Intra- and interspecies variability in mercury concentrations in Texas marine fish and shellfish
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Mercury (Hg) is a toxic pervasive global pollutant that can bioaccumulate in marine organisms and biomagnify in marine food webs. The Gulf of Mexico has a higher concentration of Hg than the connecting Atlantic Ocean. Humans are mainly exposed to Hg through seafood consumption and the per capita rate of fish consumption is higher in Gulf states, potentially exposing the seafood consuming public to elevated concentrations of Hg. This study investigated the concentration of Hg in 26 species of fish and 4 species of shellfish (n = 1,468 individuals) caught along the Texas coast during 2016 and 2017 using a Direct Mercury Analyzer, and investigated the relationship between Hg concentration and body size for 26 of these species. A significant positive relationship was found between Hg concentration and body size in 7 nearshore fish species, 10 offshore fish species, and 1 shellfish species, indicating that Hg was bioaccumulating over time in these species. In comparison, there was a negative relationship between Hg concentration and body length in stripped mullet, possibly as a result of growth dilution. No relationship was observed in 7 of the species investigated which could be a result of low sample size and/or narrow range in body length. Spatial differences in Hg concentration were investigated in 4 residential species; no difference in Hg concentration was observed among sites for southern flounder, but there was a site difference for red drum, spotted seatrout, and black drum. Overall, when combined together, offshore fish had the highest wet wt Hg concentration (1.61 µg/g) followed by nearshore fish (0.175 µg/g) and shellfish (0.035 µg/g). For individual species, the average wet wt Hg concentration was highest in blue marlin (11.6 µg/g) and sailfish (1.21 µg/g) and lowest in brown shrimp (0.0086 µg/g) and American oyster (0.006 µg/g). Three offshore fish species (blue marlin, sailfish, and king mackerel) had an average Hg concentration that exceeded the FDA action limit of 1 µg/g wet wt and 7 offshore species exceeded the Texas State Department of Health Services (TSDHS) health-based standard of 0.7 µg/g wet wt. In comparison, gafftopsail catfish was the only nearshore fish species that had an average Hg concentration that exceeded the EPA human health criterion of 0.3 µg/g wet wt, and no shellfish species exceeded the EPA criterion. While shellfish are safe to eat due to their very low Hg concentration, offshore fish species and some nearshore fish species should still be consumed in moderation due to their high Hg concentration.