Pesticides provide essential protection in the production of many agricultural commodities. However, increasing pesticide use as a result of increased production has led to community concern about the social and environmental impacts of pesticide residues. Of particular concern is the contamination of irrigation run-off and drainage water, agricultural soils and horticultural products.

Pesticide residues in soil have been detoxified by introducing and/or encouraging the growth of microorganisms capable of detoxifying the residues on site – a technology known as bioremediation. This method of bioremediation is based on traditional composting techniques and relies on microbial growth to metabolise the toxicants. The detoxification process is generally slow, taking weeks to months to accomplish. Furthermore, the methodology is not suited to the generally low aeration and nutrient content of contaminated water. However, the microorganisms capable of breaking down toxicants in contaminated soil can be sources of enzymes capable of detoxifying pesticide residues in such a low aeration, low nutrient medium. The application of such enzymes is particularly suited to pesticide-contaminated water in that they can achieve rapid remediation without the addition of nutrients or aeration.

The problem of pesticide contamination of water needs to be addressed prior to its release into the waterways. CSIRO Entomology, in conjunction with Orica Australia Pty Ltd. and CSIRO Molecular Science, has successfully developed enzyme-based bioremediation technologies for detoxifying pesticides in contaminated water prior to its release off-farm. For example, an organophosphate degrading enzyme has proven to be an effective and powerful tool for the rapid degradation of pesticide residues in agricultural and rinsate water. In a recent field trial, methyl parathion levels in 80,000 L of fast flowing run-off water in cotton farm drainage channels were reduced by 90% in less than ten minutes. This is a low concentration/high volume source of pesticide-contaminated water that also contains high levels of silt and other particulate matter. In a second field trial, enzyme treatment of rinsate from the washdown of pesticide spray equipment achieved a reduction in methyl parathion concentration of 90% in 10 minutes, and 99% after 1 hour. In contrast to the run-off water in the first trial, this rinsate is a high concentration/low volume source that also contains organic solvents. The application range of the technology has been broadened further to include diazinon detoxification in spent sheep-dip liquor, and the treatment of methyl parathion residues on the surface of leafy green vegetables. In a recent laboratory trial, the concentration of diazinon was reduced from 4.7 parts per million to below 1 part per billion (99.98% reduction), within 1 hour. In the trial involving leafy green vegetables, residues on the surface of baby bok choy were reduced by up to 95%. Given the complex nature of the surface of bok choy, this trial further demonstrated the utility of the enzyme technology.

Our research currently focuses on several major insecticide classes including organophosphates, carbamates, synthetic pyrethroids and the organochlorine, endosulfan. This project centres around the isolation of enzymes that degrade the toxic metabolite of endosulfan, endosulfan sulfate. As a result of this project we have isolated a bacterium that degrades endosulfan sulfate. This bacterial strain was isolated by providing endosulfan sulfate as the only source of sulfur to a soil microbial population. Sulfur is an essential component of living matter. Therefore only bacteria that could release the sulfur from endosulfan could survive. Removal of sulfur from endosulfan sulfate results in substantial detoxification. The enzyme responsible for this activity was cloned and characterised. The feasibility of conducting field trials of this enzyme in irrigation run-off was assessed in collaboration with our commercial partner, Orica Australia Limited. The requirement of co-factors for activity meant that alternative, more stable co-factors would need to be found, or another (non-co-factor requiring) gene / enzyme system isolated.