Elevated arsenic concentrations in bivalves from the southeast coasts of the USA

Since 1986, the National Oceanic and Atmospheric Administration (NOAA) National Status and Trends (NS&T) Program, Mussel Watch Project (MWP) has been analyzing contaminants in bivalves (oysters and mussels) collected along the coastal USA. Compared to the rest of the USA, the oysters collected from sites located along the southeastern coasts, from North Carolina to the Florida panhandle, display high concentrations of arsenic (As) in their soft tissues. In this area, As concentrations can be elevated in sediments and in bivalves, although exact spatial correspondence between the two is infrequent. As concentrations in waters and food (plankton and suspended particles) directly surrounding the mollusks collected in winter are not unusually high. Phosphate deposits and soil pesticide residues are the hypothesized main sources of this As, and the enrichment mechanism appears to result from a mixture of processes including atmospheric deposition, river and aquifer inputs, and ocean up-welling. In the southeast oysters, the large bio-accumulation of As may also be affected by the seasonal cycle of adsorption/solubilization of As observed in several estuarine and coastal areas, by local physico-chemical parameters such as temperature, salinity, and the nature of sediments (e.g. high contents in iron, calcium, phosphate, and organic material). Even at these very high concentrations, the As present in the southeastern oysters does not appear to present a health threat to humans or to marine life.