In situ measurement of polychlorinated biphenyls in the waters of San Diego Bay, California.

Sediments of San Diego Bay (SDB) are known to contain elevated levels of polychlorinated biphenyls (PCBs). While numerous efforts have been made to monitor the spatial or temporal trends of contamination in SDB, no studies have been directed toward measurements of water column contamination. We measured PCB concentrations in the water column of SDB with an in situ sampling system. Except for one sample collected near the bay mouth, all other samples contained higher PCB concentrations than the 30-day average discharge limit established by the California Ocean Plan. The highest concentrations of water column PCBs occurred in the Central Bay, consistent with the previous findings that sediments in the Central Bay contained higher PCB levels than those in the North and South Bays. Based on the water volume of 2.2 x 10(8) cm3 at a lower water level, it was estimated that approximately 1,000 g of PCBs is transported out of SDB via tidal exchange annually. This indicates that water column transport driven by tidal exchange is a viable mechanism reducing PCB contamination within SDB.