Mechanistic understanding of low methylmercury bioaccessibility from crayfish (Procambarus clarkii) muscle tissue

Recent research indicates that dietary exposure to mercury and other metals from crayfish consumption poses a human health concern, particularly in regions with high crayfish-consuming populations. To better understand consumption risk from methylmercury (MeHg), we quantified MeHg bioaccessibility in edible tail muscle of cooked red swamp crayfish (Procambarus clarkii, collected from seven cities in China), versus cooked fillet tissue of two finfish species: yellow croaker (Larimichthys polyactis) and snakehead (Channa argus). Results indicated that digestive solubilization rate (DSR) of MeHg in crayfish (7.8±3.9% for restaurant-crayfish and 9.8±0.8% for market-crayfish) was lower than the rate in yellow croaker (25.8±2.7%) and snakehead (26.2±4.7%) tissue, suggesting that relatively low MeHg bioaccessibility in crayfish may reduce dietary exposure to humans. Three possible mechanisms for the reduced MeHg DSR in crayfish tissue were examined: MeHg-Se interactions, MeHg subcellular fractionation, and Hg-amino acid binding. Selenium concentrations were comparable among the examined species, and no significant relationship was observed between tissue Se and MeHg DSR. Similarly, observed differences in subcellular fractionation of MeHg could not explain the species-specific MeHg DSR. Therefore, MeHg-Se interactions and MeHg subcellular fractionation do not explain the relatively low MeHg bioaccessibility in crayfish. Significantly higher cysteine and arginine content was found in crayfish than in the finfish. We suspect that the lower MeHg bioaccessibility of crayfish tail muscle may be attributed to the higher cysteine concentrations, and thus, stronger MeHg-protein binding in crayfish. These results support the interpretation that bioaccessibility differences will alter risk interpretations for MeHg, especially when comparing hazard across aquatic food types.