Chlorinated hydrocarbon pesticides and polychlorinated biphenyls in sediment cores from San Francisco Bay

Sediment cores of known chronology from Richardson and San Pablo Bays in Sa n Francisco Bay, CA, were analyzed for a suite of chlorinated hydrocarbon p esticides and polychlorinated biphenyls to reconstruct a historic record of inputs. Total DDTs (DDT = 2,4'- and 4,4'-dichlorodiphenyltrichloroethane a nd the metabolites, 2,4'- and 4,4'-DDE, -DDD) range in concentration from 4 -21 ng/g and constitute a major fraction (> 84%) of the total pesticides in the top 70 cm of Richardson Bay sediment. A subsurface maximum corresponds to a peak deposition date of 1969-1974. The first measurable DDT levels ar e found in sediment deposited in the late 1930's. The higher DDT inventory in the San Pablo relative to the Richardson Bay core probably reflects the greater proximity of San Pablo Bay to agricultural activities in the waters hed of the Sacramento and San Joaquin rivers. Total polychlorinated bipheny ls (PCBs) occur at comparable levels in the two Bays(< 1-34 ng/g). PCBs are first detected in sediment deposited during the 1930's in Richardson Bay, about a decade earlier than the onset of detectable levels of DDTs. PCB inv entories in San Pablo Bay are about a factor of four higher in the last fou r decades than in Richardson Bay, suggesting a distribution of inputs not a s strongly weighed towards the upper reaches of the estuary as DDTs, The sh allower subsurface maximum in PCBs compared to DDT in the San Pablo Bay cor e is consistent with the imposition of drastic source control measures for these constituents in 1970 and 1977 respectively. The observed decline in D DT and PCB levels towards the surface of both cores is consistent with a dr amatic drop in the input of these pollutants once the effect of sediment re suspension and mixing is taken into account. (C) 1999 Elsevier Science B.V. All rights reserved.