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 su ite of 3-6 ring polynuclear aromatic hydrocarbons (PAHs) increased wit h the organic carbon content and with the amount of fines in surface s ediments collected from a mudflat in San Francisco Bay along an intert idal 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 hig h 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, indic ating heterogeneity in partitioning behavior along this spatial gradie nt. A plausible explanation for these trends in the partitioning behav ior is a heterogeneity of the sediment organic carbon matrices, princi pally the content of highly aromatic soot particles; an increase in K- oc' might be anticipated in association with the lower activity coeffi cients of the aromatic PAHs in a highly aromatic solid phase matrix. I f correct, this interpretation would qualify the utility of equilibriu m partitioning models in formulating sediment quality criteria for PAH s.