Polycyclic aromatic hydrocarbons in bivalves from the San Francisco estuary: Spatial distributions, temporal trends, and sources (1993-2001)

Bivalve tissue samples were examined over a range of spatial and temporal scales (1993-2001) to determine PAH distributions, trends, and possible sources. Mussels (Mytilus californianus), oysters (Crassostrea gigas), and clams (Corbicula fluminea) were deployed for three months in the estuary at stations remote from known point source discharges. The range of ∑PAH detected in bivalves was oysters 184-6899 μg/kg dry wt (mean 678 μg/kg dry wt), mussels 21-1093 μg/kg dry wt (mean 175 μg/kg dry wt), and clams 78-720 μg/kg dry wt (mean 323 μg/kg dry wt). Linear regression analysis showed no statistically significant (p > 0.05) temporal trends in clam and mussel ∑PAH at any of the deployment stations or estuary segments. On the other hand, a statistically significant (p < 0.05) decreasing trend was found in ∑PAH in oysters at the Petaluma River station, and in the North Estuary segment. PAH isomer pair ratios applied as diagnostic indicators suggested that the bioaccumulated PAH were derived primarily from petroleum combustion, with lesser amounts derived from biomass and coal combustion, and unburned petroleum.