Determinants of trace element accumulation in soft-shell clams (Mya arenaria) in Eastern Canada and implications for human consumption

Marine clams are an important country food with high nutritional value while being a route of human exposure to metals. The fresh- and salt-water interface in estuaries may impact metal speciation, leading to changes in bioavailability and bioaccumulation in clams. We evaluated which environmental variables correlate best with bioaccumulation of total mercury (THg), methylmercury (MeHg), and the sum of rare earth elements (ΣREEY) by the soft-shell clam (Mya arenaria) at the mouth of two contrasting rivers. We measured essential and non-essential elements, and nine arsenic (As) species in clams to assess the consumption risks and benefits to consumers. Results showed that clams near the coast of the higher DOC and dammed Romaine River yielded higher THg, MeHg, and ΣREEY concentrations than clams collected at the mouth of the undammed Mingan River. Clams more exposed to saline waters, as inferred from carbon (δ¹³C) and sulfur (δ³⁴S) isotopic signatures, had lower THg, MeHg, and ΣREEY bioaccumulation. Positive correlations were identified between THg in clams and sediments, as well as ΣREEY concentrations in both matrices, suggesting a transfer to clams from this compartment through filter feeding. The evaluation of the nutritional intake indicated that clams were a good source of iron (Fe) and selenium (Se). More than 40 % of total As were organic forms of arsenobetaine (AsB). Therefore, a monthly portion of 188 g of soft-shell clam for elderly adults and pregnant or childbearing women and a monthly portion of 94 g for children should not lead to intake risks from non-essential elements.