Mammals chlorpyrifos

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... 

Chlorpyrifos lethality to selected birds and mammals via single oral dose route of administration... 

Fish rapidly absorb, metabolize, and excrete chlorpyrifos from the diet (Barron etal. 1991). The mechanism of action of chlorpyrifos occurs via phosphorylation of the active site of acetylcholinesterase after initial formation of chlorpyrifos oxon by oxidative desulfuration. In studies with channel catfish (Ictalurus punctatus), the oral bioavailability of chlorpyrifos was 41%, substantially higher than in mammals. Catfish muscle contained less than 5% of the oral dose with an... 

LD50 values, based on a single oral dose, ranged from 5 to 157 mg chlorpyrifos/kg body weight (BW) in birds, and from 151 to 1000 in mammals. However, 7 of 14 avian species had reported LD50 values of <25.0 mg/kg BW (Table 14.5). As little as 2 mg/kg BW to nestling red-winged... 

Table 14.5 Chlorpyrifos Lethality to Selected Birds and Mammals via Single Oral Dose Route of Administration (Values are in mg chlorpyrifos/kg body weight lethal to 50% within 14 days.)...

Clements, R.O. and J.S. Bale. 1988. The short-term effects on birds and mammals of the use of chlorpyrifos to control leatherjackets in grassland. Ann. Appl. Biol. 112 41-47. 

Extraordinary selectivity has been accomplished with the parathion-type of insecticide by incorporating Q or CH3 groups in the meta position of the aryl ring. These groups interact sterically with acetylcholinesterase (AChE), increasing the affinity for the insect enzyme and decreasing it with the mammalian enzyme. Selectivity also is enhanced by differences in the rates of microsomal oxidation of P=S to P=0 and in hydrolytic detoxication between insects and mammals. The compounds, fenitrothion, fenthion, ronnel, bromophos, iodofenfos, chlorpyrifos—methyl, and pirimiphos —methyl, and dicapthon are used widely in public health, household, and agricultural pest control. 

The insecticides could have various effects on the nervous system but are unlikely to cause harm unless drunk in significant quantities. Chlorpyrifos is an organophosphate insecticide, and so could inhibit the enzyme acetylchoHnesterase in the blood and nervous tissue. It can have a cumulative effect, and so after repeated use, say on a daily basis, the level of inhibition may be sufficient to cause unpleasant or even life-threatening effects (as described on pp. 98-103). These include difficulty in breathing, muscular weakness, and convulsions. Organophosphates vary greatly in their potency, however, and the more toxic are now less readily available. Those for home use are the least poisonous to humans and other mammals. 

Chlorpyrifos and parathioris observed in vitro and in vivo metabolism in mammals is dominated by oxidative attack at the P=S double bond [54]. It is assumed that the phosphooxathiiran species sketched in Figures 1 and 2 are created first, which are subsequently hydrolyzed to the observed metabolites These are the respective oxons, diethylphosphate, diethylphosphothioate, and finally p-nitrophenol and... 

Fish rapidly absorb, metabolize, and excrete chlorpyrifos from the diet. The mechanism of action of chlorpyrifos occurs via phosphorylation of the active site of acetylcholinesterase after initial formation of chlorpyrifos oxon by oxidative desulfuration. In studies with chaimel catfish (Ictalurus punctatus), the oral hioavailability of chlorpyrifos was 41%, substantially higher than in mammals. Catfish muscle contained less than 5% of the oral dose with an elimination half-life (Tbl/2) of 3.3 days. Chlorpyrifos residues in whole catfish were more than 95% chlorpyrifos, while bile and urine primarily contained metabolites. The dephosphorylated metabolite trichloropy-ridinol (TCP) was the major metabolite in the blood while the glucuronide conjugate of TCP was the major metabolite in mine and bile. The toxic metabolite, chlorpyrifos oxon, was not detected in blood, tissues, or excreta. Extensive metabolism resulted in a low potential for chlorpyrifos to accumulate in catfish from dietary exposure. In both fish and mammals, TCP is a major biotransformation product. Chaimel catfish rapidly distribute waterborne chlorpyrifos into the blood and more slowly to peripheral tissues, with concentrations highest in fat and lowest in muscle. As was true with dietary chlorpyrifos, TCP was the major metabolite in blood and the glucuronide conjugate of TCP was the major metabolite in urine and bile. Pharmacokinetics and metabolism of waterborne chlorpyrifos in channel catfish were similar to the disposition of chlorpyrifos in other vertebrates. 

Lethal and sublethal effects of chlorpyrifos under controlled conditions are summarized for selected species of aquatic invertebrates and vertebrates, and for representative species of birds, and mammals. 

Chlorpyrifos is acutely toxic to some species of aquatic invertebrates and teleosts at nominal water concentrations ranging between 0.04 and l.lp,g/L. Acute single-dose oral LD50 values of chlorpyrifos to susceptible avian species ranged from 5.0 to 13.0mg/kg BW. Mammals were comparatively tolerant to... 

Hexaflumuron has very low toxicity to mammals so its manufacturing facility would offer little interest to terrorists seeking explosive or hazardous targets. It is a replacement for the neurotoxic pesticide chlorpyrifos a broad-spectrum chlorinated organophosphate... 

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