Long term accumulation of individual PCBs, dioxins, furans, and trace metals in Asiatic clams from the Rio de la Plata Estuary, Argentina

The long-term accumulation of individual polychlorinated biphenyls (PCB), dioxins (CDD), furans (CDF), and selected trace metals was studied in Asiatic clams of increasing size covering a 0.5-4-year growth period. 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 with log K-DW < 6 showed nonsignificant slopes, indicating steady-state conditions or negative values (i.e., PCB 31 and 49) reflecting selective degradation. Penta and hexa CB with log K-DW, 6-7 (total surface area = 240-270 Angstrom(2)) were preferentially accumulated, and the slopes increased with log K-ow. Except for congener 180, which continued this linear trend, hepta and octaCB showed a reduced long-term accumulation due to unfavorable stereochemistry. The selective enrichment in congeners 153, 138, 118, and 180 explained 74% of the total PCB increase 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 70-400 pg/g, respectively), indicating a more rapid long-term kinetics. PCBs accounted for 83-88% of the total toxic equivalents (TEQ) calculated for the clams; pentaCBs 126 and 118 represented similar to 60 and 10% TEQ, respectively. The preferential bioaccumulation of planar PCBs 77-126, 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 trend with clam size (22-41 mu g/g dw), similar to PCBs, suggesting continuous passive bioaccumulation. Bioregulation appeared to be effective for Zn whose concentrations increased from 10 to 22 mm clams (150-190 mu g/g dw) and returned to initial values in larger animals. Ni levels were very homogeneous (3.5 +/- 0.4 mu g/g dw) and showed no clear pattern with clam size.