The effects of changes in atmospheric mercury deposition on the bioaccumulation of mercury by fish

To improve our understanding of the effects of reductions in mercury (Hg) emissions on concentrations of this contaminant in fish, the present study examined the relationship between the deposition rate of atmospheric Hg and its concentration in the environment and food web of aquatic ecosystems. Different rates of atmospheric Hg deposition (1 to 15 times 7.1 mug Hg·m -2·yr-1) were simulated in large, in-lake mesocosms by adding multiple doses of inorganic Hg (enriched with 202Hg). The experimentally-added Hg was quickly converted to methylmercury and incorporated into all levels of the food web within the 10-week experiment. Concentrations of the experimentally-added Hg in the environment and in the food web were directly proportional to Hg loading rates. This study suggests decreases in atmospheric Hg deposition will: (i) immediately remove a pool of Hg from aquatic ecosystems that would otherwise be quickly methylated and bioaccumulated by aquatic biota; and (ii) result in proportional changes in the MeHg content in biota that is derived from newly-deposited atmospheric Hg.