Effect of Land Cover on Ecoregion‐Scale Spatial Patterns of Mercury Contamination of Largemouth Bass in the Southeastern United States

Abstract

Consumption of methylmercury (MeHg)‐contaminated fish is the primary source of MeHg in humans and poses a hazard to human health. Because of widespread atmospheric deposition of inorganic mercury (IHg), all water bodies in the United States have been contaminated with Hg. In aquatic ecosystems, IHg is converted to MeHg, which biomagnifies, reaching high concentrations in piscivorous fish. It is not possible for governmental agencies to monitor fish from every waterbody to determine if concentrations of MeHg in fish are hazardous to human health. To help government agencies focus their monitoring efforts, it is critical that we develop the ability to predict regions where waterbodies are most likely to contain fish with hazardous concentrations of MeHg. The objective of the present study was to examine the relationship between MeHg contamination of largemouth bass (Micropterus salmoides), a popular piscivorous gamefish, and land cover in 24 ecoregions across 15 states in the southeastern United States. In our study we demonstrate for the first time that 72% of the variance in average concentrations of MeHg in largemouth bass between ecoregions of the southeastern United States can be explained by the percentage coverage by evergreen forests, emergent herbaceous wetlands, and pasture/hay. Land cover determines the sensitivity of freshwater systems to atmospheric IHg deposition, and the present study suggests that at the ecoregion scale, MeHg bioaccumulation in piscivorous gamefish, and ultimately the health hazard that these MeHg‐contaminated fish pose to humans, can be in part predicted by land‐cover type. Environ Toxicol Chem 2022;41:2386–2394. © 2022 SETAC

Potential Health Risks of Methylmercury Contamination to Largemouth Bass in the Southeastern United States

“…Although previous studies have demonstrated that largemouth bass in the southeastern United States have concentrations of MeHg in fillets of dorsal muscle tissue that are high enough to pose a threat to human consumers (see Drenner et al, 2022), the present study is the first to examine the potential risk of MeHg to the health of largemouth bass of the southeastern United States. Largemouth bass size is an important variable affecting MeHg concentrations and potential risk because MeHg increases in largemouth bass as they age and grow (Chumchal et al, 2008), and the concentration of MeHg determines the types of adverse health effects that largemouth bass may experience (Figure 1).…”

“…If multiple sampling events (sampling times or locations) occurred in the same lotic water body and were within 1 km of each other, they were merged in the same manner (Drenner et al, 2022). After merging sampling events, ecoregions contained from nine to 347 sites, with an average of 93 sites per ecoregion (Drenner et al, 2022).…”

“…Bloom (1992) found that 99% of the total Hg in largemouth bass is MeHg, and the USEPA (2000) recommends analyzing the concentration of total Hg in fish tissues as a proxy for the concentration of MeHg (Drenner et al, 2022). Therefore, we assumed that 100% of total Hg in largemouth bass was MeHg (Drenner et al, 2022). We assessed the potential level of risk posed by MeHg to largemouth bass by comparing whole‐body MeHg concentrations in largemouth bass from each site to Hg concentration benchmarks for adverse effects on fish health developed by Lepak et al (2016).…”

“…Bloom (1992) found that 99% of the total Hg in largemouth bass is MeHg, and the USEPA (2000) recommends analyzing the concentration of total Hg in fish tissues as a proxy for the concentration of MeHg (Drenner et al, 2022). Therefore, we assumed that 100% of total Hg in largemouth bass was MeHg (Drenner et al, 2022).…”

“…These size designations span the sizes of fish caught by anglers and were proposed by Gabelhouse (1984) to facilitate communication between fisheries professionals. Bloom (1992) found that 99% of the total Hg in largemouth bass is MeHg, and the USEPA (2000) recommends analyzing the concentration of total Hg in fish tissues as a proxy for the concentration of MeHg (Drenner et al, 2022). Therefore, we assumed that 100% of total Hg in largemouth bass was MeHg (Drenner et al, 2022).…”