Submitted to: Israel Journal of Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/29/2002
Publication Date: 8/9/2002
Citation: WU, J., LAIRD, D.A. HYDROLYSIS OF CHLORPYRIFOS IN AQUEOUS AND COLLOIDAL SYSTEMS. ISRAEL JOURNAL OF CHEMISTRY. 2002. V. 42. P. 99-107.
Interpretive Summary: Chlorpyrifos is an insecticide that is widely used for control of insect pests in production agriculture. Chlorpyrifos is extremely toxic to humans, animals, birds, and fish as well as insects. Exposure of non-target organisms to chlorpyrifos is most likely to occur when the insecticide is transported off of the field where it was applied. Because chlorpyrifos sticks very tightly to soil particles we thought that there was a risk that it could be transported with eroded soil from agricultural fields to streams and rivers. In water, chlorpyrifos degrades rapidly to nontoxic compounds. We discovered that chlorpyrifos stuck to soil particles suspended in water (suspended sediment) degrades more slowly than chlorpyrifos in water without the suspended sediment. We also discovered that suspended sediments can act as a reservoir to slowly release chlorpyrifos back to the water. This research is important to scientists and environmentalists who want to understand the fate of pesticides in the environment. The research may also help action agencies responsible for regulating the use of pesticides in determining which practices are acceptable and which should be banned.
Technical Abstract: Hydrolysis of chlorpyrifos [o,o-diethyl o-(3, 5, 6-trichloro-2-pyridyl) phosphorothioate] to TCP (3,5,6-trichloro-2-pyridinol) is an important degradation process influencing the fate of chlorpyrifos in aquatic environments. The effects of water chemistry and suspended colloids (smectites, humic acid and river sediment) on the hydrolysis of chlorpyrifos were investigated in this study. Chlorpyrifos was incubated in various aqueous and colloidal systems at 23 (plus or minus) 2 deg C for up to 100 days, and aqueous phase concentrations of chlorpyrifos and TCP were determined using solid phase extraction-high performance liquid chromatography (SPE-HPLC). Chlorpyrifos degraded in the aqueous solutions with half-lives ranging from 27 to 158 days, depending on the initial concentration of chlorpyrifos and the chemistry of the aqueous solutions. The rate of degradation was slower in systems containing low concentrations of suspended colloids (1 g L**-1) than in the control (0.01 M CaCl2, with no colloids) and negligible hydrolysis of chlorpyrifos was found for concentrated colloidal systems (20 g L**-1). Total recoveries of chlorpyrifos for the concentrated colloidal systems ranged from 78% to 97% with a tendency to decrease with incubation time. The study indicates that the formation of chlorpyrifos-colloid complexes inhibits the hydrolysis of chlorpyrifos in aqueous systems and that chlorpyrifos-colloid complexes may act as a buffer by slowly releasing chlorpyrifos to the aqueous solution.