Elementos-traço (Hg, Ag, Se) em toninhas (Pontoporia blainvillei) do Sudeste do Brasil

Abstract

The franciscana (Pontoporia blainvillei) is a small cetacean considered as the most endangered dolphin species in the South Atlantic. Anthropogenic activities, such as contamination by trace elements, contribute intensively and progressively to the population decline and habitat degradation of this species. In this context, the aim of the present study was to measure THg, Ag, and Se concentrations in muscle and liver of 49 Pontoporia blainvillei specimens using the atomic absorption spectrometry method. Additionally, hepatic molar ratios of Se:THg and Se:THg + (0.5 × Ag) were calculated to infer the detoxification processes of Hg and Ag, mediated by Se, an essential element for the performance of physiological activities. Tissue samples were obtained from individuals stranded or incidentally captured along the coasts of Espírito Santo, Rio de Janeiro, and São Paulo, Brazil, between 2015 and 2023. These states host three franciscana populations, classified as Franciscana Management Areas (FMA) Ia, IIa, and IIb, respectively. Liver showed the highest concentrations of THg and Se in all populations and of Ag in FMAs Ia and IIb (Wilcoxon, p < 0.05). Specimens from FMA IIa, a recently monitored and poorly studied population, exhibited significantly higher levels of THg in muscle and liver and of Se in muscle according to the Generalized Linear Model. Conversely, FMA IIa displayed the lowest Ag concentrations in both tissues, while the highest Se concentrations in the liver were recorded in individuals from FMA IIb. The expected molar ratio of Se:THg in the liver of marine mammals for an efficient detoxification process is 1. However, all populations analyzed in this study presented ratios exceeding this agreed value. Notably, individuals from FMA IIb exhibited the highest values, suggesting a substantial excess of Se that could potentially play a role in detoxifying other unknown toxic elements. This study is the first to analyze Ag concentrations in franciscana muscle and provides new insights into the dynamics of toxic element detoxification mediated by Se in this species.