Mercury-selenium concentrations in silky sharks (Carcharhinus falciformis) and their toxicological concerns in the southern Mexican Pacific.

Mercury- Selenium concentrations were determined in 136 samples of Carcharhinus falciformis (Silky shark) sampled from the Chiapas coast, Gulf of Tehuantepec, Mexico during August 2014 - January 2015. Average Hg concentrations in neonates and juveniles (all values in µg g-1 w.w.) were found to be 0.115 and 0.129 respectively, below the maximum permissible limit of 1 µg g-1 set by the Mexican government. However, excess Se values (all values in µg g-1 d.w.) observed in neonates (5.366) and juveniles (2.815) prove to maintain antioxidant ability by inducing Hg excretion and reducing its toxicity. Calculated Biomagnification Factor (BMFTL) denoted high values for the prey C.hippurus, signifying absolute magnification of Hg and Se along the food chain. This study provides key toxicological evidences of Hg- Se interaction and their effects in marine systems and human health.