Historical record and fluxes of DDTs at the Palos Verdes Shelf Superfund site, California.

Marine sediments at many locations in the world are contaminated with a wide range of persistent organic pollutants. The Palos Verdes Shelf (PVS) is located in the ocean off the coast of Los Angeles, California and has been listed as a Superfund site by the US EPA since 1997, because of heavy contamination of DDTs and PCBs. However, little is known about the historical trend in the deposition of DDTs as a result of decades-long discharge of wastewater effluents. In this study, sediment cores were taken from the PVS site and determined for DDT and its metabolites including DDE and DDD (denoted as DDTs). Individual DDTs were found in the majority (95%) of the samples analyzed. The highest ∑DDT concentrations were found in three cores along the 60-meter isobath with geometric means of 31300, 7490, and 5010ng/gdw and medians of 82400, 17300, and 5200ng/g dw, respectively. Among DDT congeners, p,p'-DDE, o,p'-DDE and p,p'-DDD were predominant, contributing to approximately 54%, 27%, and 14% of the ΣDDTs in sediment. The vertical profiles of concentrations of contaminants in the sediment cores were examined. For most of the cores, a steady increase in the concentrations of DDTs during 1940s to 1980s was observed, while the concentrations declined gradually toward the surficial layers. On the basis of the mass flux of DDTs calculated and the area of the PVS Superfund site, we estimated the total deposition amount of DDTs in sediment and the deposition amount of ΣDDTs in this region during 1947-1971 was 132 tons, which was fairly close to what was reported in earlier studies for industrial wastewater discharge in the PVS site (870-1450tons). Our findings suggest that the elevated levels of DDTs in sediment from the PVS site are linked to the discharge of these contaminants between the 1940s-1980s.