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John F. Quensen III,* Sherry A. Mueller, Mahendra K. Jain, James M. Tiedje
DDT is reductively dechlorinated to DDD and dehydrochlorinated to DDE; it has been thought that DDE is not degraded further in the environment. Laboratory experiments with DDE-containing marine sediments showed that DDE is dechlorinated to DDMU in both methanogenic and sulfidogenic microcosms and that DDD is dehydrochlorinated to DDMU three orders of magnitude more slowly. Thus, DDD does not appear to be an important precursor of the DDMU found in these sediments. These results imply that remediation decisions and risk assessments based on the recalcitrance of DDE in marine and estuarine sediments should be reevaluated.
DDT [1,1,1-trichloro-2,2,bis(p-chlorophenyl)ethane] was one of the first synthetic pesticides to gain wide acceptance. Initially its use greatly enhanced crop yields, but pest species rapidly developed resistance so that its use in agriculture in the United States began to decline by 1959. It was effective longer in controlling mosquito-borne malaria ( I ) and is still used for that purpose in some tropical countries.
Because of environmental concerns, the use of DDT was banned in the United States and in some other countries in the early 1970s. By that time, however, it was distributed globally. Both DDD [1,1-dichloro-2,2,-bis(p-chlorophenyl)ethane] and DDE [1,1-dichloro-2,2,-bis(p-chlorophenyl)ethylene] existed as by-products in commercial DDT formulations, and both may be formed by environmental degradation of DDT. DDT, DDD, and DDE (collectively DDX) are found, in various proportions, in soils and sediments and have been reported at 3422 out of 22,000 sites identified as posing a danger to humans and animal life by the U.S. Environmental Protection Agency (EPA) in its National Sediment Quality Survey.
One such marine site is the continental shelf off of the Palos Verdes Peninsula in southern California. Sediment core data collected over the last two decades by the Los Angeles County Sanitation District and the U.S. Geological Survey show that DDE is the most prevalent of the DDX compounds present in the shelf sediments and imply that the mass of DDE is decreasing with time (2, 3). Bioturbation has been proposed as a mechanism responsible for this trend (3) because DDE is viewed as a recalcitrant compound (4). However, the concentration of trace metals in the sediments has remained constant...