Polychlorinated biphenyls in nonaccumulating, century-old sediments: Sources, signatures, and mechanism of introduction

This study documents the occurrence of highly chlorinated PCB congeners in stream sediment deposited over 100 years ago. Penta- to heptachlorinated co ngeners (> 80%) have been found at concentrations up to 78.8 ng/g (dw) in c ore samples of a small, rural tributary of Lake Ontario. Lower chlorinated congeners and other organochlorine compounds occur sporadically; Pb-210 and Cs-137 are lacking. The most plausible mechanism is accumulation of dissol ved-phase PCBs in permeable sediments adjacent to the creek channel. The si milarity between core and air samples collected in the drainage basin sugge sts derivation from a residual fraction of atmospherically derived PCB cong eners.