Biodegradation of the synthetic pyrethroid cypermethrin in used sheep dip.

Abstract

To investigate the breakdown of cypermethrin synthetic pyrethroid (SP) insecticide-based used sheep dip (USD), with its indigenous microbial community and two previously isolated SP-degrading microorganisms. Cultures of USD (50 ml) containing 250 ml l(-1) cypermethrin were inoculated with the SP-degrading organisms and incubated at 25 degrees C with agitation at 80 rev min(-1) for 14 days. The viable cell counts and concentration of cypermethrin were monitored. A non-stimulated control was also carried out. The previously isolated bacteria were the most effective at degrading cypermethrin, leaving approximately two-thirds the concentration of SP as was found in the control. The non-stimulated cultures showed negligible breakdown of SP over the experimental period. The previously isolated SP-degrading bacteria could have a use in the treatment of SP USD. In situ treatment of SP-based USDs to detoxify the active ingredient before disposal could be very useful in helping to deal with agricultural pesticide waste. Such an approach, or by ex situ treatment would be more preferable to current methods, such as those of incineration and disposal to land.