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

Widespread mercury (Hg) contamination of freshwater systems, due primarily to deposition of atmospheric inorganic Hg (IHg), poses a potential threat to recreational fisheries. In aquatic ecosystems, IHg is converted by bacteria to methylmercury (MeHg), a potent toxin that bioaccumulates in consumers and biomagnifies through the food web, reaching elevated concentrations in fish. Methylmercury has concentration-dependent sublethal effects on fish, including reductions in reproductive output. In the present study, we conducted the first analysis of the potential health risks of MeHg contamination to largemouth bass (Micropterus salmoides), a popular game fish, in the southeastern United States. To assess the potential health risk posed by MeHg to largemouth bass, we compared MeHg concentrations in three sizes of adult largemouth bass to benchmarks associated with the onset of adverse health effects in fish. We also determined how the risk posed by MeHg to largemouth bass varied spatially throughout the southeastern United States. Our study suggests that in the southeastern United States MeHg poses a potential risk to largemouth bass health and that MeHg contamination may be detrimental to the fisheries of this economically important species of game fish. Environ Toxicol Chem 2023;42:1755-1762. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Effects of developmental exposure to neurotoxic algal metabolites on predator-prey interactions in larval Pimephales promelas.

Harmful algal blooms are a growing environmental concern in aquatic systems. Although it is known that some of the secondary metabolites produced by cyanobacteria can alter predator-prey dynamics in aquatic communities by reducing foraging and/or predator evasion success, the mechanisms underpinning such responses are largely unknown. In this study, we examined the effects of a potent algal neurotoxin, ß-N-methylamino-L-alanine (BMAA), on the development and behavior of larval Fathead Minnows, Pimephales promelas, during predator-prey interactions. We exposed eggs and larvae to environmentally relevant concentrations of BMAA for 21 days, then tested subjects in prey-capture and predator-evasion assays designed to isolate the effects of exposure at sequential points of the stimulus-response pathway. Exposure was associated with changes in the ability of larvae to detect and respond to environmental stimuli (i.e., a live prey item and a simulated vibrational predator), as well as changes in behavior and locomotor performance during the response. Our findings suggest that chronic exposure to neurodegenerative cyanotoxins could alter the outcomes of predator-prey interactions in natural systems by impairing an animal's ability to perceive, process, and respond to relevant biotic stimuli.

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

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.