Waste-eating bacteria break down DDT
Chicken and cow manure, old newspapers, straw and wood chips can be used to clean up land contaminated with dangerous chlorinated pesticides such as DDT, according to Canadian scientists at the life sciences firm AstraZeneca.
The team at AstraZeneca has developed a bioremediation process, using local bacteria that feed on organic waste, to break down hazardous substances into less harmful by-products. The soil bacteria convert chlorinated pesticides to less toxic by-products by using enzymes known as dehalogenases to chop out offending chlorine groups. They hope U.S. landowners liable for cleaning up contaminated sites, such as old chemical plants, will adopt their technique.
The AstraZeneca researchers mixed tainted soil with large amounts of waste to make what was effectively a huge compost heap. The soil was tilled and aerated every few weeks, which provided both the nutrients and a cycle of alternating anaerobic and aerobic conditions for local bacteria to degrade the pesticides.
In a year-long test at an old pesticide factory in Tampa, Fla., AstraZeneca's process, called Xenorem, cut DDT levels in the soil by more than 95 percent. DDT is considered one of the worst pollutants because its breakdown products, such as DDE, were thought to be almost indestructible. Recent research, however, has shown that DDE can be degraded. Bacteria reduced levels of DDE, DDD and other chlorinated pesticides to below EPA safety limits in the Tampa trial. Earlier trials using pollutants marked with radiocarbon confirmed that the detection rates were accurate.
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This article originally appeared in the 07/01/1999 issue of Environmental Protection.
Gerald F. Connell, ChE is a consultant, retired after 30 years with Capital Controls Group, Severn Trent Service Inc., Colmar, Pa. Mr. Connell is author of "The Chlorination/Chloramination Handbook," published by the American Water Works, and a forthcoming "Chlorination/Dechlorination Handbook" to be published by WEF.