The spatial distribution, degree of pollution and major sources of PCBs were evaluated in surficial sediments within the heavily urbanized and industrialized Izmit Bay and its main freshwater inputs. Sigma PCB concentrations range from 2.90 to 85.4 ng g(-1) in marine sediments and from ND to 47.7 ng g(-1) in freshwater sediments. Results suggest that high concentrations of Sigma PCBs were localized around a chlor-alkali plant and an industry that handles bulk liquid, dry and drummed chemicals, and petroleum products in the Bay. Using a chemical mass balance receptor model (CMB), major sources of PCBs in the region were investigated. The CMB model identified Aroclor 1254 and 1260 to be the major PCB sources in marine sediments and the less chlorinated Aroclor 1248 and 1242 as the major PCB sources in freshwater sediments. The potential sources for the PCBs were briefly discussed in terms of their use in various industrial applications. (C) 2010 Elsevier Ltd. All rights reserved.