Enzymic degradation, diazinon

Greenhouse soil was treated at 500, 1000, 2000 and 5000 ppm with Diazinon 4E. Parathion hydrolase was added to the soil to determine the efficacy of the enzyme to rapidly degrade diazinon during a spill situation. The half-life of the diazinon in the 500 ppm treatment without enzyme present was 9.4 days while the half-life of diazinon in the 500 ppm treatment with enzyme present was one hour. The half-lives of diazinon in the 1000, 2000 and 5000 ppm treatments with enzyme present were 1.2, 5.6 and 128 hours (5.3 days), respectively. These data indicate that parathion hydrolase can be used effective " to rapidly reduce large concentrations of diazinon in soil. 

Most of the studies done, by Munnecke were small scale laboratory studies. The efficacy of parathion hydrolase has not been tested under field conditions. It was the major objective of our study to determine the usefulness of parathion hydrolase for the decontamination of high concentrations of formulated diazinon in soil under greenhouse conditions. A secondary, but very important, objective was to determine if the enzyme could be handled in a practical fashion as would be done in the field and retain its ability to degrade diazinon. 

The success of this technique has hinged upon the knowledge that many xenobiotic-degrading genes are resident on extrachromosomal pieces of DNA called plasmids (23). Pesticide degradation plasmids were first described for 2,4-D and MCPA (29-311. Plasmids are also known to code for enzymes degrading 2,4,5-T (12.) and the OP insecticide diazinon (2Z) Several copies of a specific plasmid occur within an individual cell, and plasmids can be transferred from a donor cell to a recipient cell. 

One important aspect of any cleanup technique, is the type of degradation products that are produced. These products must be known in order to assess their potential environmental impact and toxicological hazards. One of the major degradation products of diazinon, oxypyrimidine was measured in soil after treatment with parathion hydrolase. Figure 6 shows that oxypyrimidine increases in soil as the diazinon is degraded by the enzyme. 

The enzyme parathion hydrolase is active enough to be used effectively to degrade high concentrations of diazinon in soil. The half-life of diazinon in soil treated at 2000 ppm was 5.6 hours. 

A second strategy that might prove useful for decontaminating pesticide wastes in soil has been the addition of hydrolytic enzymes derived from microorganisms (12,22). Organophosphorus insecticides such as parathion and diazinon are most susceptible to decontamination by enzymes. Some success has been realized with immobilization of degradative enzymes on inert surfaces through which wastewater is passed and detoxified. 

Biological. Sethimathan and Yoshida (1973a) isolated a Flavobacterium sp. (ATCC 27551) from rice paddy water that metabolized diazinon as the sole caibon source. Diazinonwas readily hydrolyzed to 2-isopropyl-4-methyl-6-ltydroxypyrimidine under aerobic conditions but less rapidly under anaerobic conditions. This bacterium as well as enrichment cultures isolated from a diazinon-treated rice field mineralized the hydrolysis product to carbon dioxide (Sethunathan and Pathak, 1971 Sethunathan and Yoshida, 1973). Rosenberg and Alexander (1979) demonstrated that two strains of Pseudomonas grew on diazinon and produced diethyl phosphorothioate as the major end product. The rate of microbial degradation increased in the presence of an enzyme (parathion hydrolase), produced by a mixed culture of Pseudomonas sp. (Honeycutt et al., 1984). 

---