BIOACCUMULATION OF POLYCHLORINATED-BIPHENYLS AND CHLORINATED PESTICIDES BY THE ASIATIC CLAM CORBICULA-FLUMINEA - ITS USE AS SENTINEL ORGANISM IN THE RIO-DE-LA-PLATA ESTUARY, ARGENTINA

Individual PCBs and chlorinated pesticides (CHLPs) were determined in water, suspended particles (SPM), sediments, and Asiatic clams to stud y their bioaccumulation kinetics and evaluate the usefulness of the cl ams as sentinel organisms. Bioaccumulation depended on the routes of u ptake and bioavailability determined by compound hydrophobicity. CHLPs were mainly present in the dissolved phase, showed a positive correla tion between the bivalve-water BAFs and K-ow's and reached steady-stat e levels before 70 days in a caging experience. These facts reflect an efficient water-gill partitioning process. In contrast, PCBs were onl y detected in the SPM, showed essentially K-ow independent bivalve-sed iment and bivalve-SPM BAFs with the lowest values for superhydrophobic heptachlorobiphenyls 174, 180, and 170, and did not reach steady-stat e levels during a 140-day exposure period. This suggests that the upta ke was hindered by their stronger affinity for SPM and the interferenc e of steric factors during intestine absorption. Corbicula fluminea ar e reliable sentinel organisms and showed clear geographical trends alo ng 150 km of the Rio de La Plata coast: a progressive decrease of PCB levels and more degraded patterns dominated by recalcitrant congeners, i.e., 153, were observed with increasing distance from the major La P lata-Buenos Aires urban center. A size-related trend overlapped with t his spatial gradient: older clams usually showed higher levels and a m ore degraded PCB signature. CHLPs showed less clear geographical trend s due to the presence of multiple sources. CHLP patterns showed a stro ng dominance of chlordane-related compounds, particularly transchlorda ne which was 2-5 times more abundant than the cis isomer. On a tempora l scale, from 1986 to 1993, Asiatic clams presented sustained PCB leve ls but showed a significant decrease of chlordane and DDT, which sugge sts reduced inputs in recent years.