Uptake and clearance of PCB congeners in Chamaelea gallina: response of oxidative stress biomarkers.

PCB uptake and clearance by clams, Chamaelea gallina, were studied in specially designed flow-through channels. After 8 weeks exposure to 10 ppb Aroclor 1254 in water, clams were depurated for 10 weeks, in the same exposure channel or after transfer to clean systems. Accumulation of the 20 congeners studied depended on its initial abundance and physicochemical properties. A linear relationship was found between log bioconcentration factor and log octanol/water partition coefficient of each form. Clearance of each PCB depended also on its initial load and solubility, being faster in clams transferred to clean systems. Exposure significantly enhanced catalase and 6-P-gluconate dehydrogenase activities, but not other antioxidative enzymes. Superoxide dismutase, low during the exposure phase, increased seven-fold during depuration. Aroclor-treated clams had higher GSH levels than controls, but decreased to 15-35% after 2 days clearance, rose to 150% after 12 days, and declined to low levels by the end of the experience. Biotransformation of PCBs to quinones and redox cycling-promoted oxidative stress might explain the increased antioxidative defenses. The biochemical changes observed at the beginning of clearance could be attributed to clam handling, by adaptation to and recovery from hypoxic/anoxic stress.