An investigation of geochemical factors controlling the distribution of PCBs in intertidal sediments at a contamination hot spot, the Clyde Estuary, UK

The concept that total organic C (TOC) is the main factor dominating the sorption of PCBs to sediment is over simplified. Numerous discrepancies are found when trying to compare concentrations predicted from laboratory observations to field concentrations. Some studies show a lack of correlation between PCB and TOC or particle size, but state that it is the origin of the organic matter or the clay swelling that is most important in determining the partitioning to sediment. It may also be argued that the discrepancies are merely a reflection of localised inputs of PCBs. An evaluation of the influence of these factors was undertaken at an intertidal site in the Clyde Estuary, previously highlighted as being highly contaminated by PCBs. Analysis of a series of sediment samples failed to show a strong correlation of PCB content with TOC or particle size. Separation into grain-size fractions and subsequent analysis suggested that both variation in organic matter source and mineralogical composition exerts an influence on congener distribution with implications for the mobility of PCBs within intertidal sediments.