Mixed Parathion

Acetaminophen, which depletes hepatic glutathione, does not potentiate the toxicity of methyl parathion in mice. A possible mechanism of action may be competition between acetaminophen and methyl parathion for mixed function oxidases and subsequent prevention of activation of methyl parathion to methyl paraoxon (Costa and Murphy 1984). Diethyl maleate, an agent that depletes cytosolic glutathione and is not an enzyme inducer, potentiates toxicity of methyl parathion in mice (Mirer et al. 1977). 

A recent method, still in development, for determining total 4-nitrophenol in the urine of persons exposed to methyl parathion is based on solid phase microextraction (SPME) and GC/MS previously, the method has been used in the analysis of food and environmental samples (Guidotti et al. 1999). The method uses a solid phase microextraction fiber, is inserted into the urine sample that has been hydrolyzed with HCl at 50° C prior to mixing with distilled water and NaCl and then stirred (1,000 rpm). The fiber is left in the liquid for 30 minutes until a partitioning equilibrium is achieved, and then placed into the GC injector port to desorb. The method shows promise for use in determining exposures at low doses, as it is very sensitive. There is a need for additional development of this method, as the measurement of acetylcholinesterase, the enzyme inhibited by exposure to organophosphates such as methyl parathion, is not an effective indicator of low-dose exposures. 

FIGURE 4.1 Degradation of parathion by a mixed culture of two pseudomonads. 

The substrate was Valencia orange leaves, with 2500 leaves per sample selected in a carefully prescribed manner (4). The trees involved were field sprayed in a conventional manner with 4 pounds of a 25% wettable powder of parathion, then sampled after 7 days and again after 11 days. Each sample was mixed thoroughly and subsampled into 125-leaf units in 2-quart Mason jars. To all units were added 250 ml. of benzene each, and they were sealed, stripped for various lengths of time, then restripped with fresh benzene, again for various lengths of time. The strip solutions were analyzed in the usual manner. 

In the adsorption with Tenax alone satisfactory results were obtained, while in the presence of mineral oil a considerable proportion of the organophos-phorus pesticides (particularly Malathion and Parathion-methyl) was not adsorbed and was recovered in the filtered water. This drawback can be overcome by adding a layer of Celite 545 which, in order to prevent blocking of the column, is mixed with silanised glass wool plugs. A number of analyses of surface and estuarine sea waters were carried out by this modified Tenax column and simultaneously by the liquid-liquid extraction technique. To some of the samples taken, standard mixtures of pesticides were also added, each at the level of 1 xg/l (i.e., in concentration from 13 to 500 times higher than that usually found in the waters analysed). One recovery trial also specifically concerned polychlorobiphenyls. The results obtained in these tests show that the two extraction methods, when applied to surface waters that were not filtered before extraction, yielded very similar results for many insecticides, with the exception of compounds of the DDT series, for which discordant results were frequently obtained. 

Mixed-function Oxidase Induction.-- Indirect evidence of environmental induction of detoxifying enzymes in the R fish has been observed as an increase in the acute toxicity of parathion and a simultaneous decrease in NADPH-dependent parathion... 

Chaturvedi et al. (1991) studied the effects of mixtures of parathion, toxaphene, and/or 2,4-D on the hepatic mixed-function oxygenase in ICR male mice. They found that a 7-day toxaphene pretreatment enhanced the hepatic biotransformation of parathion and its metabohte paraoxon, both in the presence and absence of NADP. However, in the absence of NADP the enhancement was minor. The authors suggested that toxaphene induced the metabohc pathways of parathion and paraoxon involving the mixed-function oxygenase and that paraoxonase is not involved in the... 

With a molecular emission cavity flame detector, relying on measurement of the 526 nm emission of HPO (see Section II.C.l and III.B.3.b), nanogram amounts of phosphates or organophosphorus compounds can be assessed in automated systems160,348. Determination of m, the time elapsed between sample ignition and maximum emission, allows the resolution of ternary or more complex mixtures of insecticides. Dicrotophos, dimethoate, malathion and parathion mixed in aqueous solution were separated and identified in nanograms per millilitre concentrations348. 

Fig. 5 SIM chromatograms obtained in NI discharge-on TSP/LC-MS of mixed reference standards (5 ppm) (top) and of a spiked (1 ppm) lean beef muscle sample (bottom). Peak identities (1) p-nitrofenol, (2) 3-chloro-4-methyl-7-hydroxycoumarin, (3) 3-methy-4-(methylthio)phenol, (4) paraoxon, (5) couma-phos oxon (6) famphur (7) 2.4,5-trichlorofenol, (8) ronnel oxon, (9) stirofos, (10) parathion, (11) cou-maphos, (12) chlorpyriphos-methyl, (13) ronnel, (14) chlcpyriphos. (From Ref. 75.)...

The high water solubility (see below) was another reason for the very frequent use of toxaphene. It was found that the solubility of other organochlo-rines increased when they were mixed with toxaphene [10]. Consequently, toxaphene was applied in mixtures together with lindane, DDT [30], and methyl -parathion [31]. 

See also Aflatoxin Algae Ammonia Asbestos Benzene Hexachloride, Mixed Isomers Brodifacoum Carbamate Pesticides Carbon Monoxide Castor Bean Copper Coumarins DDT (Dichlorodiphenyltrichloroethane) DEET (Diethyltoluamide) Dichlorvos Dieldrin Ethylene Glycol Hydrogen Sulfide Lead Malathion Methane Molybdenum Mushrooms, Coprine Mushrooms, Cyclopeptide Mycotoxins Nitrites Oleander Organochlorine Insecticides Organophosphates Paraquat Parathion Pyrethrins/Pyrethroids Selenium Sodium Strychnine Sulfur Dioxide Thallium Warfarin. 

Ludke, J.L., J.R. Bibson and C.I. Lusk. Mixed function oxidase activity in freshwater fishes aldrin epoxidation and parathion activation. Toxicol. Appl. Pharmacol. 21 89-97, 1972. 

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