This project was designed to evaluate the extent and magnitude of Persistent Organic Pollutant (POP) exposure in organisms that occupy the lowest trophic levels in the pelagic ecosystem of Puget Sound, and to gain a better understanding of the pathways of contaminants within this food web. To this end zooplanktonic krill, Euphausia pacifica and Thysanoessa spp, an important food source for pelagic fish in the Puget Sound, and phytoplankton, primary producers at the base of the pelagic food web, were sampled and analyzed for toxic contaminants. Non-migratory pelagic fish species that feed primarily on krill, including Pacific hake (Merluccius productus) and walleye pollock (Theragra chalcogramma), as well as their predators, harbor seals (Phoca vitulina) were assessed in two companion studies. We measured the concentration of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), organochlorine pesticides (OCPs), and polycyclic aromatic hydrocarbons (PAHs) in phytoplankton and krill from a broad range of locations representing as wide a range of putative contaminant loadings possible. Because of technical difficulties in isolating phytoplankton from other particulate organic matter, we filtered seawater through 20-Ã¬m mesh to select particle sizes that would maximize retention of phytoplankton, but allow smaller particles to pass. The resulting size-selected organic matter was termed Particulate Organic Matter (POM) for this study. POPs, including PCBs, PBDEs, DDTs, and PAHs in both POM and krill exhibited a correlation with urban waters, suggesting urban waters represent areas where POPs enter the pelagic food chain. The Basin-pattern of PBDE accumulation in krill was similar to PCBs; high concentrations in urbanized waters and low concentrations in less developed, more ocean-influenced basins â€" suggesting a similar mechanism of loading and dispersal in Puget Sound. Overall, PAHs were detected more often and in greater concentration than all other POPs in this study. The greatest concentrations of most POPs were observed in Elliott Bay, one of the two urbanized Basins in this study. This implicates urban waters as an important point of entry for POPs into the pelagic food web. OCPs were observed in low concentration in many krill samples, but were below the limit of detection for most POM samples. Dieldrin was higher in E. pacifica from the Whidbey Basin than other Basins. PAHs in some POM appeared to be related to small-scale (sub-basin) shoreline locations relative to nearby land use or activities. Aside from Elliott Bay the next greatest PAH concentrations in POM were observed near to shore, and near to obvious PAH sources e.g., marinas and ferry terminals, even in otherwise relatively undeveloped Basins.