Mercury exposure and Selenium interactions in South American sea lions (Otaria flavescens) from Patagonia, Southwestern Atlantic Ocean.

Mercury (Hg) and selenium (Se) concentrations were analyzed in diverse internal tissues (muscle n = 10, liver n = 10, kidney n = 9 and lung n = 8), and the skin (n = 10) of -the South American sea lion (SASL)-stranded on the beaches of marine protected areas in Patagonia, Argentina. Elemental concentrations (expressed in μg g-1 DW (Dry Weight)) were determined using Instrumental Neutron Activation Analysis (INAA). Mercury accumulated primarily in the liver, followed by the kidney, muscle, lung, and skin. Selenium also showed highest accumulation in the liver, followed by the kidney, lung, muscle, and skin. Significant positive correlations between Hg and Se concentrations were observed across all tissues. Hg levels increased with age and total body length (TBL), indicating bioaccumulation over time. Positive linear relationships between Hg and Se concentrations in the skin and internal organs suggests that skin biopsies may be used as a tool for monitoring Hg exposure in wild populations. The Se:Hg molar ratio indicates a potential protective role of Se against Hg toxicity; Se was present in molar excess relative to Hg in most organs examined, especially in lung and skin. In the liver, the ratio was close to 1 suggesting a limited protective effect of Se to Hg toxicity by forming stable compounds that accumulate in this organ. SASL feeds on prey that are also commercially important, making the monitoring of Hg in their environment relevant for both human health and guiding conservation strategies for the species.