Harvestable‐size largemouth bass Micropterus salmoides were collected from 53 Florida lakes to determine relationships between mercury concentration in fish and physical and chemical lake characteristics. Diverse lakes with a broad range of sizes (15–181,000 hectares), pH (3.6–9.1), and alkalinities (1.2–128 mg/L as CaCO3) were sampled. Total mercury concentrations in axial muscle of individual fish ranged from 0.04 to 2.04 μg/g wet weight and were positively correlated with fish age (strongest correlation) and size. There was no difference in the rate of mercury accumulation by age between the sexes, even though females grew faster. Chemical characteristics oflakes strongly influenced the bioaccumulation ofmercury in largemouth bass. Mercury concentrations, standardized to age‐3 fish for comparison among lakes, ranged from 0.04 to 1.53 μg/g and were negatively correlated with alkalinity, calcium, chlorophyll a, conductance, magnesium, pH, total hardness, total nitrogen, and total phosphorus. No significant correlations were observed between the standardized fish mercury concentration and lake color, secchi transparency, tannic acid, or surface area. Linear regression revealed that pH accounted for 41% of the variation in the standardized fish mercury concentration. Multiple regression revealed that chlorophyll a and alkalinity accounted for 45% of the variation in the standardized fish mercury concentration. Mercury concentrations were significantly higher in lakes with either pH less than 7, alkalinity less than 20 mg/L as CaCO3, or chlorophyll a less than 10 μg/L.

Rates of mercury accumulation were examined in male and female largemouth bass (Micropterus salmoides) from Lake Tohopekaliga, Florida, to establish methods for fish consumption advisories for the protection of human health. In addition, concentrations were determined in five lower trophic level fish species. Total mercury concentrations in adult largemouth bass muscle tissue ranged from 0.16 to 1.10 micrograms/g (fresh weight) and increased as fish increased in size and age. Whole-body mercury concentrations of 1990 year-class largemouth bass increased from 0.05 microgram/g at 20 mm and to 0.32 microgram/g at 320 mm (age 2). Significant differences were found in the rates of accumulation between sexes for length and weight, but not for age. Therefore, standardized mercury concentrations were determined using bass age to make comparisons among sampling dates. Although there were significant differences in adjusted mean mercury concentrations among two sampling dates, mercury content of standard-age bass remained relatively constant over time. Largemouth bass exceed the Florida Health Advisory level for limited consumption of fish (0.50 microgram Hg/g) based on a mean concentration of 0.59 microgram/g for 64 bass. Advisories based on fish morphological characteristics (i.e., length, weight) or age are not possible for Lake Tohopekaliga due to differences in mercury accumulation in male and female bass. Lower trophic level species of sport fish did not exceed the limited consumption level.

Mercury is a widespread environmental contaminant with exposures eliciting a well-documented catalog of adverse effects. Yet, knowledge regarding the underlying mechanisms by which mercury exposures are translated into biological effects remains incomplete. DNA methylation is an epigenetic modification that is sensitive to environmental cues, and alterations in DNA methylation at the global level are associated with a variety of diseases. Using a liquid chromatography tandem mass spectrometry-based (LC-MS/MS) approach, global DNA methylation levels were measured in red blood cells of 144 wild American alligators (Alligator mississippiensis) from 6 sites with variable levels of mercury contamination across Florida’s north-south axis. Variation in mercury concentrations measured in whole blood was highly associated with location, allowing the comparison of global DNA methylation levels across different “treatments” of mercury. Global DNA methylation in alligators across all locations was weakly associated with increased mercury exposure. However, a much more robust relationship was observed in those animals sampled from locations more highly contaminated with mercury. Also, similar to other vertebrates, global DNA methylation appears to decline with age in alligators. The relationship between age-associated loss of global DNA methylation and varying mercury exposures was examined to reveal a potential interaction. These findings demonstrate that global DNA methylation levels are associated with mercury exposure, and give insights into interactions between contaminants, aging, and epigenetics.

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