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PubMedDate not supplied

Estimation of the LD1 and extrapolation of the LD0.1 for five organothiophosphate pesticides.

The oral LD50's for five organothiophosphate pesticides have been determined in CD-1 strain male and female mice. The values in mg/kg are: parathion, 15.0 and 14.3; methyl parathion, 14.5 and 19.5; guthion, 7.15 and 6.35; imidan, 25.2 and 23.1; sumithion, 1,045 and 1,220 respectively. Toxicity was greater parathion but there was no difference in the males. The relationship between chemical structure and toxicity has been discussed. The addition of a methyl group in the meta position of the nitrophenyl group (sumithion) decreased toxicity 72 times compared to methyl parathion. The predicted LD1 and extrapolated LD0.1's have been determined for the five organothiophosphates and the conditions required for accurate results have been established. It has been shown that the slopes of the curves (males vs. females) obtained with 50, 100 and 660 animals are parallel for all compounds health implications of exposure to low levels of environmental pesticides have been discussed.

Animals↗

PubMed1990

Evaluation of estimations in vitro of tissue/blood distribution coefficients for organothiophosphate insecticides.

Physiologically based pharmacokinetic (PBPK) modeling of foreign chemicals is dependent on the accurate determination of their tissue/blood distribution coefficients, Kp (partition coefficients). The present study was undertaken to evaluate the validity of the in vitro estimation of the Kp values of the organothiophosphate insecticides parathion and methyl parathion by equilibrium dialysis. Data derived from previously published studies that utilized single-pass perfusions of mouse livers in situ with parathion or methyl parathion were analyzed to determine liver/perfusate Kp values from the equation Kp = (t 1/2ss) (Q)/(0.693) (VH), where Kp is the liver/perfusate distribution ratio, t 1/2ss is the half-life for approach to steady state of the chemical, VH is the liver volume, and Q is the perfusate flow rate. Kp values for methyl parathion were calculated to be 16.4 +/- 7.5 and 9.5 +/- 2.7 (mean +/- SD) for perfused livers and equilibrium dialysis, respectively, while estimates of Kp for parathion were 15.6 +/- 6.3 and 19.5 +/- 5.5 for perfused livers and equilibrium dialysis, respectively. These results indicate that equilibrium dialysis can be utilized to give an accurate estimate of tissue partitioning of parathion and methyl parathion from perfusate into perfused mouse livers.

Animals↗

PubMed2006

NMR investigation of the behavior of an organothiophosphate pesticide, chlorpyrifos, sorbed on soil components.

Phosphorus-31 nuclear magnetic resonance (31P NMR) was used to follow the decomposition of chlorpyrifos (an organothiophosphate pesticide) adsorbed on soil, humic acid, partially hydrated kaolin clay, and partially hydrated montmorillonite clay at high concentration (typically 2-10 wt %). Solid-state 31P NMR (using magic-angle spinning and cross polarization or direct polarization) and liquid-solution 31P NMR of DMSO and acetone extracts indicate that chlorpyrifos is initially physisorbed, appearing by solid-state 31P NMR to exhibit significant motion on the molecular level, which results in almost liquidlike solid-state spectra. Over periods ranging from hours to years, the signals due to unreacted chlorpyrifos sorbed on the clays diminish and are replaced by new 31P NMR peaks resulting from hydrolysis, isomerization, mineralization, and oxidation reactions. The 31P NMR signal characteristics indicate that these decomposition products are much more tightly bound to the clay than is chlorpyrifos. Solid-state 13C and 27AI NMR spectra were less useful for following the decomposition of chlorpyrifos than those obtained by 31P NMR. Solid-state 31P NMR results indicate that a chlorpyrifos loading level of 10% by weight, used in some of the samples to facilitate 31P NMR detection of less-than-dominant decomposition products, exceeds the adsorption capacity of the soil, humic acid, and kaolinite tested, but not Ca2+ -exchanged montmorillonite. This pattern is consistent with intercalation into the montmorillonite, but only surface adsorption on kaolinite.

Adsorption↗

PubMed2006

NMR investigation of the behavior of an organothiophosphate pesticide, chlorpyrifos, sorbed on montmorillonite clays.

Phosphorus-31 nuclear magnetic resonance (31P NMR) was used to explore the decomposition of chlorpyrifos (an organothiophosphate pesticide) sorbed at high concentration (typically 2-10 wt %) on partially hydrated montmorillonite clays in four different cation-exchanged forms (Ca2+, Cu2+, Zn2+, and Al3+). Solid-state 31P NMR (using magic-angle spinning and cross polarization or direct polarization) and liquid-solution 31P NMR of DMSO and acetone extracts indicate that chlorpyrifos is initially physisorbed, appearing by solid-state 31P NMR to exhibit significant motion on the molecular level, which results in almost liquidlike solid-state spectra. Over periods ranging from hours to years, the signals due to unreacted chlorpyrifos diminish and are replaced by new 31P NMR peaks resulting from hydrolysis, isomerization, mineralization, and oxidation reactions. The 31P NMR signal characteristics indicate that these decomposition products are much more tightly bound to the clay than is chlorpyrifos. Partially hydrated Cu(II)- and Al-montmorillonites most effectively catalyzed chlorpyrifos decomposition (but with different product distributions); Ca-montmorillonites (and, as previously shown, kaolin) were least effective. Solid-state 13C and 27Al NMR spectra were less useful for following the decomposition of chlorpyrifos than those obtained by 31P NMR. Pesticide loading levels (1-10% w/w) that are very much higher than those typically found in the environment were used to facilitate 31P NMR detection of less-than-dominant decomposition species.

Adsorption↗

PubMed2006

NMR investigation of the behavior of an organothiophosphate pesticide, methyl parathion, sorbed on clays.

The decomposition of methyl parathion (an organothiophosphate pesticide) sorbed on partially hydrated kaolin and montmorillonite clays (in Ca2+, Cu2+, Zn2+, and Al3+ forms) at high concentration (typically 1-10 wt %) has been examined by nuclear magnetic resonance (NMR), using solid-state 31P NMR (based on magic-angle spinning and cross polarization or direct polarization) and liquid-state 31P NMR of DMSO and acetone extracts. The results indicate that methyl parathion is initially physisorbed, appearing by solid-state 31P NMR to exhibit substantial molecular-level motion. The signals due to unreacted methyl parathion diminish and are replaced by new 31P NMR peaks resulting from hydrolysis, isomerization, and oxidation reactions over periods ranging from hours to years. 31P NMR characteristics indicate that these decomposition products are much more tightly bound to the clay than is methyl parathion. Methyl parathion decomposition is most effectively catalyzed by partially hydrated Cu(II)- and Al-montmorillonites (but with different product distributions); Ca-montmorillonite and kaolin were least effective.

Adsorption↗

PubMed2003

Lipopolysaccharide (LPS) induced activation of the immune system in control rats and rats chronically exposed to a low level of the organothiophosphate insecticide, acephate.

Lipopolysaccharide (LPS), a key inflammatory component of gram-negative bacteria, induces a distinctive pattern of cytokine release that regulates inflammation. An alteration in the LPS response may play a fundamental role in the pathogenesis of a number of inflammatory diseases. Therefore, this study was conducted to determine whether chronic exposure to a low level of acephate (Ace), a commonly used organophosphate insecticide, impaired the LPS response in rats. This study showed that LPS injection in control rats caused (1) a time-dependent increase in blood lymphocyte enumeration and differentiation, and (2) a sequential increase the pro-inflammatory (interleukin-1beta (IL1beta), tumor necrosis factor-alpha (TNFalpha), interferon-gamma (INTgamma), and inducible nitric oxide synthase (iNOS)) and anti-inflammatory (interleukin-4 (IL-4), corticotropin-releasing factor (CRF), and blood corticosterone (Cort)) cytokines. The pro-inflammatory cytokines increased after 30 min, while the anti-inflammatory cytokines increased 3 h after LPS injection. An increase in proinflammatory cytokines increased lymphocyte enumeration and differentiation, while the increase in anti-inflammatory cytokines re-established homeostasis. In comparison to the control rats, the Ace-exposed rats exhibited (1) lower levels of IL1beta, TNFalpha and iNOS, (2) higher levels of CRF and Cort, and (3) lower levels of IL-4 in blood and/or brain samples. The abnormal cytokine production may be associated with abnormal phenotypic distribution of B and T cells. Blood IgMhi IgDhi, IgMlo IgDlo and CD8+ CD45RA- CCR7+ cells were elevated, while IgMlo IgDhi, IgMhi IgDlo, IgMin IgDlo, CD8+ CD45RA+ CCR7+ and CD8+ CD45RA- CCR7 cells were depressed in Ace-exposed rats. Thus, chronic low-level Ace exposure may impair the lineage commitment in lymphocytes, possibly by altering cytokine signaling in the brain.

Animals↗

PubMedDate not supplied

[Stereospecific action of organothiophosphate amino acid derivatives on nervous system esterase activity in the cockroach].

The effect of optic isomers of Rp- and Sp-CH3(C2H5O)P(O)SCH2C(O)NHCH5-COOC2H5(EH-13), Rc- and Sc-(C2H5O)2P(O)SCH2C(O)NHCH (i-C3-H7)COOC2H5.(SH.-156), RpRc-, SpSc-, and SpRc-CH3(C2H5O)P(O) SCH2C(O)NHCH(i-C3H7)-COOC2H5(Sh.-142) on the fraction composition of esterases from the nervous tissue of American cockroach was investigated. Esterases were separated by polyacrylamide gel disc-electrophoresis. Sp-(EH-13) and Rc-(Sh.-156) were shown to inhibit carboxy esterase to a greater extent than their antipodes. Stereoisomers of the substance (Sh.-142) were found to influence activity of carboxy esterase molecular forms in a different way. It is postulated that the active surface of molecules of certain carboxy esterase isoenzymes may have stereospecific structure.

Amino Acids↗

PubMed1988

The role of glutathione in the detoxification of the insecticides methyl parathion and azinphos-methyl in the mouse.

The dimethyl-substituted organothiophosphate insecticides methyl parathion and azinphos-methyl are thought to undergo glutathione-mediated detoxification in mammals. In the present study, depletion of hepatic glutathione in the mouse by pretreatment with diethyl maleate potentiated the acute toxicities of methyl parathion and azinphos-methyl, whereas depletion of hepatic glutathione by pretreatment with buthionine sulfoximine did not. Furthermore incubation of 50 microM methyl parathion with mouse hepatic microsomes for 5 min in the presence of 1 mM diethyl maleate led to significantly greater (p less than 0.05) production of methyl paraoxon, compared to incubations in the absence of diethyl maleate. Conversely, 1 mM diethyl maleate had no effect on metabolic activation of azinphos-methyl by mouse hepatic microsomes, while 10 mM inhibited slightly production of azinphos-methyl oxon from azinphos-methyl. These results suggest normal levels of hepatic glutathione are not required for detoxification of methyl parathion or azinphos-methyl in the mouse. Moreover the potentiation of the acute toxicity of methyl parathion following diethyl maleate pretreatment could result, at least in part, from enhanced production of methyl paraoxon. However, diethyl maleate likely acts through another mechanism(s) as well since it did not enhance the metabolic activation of azinphos-methyl in vitro. These data raise serious doubts about the participation of glutathione in the detoxification of methyl parathion and azinphos-methyl in vivo in the mouse.

Animals↗

PubMed1991

Cytogenetic biomonitoring of an Italian population exposed to pesticides: chromosome aberration and sister-chromatid exchange analysis in peripheral blood lymphocytes.

Chromosome aberrations (CA) and sister-chromatid exchanges (SCE) were measured in lymphocytes of (A) 32 healthy individuals working in the flower industry and exposed to pesticides, (B) 32 individuals exposed as above and hospitalized for bladder cancer, and (C) 31 controls. Compounds to which floriculturists were exposed included 18 nitro-organic herbicides and fungicides, 9 nitro-organic fungicides, 12 organophosphate and organothiophosphate insecticides, 4 hydrocarbon derivative herbicides and 5 inorganic fungicides and insecticides. 150 and 70 metaphases per individual were scored for CA and SCE, respectively. A significant increase in the incidence of CA and SCE was observed in both exposed groups. Cancer patients showed the presence of rare rearrangements (dicentrics, rings and quadriradials) that were not observed in controls and were present at a lower frequency in healthy exposed people. Hyperdiploid and polyploid metaphases were also significantly increased in the 2 exposed groups compared to controls. Stratifying for age or smoking habits, although affecting the significance of individual data, did not change the substance of the results.

Adult↗

PubMed1991

The effect of glutathione monoethyl ester on the potentiation of the acute toxicity of methyl parathion, methyl paraoxon or fenitrothion by diethyl maleate in the mouse.

Depletion of hepatic glutathione in the mouse by pretreatment with diethyl maleate (DEM) is known to potentiate the acute toxicities of many dimethyl-substituted organothiophosphate insecticides. However, certain studies have raised doubts regarding the participation of glutathione in the detoxification of methyl parathion in the mouse, and hence the putative mechanism of action of DEM-induced potentiation of this insecticide. The present study evaluates the hypothesis that DEM potentiates the acute toxicities of methyl parathion, methyl paraoxon, and fenitrothion by a mechanism other than glutathione depletion. One hour following pretreatment of mice with DEM (0.75 ml/kg i.p.), glutathione was markedly depleted and the acute toxicities of methyl parathion, methyl paraoxon and fenitrothion were potentiated. Administration of glutathione monoethyl ester (20 mmol/kg p.o.) to DEM-pretreated mice attenuated DEM-depletion of hepatic glutathione, or maintained glutathione at or above control levels. However, glutathione monoethyl ester did not alter the DEM-induced potentiation of the lethality of these insecticides. Furthermore, administration of glutathione monoethyl ester to naive mice increased hepatic glutathione levels, but did not affect the percentage of animals succumbing to a challenge dose of methyl parathion, methyl paraoxon, or fenitrothion. These data indicate that DEM potentiates the toxicity of methyl parathion, methyl paraoxon or fenitrothion by a mechanism unrelated to hepatic glutathione content.

Animals↗

PubMed1992

Biotransformation of the insecticide parathion by mouse brain.

The acute toxicity of organothiophosphate insecticides like parathion results from their metabolic activation by cytochromes P450. The present study is directed towards the characterization of cytochrome-P450-dependent metabolism of parathion by various mouse brain regions. Intraperitoneal administration of [35S]parathion to mice led to covalently bound [35S]sulfur in various tissues, indicating their capacity to oxidatively desulfurate this insecticide. Liver contained the greatest amount of covalently bound sulfur, and brain the least. Among individual brain regions the olfactory bulb and hypothalamus possessed the highest levels of sulfur binding when expressed on a per milligram tissue basis. However, when expressed on a per brain region basis, sulfur binding was greatest within the cortex as a result of the large mass of this region, compared to the hypothalamus and olfactory bulb. Incubation of the 78,000 x g fraction of mouse brain with parathion resulted in formation of p-nitrophenol, although paraoxon could not be detected. However, given the current understanding of parathion metabolism by cytochromes P450, and given that paraoxon can rapidly disappear through phosphorylation of serine hydroxyl groups, it is reasonable to assume that at least some paraoxon was formed. Production of p-nitrophenol required NADPH and was inhibited by carbon monoxide. In vitro incubations of parathion with the 78,000 x g fraction of mouse brain indicated that the hypothalamus and olfactory bulb had the greatest capacity to produce p-nitrophenol. These results demonstrate that various mouse brain regions possess different capacities to metabolize parathion.

Animals↗

PubMed2003

Intestinal permeability of chlorpyrifos using the single-pass intestinal perfusion method in the rat.

The intestinal transport of chlorpyrifos (CPF), an organothiophosphate pesticide, was investigated using the single-pass intestinal perfusion (SPIP) technique in male, Sprague-Dawley rats. SPIP was performed in each isolated region of the small intestine (i.e. duodenum, jejunum and ileum) with three concentrations of CPF (0.1, 2.0 and 10 microM) at a flow rate of 0.25 ml/min. Preliminary binding and stability studies were conducted to ensure that the loss of CPF in the SPIP study can be attributed to intestinal absorption. The effective permeability (P(eff)) of CPF was determined for each segment and concentration. CPF exhibits a high intestinal permeability over the length of the small intestine indicative of compounds that are well absorbed. Decreases in permeability values at the highest CPF concentration studied in the duodenum and ileum suggest a saturable transport process. Based on these results, passive, transcellular diffusion dominates the intestinal transport mechanism of CPF, with a saturable transport process evident in the duodenum and ileum. The P(eff) of CPF is in the range of drugs with high intestinal permeability and high fraction of dose absorbed indicating that CPF readily crosses the intestine. The dependence of CPF's P(eff) on concentration in the duodenum and ileum suggests that CPF is transported by a combination of mechanisms across the intestine. Using established relationships, the human fraction dose absorbed for CPF was estimated to be >99%. The permeability values obtained from this study may be useful in models of exposure assessment.

Algorithms↗

PubMed1968

Propanil hydrolysis: inhibition in rice plants by insecticides.

Hydrolysis of the herbicide propanil (3', 4'-dichloropropionanilide) by rice plants is inhibited by insecticides. The inhibitory activity of an organophosphate such as paraoxon in vivo and in vitro is significantly stronger than that of an organothiophosphate such as parathion. The injury to rice plants by insecticides sprayed on them with propanil seems to be caused by the inhibition of the propanil detoxifying enzyme.

Anilides↗

PubMed1993

Inhibitory effect of fenthion and diazinon on the contraction of rat aorta, and its contribution to lethality.

Fenthion and diazinon, P = S type organothiophosphates which are precursors of cholinesterase inhibitors, cause remarkable atropine-insensitive hypotension in rats when administered intravenously in lethal doses. We investigated their effects on isolated rat aorta and atria to reveal the site of action. Fenthion and diazinon inhibited both types of contractions induced by high K+ solution and norepinephrine in aortic preparations from which the endothelium was removed. IC50 values (under [Ca2+] = 1.5 mM) were 2 x 10(-5) M and 7 x 10(-5) M, respectively. However, the atrial preparations were relatively resistant, since fenthion showed no effect up to 10(-3) M and diazinon at 10(-4) M exhibited a slight inhibition which was antagonized by atropine. The hypotensive effect of fenthion or diazinon was therefore attributable to the direct inhibiting action on the arterial muscle tone, which may be independent of the activation of muscarinic receptors. The results suggested that fenthion and diazinon affect movement and/or utilization of calcium in the aortic muscle cells, since an increase in the calcium concentration in the bathing solution antagonized their inhibitory effect.

Acetylcholine↗

PubMed1987

Fatal parathion poisoning in Sierra Leone.

In May and June 1986, 49 persons in Sierra Leone were acutely poisoned by the organothiophosphate insecticide, parathion. Fourteen people died. Illness occurred in three episodes at two different locations that were 44 km apart. A study of 21 cases and 22 household controls was undertaken to explore which factors were associated with the development of the symptoms. Cases were more likely than controls to have eaten bread in the 4 hours before becoming ill (odds ratio, 12.7; 95% confidence interval, 2.4-83.8). Scrapings of residue from the floor of the truck that had brought the wheat flour from the mill to the general store where the baker purchased it were positive for parathion, suggesting that the flour had been contaminated during transport. Pesticide poisoning is a common problem in the developing world, and public health measures such as restricting the use of parathion may help to prevent fatal poisonings.

Adolescent↗

PubMedDate not supplied

Genotoxicity evaluation of buprofezin, petroleum oil and profenofos in somatic and germ cells of male mice.

The two pest control agents, buprofezin and petroleum oil (Super Royal), were tested to evaluate their potential mutagenicity, in comparison with the organophosphorus insecticide profenofos. Chromosomal aberration analysis was used in both somatic and germ cells of male mice. Single oral treatment at three different dose levels (1/16, 1/8 and 1/4 LD50) for each insecticide induced an increase in the percentage of chromosomal aberrations in bone-marrow cells 24 h post-treatment, indicating a dose-dependent relationship. The percentage of chromosomal aberrations reached 23 +/- 0.73, 10.5 +/- 0.64 and 15 +/- 1.4 after treatment with the highest tested dose of profenofos, buprofezin and Super Royal, respectively. Such percentages did not exceed the corresponding value of the positive control, mitomycin C (29.2 +/- 0.69). The percentage of chromosomal aberrations induced by the different doses of profenofos was still highly significant even after excluding gaps. The same trend of results was noticed only at the highest tested dose of buprofezin and Super Royal. With respect to germ cells, profenofos is also a potent inducer of chromosomal aberrations in 1ry spermatocytes, giving percentages of 14 +/- 1.3 and 19 +/- 1.6 at the two higher doses of 4.25 and 8.5 mg kg(-1) body wt., respectively. Buprofezin and Super Royal had no significant effect on mouse spermatocytes at the tested concentrations. The various types of induced aberrations were examined and recorded in both somatic and germ cells. In conclusion, the present investigation indicates that the two pest control agents buprofezin and Super Royal are relatively much safer compounds than the conventional organophosphorus insecticides.

Animals↗

PubMed2000

Characterization of esterases associated with profenofos resistance in the tobacco budworm, Heliothis virescens (F.).

The utility of microplate and electrophoretic assays for detection of biochemical and physiological mechanisms underlying resistance to profenofos in the tobacco budworm, Heliothis virescens (F.), was assessed. Esterase (EST) activities were significantly higher in profenofos-resistant than -susceptible larvae, and activities were highly correlated (r(2) = 0.87) with resistance to profenofos. Both qualitative and quantitative variation was observed in electrophoretic gels stained with alpha- and beta-naphthyl acetates. Staining of ESTs was more intense with resistant larvae than those from a susceptible strain. In addition, a band (designated A') was expressed in larvae from profenofos-resistant strains, but not in larvae from an insecticide-susceptible strain. The frequency of expression of A' increased following selection with profenofos and was detected in 100% of the individuals from a profenofos-selected strain. The appearance of this band coincided with the decreased expression of a second band (designated A). A similar pattern (overexpression of A' and underexpression of A) also was observed in larvae from field-collected strains. Finally, reduction in the activity or the sensitivity of acetylcholinesterase to inhibition by chlorpyrifos oxon was observed in laboratory-selected and field-collected larvae that expressed resistance to profenofos. These results suggest that microplate and electrophoretic assays can be utilized as complementary tools for detecting and monitoring profenofos resistance in H. virescens.

Acetylcholinesterase↗

PubMed1987

A behavioral evaluation of pest control workers with short-term, low-level exposure to the organophosphate diazinon.

Neurobehavioral effects of short-term, low-level exposure to diazinon were investigated among 99 pest control workers tested before and after their work shift with a computer-assisted neurobehavioral test battery. Each subject completed a brief neurological screening examination, a symptom questionnaire, and tests of concentration, eye-hand coordination, pattern recognition, visual memory, and finger tapping. The diazinon metabolite diethylthiophosphate (DETP) was measured in pre- and post-shift urine samples collected from 46 diazinon applicators applying granulated diazinon onto residential properties with lawn spreaders, and 56 non-applicators. Post-shift median DETP for applicators and non-applicators was 24 and 3 ppb, respectively. Full shift, whole body exposure to diazinon was quantitated for 19 subjects using personal air monitoring and passive badges. Median diazinon exposure for applicators and non-applicators was 2.1 and 0.03 mg, respectively. Mean duration of pesticide application was 39 days (SD = 12 days) before testing. No adverse DETP-related changes in pre- or post-shift neurobehavioral function were found with multiple linear regression models after adjusting for age, sex, education, and ethanol intake, although Symbol-Digit pairing speed was slower among the applicators as a group. The prevalence of 18 symptoms possibly related to diazinon exposure was not elevated among applicators. The study failed to demonstrate diverse behavioral effects of short-term, low-level diazinon exposure in a pest control program which emphasized personal protective equipment and direct supervision.

Adult↗