Depositional time trends and remobilization of PCBs in lake sediments

The vertical distribution of PCBs was measured in a dated core from the profundal sediments of Esthwaite Water, U.K. The resulting historical record of Sigma PCB deposition agreed well with published U.K. production data. Ratios between the various PCB homolog groups revealed significant compositional variations with depth. Sediments deposited in the last similar to 10 years and sediments deposited before PCB production began are both relatively enriched in the less chlorinated homolog groups. When considered with other available data, these enrichments provide evidence for post-depositional mobility of PCBs favoring the more aqueous soluble and volatile compounds. The results lend further support to a growing body of evidence that recyling of PCBs is occurring between the sediments and overlying waters, associated with solubilization and diffusive transport.