Mercúrio e metil mercúrio em carapaça da tartaruga marinha Caretta caretta (LINNAEUS, 1758), no Nordeste do Brasil e seu uso potencial em monitoramento ambiental

Abstract

Several marine ecosystems are under severe mercury (Hg) anthropogenic contamination, which reflects in a greater exposure of the species that inhabit or use these contaminated areas. Consequently, the concentration of Hg in long-lived animal species, such as sea turtles, is generally high. Thus, researchers around the world have been suggesting these organisms as Hg biomonitors. However, due to their endangered species status, special care is required in their handling, particularly in the use of non-invasive methods for the determination of Hg in these animals. In this context, the main objective of this study was to evaluate the concentration of Hg and methyl-Hg (CH₃Hg⁺) in carapace fragments, a non-invasive approach, in Caretta caretta found in the South-West Atlantic Tropical and to determine the influence of feeding habits, size and reproductive status of these animals on the concentrations of Hg. Samplings were carried out in coastal areas of northeastern Brazil, totaling 82 individuals sampled during spawning and beaching events, recorded between 2009 and 2016. The individuals presented a Curved Carapace Length between 55 and 107 cm, with a mean of 97 ± 8.5 cm, and a Curvilinear Carapace Width between 50 and 99 cm, with a mean of 88 ± 7 cm. Concentrations of total Hg were very variable (3.3 ng.g-1 at 1672 ng.g-1 , with a mean of 142 ± 270 ng.g-1 ). No significant difference was found in Hg concentrations in carapace fragments between re-migrant turtles and those that first arrived on those beaches. Therefore, there is no relation between the concentrations of total Hg and the migratory status of the animals. Maternal transfer as a method of Hg excretion, inferred through the quantification of Hg in egg shells, does not seem to influence Hg levels in females with a higher number of spawning. The percentage of methylHg found in carapace fragments of 18 individuals showed values in the range of 0,5 – 32,6% and was not correlated with the total Hg content. The concentration of carbon (13C) and nitrogen ( 15N) isotopes measured in samples from ten individuals showed that all are at a high trophic level, but no relation was also observed with the concentrations of total Hg. The results obtained were not able to explain the causes of the wide variation in Hg concentrations in C. caretta carapace, suggesting that, unlike that observed for other sea turtle species, carapace fragments of C. caretta are not of interest to environmental monitoring purposes. Further studies focused on the internal processes of the organism, such as the chemistry and the type of carapace growth, are necessary to explain the observed variation in Hg concentrations in order to verify or discard their use in environmental monitoring and, if positive, to standardize a methodology for collecting and analyzing carapace fragments of this species for purposes of environmental monitoring.