YoungMya arenaria were exposed to cadmium-109 sorbed to humic acid, bentonite, protein (albumin), mud-type sediment and filtered estuarine water in a 24-hour static assay. After 31/2 hours, shells had sorbed twice as much as cadmium as tissues. Cadmium-109 was linearly accumulated over 24 hours byMya exposed to cadmium in estuarine water and bentonite-sorbed cadmium. Protein (albumin)-sorbed cadmium was not accumulated byMya. Final 24-hour average accumulation levels of sorbed cadmium compared to cadmium in estuarine water were: bentonite-cadmium, 100%; humic acidcadmium, 60%; mud sediment-cadmium, 33%; albumin-cadmium, 12%.