Assessment of mercury bioaccumulation in a tropical elasmobranch assemblage

Environmental context Mercury (Hg) is a non-essential metal that can accumulate in aquatic biota, including top predators such as elasmobranchs (sharks and rays) and biomagnifying along the trophic web. This study provides data on Hg total, methylmercury (MeHg) and stable isotopes (δ13C and δ15N) for 13 elasmobranch taxa in the Equatorial Western Atlantic Ocean, relating biological and ecological properties with Hg concentrations and the estimated human consumption risk. Rationale Elasmobranchs widely consume fish, making understanding Hg bioaccumulation crucial. Little is known about Hg distribution in their bodies beyond muscle tissue and the associated health risks for both animals and humans who consume them. Methodology This study evaluated Hg, methyl-Hg (MeHg) and stable isotopes (δ13C and δ15N) in the muscle, liver and brain of 13 elasmobranch taxa landed by artisanal fisheries on the Western Equatorial Atlantic Ocean. Results The study revealed that Hg concentrations were highest in muscle tissue, whereas the brain exhibited the greatest percentage of MeHg. Significant correlations between Hg levels and body size, as well as between muscle and brain Hg concentrations, were observed in sharks. Stable isotope values indicated dietary and habitat diversity, and a significant correlation between Hg (log10) and δ15N was found. Mercury concentrations exceeded thresholds for harmful effects in ~76% of the analysed taxa and were also detected in embryos. These taxa also surpassed the local consumption limits, highlighting a potential risk. Discussion The results demonstrated bioaccumulation and biomagnification of Hg in the studied taxa. Muscle Hg was a good predictor of brain Hg levels as a result of the significant correlation between these variables. The high proportion of MeHg in the brain indicates rapid transport of Hg to this organ. Observed Hg concentrations in juveniles and adults may affect their health, whereas concentrations in embryos indicate possible transfer of Hg from the mother to the embryos. This study advises caution when consuming various elasmobranchs, depending on the consumer’s weight and meal frequency.