Understanding the antagonism of Hg and Se in two shark species from Baja California South, México

Mercury and Selenium concentrations were determined in the muscle and liver tissues of Silky shark (Carcharhinus falciformis) and Smooth Hammerhead shark (Sphyrna zygaena) caught off Todos Santos, Southern Baja California, Mexico during August–December 2014. The average mercury concentrations in C. falciformis [(mg/kg) muscle: 3.04; liver: 3.95] and S. zygaena (muscle: 5.23; liver: 3.39) exceeded the permissible limit of 1.0 mg/kg established by the Mexican government. Biomagnification Factors (BMF) to understand the prey-predator relations were also calculated and it was observed that all BMFs were >1 indicating absolute biomagnification of Hg. Additional Se concentrations were found in C. falciformis: 5.34 mg/kg and S. zygaena: 3.29 mg/kg resulting in a molar excess of Se over Hg. Thus, our results prove to offer the basic strategies of Hg-Se biogeochemical processes in marine sharks.