Total mercury in three small tunas from southeastern Brazil: stable isotope relations and human risk assessment

Mercury (Hg) bioaccumulation can be highly variable in marine species. Its concentration is influenced by several physico-chemical and biotic processes, including size, age, diet composition and foraging habitats. Herein, we addressed total mercury (THg) concentrations in three small tuna species in Brazil: the frigate tuna Auxis thazard, the little tunny Euthynnus alletteratus and the skipjack tuna Katsuwonus pelamis. Samples were collected from commercial landings in the SE Brazilian coast from 2017 to 2019. The influence of trophic ecology and habitat preference on Hg accumulation was assessed through stable isotope [carbon (δ13C) and nitrogen (δ15N)] measurements. Additionally, the human health risk regarding the species consumption was assessed by the estimated weekly intake (EWI) and the provisional tolerable weekly intake (PTWI) for total consumers, adult men and adult women. Variables such as size and age were positively correlated to Hg, due to the bioaccumulation process. Trophic position appears to positively influence the mercury concentrations for A. thazard and K. pelamis, since relationship between δ15N and THg was significant. For E. alletteratus, the lack of relationship suggests that δ15N values do not vary much among adult fish (> 300mm). Muscle THg concentrations in the three species did not exceed the established tolerable limit for mercury by Brazilian and international organs, as indicated by the %PTWI. This finding suggests that the consumption of those species caught off southeast Brazil at the considered amounts does not present a risk for healthy adults.