Partitioning of hydrophobic organic contaminants to resuspended sediments and plankton in the mesohaline Chesapeake Bay

Abstract

Abstract Concentrations of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were measured in four sizes of suspended particles and in the dissolved phase in surface and bottom waters of the mesohaline Chesapeake Bay from 1990 to 1992. The distribution of these hydrophobic organic contaminants (HOCs) between particles from differing sources (i.e. primary production or sediment resuspension) was measured. Suspended particles in Chesapeake Bay surface waters (3 m depth) are mainly plankton while those in bottom waters (2 m above bottom) are a mixture of resuspended surficial sediments and plankton and detritus which have settled from surface waters. On a dry weight basis, concentrations 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 concentrations of HOCs in large (> 202 μm) particles (up to 500 ng/g of total PCB and 4 μg/g of dibenz[a,h]-anthracene) may be due to accumulation in Zooplankton. Despite this enrichment, settling of these large particles contributes little to the overall HOC settling fluxes because the large particles comprise a very small fraction (0.5–2.8% by weight) of the particle population. On short time scales (e.g. hours to days), intense episodes of sediment resuspension may control the concentrations and distributions of HOCs in the water column of the Chesapeake Bay. However, over longer time scales, incorporation of HOCs into organic-rich particles and burial in bottom sediments likely controls the cycling and long-term residence times of HOCs.