The Science of the TotaI Environment, Supplement 1993 Elsevier Science Publishers B.V., Amsterdam 1439 Differences in polychlorobiphenyl (PCB) contamination patterns in various environmental matrices L. Turrio-Baldassarri, A. di Domenico, A.R. Fulgenzi, N. Iacovella and C. La Rocca Laboratory of Comparative Toxicology and Ecotoxicology, Istituto Superiore di Sanith, Rome, Italy ABSTRACT Isomer-specific determination of polychlorobiphenyls (PCB) was performed on various matrices, including the following: sea bottom sediment and molluscs (Mytilus galloprovincialis and Scapharca inaequivalvis) from the Northern Adriatic sea; cheese and the milk used in its production; human milk; Italian total diet; sludge from a wastewater treatment plant. Forty-five congeners were quantitated and the results were illustrated in the form of bar graphs, for visual comparison as PCB contamination profiles. Different matrices show different PCB contamination profiles, concerning both multiplicity and congener distribution. The importance of determining mono-ortho substituted congeners is also demonstrated. Key words: PCB contamination; Italian diet; Milk; Molluscs; Sludge INTRODUCTION In recent years increasing concern about the toxicity of some dioxin-like PCB congeners has spurred the need for isomer-specific analysis of PCBs. These compounds do indeed have toxic characteristics which may be expressed in terms of 'Toxicity Equivalents' (TEQs) of 2,3,7,8- tetrachlorodibenzo-p-dioxin (Safe, 1990; EPA, 1991; Ahlborg 1992). This toxicity scale has been widely employed to represent the toxic properties of compounds, such as polychlorodibenzodioxins (PCDDs) and polychlorodibenzofurans (PCDFs), belonging to the same family of 2,3,7,8- TCDDs or closely related. Some foods have a dioxin-like PCB congener content that, when computed in 2,3,7,8-TCDD TEQs, is comparable to or even higher than the content of PCDDs + PCDFs, expressed in the same scale (Niimi and 1993 Elsevier Science Publishers B.V.