Bacteria That Gorge On Rotting Waste Can Break Down DDT

May 05, 1999

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.

Finding a practical way to clean up contaminated land is tricky. Digging up soil and moving it elsewhere is no longer acceptable, sealing it in a landfill site is now illegal in the US, and heating it in massive kilns to burn off offending pesticides is expensive.

The team at AstraZeneca has come up with an alternative, using local bacteria that feed on organic waste to break down hazardous substances into less harmful by-products in a process called bioremediation. 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 the landowners in the US who are liable for cleaning up tens of thousands of contaminated sites, such as old chemical plants, will adopt their technique.

The AstraZeneca researchers mixed tainted soil with large amounts of the 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, Florida, AstraZeneca's process, called Xenorem, cut DDT levels in the soil by more than 95 per cent. DDT is considered one of the worst pollutants because its breakdown products, such as DDE, were thought to be almost indestructible. But recent research has shown that DDE can be degraded (This Week, 9 May 1998, p 16) and in the Tampa trial the bacteria reduced levels of DDE, DDD and other chlorinated pesticides to below US Environmental Protection Agency safety limits. Earlier trials using pollutants marked with radiocarbon confirmed that the detection rates were accurate.

Stauffer Management Company, a subsidiary of AstraZeneca, has patented the technology, which it presented to a bioremediation symposium in San Diego last week. The company is now modifying the process so that it can break down other persistent organic pollutants such as PCBs and TNT (see report below).

The new technique will remove contaminants at around half to two-thirds of the price of incineration, the next best solution, says Frank Peter, AstraZeneca's director of environmental services. It can also be carried out on site and is environmentally friendly, using natural waste products to help indigenous bacteria gobble up pollutants. "It solves two problems at once," he says.
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Author: Matt Walker
New Scientist issue 8 May 1999

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