LONG-TERM ACCUMULATION OF INDIVIDUAL PCB, DIOXINS, FURANS, AND TRACE-METALS IN ASIATIC CLAMS FROM THE RIO-DE-LA-PLATA ESTUARY, ARGENTINA

The long-term accumulation of individual polychlorinated biphenyls (PC B), dioxins (CDD), furans (CDF), and selected trace metals was studied in Asiatic clams of increasing size covering a 0.5-4-year growth peri od. PCB bioaccumulation was congener-specific and related to compound hydrophobicity and stereochemistry as indicated the contrasted slopes obtained for the concentration vs size regressions. Tri and tetraCB wi th log K-DW < 6 showed nonsignificant slopes, indicating steady-state conditions or negative values (i.e., PCB 31 and 49) reflecting selecti ve degradation. Penta and hexa CB with log K-DW, 6-7 (total surface ar ea = 240-270 Angstrom(2)) were preferentially accumulated, and the slo pes increased with log K-ow. Except for congener 180, which continued this linear trend, hepta and octaCB showed a reduced long-term accumul ation due to unfavorable stereochemistry. The selective enrichment in congeners 153, 138, 118, and 180 explained 74% of the total PCB increa se observed from 10 to 35 mm clams (446-871 ng/g dw). CDD and CDF also increased with size but with much steeper gradients (136-790 and 70-4 00 pg/g, respectively), indicating a more rapid long-term kinetics. PC Bs accounted for 83-88% of the total toxic equivalents (TEQ) calculate d for the clams; pentaCBs 126 and 118 represented similar to 60 and 10 % TEQ, respectively. The preferential bioaccumulation of planar PCBs 7 7-126, mono-ortho-substituted 118 and tetra-hexa CDD/CDF accounted for 95% of the TEQ increase observed from 10 to 35 mm clams (7.1-13.1 pg/ g wet weight). Among trace metals, Cu showed a consistent increasing t rend with clam size (22-41 mu g/g dw), similar to PCBs, suggesting con tinuous passive bioaccumulation. Bioregulation appeared to be effectiv e for Zn whose concentrations increased from 10 to 22 mm clams (150-19 0 mu g/g dw) and returned to initial values in larger animals. Ni leve ls were very homogeneous (3.5 +/- 0.4 mu g/g dw) and showed no clear p attern with clam size.