Mercury and selenium concentrations and their toxicological implications in silky sharks Carcharhinus falciformis (Elasmobranchii: Chondrichthyes) in the northwestern Indian Ocean

Abstract

Mercury (Hg) and selenium (Se) were assessed in silky sharks, Carcharhinus falciformis, a carnivorous apex predator and an important resource in the Indian Ocean. Muscle from the caudal peduncle was collected from individual sharks and analyzed using ICP-MS. Results showed that 40% of the specimens exceeded the allowed limits (1.00μg/g ww) of Hg. The mean Hg concentration (1.39 ±1.44μg/g ww) was also higher than the limits. The mean Se concentration in shark muscle was 0.324 ±1.44μg/g ww. The mean Se/Hg molar ratio was 2.23 (range: 0.17–24.5), with 30% of individuals exceeding 1.0, showing a protective effect of Se against Hg. However, for individual sharks’ mean Se health benefit value (Se-HBV) was −3.83. The risks of consuming silky sharks by male and female adults were also calculated. Results showed that the estimated weekly intake (EWI) was 2.9 to 3.5 times higher than the provisional tolerable weekly intake (PTWI). Consumption risks based on hazard quotient (HQ), estimated daily intakes (EDI), and EWI exceeded the threshold for fish consumption by adults, posing immediate health concerns.