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Biotransformation of the organophosphorus insecticides parathion and methyl parathion in male and female rat livers perfused in situ.

Although numerous previous reports have characterized the mammalian biotransformation of the organophosphorus insecticides parathion and methyl parathion, questions still remain regarding the toxicological significance of certain metabolic pathways in vivo. The present study utilized rat liver perfusions in order to better characterize the hepatic biotransformation of parathion and methyl parathion in intact liver. Single-pass liver perfusions with parathion and methyl parathion over a range of perfusate concentrations of 10-80 microM resulted in the appearance of paraoxon and methyl paraoxon, respectively, in effluent. Furthermore, rat blood did not have the capacity to prevent transport of paraoxon and methyl paraoxon to extrahepatic tissues, suggesting that oxon produced hepatically can distribute to extrahepatic tissues. In addition, striking sex differences were noted in the metabolite profile of parathion and methyl parathion in perfused livers. However, these differences could not account for the observation that females are more susceptible to parathion, but less susceptible to methyl parathion, compared to males. And finally, S-methyl glutathione or S-p-nitrophenyl glutathione could not be detected in effluent or bile of livers from either sex perfused with methyl parathion, suggesting that glutathione-dependent detoxification of this insecticide does not occur to any significant degree in intact rat liver.

Animals↗
PubMed1992

Prolonged toxicity with intermediate syndrome after combined parathion and methyl parathion poisoning.

A prolonged type of organophosphate toxicity, previously characterized as the Intermediate Syndrome, has been recognized in 6 out of 7 prospectively studied patients poisoned by insecticide containing parathion and methyl parathion in equal proportions. The clinical characteristics included respiratory paresis, weakness in the territories of several motor cranial nerves, neck flexors and proximal limb muscles, and depressed tendon reflexes, all lasting for several days or weeks. Electromyography in the early stages disclosed diverse types of impaired neuromuscular transmission. EMG normalization preceded clinical recovery. Severe plasma butyrylcholinesterase and erythrocyte acetylcholinesterase inhibition persisted along with the occurrence of Intermediate Syndrome-related symptoms. We conclude that combined parathion and methyl parathion poisoning is more likely to induce Intermediate Syndrome than parathion poisoning alone. The mechanisms underlying this difference remain obscure. The Intermediate Syndrome shows clinical and electromyographic hallmarks of combined postsynaptic impairment of neuromuscular transmission.

Adult↗
PubMed1979

Accelerated parathion degradation in soil inoculated with acclimated bacteria under field conditions.

The feasibility of decontaminating soil at parathion spillage or disposal sites by inoculation with a highly acclimated culture of parathion-degrading bacteria was demonstrated under in situ field conditions. The acclimated culture (AC), capable of utilizing parathion as a sole carbon and energy source, was inoculated into Yolo silt loam soil in which parathion was applied at rates up to 5000 kg/ha. The AC was shown to be capable of completely degrading parathion in soil containing up to 1250 kg/ha of parathion within 35 days. A slower rate of parathion degradation by the AC was observed when the pesticide was applied as the commercial 46.5% emulsifiable concentrate than when applied as the 98% technical grade. The ability of the AC to degrade parathion deteriorated at application rates greater than 1250 kg/ha. The AC may have been adversely affected by the accumulation of the parathion hydrolytic products, p-nitrophenol and ionic diethyl thiophosphate, which were tentatively identified in soil samples.

Biodegradation, Environmental↗
PubMed1992

Methyl parathion induced regional alterations in the regulatory proteins during critical stage of central nervous system development in albino rat pups.

Sublethal doses of methyl parathion (O,O-dimethyl-O-nitrophenyl- thiophosphate) injected intraperitoneally to 15 and 21 day old rat pups induced regional alterations in the central nervous system (CNS) in the levels of total RNA, total proteins, modulatory protein Calmodulin (CaM), in the activity levels of membrane bound enzyme Ca(2+)-ATPase and phospholipids. Levels of RNA and total proteins increased considerably in 15 days old methyl parathion treated (MPT) rat pups. Contrary to this the RNA and total protein content exhibited remarkable decrease in 21 day old methyl parathion treated animals. Calmodulin level showed an increase in cerebral cortex and brain stem and decrease in cerebellum and spinal cord in 15 day old methyl parathion treated rat pups. Whereas the level of Calmodulin decreased in cerebral cortex and cerebellum and increased in brain stem and spinal cord in 21 day old methyl parathion treated rat pups. Activity levels of calcium dependent ATPase showed significant inhibition in all the regions of Central Nervous System (CNS) of 15 and 21 day old methyl parathion treated rat pups. Phospholipids showed a general increase in all the regions of Central Nervous System on methyl parathion exposure. In the light of these observations, it has been suggested that the molecular regulatory mechanisms involving Ca2+/CaM are rendered inefficient due to toxic impact of methyl parathion.

Animals↗
PubMed1977

Airborne and surface residues of parathion and its conversion products in a treated plum orchard environment.

Airborne pesticide residues were collected both within and downwind from a parathion-treated plum orchard by high volume sampling through XAD-4 macroreticular resin. Levels of paraoxon in excess of 100 ng/m3 were found in orchard air, along with parathion, during the early days of two 21-day sampling studies. Paraoxon:parathion ratios in the orchard air were relatively constant, averaging ca. 0.5 for days 1 to 21 following treatment. Likely sources of airborne paraoxon include vaporization and dislodgement from soil and leaf surfaces, and chemical conversion of parathion in the air. Support for the latter came from observation of an increased paraoxon:parathion ration in air samples collected downwind from the orchard. Atmospheric conversion of parathion to paraoxon, accelerated by sunlight, was indicated by both field and laboratory studies. Overall dissipation of parathion from the orchard air, soil, and leaf tissue proceeded to a considerable extent through breakdown to paraozon under the dry climatic conditions of these studies. Eventual conversion to the relatively stable breakdown product, p-nitrophenol, was indicated from analysis of air in the orchard vicinity.

Air↗
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↗
PubMed1978

Fate of parathion in artificially fortified grape juice processed into wine.

"Semellon" grape juice fortified with a high level of 25 ppm parathion was fermented using Saccharomyces cerevisiae var. ellipsoideus. After 12 days inte parathion levels in the wine and lees were 10.3 and 156 ppm, respectively; the paraoxon, aminoparathion, and p-nitrophenol levels in the wine were 0.16, 0.20, and 4.5 ppm, respectively, and in the lees were 0.04, 3.1 and 10 ppm, respectively. Thus, hydrolysis of parathion to p-nitrophenol and parathion sorption to sedimented particulate matter were important pathways for parathion residue reduction in the wine. The 56-day-old finished wine just prior to bottling contained 8.8 ppm parathion, 0.04 ppm paraoxon, 0.21 ppm aminoparathion, and 3.0 ppm p-nitrophenol. Two months storage at 24 degrees, 12 degrees, 4 degrees, and -20 degrees C had no effect on paraoxon and aminoparathion residue levels in the wine; parathion residues in wine decreased at all storage temperatures.

Drug Stability↗
PubMed1976

Deldrin and parathion interaction in the prostate and liver of the mouse.

The oral administration of dieldrin (1.25 mg/kg daily x 5 or 10) and/or parathion (5.2, 2.6, or 1.3 mg/kg daily x 5 or u0) caused significant alterations in the metabolism of [1,2-3H]testosterone by the anterior prostate gland and by the hepatic microsomal enzyme system in the mouse. A 5-day parathion treatment followed by another 5-day treatment with dieldrin led to significant increases in the levels of [3H]androstanediol a [3H]androstenedione formed by the prostate gland in vitro. Dieldrin alone, dieldrin plus parathion, or dieldrin administration followed by parathion treatment caused significant reductions in the levels of [3H]androstenedione formed by hepatic microsomal enzymes. Concomitantly, significant increases were observed in hepatic 7alpha-and 6beta-testosterone hydroxylase activities in animals treated with parathion followed by dieldrin administration. The present findings revealed that the administration of parathion or dieldrin leads to changes in the metabolism of male sex hormones in mouse liver and sex accessory organs. In addition, the simultaneous administration of parathion and dieldrin leads to an interaction that can alter the biologic effects of either compound.

Androgens↗
PubMed1977

Parathion utilization by bacterial symbionts in a chemostat.

A continuous-culture device was used to select and enrich for microorganisms, from sewage and agricultural runoff, that were capable of using the organophosphorus insecticide parathion as a sole growth substrate. Parathion was dissimilated by the highly acclimated symbiotic activities of Pseudomonas stutzeri, which non-oxidatively and cometabolically hydrolyzed the parathion to ionic diethyl thiophosphate and p-nitrophenol, and P. aeruginosa, which utilized the p-nitrophenol as a sole carbon and energy source. Ionic diethyl thiophosphate was found to be inert to any transformations. Methyl parathion was dissimilated in an analogous way. The device functioned as a chemostat with parathion as the growth-limiting nutrient, and extraordinarily high dissimilation rates were attained for parathion (8 g/liter per day) and for p-nitrophenol (7 g/liter per day). This is the first report of parathion utilization by a defined microbial culture and by symbiotic microbial attack and of dissimilation of an organophosphorus pesticide in a chemostat.

Hydrolysis↗
PubMed1975

Degradation of parathion applied to peach leaves.

Parathion was applied to peach trees in three different formulations 70 days before harvest. Leaf samples were taken periodically through the 70-day period and gas-liquid chromatographic analyses were conducted for dislodgable and penetrated residues. Analyses were also conducted for paraoxon and the s-ethyl isomer of parathion. Punched samples were compared to whole-leaf samples; generally residue levels for both types corresponded closely. A new experimental formulation, encapsulated parathion, produced highest levels of total parathion throughout the 70-day study, but even this formulation resulted in low total residue levels around 1 ppm at time of harvest. Degradation of the s-ethyl isomer of parathion was generally very rapid in all formulations studied. Dislodgable residues of paraoxon may be significant in some formulations and should be included in parathion degradation studies. Much of the parathion found on peach leaves throughout the growing season was dislodgable residue, but this depended considerably on the formulation used.

Biodegradation, Environmental↗
PubMed1979

Sorption-desorption characteristics of methyl parathion by clays.

Methyl parathion (O,O-dimethyl O-(4-nitrophenyl) phosphorothioate) adsorption was studied on montmorillonite, kaolinite, halloysite, natural zeolite, ion exchange resins and calcium carbonate. Methyl parathion was highly adsorbed by montmorillonite, followed by zeolite, and very little adsorption was obtained on kaolinite and halloysite. Calcium carbonate did not exhibit any adsorption. The values of the partial molar free energy "delta G" were calculated for all systems. For the montmorillonite-methyl parathion system, the calculated partial molar heat of adsorption "delta H", and the conformity of the data to Freundlich equation indicated a possible physical mechanism of adsorption. Increasing acetone concentration decreases methyl parathion adsorption and dehydration increased adsorption in the nonaqueous system. Moreover, the increased adsorption on the swollen clay indicated that methyl parathion was adsorbed on the interlamellar surfaces of the clay. This was also in agreement with the results of the desorption studies, since the insecticide was not desorbed using the same aqueous acetone solution. This indicated that methyl parathion was adsorbed as a water-insoluble organic compound.

Adsorption↗
PubMed1975

Changes in cross-resistance spectrum resulting from methyl parathion selection of Culex tarsalis Coq.

Larvae of a field strain of Culex tarsalis Coq. manifesting a broad spectrum of resistance to organophosphorus (OP) insecticides were selected further by methyl parathion pressure in the laboratory. There was a 6.9 times further increase in resistance to methyl parathion in larvae, i.e., from 13.4 times level of resistance in the parental strain to 93.5 times level in the F11 generation. With the exception of fenthion and malathion, cross resistance in larvae the parental strain. The F11 larval population exhibited high levels of cross-resistance to chlorpyrifos (29.6 times), fenitrothion (49.4 times), parathion (55.6 times), fenthion (76.8 times), and chlorpyrifos-methyl (253.8 times). The high levels and broad spectrum of resistance to diverse OP compounds suggest the involvement of more than one mechanism in resistance. Larval selection also affected the spectrum of OP resistance in adults. The F11 adult population exhibited high levels of resistance to dichlorvos (48 times) and chlorpyrifos-methyl (40.1 times) insecticides propoxur, Mobam, Landrin or carbaryl, or to the chrysanthemate insecticide cismethrin. Resistance to the OP insecticides methyl parathion, parathion, fentirothion, fenthion and chlorpyrifos-methyl was found to be fairly stable over nine generations in the absence of methyl parathion selection pressure.

Animals↗