It binds tightly to soil particles and is degraded by biological and chemical processes within several weeks. Degradation is faster in flooded soil. Residues of parathion can persist for many years, but usually remain in the upper 6 inches of soil. Sunlight can convert parathion into the active metabolite paraoxon, which is more toxic than parathion. In open water, parathion will usually disappear within a week, mainly by adsorption to suspended particles and bottom sediments.
Adsorbed parathion is subject to degradation by microorganisms and chemical hydrolysis.
In orange groves, the half-life of parathion is as long as one month. Usually, it is closer to one-two weeks. Most crops tolerate parathion very well. At temperatures above 120 degrees C, parathion decomposes and may develop enough pressure to cause containers to explode. Parathion poses a fire and explosion hazard in the presence of strong oxidizers.