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Abstract. Thirteen sediment cores of 1.5-6 m depth were collected from the lower Passaic River in Newark, New Jersey and assayed for metals, total petroleum hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), and Aroclor ® and coplanar polychlorinated biphenyls (PCBs). Chronological profiles of chemical concentrations at specified depths and sediment accumulation rates in each core were determined by 137Cs and 21°Pb radioisotope measurements. Temporal concentrations of these chemicals were compared to available benchmark sediment toxicity values to assess historic and current toxic hazards to aquatic organisms. Elevated concentrations of several metals, including copper, lead, mercury, nickel, and zinc, were found in surface and buried sediments at concentrations that greatly exceeded Long and Morgan (1991) Effects Range-Low (ER-L) and Effects Range-Median (ER-M) values. Aroclors ® 1242, 1248, and 1254 and several PAHs were also found at concentrations exceeding Long and Morgan (1991) benchmark toxicity values. In general, the highest metal and PAH concentrations were found in sediment deposited prior to the 1960s. Elevated PCB concentrations were found in sediment deposited between 1950 and 1980. The results indicate that the lower Passaic River is heavily contaminated due to recent and historical municipal and industrial discharges from local and upstream sources. The primary sources of PCBs, PAHs, and metals appear to be discharges of industrial effluents either directly into the waterway or through combined sewer overflows. Additional inputs are probably from urban runoff entering through combined sewer overflows and storm drains.