MERCURY IN PRECIPITATION AND ITS RELATION TO BIOACCUMULATION IN FISH - A LITERATURE-REVIEW

Increases in industrial mercury (HE) emissions in recent years have le d many researchers to believe that Hg from the atmosphere constitutes a main source of Hg to aquatic biota in the absence of point source di scharges. Established background levels for fish (0.2-1.0 mg kg(-1)) n ow exceed the pre industrial level of 0.15 mg kg(-1), suggesting an an thropogenic origin. This review of recent literature illustrates how l evels of mercury (Hg) species in the atmosphere are effectively transp orted into the aquatic arena, where chemical parameters combine to det ermine bioaccumulation rates in fish. Limited studies on methyl mercur y (MeHg) in precipitation shown that concentrations average from 5% of total-I-Ig (T-Hg), to 1% in industrial regions. Observations of incre ased Hg is snow and precipitation from the Arctic Circle, related to p oleward atmospheric circulation patterns, also demonstrate a spring ma ximum accompanying ozone depletion. Increases in oxidants and soil der ived Hg in the atmosphere during the summer best explain summer Hg max imums observed in precipitation, while increased temperatures raise fi sh metabolism increasing Hg uptake through respiration and ingestion r ate. The major route of entry for MeHg to fish appears to be biomagnif ication, after input from precipitation, runoff and inlake methylation . Regions buffered against acid precipitation maintain low fish-Hg lev els by reduced MeHg production and maintaining gill function. When con sidering the bioaccumulation of Hg in fish this study shows that there are many variables to consider, not all of which originate from insid e the aquatic arena. Both catchment and atmospheric processes combine with aquatic variables to dictate the overall levels of MeHg observed in fish tissue. There now appears to be sufficient knowledge to develo p an axiom for the identification of aquatic systems likely to be susc eptible to bioaccumulation from atmospheric derived Hg.