Diazinon - Chemistry and environmental fate: A California perspective

Abstract

Diazinon, first introduced in USA in 1956, is a broad-spectrum contact organophosphate pesticide that has been used as an insecticide, acaricide, and nematicide. It has been one of the most widely used insecticides in the USA for household and agricultural pest control. In 2004, residential use of diazinon was discontinued, and in 2009, diazinon was phased out of all agricultural uses. Consequently, the amounts of diazinon applied have been drastically decreased. For example, in California, the amount of diazinon applied decreased from 501,784 kg in 2000 to 64,122 kg in 2010. Diazinon has a K∞ value of 40-432, and is considered to be moderately mobile in soils. Diazinon residues have been detected in groundwater, drinking water wells, monitoring wells, and agricultural wells. The highest detection frequencies and highest percentages of exceedance of the water quality criterion value of 0.1 μg/L have been reported from the top five agricultural counties in California that had the highest diazinon use. Diazinon is transported in air via atmospheric processes such as direct air movement and wet deposition in snow and rain, although concentrations decrease with distance and elevation from the source. In the environment, diazinon undergoes degradation by several processes, the most important of which is microbial degradation in soils. The rate of diazinon degradation is affected by pH, soil type, organic amendments, soil moisture, and the concentration of diazinon in the soil, with soil pH being a major in fl uencing factor in diazinon degradation rate. Studies indicate that soil organic matter is the most important factor that in fl uences diazinon sorption by soils, although clay content and soil pH also play an important role in diazinon sorption. Diazinon is very highly to moderately toxic to aquatic organisms. Diazinon inhibits the enzyme acetylcholinesterase, which hydrolyzes the neurotransmitter acetylcholine and leads to a suite of intermediate syndromes including anorexia, diarrhea, generalized weakness, muscle tremors, abnormal posturing and behavior, depression, and death. Differences in metabolism among species and exposure concentrations play a vital role in diazinon's bioaccumulation among different aquatic organisms in a wide range of accumulating rates and efficiencies. © 2013 Springer New York.