Grain-Size Distribution of Polychlorobiphenyls in Coastal Sediments

Congener-specific analyses of PCBs in marine sedi ments were undertaken to gain a better understanding of the distribution of this class of contaminants in relation to the grain-size of sediments. Twenty PCB congeners, selected for their potential toxicity and/or for their occurrence in the environmental samples, were studied in five grain-size sediment fractions (from φ > 800 μm to φ < 15 μm) and in the vegetal fragment fraction collected by flotation. PCB content and distribution profiles were observed in different grain-size fractions, and these were compared to that of the bulk sediments. Despite different contamination levels shown by the three studied sediments (from 29 to 181 ng g-1 in dry sediment for the sum of the 20 PCB congeners), trends were observed: preferential accumulation of PCBs with finest fractions and vegetal fragment fraction and specific association of low chlorinated congeners with the sand-size fractions (φ > 63 μm) and of high chlorinated congeners with the silt-size fractions (φ < 63 μm). This study illustrates the requirement of a good knowledge of the sediment grain-size composition when evaluating the toxicity and the availability of PCBs to aquatic biota.