| Abstract
| - Analysis of sediment cores from one location on the continentalshelf off Palos Verdes, CA, indicates that in situ reductive dechlorination rates of p,p′-DDEare 0.051 ± 0.006 yr−1.
- From 1947 to 1971 the world’s largest manufacturer of DDTdischarged process wastes into the sewers of Los Angeles County. Roughly870-1450 t of DDT were released to the ocean off Palos Verdes,CA, a portion of which (∼100 t) resides in sediments on thecontinental shelf and slope. The most abundant DDT compound in thesediments, p,p′-DDE, is degrading by reductivedechlorination, but the rate of transformation and factors controllingit are not well understood. In order to estimate in situ transformation rates and predict the long-term fate of p,p′-DDE, box cores were collected in 1992 and 2003 from a singlelocation on the Palos Verdes Shelf and analyzed for 8 DDT compoundsand 84 polychlorinated biphenyl (PCB) congeners. The PCBs show noevidence of dechlorination, and inventories did not change between1992 and 2003. By contrast, the inventory of p,p′-DDEdecreased by 43%, whereas that of p,p′-DDMU,the putative reductive dechlorination product, increased by 34%. Thefirst-order transformation rate for p,p′-DDEat the study site is 0.051 ± 0.006 yr−1. Amultistep reaction model suggests that inventories of p,p′-DDE and p,p′-DDMU will continueto decline, whereas that of p,p′-DDNU willreach a maximum around 2014.
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