Abstract
Eastern oysters (Crassostrea virginica) were exposed to [^14^C]chlorpyrifos (O,O‐diethyl‐O‐[3,5,6‐trichloro‐2‐pyridyl] phosphorothioate) at an average measured seawater concentration of 0.6 μg/L under flow‐through conditions for 28 d. The compound O,O‐diethyl‐O‐(3,5‐dichloro‐6‐methylthio‐2‐pyridyl)phosphorothioate (DMP) was extracted and identified as the single metabolite observed, and this metabolite constituted the majority of the total [^14^C] activity in the oyster at all sampling times. Once oysters were exposed to clean water, both chlorpyrifos and DMP residues cleared rapidly from whole oysters, with elimination half‐lives of <3 d. A simple two‐compartment uptake/elimination model was adequate to describe total [^14^C] activity in whole oysters, edible tissue, and oyster liquor. The average bioconcentration factors (BCFs) for total [^14^C] activity in whole oysters, edible tissue, and oyster liquor were 565, 1,400, and 35 ml/g, respectively. The parent [^14^C]chlorpyrifos accumulated to a peak residue concentration of 135 μg/kg in whole oyster tissue, representing an empirical [^14^C]chlorpyrifos BCF value in the oyster of approximately 225 ml/g; the BCF value for [^14^C]chlorpyrifos was lower than the BCF for total [^14^C] activity in whole oysters and edible tissue because of extensive metabolism to DMP and oyster elimination processes.