Chlorpyrifos structure

Rates of hydrolysis may be influenced by the presence of dissolved organic carbon, or organic components of soil and sediment. The magnitude of the effect is determined by the structure of the compound and by the kinetics of its association with these components. For example, whereas the neutral hydrolysis of chlorpyrifos was unaffected by sorption to sediments, the rate of alkaline hydrolysis was considerably slower (Macalady and Wolf 1985) humic acid also reduced the rate of alkaline hydrolysis of 1-octyl 2,4-dichlo-rophenoxyacetate (Perdue and Wolfe 1982). Conversely, sediment sorption had no effect on the neutral hydrolysis of 4-chlorostilbene oxide, although the rate below pH 5 where acid hydrolysis dominates was reduced (Metwally and Wolfe 1990). 

The urine samples were analyzed using a modified version of a published method.8 The method involved fortification of the urine samples with an internal standard 3,4,5-trichloro-2-pyridinyl, which is a structural isomer of the 3,5,6-TCP metabolite of chlorpyrifos hydrolysis of labile acid conjugates to 3,5,6-TCP solvent extraction derivitization to the f-butyl-dimethylsilyl ester of 3,5,6-TCP and subsequent negative-ion chemical ionization gas chromatography/mass spectrometry (GC/MS) analysis. Creatinine was determined in urine using a modification of a method of Fabiny and Erting-shausen.9... 

In 1985, Berteau and Mengle (1985) of the California Department of Health Services and Maddy of the Department of Food and Agriculture conducted a preliminary review of pesticides used indoors. They noted several cases (six) from the Pesticide Illness Surveillance system in which illness was reported after structural pest control. Hypothetical exposure estimates for infants, children, and adults following label use for propoxur, DDVP, and chlorpyrifos were sometimes greater than toxic levels. In 1987, Berteau et al. (1989) reiterated the concern about the potential magnitude of indoor exposures, particularly for children. 

Figure 14.1 Structures of chlorpyrifos and some of its metabolites. (Modified from Barron, M.G., S.M. Plakas, and PC. Wilga. 1991. Chlorpyrifos pharmacokinetics and metabolism following intravascular and dietary administration in channel catfish. Toxicol. Appl. Pharmacol. 108 474-482.)...

Turfgrass chemicals are by no means the only toxic hazard faced by average people, nor indeed the most unjust or egregiously unfair one, of course. Consider, for example, the disproportionately high exposure of inner city residents to propoxur, chlorpyrifos, diazinon, and permethrin used to treat the insects and pests that are an everyday part of life in poorly maintained structures, rented by absent and indifferent landlords. The use of such chemicals in lawn management is far less directly utilitarian than in inner city homes, however such urban residents face a health hazard where lawn managers face a mere nuisance, if that. 

Chlorpyrifos is a organophosphate pesticide with the structure listed below. 

First, draw out the hydrogen suppressed structure for chlorpyrifos and assign delta values to each of its atoms as shown below. For 1%, the delta value for each atom is equal to the number of atoms it is bonded to. 

Structure 4.14 T jj oc2h5 C1 / N" 0—p—OC2H5 II s Chlorpyrifos 0,0-Diethyl 0-(3,5,6-trichloro-2-pyridyl)Phosphorothioate... 

Unfortunately, it is not possible to accurately predict rates of volatilization or project air concenpations based on vapor pressures. Even when ambient conditions, substtates and formulations are similar, emission rates for pesticides will depend on other factors such as the concenttation and molecular structure of the active ingredient. Jackson and Lewis (1981) compared emission rates from three kinds of pest conttol sttips in the same room under constant conditions of temperature (21 1 °C) and humidity (50 20 %) and found that room air concentta-tions over a period of 30d were much higher for diazinon than for chlorpyrifos, but similar to those for propoxur [2-(l-methylethoxy)phenylmethylcarbamate]. On Day 2 , room air levels were 0.76 pg/m for diazinon, 0.14 pg/m for chlorpyrifos and 0.79 pg/m for propoxur. After 30 d, the air concenttations were 1.21, 0.16 and 0.70 pg/m, respectively. The vapor pressure of diazinon is nearly 100 times higher than that of chlorpyrifos and nearly 1000 times lower than that of propoxur (4 x 10 kPa at 20 °C). 

Fenske, R.A. and K.P. Elkner (1990). Multi-route exposure assessment and biological monitoring of urban pesticide applicators during structural control treatments with chlorpyrifos, Toxicol. Ind. Health, 6, 349-371. 

Conventional control of termites is heavily reliant upon prophylactic application of liquid insecticides to form a soil barrier around and beneath a structure to termite entry. These barriers, designed to repel or kill termites, degrade over time and must be reapplied every 5-10 years. A barrier termiticide application requires significant quantities of active ingredient, 5-10 kg, carried in 300 to 600 liters of water. Conventional products used as soil termiticides include organophosphates such as chlorpyrifos and isofenphos. 

Figure 1 Structures of the phosphorothioate insecticides chlorpyrifos and methyl parathion and their corresponding oxygen analogs.

The toxic effects of some pesticide mixtures are additive, particularly when their toxic mechanisms are identical. The additive effects of the organophosphates chlorpyrifos and diazanon were demonstrated in one study. T Another study found the s-triazine herbicides atrazine and cyanazine to show additive toxic effects. Not all mixtures of similar pesticides produce additive effects, however. In one study, mixtures of five organophos-phate pesticides (chlorpyrifos, diazinon, dimethoate, acephate, and malathion) were shown to produce greater than additive effects when administered to laboratory animals. Another article discusses nonsimple additive effects of pyrethroid mixtures. Despite the similarities in their chemical structure, pyrethroids act on multiple sites, and mixtures of these produce different toxic effects. 10 ... 

Some pressure treating facilities use a mixture of IPBC and an insecticide such as permethrin or chlorpyrifos to treat structural members for above-ground end-uses that are largely protected from the weather. The advantage of this treatment is that it is colourless and allows the wood to maintain its natural appearance. 

OP insecticide with a structure similar to malathion, which is not a substrate for PON (Li et aL, 2000). As also predicted, PON mice showed a dramatically increased sensitivity to chiorpyrifos-oxon and diazoxon (Shih et ai., 1998 Li et ai, 2000). PONl mice showed an intermediate sensitivity to diazoxon toxicity (Li ef al, 2000). PONl null mice showed only a slight increase in sensitivity to the toxicity of chlorpyrifos and diazinon (Shih et a ., 1998 Li el al., 2000). The most surprising observation was that PONl null mice did not show an increased sensitivity to paraoxon, the substrate after which the enzyme was named, despite having no paraoxonase activity in plasma and liver (Li ei ai. 2000). 

Foimaiion of in vitm blood-brain barrier (BBB) with astrocytes on "abluminar side, endothelial cells on luminal side chlorpyrifos metabolized on luminal side chlorpyrifos and its metabolites cross BBB and inhibit earbo.xylesCerase and cholinesterase in endothelial cells chlorpyrifos impairs BBB structure and integrity. Astrocytes, which are required for BBB integrity, are a potential target for chloipyrifos toxicity in this model. 

Parran, D, K., Magnin, G. Li, W., Jortner, B S., and Ehrich, M. (2005), Chlorpyrifos alters functional integrity and structure of ati in vitro BBB model Co-cultorcs of bovine endothelial cells and neonatal rat a.strocytcs. NeuroToxicology 26, TT-S. ... 

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