Killer cornered

Persistent weed killers meet their match

 
Published: Wednesday 31 March 1999

 Gassed: a crop duster sprayin allan Walker and his colleagues at Horticulture Research International, a British government-owned research agency in Warwickshire, uk , have discovered a strain of bacteria that degrades phenylureas, the most widely used herbicide family in Europe. Spraying the phenylureas -eating bacteria on to the soil could soon destroy these herbicide that frequently leak into ponds, streams and other water bodies wrecking havoc on fish and other aquatic creatures.

Phenylureas continues to exist in the soil for up to a year, and frequently, these residues are washed into the streams and other water bodies, where they end up contaminating the water and affecting aquatic life. One well-known member of the phenylureas family is diuron, which is used to keep surfaces, railway tracks for instance, free of weeds. It is a weak carcinogen and is known to affect fish fatally. Isoproturon, the most widely used phenylureas herbicide, used by wheat and barley farmers to control blackgrass - a weed may also prove to be a hazardous chemical for fish.

Walker and his team discovered a diuron-destroying strain of Arthrobacter in fields that had previously been treated with herbicide. The team later found out that the new strain, codenamed d 47, has a taste for other phenylureas too. "The Arthrobacter species we found can degrade them all," Walker was quoted by the British science journal New Scientist . The researchers have traced the herbicide-destroying genes to a tiny dna loop , called a plasmid, that is unique to Arthrobacter d 47. Walker's results were published in a recent issue of Soil Biology and Biochemistry . However, Walker says several important questions will have to be dealt with before the bacteria can be used to clean fields of herbicide residues. Would they persist, and prevent herbicide sprayed the following season from doing their job? he asks.

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