David L. Taylor, Colby C. Peters, Christopher Parkins, M. Conor McManus
Mercury (Hg) contamination in estuarine and coastal fishes represents a persistent risk to human health due to its neurotoxicity and potential for bioaccumulation, yet spatial, seasonal, and long-term variability in exposure remains poorly characterized. We conducted a multiscale spatiotemporal assessment of total Hg concentrations in the muscle tissue of eight recreationally harvested fish species (n = 3186) collected from Narragansett Bay, Rhode Island Sound, and Block Island Sound (RI, USA) during May-October from 2006 to 2024. To facilitate integrated comparisons across species, Hg concentrations were normalized using intraspecific regression-based residuals that account for length-specific bioaccumulation patterns. Normalized fish Hg residuals differed significantly among locations, with elevated concentrations at mid-bay estuarine sites relative to offshore waters. Seasonal patterns were evident, with peak Hg residuals occurring in early to mid-summer (June-July) followed by declines in fall (October). Long-term analyses revealed an approximately 26% increase in size-standardized Hg concentrations over the study period, concurrent with increasing water temperatures and shifts in nutrient conditions. Spatial, seasonal, and interannual variability in Hg concentrations corresponded with differences in landscape composition, proximity to wastewater inputs, sediment methylation potential, and water-column biogeochemistry, underscoring the interaction of local, fine-scale environmental processes and anthropogenic influences with broader environmental change. These results indicate that fish consumption advisories based on generalized species averages may mischaracterize human exposure to dietary Hg. Incorporating intraspecific information on fish body size, harvest location, and season could improve the efficacy of advisories and better characterize Hg exposure risk in estuarine and coastal fisheries.