Mercury and selenium concentrations in the oysters Saccostrea palmula and Crassostrea corteziensis from coastal lagoons of Northwest Mexico and the risk assessment on human health

Abstract

The toxicity of mercury (Hg) in bivalves can be reduced when it is associated with selenium (Se) as mercury selenide, a stable non-toxic compound. Mercury and Se were seasonally studied (summer 2019-spring 2020) in the soft tissue of oysters Saccostrea palmula and Crassostrea corteziensis from four coastal lagoons of Northwest Mexico. The higher Hg concentration (≈ 0.13 µg g−1, wet weight) in both oyster species were obtained in summer−autumn 2019. Mercury level was similar among the coastal lagoons and did not exceed the limit established by the Norma Official Mexicana, the World Health Organization, and the Food and Drug Agency (< 1.0 μg g−1 Hg). The higher Se concentration (≈ 4.55 µg g−1) occurred in spring 2020 for both oyster species. Regarding Se/Hg molar ratios, they were above 1; the positive selenium health benefit value index suggested that Se concentration in oysters could reduce the potential toxic effect of Hg; and the hazard quotient for Hg (methylmercury) and Se in both species was below 1. Therefore, the consumption of S. palmula and C. corteziensis not represented a risk due to Hg ingestion. Continuous monitoring of the Se/Hg ratio is recommended in oysters from NW Mexico for a more precise assessment of human health risk.