A Screening Level Probabilistic Risk Assessment of Mercury in Florida Everglades Food Webs

A screening level probabilistic assessment of risks was performed on three species of piscivorous wildlife at the top of Everglades aquatic food webs: the American alligator (Alligator mississippiensis), the great egret (Egretta alba), and the raccoon (Procyon lotor varius). Ranges of dietary exposure concentrations (and probability distribution functions) were derived for two general areas of the Everglades: Shark Slough and the south-central Everglades (highly contaminated with Hg), and the northern Everglades (a lower Hg contaminated area in and near Water Conservation Area 1). Ranges of toxicity reference values and probability distribution functions were derived from literature on the toxicity of dietary methyl Hg to birds and mammals. Probability distributions of risk estimates for each receptor were generated using Monte Carlo simulations and indicated that piscivorous wildlife feeding in the south-central region of the Everglades are at high risk from consumption of Hg-contaminated prey. Alligators had 100% exceedences of chronic risk thresholds, and great egrets had 99% exceedences. In the northern Everglades, exceedences of chronic risk thresholds were substantially lower but were still present (6–34% exceedences). Results support previous studies suggesting that top predators of the Everglades may be at risk from Hg contamination and indicate that Hg risks are location-dependent.