Biodegradation diazinon

Sethunathan, N. and MacRae, I.C. Persistence and biodegradation of diazinon in submerged soils, J. Agtlc. Food Chem., 17(2) 221-225, 1969. 

Diazinon. 2-Isopropyl-6-methyl-4-hydroxypyrimidine, the hydrolysis product of diazinon, did not condition the soils for enhanced degradation of diazinon (Table II). Despite the low microbial toxicity and high availability (discussed elsewhere in this chapter), the hydroxypyrimidine metabolite did not predispose soils for rapid degradation of diazinon. Enhanced biodegradation of diazinon in rice soils has been previously reported (1). Evidently, the soil we studied did not contain microbes capable of adapting for diazinon enhanced degradation. 

The hydrolysis products of some pesticides susceptible to enhanced degradation (isofenphos, diazinon, carbofuran) yielded higher EC50 values, reflecting their low toxicity to bacteria (Table V). Conversely, some pesticides with little or no propensity for enhanced biodegradation yield hydrolysis products that show considerable antibacterial activity (chlorpyrifos, 2,4,5-T). 

Diazinon applied to paddy water at 2 kilogram/ha active ingredient every 20 days has controlled for several years common insect pest of rice at the International Rice Research Institute. After its continuous use for three and a half years, its efficiency for controlling rice brown planthoppers Nilaparvata lugens Stal) declined. Preliminary studies indicated that biodegradation might be involved. Detailed studies were undertaken and reported elsewhere (17). However, brief descriptions of the procedures used will be provided for better clarity to the reader. 

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