Particle-related biogeochemical cycles of hydrophobic organic contaminants in estuarine waters

The distributions of hydrophobic organic contaminants (HOCs), including polycyclic aromatic hydrocarbon (PAHs) and polychlorinated biphenyls (PCBs), in different sizes of suspended particles, in settling particles, in sediments, and in the dissolved phase were studied in the Chesapeake Bay. Samples were collected from the water column at a depth of 3 m and from 2 m above the bottom at the HI buoy station in the mesohaline Chesapeake Bay from October 1990 to August 1992. Since PCBs and PAHs strongly associate with natural particles, estuarine particle dynamics resulting in especially high concentrations of suspended particles play a critically important role in the transport of HOCs.;Elevated concentrations of HOCs (up to 500 ng/g of total PCB and ;In the Chesapeake Bay, particulate HOCs are mainly transported by settling of suspended particles and by resuspension of surficial sediments. Resuspension fluxes of HOCs, up to 5 ;The sorption kinetics of PCBs to the Chrysophyte Isochrysis galbana and a model submicron particle were found to follow a two-step mechanism in a laboratory study. The overall extent of PCB sorption was determined by the second step of the sorption, since the rapid first step reached "pseudo-equilibrium" in a few minutes. The second step mass transfer coefficients of PCB congeners to cultured phytoplankton were constant (0.02 cm/hr) after 15 minutes and about 5 times lower than those to submicron particles. By using the laboratory measured mass transfer coefficients of PCBs, the phytoplankton in the mesohaline Chesapeake Bay were estimated to have been exposed to PCB congeners for 6-15 days. Sorption of PCBs to suspended particles in the water column of the Chesapeake Bay are far away from a simple linear two-phase sorptive equilibrium. The high variation in PCB distribution coefficients in phytoplankton of the Chesapeake Bay may be adequately interpreted by a kinetic three-phase sorption model.