Accumulation of total mercury and methyl mercury in insect larvae of hydroelectric reservoirs

Abstract

Mean total mercury (Hg) and methyl mercury (MeHg) concentrations in insect larvae from hydrolelectric reservoirs were 3-5 times (up to 10 times) higher than in their counterparts from natural lakes. Taxonomic differences, which may be related to feeding behavior, and substrate type (lake sediment or flooded soils) together explained a large part of the total variability of total Hg (r2 = 0.64) and MeHg (r2 = 0.79) concentrations in insects. MeHg concentrations in flooded soils increased from 0.3-2 ng Hg cdot g dry weight-1 after 1-2 years of flooding to 15-2 ng Hg cdot g dry weight-1 after 16 years of impoundment. Total Hg and MeHg concentrations in insect larvae followed a similar pattern, but only weak correlations of both total Hg and MeHg concentrations were found between flooded soils and insect larvae, suggesting that factors other than MeHg content of flooded soils also affect the accumulation of these compounds in insects. Our results indicate that suspended particulate matter eroded from flooded soils by wave and ice action and bacterial activity enhanced by the release of labile carbon and nutrients from the flooded soils may indirectly transfer MeHg from flooded soils to insect larvae.