The hydrolysis rate of chlorpyrifos,O-O-diethylO-(3,5,6-trichloro-2-pyridyl) phosphorothioate, and its dimethyl analog, chlorpyrifos-methyl, in dilute aqueous solution

Abstract

Abstract. The hydrolysis rate of chlorpyrffos (the active ingredient of DURS-BAN @ and LORSBAN | insecticides, registered trademarks of The Dow Chemical Company, Midland, Michigan) in water followed simple first-order kinetics over the concentration range, 3 x 10 -9 to 3 x 10-ZM. In buffered distilled water at 25~ and pH 8. I, 6.9, and 4.7, the haft-life was 22.8, 35.3, and 62.7 days, respectively. Additional data were obtained for rates at 15 ~ and 35~ The activation energy for the reaction under these conditions was 21.2 kcal/mole. A 16-fold rate enhancement was demonstrated in canal and pond water at 25~ Likewise, there was a catalytic effect on the hydrolysis rate in the presence of copper (II) ion.The same information was generated for chlorpyrffos-methyl, the dimethyl analog of chlorpyrifos. In this case, the corresponding "half-life values for hydrolysis at 25~ and pH 7.8, 6.7, and 4.2 were 12.7, 17.4, and 22.8 days, respectively. The activation energy was 20.8 kcal/mole, not significantly different from that for chlorpyrffos. A hydrolysis rate enhancement also occurred for chlorpyrifos-methyl in canal water.Qualitatively, the products of chlorpyrifos hydrolysis were 3,5,6-trichloro-2-pyridinol (I), O-ethyl O-hydrogen O-(3,5,6-trichloro-2-pyridyl) phosphorothioate (II), and O, O-dihydrogen O-(3,5,6-trichloro-2-pyridyl) phosphorothioate (III). In the case of chlorpyritbs-methyl, the hydrolysis products were compound I and the methyl analog of compound II.Because of the need to evaluate the fate of pesticides in the environment to which they may be applied, a study was carried out to determine the fate of chlorpyrifos in water. The efficacy of this compound has been well demonstrated (Collier and Dieter 1965, Gray 1965, Kenaga et al. 1965. The dimethyl analog, chlorpyrifosmethyl, was included in this study. The investigation reported herein defines the hydrolysis rates at different pH and temperature values, gives the observed activation energy for the reaction, and describes the hydrolysis products.

Ecotoxicology of Chlorpyrifos

“…Water column half-lives of less than 0.08-2.4 d and sediment half-lives of 0.8-16.3 d have been reported from a number of field investigations (Racke 1993). Hydrolytic degradation in natural waters has been found to be substantially greater than in sterile distilled water at similar pH; for example, Meikle and Youngson (1978) reported a IS-fold enhancement of the chlorpyrifos hydrolysis rate in canal water compared with distilled water.…”

Identification and characterization of chlorpyrifos-methyl and 3,5,6-trichloro-2-pyridinol degrading Burkholderia sp. strain KR100

“…Because of this, much effort has been focused on them as potential sources of biological agents for the remediation of soil, water, or crop contaminated with OPs. The hydrolytic degradation of CM has been characterized in the aquatic and soil environments (Meikle and Youngson 1978;Tomlin 2003). The most common pathway of hydrolytic degradation of the phosphorothioate involves formation of 3,5,6-trichloro-2-pyridinol (TCP) by microorganisms.…”

Evaluation of evidence that the organophosphorus insecticide chlorpyrifos is a potential persistent organic pollutant (POP) or persistent, bioaccumulative, and toxic (PBT)

“…In aquatic systems at 25°C, half-lives of 73, 72, and 16 days were measured at pH 5, 7, and 9, respectively [summarized in 67]. In distilled water, in the absence of light and microorganisms, the halflife ranged from as little as 0.01 to 210 days, depending on pH [68][69][70] (see Additional file 1: Table S4D). Data for halflife measured in distilled were not included in the assessment as this matrix is not environmentally realistic.…”

“…The geometric mean half-life for all laboratory-based data without exclusion of studies was 21 days [15]. When studies conducted with waters from European locations ( Figure 5 and Additional file 1: Table S4A) [75,76] and non-European locations ( Figure 5 and Additional file 1: Table S4B) [69,70,73,74] were considered separately, the geometric means were 2.2 and 11 days, respectively. There were no field data from the EU, but the geometric mean of field data from non-EU locations [77,78] was 6 days (see Additional file 1: Table S4C).…”

“…In their simulations of the dynamics of CPY in aquatic systems, the US EPA [27] used an aqueous hydrolysis halflife of 81 days at pH 7.0. In surface waters measured in the laboratory, half-lives of CPY ranged from 1.29 to 126 days [69,70,73,74] (see Additional file 1: Table S4B). …”