Abstract
This case study summarizes an assessment of risk of methylmercury (MeHg) exposure to fish-eating birds foraging at Stormwater Treatment Area-2 (STA-2). This assessment was required as a special condition for a permit modification authorizing flow-through operation of STA-2 Cell 1 without it first satisfying formal mercury start-up criteria. The assessment estimates the risks posed by MeHg to the great egret (Ardea albus) and the bald eagle (Haliaeetus leucocephalus). Exposure models were based on literature-derived life history parameters combined with site-specific MeHg concentrations in water, sediment, and fish. To assess risk, daily MeHg intake by females and cumulative MeHg consumed by nestlings were compared to literature-derived effects thresholds. The results indicated the likelihood was low that MeHg exposures to birds foraging throughout STA-2 would exceed effects thresholds at the time of this assessment. Birds foraging exclusively from Cell 1 or the small discharge canal were predicted to experience greater exposures and could be at potential risk. However, this worst-case risk was comparable or lower than risk levels encountered in nearby water conservation areas or the Everglades National Park.