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 detecti
Contact: Claire Bowles