Partitioning of Polynuclear Aromatic Hydrocarbons between Sediments from San Francisco Bay and Their Porewaters

The in situ sediment−porewater partition coefficients ( K oc ‘s) of a suite of 3−6 ring polynuclear aromatic hydrocarbons (PAHs) increased with the organic carbon content and with the amount of fines in surface sediments collected from a mudflat in San Francisco Bay along an intertidal gradient during the dry and wet seasons in 1993−1994. The K oc ‘s were an order of magnitude or more higher during the wet period of high surface runoff than during the dry season; the in situ measurements bracketed the corresponding values of K ow . Moreover, K oc ‘ decreased from the high- to the low-intertidal zone during the dry season, indicating heterogeneity in partitioning behavior along this spatial gradient. A plausible explanation for these trends in the partitioning behavior is a heterogeneity of the sediment organic carbon matrices, principally the content of highly aromatic soot particles; an increase in K oc ‘ might be anticipated in association with the lower activity coefficients of the aromatic PAHs in a highly aromatic solid phase matrix. If correct, this interpretation would qualify the utility of equi librium partitioning models in formulating sediment quality criteria for PAHs.