Organophosphorus pesticides chlorpyrifos

Barr, D.B., and J. Angerer. In press. Potential uses of biomonitoring data A case study using the organophosphorus pesticides chlorpyrifos and malathion. Environ Health Perspect. [online]. Available http //ehp.niehs.nih.gov/docs/2006/9062/abstract.html [accessed Aug. 21,2006],... 

Foxenberg RJ, Ellison CA, Knaak JB, Ma C, Olson JR (2011) Cytochrome P450-specific human PBPK/PD models for the organophosphorus pesticides chlorpyrifos and parathion. Toxicology 285 57-66... 

Odenkirchen, E.W. 1987. Hazards of Chlorpyrifos, an Organophosphorus Pesticide, to Natural Resources A Review. M.A. Thesis. The American University, Washington, D.C. 63 pp. 

The first six organophosphorus and chlorinated organophosphorus pesticides dominate wheat-based products. Exhibit 7 shows that virtually all wheat-based products are, at a minimum, contaminated with malathion and chlorpyrifos-methyl. These data also suggest that although corn-based products can contain malathion and chlorpyrifos-methyl, they are much less likely to be contaminated by the first six organophosphorus and chlorinated organophosphorus pesticides. 

Organophosphorus pesticides Acephate , Azinphos-methyl , Chlorpyrifos , Chlorpyriphos-methyl , Diazinon , Dichlorvos (DDVP), Dicrotophos , Dimethoate , Disulfoton , Ethoprop , Eenamiphos , Eenitrothion , Fenthion , Fosthiazate , Malathion , Methamidophos , Methidathion , Methyl-parathion , Mevinphos , Naled , Oxydemeton-methyl , Para-thion , Phorate , Phosalone , Phosmet , Pirimiphos-methyl , Profenofos , Terbufos , Tetrachlorvinphos , Trichlorfon . 

Blanche , P.-F., and A. St. George. 1982. Kinetics of chemical degradation of organophosphorus pesticides hydrolysis of chlorpyrifos and chlorpyrifos-methyl in the presence of copper(II), Pesticide Sci., 13 85-91. 

An established and well understood interaction. The organophosphorus pesticides are potent anticholinesterases used in agriculture and horhcul-ture to control insects on crops, and in veterinary practice to control various ectoparasites. They are applied as sprays and dips. Anyone who is exposed to these toxic pesticides may therefore show changes in their responses to neuromuscular blockers. Widely used organophosphorus pesticides include azamethiphos, bromophos, chlorpyrifos, clofenvinfos. 

Pesticide solution A commercial pesticide, containing 40% chlorpyrifos (Noposion, China) was used. Chlorpyrifos is an organophosphorus pesticide, normally used in the paddy, wheat, cotton, fruit trees, and vegetables. Distilled water was prepared in order to provide the solutions with different concentrations. A total of 24 concentration levels, from 1 mg/kg to 400 mg/kg of active ingredient were diluted based on the amount of chlorpyrifos. After preparation, the solutions were kept in conical flasks and preserved in a cool place in order to prevent chemical degradation and contamination. 

Both of the above organophosphorus pesticides should have similar gas-phase tropospheric lifetimes based on stroctural activity relationship model predictions (2/). OH rate measurements for the two OPs when conducted at 5° C increments between 60 and 85° C, however, showed a significant difference in reactivity. The rate of OH oxidation for diazinon was found to be ca. three to four times more rapid than for chlorpyrifos widi observed tropospheric lifetimes of ca. 1 and 4 hours, respectively. Tlie difference in observed reactivity was not due to wall sorption since both conqxtunds behaved similarly in the gas-phase. 

Quistad, G.B., Nomura, D.K., Sparks, S.K, et al., 2002. Cannabinoid CBl receptor as a target for chlorpyrifos oxon and other organophosphorus pesticides. Toxicol. Lett. 135, 89-93. 

Malathion is a widely used member of a class of pesticides known as organophospate derivatives. It is biodegradable and less toxic (LDg for female rats is 1000 mg/kg) than DDT. Several other organophosphorus compounds are modifications of this basic structure. They include dimethoate (LD = 387 mg/kg), chlorpyrifos (LD q = 95-270 mg/kg), and methyl parathion (LD o = 18 -50 mg/kg). These organophosphates often are used in the treatment of many pests that are found on vegetables, or, in the case of methyl parathion, on cotton plants. 

Organophosphorus hydrolase (OPH, EC 3.1.8.1) is a homodimer with a binuclear metal center. OPH has broad substrate specificity and can hydrolyze organophosphate pesticides such as methyl paradiion, ediyl parathion, paraoxon, chlorpyrifos, coumaphos, cyanophos and diazinoa Table I 9,12-14). The enzymatic hydrolysis rates are 40 - 2450 times faster than chemical hydrolysis at pH 7.0 and the enzyme is reported to be stable at ten ratures of up to 4S-S0°C (3). However, hydrolysis rates varied from very fast for phosphotriesters and phosphothiolester pesticides (P-0 bond) such as paraoxon (ken > 3800s ) and coumaphos (kcat = 800s ) to limited hydrolysis for Diazinon (kcat == 176 s ) and fensulfothion (l a, = 67 s ) (14). 

---