Diazinon degradation

Diazinon (phosphorothioic acid 0,0-diethyl 0-(6-mcthyl-2-(l-mcthylcthyl)-4-pyrimidinyl) ester) is an organophosphorus compound with an anticholinesterase mode of action. It is used extensively to control hies, lice, insect pests of ornamental plants and food crops, as well as nematodes and soil insects in lawns and croplands. Diazinon degrades rapidly in the environment, with half-time persistence usually less than 14 days. But under conditions of low temperature, low moisture, high alkalinity, and lack of suitable microbial degraders, diazinon may remain biologically active in soils for 6 months or longer. 

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. 

Although diazinon has been detected in groundwater samples in both the United States and Canada (Cohen 1986 EPA 1989a Frank et al. 1987, 1990b HazDat 1996), no studies were identified concerning diazinon transformation and degradation processes within aquifers. Based on theoretical considerations, abiotic hydrolysis mechanisms would be expected to degrade diazinon within a few months (Chapman and Cole 1982 Cowart etal. 1971). 

Analyses of residues in the soils after incubation showed that the persistence of diazinon was considerably shorter in the previously treated soil than in the untreated soil. The half-life value for diazinon in previously treated soil was 1.7 days while in the untreated soil it was 9.9 days. Most of the insecticide added to the previously treated soil was lost within 10 days. Paddy water from the same fields were tested also for diazinon-degrading activity (17). Again water from a rice field treated previously with diazinon inactivated the insecticide more rapidly than did the water from an untreated field. In the water from the previously treated field the insecticide dissipated completely within 3-5 days of incubation after an initial lag of 1-2 days (17, 18). Table II summarizes the results of the study on the stability of diazinon in soil and paddy water. The data indicated clearly that a factor capable of degrading diazinon developed in rice fields of the Institute farm after insecticide applications. The diazinon-degrading factor, found in the diazinon-treated rice fields in the Institute farm, was noticed also in three other locations in the Philippines (19). 

Aerobic conditions during incubation favored the degradation although some degradation occurred also under anaerobic conditions (17). Perhaps, facultative anaerobes are involved in the degradation. This view is supported by the observation that a Flavobacterium sp. isolated from paddy water of treated field could degrade diazinon under aerobic and anaerobic systems but more rapidly under aerobic conditions (20). 

Isolating Flavobacterium sp. with exceptionally high ability to metabolize diazinon as sole carbon source and other bacteria (Arthrobacter sp. and Corynebacterium sp.), which could degrade diazinon only in the presence of additional carbon source, provides strong evidence that microbes rapidly inactivate diazinon in the rice field. 

Earlier reports show that microorganisms metabolize diazinon either in the presence of additional carbon source (2, 17, 23, 27, 28) or syner-gistically by the action of two microorganisms (24). Bacteria capable of degrading diazinon are listed in Table V. These studies show clearly that attempts to isolate a bacterium utilizing diazinon as sole carbon source have been unsuccessful. In this report, using a maximum dilution-frequency technique, we have succeeded in isolating a Flavobacterium sp. from paddy water of diazinon-treated fields that could metabolize diazinon as sole carbon source. 

Degradation of the insecticide chlorpyrifos has been examined in solutions of aqueous chlorine in which the primary oxidant is hypochlorous acid/hypochlorite. The final product was 2,3,5-trichloropyrid-2-one produced either directly, or via initial oxidative conversion of the thioate ester by replacement of the sulfur with oxygen (Duirk and Collette 2006). An analogous oxidation was found with diazinon (Zhang and Pehkonen 1999). 

Diazinon degrades rapidly in plants, with half-time persistence usually less than 14 days. However, persistence increases as temperatures decrease, and is longer in crops with a high oil content (Table 16.1). In water, diazinon breaks down to comparatively nontoxic compounds with little known hazard potential to aquatic species (Meier et al. 1976 Jarvinen and Tanner 1982), although the degradation rate is highly dependent on pH (Table 16.1). The half-time persistence of... 

Forrest, M., K.A. Lord, N. Walker, and H.C. Woodville. 1981. The influence of soil treatments on the bacterial degradation of diazinon and other organophosphorus insecticides. Environ. Pollut. 24A 93-104. 

Meier, E.R, M.C. Warner, W.H. Dennis, W.F. Randall, and T.A. Miller. 1976. Chemical Degradation of Military Standard Formulations of Organophosphate and Carbamate Pesticides. I. Chemical Hydrolysis of Diazinon. U.S. Army Med. Bioengin. Res. Dev. Lab., Fort Detrick, Frederick, MD. Tech. Rep. 7611. 32 pp. 

Bro-Rasmussen, R, Noddegaard, E., and Voldum-Clausen, K. Degradation of diazinon in soil, / ScL Food Agile., 19 278-282, 1968. 

Sethunathan, N. and Pathak, M.D. Development of a diazinon-degrading bacterium in paddy water after repeated applications... 

Suett, D.L. Persistence and degradation of chlorfenvinphos, diazinon, fonofos, and phorate in soils and their uptake by carrots. Pestle. Sci., 2(3) 105-112. 1971. 

Konrad JG, Chester G (1969) Soil degradation of diazinon, an organophosphate insecticide. J Agri Food Chem 17 226-230... 

Degradation of Diazinon in Greenhouse Soil by Parathion Hydro-lase... 

Figure 5 shows the degradation of diazinon in soil at 2000 ppm by parathion hydrolase. It is easy to see that degradation is very rapid and effective - reaching safe environmental levels by 24 hours. 

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. 

D. Rosenblatt. "Degradation of Diazinon by Sodium Hypochlorite, Chemistry and Tox." Env. Science Tech., 13, 594 (1979). 

---