Abstract
Methylmercury (MeHg) is a contaminant of global concern that bioaccumulates and bioamagnifies in marine food webs. Lower trophic level fauna are important conduits of MeHg from sediment and water to estuarine and coastal fish harvested for human consumption. However, the sources and pathways of MeHg to these coastal fisheries are poorly known particularly the potential for transfer of MeHg from the sediment to biotic compartments. Across a broad gradient of human land impacts, we analyzed MeHg concentrations in food webs at ten estuarine sites in the Northeast US (from the Hackensack Meadowlands, NJ to the Gulf of Maine). MeHg concentrations in water column particulate material, but not in sediments, were predictive of MeHg concentrations in fish (killifish and Atlantic silversides). Moreover, MeHg concentrations were higher in pelagic fauna than in benthic-feeding fauna suggesting that MeHg delivery to the water column from methylation sites from within or outside of the estuary may be an important driver of MeHg bioaccumulation in estuarine pelagic food webs. In contrast, bulk sediment MeHg concentrations were only predictive of concentrations of MeHg in the infaunal worms. Our results across a broad gradient of sites demonstrate that the pathways of MeHg to lower trophic level estuarine organisms are distinctly different between benthic deposit feeders and forage fish. Thus, even in systems with contaminated sediments, transfer of MeHg into estuarine food webs maybe driven more by the efficiency of processes that determine MeHg input and bioavailability in the water column.
Highlights
Mercury (Hg) exposure from fish and seafood consumption results in both human and wildlife health effects [1,2,3,4,5]
Sediment data collected across ten sites showed a significant positive linear relationship between %LOI and log-transformed THg (p = 0.039, n = 10; Figure 2), the relationship between %LOI and log MeHg (p = 0.17, n = 10; Figure 2) was not significant
Biota Using multiple regression models to determine the variables best accounting for variation in MeHg concentrations in biota, we found that the concentrations in the different biota were associated with different sediment and water column compartments (Table 1; Table S2 in File S1)
Summary
Mercury (Hg) exposure from fish and seafood consumption results in both human and wildlife health effects [1,2,3,4,5]. While much of the research on food web processes influencing Hg concentrations in fish has been conducted in freshwater systems, approximately 90% of fish consumed in the US comes from estuarine and marine systems [6] In these marine ecosystems, transformation of Hg to its most biologically toxic and available form, methylmercury (MeHg), is thought to occur primarily in estuarine and coastal sediments [7,8,9] where contaminant concentrations are highest, and in the oxygen minimum zone in the open ocean [10]. The MeHg formed in sediments can enter the benthic food web directly through deposit feeding in the sediments by benthic infauna, which can be consumed by predatory fish [17] It can be directly transferred into the water column via advection and diffusion from sediments, or as a result of desorption from resuspended sediments [11,18]. Once in the water column, MeHg can be taken up by the pelagic food web
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