path analysis revealed that the concentrations of total organic carbon had a critical influence on the bioaccumulation of mercury. This reflects the role of humic matter in the transportation of mercury to lake water and sediments, and perhaps also a stimulating effect on the microbial methylation of mercury. Lake depth influenced the concentration of mercury in sediments, probably due to the complexation of mercury with sedimenting humic matter. The effect of such sediment on mercury concentrations in fish indicated that there exists a concentration-dependent production and release of methyl mercury to the biota. Selenium deposited from the atmosphere seemed to lower the bioavailability of mercury to fish. No effect of pH could be detected. The strong effect of total organic carbon implies that even moderate atmospheric deposition rates may result in relatively high mercury levels in fish, if other local environmental factors favour this.