TIDAL RIVER SEDIMENTS IN THE WASHINGTON, DC AREA .2. DISTRIBUTION ANDSOURCES OF ORGANIC CONTAMINANTS

Concentrations of aliphatic, aromatic, and chlorinated hydrocarbons we re determined from 33 surface-sediment samples taken from the Tidal Ba sin, Washington Ship Channel, and the Anacostia and Potomac rivers in Washington, D.C. In conjunction with these samples, selected storm sew ers and outfalls also were sampled to help elucidate general sources o f contamination to the area. All of the sediments contained detectable concentrations of aliphatic and aromatic hydrocarbons, DDT (total dic hlorodiphenyltrichloroethane), DDE (dichlorodiphenytdichloroethene), D DD (dichlorodiphenyldichloroethane), PCBs (total polychlorinated biphe nyls) and total chlordanes (oxy-, alpha-, and gamma-chlordane and cis + trans-nonachlor). Sediment concentrations of most contaminants were highest in the Anacostia River just downstream of the Washington Navy Yard, except for total chlordane, which appeared to have upstream sour ces in addition to storm and combined sewer runoff. This area has the highest number of storm and combined sewer outfalls in the river. Poto mac River stations had lower concentrations than other stations. Total hydrocarbons (THC), normalized to the fine-grain fraction (clay + sil t, <63 mu m), ranged from 120 mu g g(-1) to 1,900 mu g g(-1) fine-grai n sediment. The hydrocarbons were dominated by the unresolved complex mixture (UCM), with total polycyclic aromatic hydrocarbons (PAHs) conc entrations ranging from 4 mu g. g(-1) to 33 mu g g(-1) fine-grain sedi ment. Alkyl-substituted compounds (e.g., C1 to C4 methyl groups) of na phthalene, fluorene, phenanthrene + anthracene, and chrysene series do minated the polycyclic aromatic hydrocarbons (PAHs). Polycyclic aromat ic hydrocarbons, saturated hydrocarbons, and the unresolved complex mi xture (UCM) distributions reflect mixtures of combustion products (i.e ., pyrogenic sources) and direct discharges of petroleum products. Tot al PCB concentrations ranged from 0.075 mu g g(-1) to 2.6 mu g g(-1) f ine-grain sediment, with highest concentrations in the Anacostia River . Four to six C1-substituted biphenyls were the most-prevalent PCBs. V ariability in the PCB distribution was observed in different sampling areas, reflecting differing proportion of Arochlor inputs and degradat ion The concentration of all contaminants was generally higher in sedi ments closer to known sewer outfalls, with concentrations of total hyd rocarbon, PAHs, and PCBs as high as 6,900 mu g g(-1), 620 mu g g(-1) a nd 20 mu g g(-1) fine-grain sediment, respectively. Highest PCB concen trations were found in two outfalls that drain into the Tidal Basin. C oncentrations of organic contaminants from sewers draining to the Wash ington Ship Channel and Anacostia River had higher concentrations than sediments of the mid-channel or river. Sources of PCBs appear to be r elated to specific outfalls, while hydrocarbon inputs, especially PAHs , are diffuse, and may be related to street runoff. Whereas most point -source contaminant inputs have been regulated, the importance of nonp oint source inputs must be assessed for their potential addition of co ntaminants to aquatic ecosystems. This study indicates that in large u rban areas, nonpoint sources deliver substantial amounts of contaminan ts to ecosystems through storm and combined sewer systems, and control of these inputs must be addressed.