A Food Web Model of Mercury Transfer from Stream Sediment to Predators of Fish for Ecological Risk Based Clean-Up Goals

Abstract

A linear steady state model of the food web linking sediment to piscivorous predators was used to derive ecological risk based clean-up concentrations for mercury in sediment of East Fork Poplar Creek (EFPC), Oak Ridge, TN. The model partitions aquatic invertebrates into two classes based on the primary source of exposure to mercury in sediment, and the prey-fish community into three classes based on differences in their diets and feeding habits. Biotransfer factors for the links between sediment and sediment-dwelling invertebrates, water and aquatic biota and fish, and prey and predators are published values. The model uses site specific data on the fraction of methylmercury in sediment, the relative abundance of prey fish, and the predicted flux of mercury from sediment. Monte Carlo analysis quantifies the uncertainty in the risk to top predators of fish. At 96 mg/kg mercury in sediment, less than 20% of the exposures exceed dietary limits for endpoint receptors. The fraction of methylmercury in sediment, the three biotransfer factors for methylmercury, and diet are sensitive parameters.

A probabilistic risk assessment of the effects of methylmercury and PCBs on mink and kingfishers along East Fork Poplar Creek, Oak Ridge, Tennessee, USA

“…They found that more than 80% of methylmercury exposures were less than the lowest‐observed‐adverse‐effect‐level (LOAEL)‐based dietary limits for great blue herons and kingfishers and less than the no‐observed‐adverse‐effect‐level (NOAEL)‐based dietary limits for mink. Some of the difference in our results and those of Burns et al [7] can be attributed to differences in approach (e.g., food web model vs tissue residues to estimate exposures and hypothesis testing vs regression methods to estimate toxic effects doses). However, a more likely explanation is that sediment is a relatively minor exposure pathway compared to water [4].…”

“…Using a sediment‐based food web model for EFPC, Burns et al [7] did not find that methylmercury posed a significant risk to piscivorous species. As with our analysis, Burns et al [7] used Monte Carlo analysis to quantify the uncertainty in the predicted exposure of an average individual for several top predator species. However, their results differed greatly from those shown in Figures 2D and 4D.…”

“…However, a more likely explanation is that sediment is a relatively minor exposure pathway compared to water [4]. As a result, the sediment‐based food web model of Burns et al [7] underestimated piscivore exposures to methylmercury at EFPC.…”

“…Previous assessments at EFPC demonstrated that mink ( Mustela vison ) and belted kingfishers ( Ceryle alcyon ) may face significant risks from exposure to mercury and PCBs, mainly because both organisms are at the top of the aquatic food chain and mercury and PCBs are persistent and bioac‐cumulative [4–7]. Mink are also known to be especially sensitive to organochlorines [8,9] and methylmercury [10].…”

A PROBABILISTIC RISK ASSESSMENT OF THE EFFECTS OF METHYLMERCURY AND PCBs ON MINK AND KINGFISHERS ALONG EAST FORK POPLAR CREEK, OAK RIDGE, TENNESSEE, USA

“…Under CERCLA, remedial options must be developed and evaluated with regard to their costs of implementation and effectiveness at reducing risks to biota [4]. Previous assessments at EFPC demonstrated that mink (Mustela vison) and belted kingfishers (Ceryle alcyon) may face significant risks from exposure to mercury and PCBs, mainly because both organisms are at the top of the aquatic food chain and mercury and PCBs are persistent and bioaccumulative [4][5][6][7]. Mink are also known to be especially sensitive to organochlorines [8,9] and methylmercury [10].…”