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Abstract
Polychlorinated biphenyls (PCBs) are anthropogenic substances that have been detected in many parts of the environment and can have major negative impacts on ecosystem and human health. A documented release of PCBs from a nylon plant occurred in 1969 on the Escambia River just upstream of the Escambia Bay estuary along the north coast of the Gulf of Mexico. Other unreported releases of PCBs also likely occurred in the river and bay. The present study sampled sediments in the river and bay and assessed the predominant parent Aroclor of PCBs, and the changes in congener profile and toxic equivalents (TEQ) since the release. United States Environmental Protection Agency (US EPA) method 1668A, which provides quantitative data for 168 elutions, was employed for the analysis according to National Environmental Laboratory Accreditation Program procedures. Correlation analysis and principal component analysis of the PCB congener profiles for the sediments and Aroclors showed that the sedimentary PCB congeners are most similar to that of early production Aroclor 1254 made prior to 1971. Chronologically the use of the early production Aroclor 1254 corresponds to the time of the release. Since the release, overall chlorination of the sedimentary PCBs has decreased by 3% as a result of a shift in chlorination homolog profile to lesser-chlorinated congeners that presumably originated from dechlorination of Aroclor PCBs and from non-Aroclor source(s) of PCB 11, a dichlorobiphenyl. Despite a likely overall decrease in the quantity of dioxin-like PCBs, the TEQ/mole of sediment PCBs, did not substantially change because of a highly toxic congener (PCB 126) that was present at trace amounts in the sediments. There was a modest increase in lesser-chlorinated O,P-congeners that are suspected to have some toxicity to mammals. These findings have relevance for the evolution of environmental PCBs, which has not been studied in this system.