PARTITIONING OF HYDROPHOBIC ORGANIC CONTAMINANTS TO RESUSPENDED SEDIMENTS AND PLANKTON IN THE MESOHALINE CHESAPEAKE BAY

Concentrations of polycyclic aromatic hydrocarbons (PAHs) and polychlo rinated biphenyls (PCBs) were measured in four sizes of suspended part icles and in the dissolved phase in surface and bottom waters of the m esohaline Chesapeake Bay from 1990 to 1992. The distribution of these hydrophobic organic contaminants (HOCs) between particles from differi ng sources (i.e. primary production or sediment resuspension) was meas ured. Suspended particles in Chesapeake Bay surface waters (3 m depth) are mainly plankton while those in bottom waters (2 m above bottom) a re a mixture of resuspended surficial sediments and plankton and detri tus which have settled from surface waters. On a dry weight basis, con centrations of most of the particulate HOCs studied were higher in the surface waters of the Chesapeake Bay than in the bottom waters, or in the flocculent and consolidated surficial sediments. Elevated concent rations of HOCs in large (> 202 mu m) particles (up to 500 ng/g of tot al PCB and 4 mu g/g of dibenz[a,h]-anthracene) may be due to accumulat ion in zooplankton. Despite this enrichment, settling of these large p articles contributes little to the overall HOC settling fluxes because the large particles comprise a very small fraction (0.5-2.8% by weigh t) of the particle population. On short time scales (e.g. hours to day s), intense episodes of sediment resuspension may control the concentr ations and distributions of HOCs in the water column of the Chesapeake Bay. However, over longer time scales, incorporation of HOCs into org anic-rich particles and burial in bottom sediments likely controls the cycling and long-term residence times of HOCs.