EFFECT OF SUBLETHAL CHLORINATED DISCHARGES ON PCB ACCUMULATION IN TRANSPLANTED ASIATIC CLAMS (CORBICULA-FLUMINEA)

From 1987-1990, uncontaminated Asiatic clams (Corbicula fluminea) were placed in cages and transplanted into two streams receiving industria l discharges to help identify and quantify polychlorinated biphenyl (P CB) contamination to the streams. Clams accumulated substantial PCB re sidues at most sites monitored, with the exception of the sites closes t to chlorinated discharges. Clams placed nearest to the chlorinated s tream reaches consistently underestimated PCB contamination, based on the amount of PCBs found in fish and sediment at those sites. In a sep arate experiment, clams exposed in stream-side tanks to untreated (tot al residual chlorine ranged from 0.02-0.07 mg-1 L daily) and dechlorin ated stream water exhibited differing degrees of valve movement, growt h, and PCB accumulation after a four-week exposure to the two treatmen ts. Clams exposed to untreated (chlorinated) stream water closed their shells more often, exhibited less growth, and accumulated substantial ly lower PCB concentrations than clams exposed to dechlorinated stream water. Clams apparently close their shells to avoid chlorine exposure , thus isolating clam tissues from PCBs found in the stream water and in die clams' food. Because chlorine and PCBs occur together in many i ndustrial discharges, this finding is a significant consideration for monitoring programs that utilize clams to assess PCB bioavailability.