Chlorpyrifos methyl oxon

Smolen, J. M., and A. T. Stone, Metal(hydr)oxide surface catalyzed hydrolysis of chlorpyrifos-methyl, chlorpyrifos-methyl oxon, and paraoxon , Soil Sci. Am. J., 62, 636-643 (1997b). 

Amperometric activity of the electrodes in thiocholine before and following exposure to solutions of pesticides was measured. Sample to sample reproducibility was found to be favourable (RSD 6.6%), as was stability with electrodes being shown to be capable of being stored for up to 2 months at —18°C. Linear detection of chlorpyrifos methyl oxon by inhibition was obtained between 1 x 10 8 and 5 x 10 8M by this approach. 

FIGURE 57.7. (A) Primary kinetic plots of ln(% NTE activity) versus time for various indicated concentrations of chlorpyrifos methyl oxon (CPMO). (B) Slopes (—E) of primary kinetic plots versus inhihitor concentration. Data are for hen hrain microsomal NTE at pH 8.0 and 37°C. Reproduced with permission from Kropp and Richardson (2003). 

FIGURE 57.8. Spectrum of log values of relative inhibitory potency (RIP) = 7i(AChE)/ i(NTE), where = himolecular rate constant of inhibition. As log(RIP) becomes more positive, cholinergic potential increases as log(RIP) becomes more negative, delayed neuropathic potential increases. CPMO-chlorpyrifos methyl oxon. DCV derivatives refer to symmetrical dialkyl-2,2-dichlorovinyl phosphate (dichlorvos) compounds. EOPF - ethyl n-octylphosphonofluoridate. Data from Kropp and Richardson (2003) Richardson (1992) and Wu and Casida (1996). 

Kropp, T.J., Richardson, R.J. (2003). Relative inhibitory potencies of chlorpyrifos oxon, chlorpyrifos methyl oxon, and mipafox for acetylcholinesterase versus neuropathy target esterase. J. Toxicol. Environ. Health Part A 66 1145-57. 

AI3-27521 BRN 1541077 Caswell No, 466CC Chlorpyrifos-methyl oxon Dimethyl 3,5,6-trichloro-2-pyridyl phosphate Dimethyl-3,5,6-trichlor-2-pyridyl-fosfat 0,0-Dimethyl 0-(3,5,6-triohloro-2-pyridyl) phos-phate Dowoo 217 ENT 27521 EPA Pesticide Chemical Code 103601 Fospirat Fospirate Fospirate methyl Fospiralo Fospiratum NSC 195058 OMS 1168 Phosphoric acid, dimethyl... 

There are marked species differences in A-esterase activity. Birds have very low, often undetectable, levels of activity in plasma toward paraoxon, diazoxon, pirimi-phos-methyl oxon, and chlorpyrifos oxon (Brealey et al. 1980, Mackness et al. 1987, Walker et al. 1991 Figure 2.10). Mammals have much higher plasma A-esterase activities to all of these substrates. The toxicological implications of this are discussed in Chapter 10. Some species of insects have no measurable A-esterase activity, even in strains that have resistance to OPs (Mackness et al. 1982, Walker 1994). These include the peach potato aphid (Myzus persicae Devonshire 1991) and the... 

Richardson, J.R., Chambers, H.W. and Chambers, J.E. (2001) Analysis of the additivity of in vitro inhibition of cholinesterase by mixtures of chlorpyrifos-oxon and azinphos-methyl-oxon. Toxicology and Applied Pharmacology, 172, 128-139. 

The concept was further extended by the French researchers to three-pesticide mixtures, chlorpyrifos-oxon (CPO), chlorfenvinphos (CFV) and azinphos methyl-oxon (AZMO) [72], The array of biosensors was designed using only two acetylcholinesterases from Drosophila melanogaster (wild type and genetically modified) and used the dynamic comprment of the inhibition profiles and an ANN to solve mixtures of CPO, CFV and AZMO insecticides at the 1-10 nM level. 

Alonso et al. 1 AChEandB131 Chlorpyrifos/ 10 nM Chlorfenvinfos/ 10 nM Azinphos methyl-oxon/10 nM [77]... 

Crew et al. 6 AChEs, B02, B04, B65, B394 and B421 Chlorpyrifos/ malaoxon Chlorfenvinfos/ dichlorvos Chlorpyrifos/ pirimiphos methyl-oxon [69]... 

Most OP pesticides are in the fourth and largest category. Many are dimethoxy or diethoxy compounds. OPs used in agriculture tend to be manufactured in the relatively stable P = S form. They are less toxic than OPs with the P = 0 (oxon) group. (Phosphates lack a sulfur atom, phos-phorothioates have a single sulfur atom, and phosphorodithioates have two sulfur atoms.) Many pesticides such as parathion, methyl parath-ion, diazinon, and chlorpyrifos are phosphoroth-ionates. 

Howard MD, Pope CN. In vitro effects of chlorpyrifos, parathion, methyl parathion and their oxons on cardiac muscarinic receptor binding in neonatal and adult rats. Toxicology 2002 170(1—2) 1—10. 

The herbicide atrazine is not toxic to midge (Chironomus tentans) larvae but has a strong synergistic effect on several organophosphorus insecHcides such as chlorpyrifos and parathion-methyl, but not to malathion. The increased rate of oxidahon to the achve toxicants, the oxons, is suggested as one of the mechanisms, and the level of CYP enzymes is elevated. Figure... 

More recently, PONl knockout PONl and PONl transgenic mice have provided important new tools to investigate the role of PONl in modulating OP toxicity. Plasma and liver from PONl mice have no detectable hydrolytic activity toward paraoxon and diazoxon, and have very limited chlorpyrifos-oxonase activity (Shih et al., 1998 Li et al., 2000). PONl mice do not differ from wild-type animals in their sensitivity to demeton-S-methyl, an OP insecticide with a structure similar to malathion and that is not a substrate for PONl (Li et al., 2000). In contrast, PON mice have a dramatically increased sensitivity to chlorpyrifos oxon and diazoxon, and a slightly increased sensitivity to the toxicity of the parent compounds chlorpyrifos and diazinon (Shih et al., 1998 Li et al., 2000). A surprising finding is that the lack of PONl did not affect sensitivity of mice to paraoxon, the substrate for which the enz5une was named, despite the absence of any paraoxonase activity in plasma and liver (Li et al., 2000). 

Materials Acety 1 cholinesterase from an electric eel, (EC 3.1.1.7,1 OOOU/mg), acetylthiocholine chloride, 5,5 -dithiobis (2-nitrobenzoic acid), D (+) trehalose dihydrate, D (+) glucose, pyridostigmine bromide, and neostigmine bromide were from Sigma Chemical/Aldrich. Aldicarb, carbaryl, carbofuran, chlorpyrifos, chlorpyrifos-oxon, dichlorvos, methomyl, malathion, malaoxon, naled, paraoxon, parathion, trichlorfon, azinphos-methyl, diclofenthion, dimethoate, dimethoate-oxon, terbufos, phosmet, and fenthion were obtained from Chem Service Corp. All others chemicals used were reagent grade. Deionized water (DI) was used for the preparation of all solutions. 

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