Acute Poisoning with Phosphamidon: Determination of Dimethyl Phosphate (DMP) as a Stable Metabolite in a Case of Organophosphate Insecticide Intoxication

Many organophosphate pesticides (OP) such as phosphamidon are unstable in aqueous solutions and especially in blood in the presence of esterases. In a case of intoxication, the phosphamidon concentration in serum decreased from 10 mg/L to 4.4 mg/L after storage at -20 degrees C for six months; nearly complete degradation was observed after three years. Dimethyl phosphate (DMP) is a metabolite of phosphamidon, mevinphos, dicrotophos, monocrotophos, dichlorvos, and trichlorfon. A gas chromatographic-mass spectrometric method with deuterated DMP-d6 as internal standard for the determination of DMP in biological material was validated. DMP was found in all of the patient's samples (3.9 and 4.9 mg/L in blood, 33.5 and 50.4 mg/L in urine, and 8.1 mg/L in gastric fluid), even after storage at -20 degrees C for up to 3 years. No hints for a degradation of DMP when spiked in fresh blood and stored at 4 degrees C for 1 week and stored in water over a time period of 10 months. Looking for the stable metabolites like DMP in cases of suspected OP intoxication is recommended.

Study of the mechanism ofFlavobacteriumsp. for hydrolyzing organophosphate pesticides

The biotransformation by Flavobacterium sp. of the following organophosphate pesticides was experimentally and theoretically studied: phorate, tetrachlorvinphos, methyl-parathion, terbufos, trichloronate, ethoprophos, phosphamidon, fenitrothion, dimethoate and DEF. The Flavobacterium sp. ATCC 27551 strain bearing the organophosphate-degradation gene was used. Bacteria were incubated in the presence of each pesticide for a duration of 7 days. Parent pesticides were identified and quantified by means of a gas-chromatography mass spectrum system. Activity was considered as the amount (micromol) of each pesticide degraded by Flavobacterium sp. Also, structural parameters obtained by means of the CAChe program package for biomolecules, the reactivity index of phosphorus, of oxygen at the P = O function and of sulfur at the P = S function, and lipophilicity (log Poct) (ALOGPS v. 2.0) were obtained for each pesticide. Pesticides were hydrolyzed at the bond between phosphorous and the heteroatom, producing phosphoric acid and three metabolites. Enzymatic activity was significantly explained by the following multiple linear relationship: Enzymatic activity = 162.2 - 9.5(dihedral angle energy) - 25.0(Total energy) - 0.51(Molecular weight). Finally, a mechanism of Flavobacterium sp. to hydrolyze pesticides was proposed.

Application of calorimetry to microbial biodegradation studies of agrochemicals in oxisols

Calorimetry was used to monitor the inhibitory effect caused by the bipyridynium diquaternary salts paraquat, diquat, and phosphamidon on microbial activity in a Red Latosol soil (Oxisol). The thermal effect was recorded on samples composed of 1.50 g of soil, 6.0 mg of glucose, 6.0 mg of ammonium sulfate, and different masses of an inhibitor ranging from zero to 8.00 mg, under a controlled moisture content of 35%. Thermal effects of each pollutant on the degradation curves of glucose in the soil were compared. Increasing amounts of the inhibitor caused a decrease in the thermal effect from -2234 to -1987 kJ mol(-1) for paraquat, -1670 to -1306 kJ mol(-1) for diquat, and -2239 to -589 kJ mol(-1) for phosphamidon. The last xenobiotic agent caused a significant inhibitory effect on the microbial activity of the soil. The results of relative efficiency, eta = deltaH/deltaH', referring to the enthalpic value with (deltaH) and without (deltaH') agrochemical in the soil, exhibited a significant correlation. From this correlation obtained for the ranges 2.00 to 8.00, 1.30 to 8.00, and 1.20 to 5.80 mg of the agrochemicals paraquat, diquat, and phosphamidon, respectively, the following eta values were calculated: 0.993 to 0.894, 0.668 to 0.522, and 0.896 to 0.236, respectively, during the degradation of glucose in the soil. The largest relative efficiency for paraquat implies that this agrochemical can be metabolized by microbial activity.

Mutagenic and genotoxic activities of four pesticides: captan, foltaf, phosphamidon and furadan

The mutagenic and genotoxic potential of four pesticides viz. captan, foltaf, phosphamidon and furadan was evaluated by the Ames mutagenicity assay and their DNA damaging ability on radiation repair defective E. coli K-12 strains respectively. The mutagenic spectrum revealed captan to be most mutagenic in the absence of metabolic activation, while the presence of S9 mix led to an attenuated mutagenic response. Foltaf, phosphamidon and furadan were detected as relatively weaker mutagens. A significant decrease in the survival of SOS defective mutants, recA, lexA and pol- of E. coli was observed as compared to their wild-type counterparts in the presence of the pesticides. The role of SOS repair genes gains further support from the Salmonella strains triggering the error-prone SOS response.

Interaction of phosphamidon with neuropathy target esterase and acetylcholinesterase of hen brain

Phosphamidon (PSM) is an organophosphorus insecticide widely used in agriculture. This study was undertaken to examine the interaction of PSM with acetylcholinesterase (AChE) and neuropathy target esterase (NTE) of hen brain in vitro and in vivo. PSM was a potent inhibitor of AChE, with an I50 of 2.9 microM and second-order rate constant (ka) of 1.2 x 10(4) M-1 min-1 at 37 degrees C. PSM-inhibited AChE aged rapidly (t1/2 = 1.9 h). Pyridinium oximes pralidoxime, trimedoxime, obidoxime and HI-6 were effective reactivators of PSM-inhibited AChE, providing up to 75% reactivation. PSM was one of the weakest inhibitors of NTE among organophosphorus compounds, with an I50 of 19 mM and ka of 1.8 M-1 min-1 at 37 degrees C. Inhibited NTE did not reactivate spontaneously and KF-induced reactivation was not obtained even at the earliest tested moments, so it was not clear whether aging of PSM-inhibited NTE occurred very quickly or the KF molecule could not affect the stability of phosphoryl-NTE bond. From the ratio of kas for NTE and AChE (0.00015) it was predicted that delayed neuropathic effects of PSM in vivo would appear only at doses far above the acute LD50. The LD50 value of PSM p.o. for hens was 9 mg/kg. Hens were treated with a single oral dose of PSM, combined with standard antidotal treatment which included atropine, physostigmine, pralidoxime and anticonvulsant midazolam. Doses of 90 and 250 mg/kg caused up to 27% and 45% NTE inhibition 48 h after poisoning, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)