Noriharu Umetsu

Toxicological properties of phosphorothioate and related esters present as impurities in technical organophosphorus insecticides

O,O,S-Trimethyl phosphorothioate, an impurity in several technical organophosphorus insecticides, when administered orally to rats at single doses as low as 15 mg/kg caused delayed mortality, with death occurring 4-22 d after treatment. Delayed toxic signs were also observed in mice, but mice were generally less sensitive than rats. O,O,S-triethyl phosphorothioate and O,S,S-trimethyl phosphorodithioate induced the same signs of intoxication at slightly higher doses. Rats treated with O,O,S-trimethyl phosphorothioate refused food and water within 24 h after treatment and did not eat or drink until the time of death. Neither injection of nutrient solution nor atropine served to reduce or block intoxication. However, the isomeric O,O,O-trimethyl phosphorothioate was a potent antagonist of the toxicity of O,O,S-trimethyl phosphorothioate. As little as 1% of the O,O,O-trimethyl isomer protected rats from the intoxicating effects of the O,O,S-trimethyl isomer at doses as high as 200 mg/kg. Rat serum carboxylesterase and cholinesterase were inhibited for prolonged periods after a single oral dose of O,O,S-trimethyl phosphorothioate, but the duration of inhibition was significantly less when the toxicant contained 1% O,O,O-trimethyl isomer.

Inactivation of esterases by impurities isolated from technical malathion.

Abstract Compounds previously identified as contaminants of technical malathion were found to diminish the activity of serum malathion carboxylesterase, liver malathion carboxylesterase, and serum cholinesterase in vitro and in vivo . The compounds tested were, in increasing order of potency, O,O,S -trimethyl phosphorodithioate, O,O,S -trimethyl phosphorothioate, O,S,S -trimethyl phosphorodithioate, and O,S -dimethyl S -(1,2-dicarboethoxy)ethyl phosphorodithioate. In vivo , the diminutions of serum esterase activity caused by these compounds were transient, with the exception of the diminutions caused by O,O,S -trimethyl phosphorothioate, which persisted for at least 54 hr. The most potent of these esterase inactivators, also known as isomalathion, is of particular interest as a possible contributor to an epidemic of malathion poisonings among malaria workers in Pakistan.

Biochemical and physiological investigations into the delayed toxicity produced by O,O,S-trimethyl phosphorothioate in rats

Abstract Oral administration of O,O,S -trimethyl phosphorothioate (OOS), an impurity in several technical organophosphorus insecticides, causes delayed toxicity in rats with death occurring up to 28 days after the treatment. The oral LD 50 was determined to be 60 mg/kg. The effect of a single nonlethal dose of OOS (20 mg/kg) on in vivo protein synthesis in different organs was determined by measurement of the incorporation of [ 14 C]leucine at 6 hr to 28 days after treatment. As early as 6 hr after OOS treatment the incorporation of [ 14 C]leucine into the liver, lung, thymus, kidney, and spleen was elevated and remained elevated for up to 7 days. With the exception of the lung, organ weights were significantly decreased during the same time period. On Day 28 after treatment, the amount of [ 14 C]leucine incorporation had decreased to the control level in all of the organs studied. Treatment with OOS at 20 mg/kg caused a significant increase in hematocrit on Days 3,5, and 7, and as early as 6 hr after treatment at 60 mg/kg. The clinical biochemistry of plasma indicated that there was no significant change from control values in the glutamic pyruvic transaminase, glutamic oxalic transaminase, lactate dehydrogenase, or alkaline phosphatase activities with the 20 mg/kg dose. The analysis of the intermediary metabolites indicated that the redox state of cytosol was more reduced on Day 5, whereas that of mitochondria was not affected by OOS. Data obtained at selected times after oral administration of a 60 mg/kg dose of OOS and that obtained from animals starved for 3 days are also discussed.

Metabolism of 2,3-dihydro-2,2-dimethyl-7-benzofuranyl (di-n-butylaminosulfenyl)(methyl)carbamate and 2,3-dihydro-2,2-dimethyl-7-benzofuranyl (morpholinosulfenyl)(methyl)carbamate in cotton and corn plants☆

Abstract The absorption, translocation, and metabolism of two new, selectively toxic derivatives of carbofuran, 2,3-dihydro-2,2-dimethyl-7-benzofuranyl (di- n -butylaminosulfenyl)(methyl)carbamate and 2,3-dihydro-2,2-dimethyl-7-benzofuranyl (morpholinosulfenyl)(methyl)carbamate, were studied in cotton and corn plants 1, 3, 6, and 10 days following both stem injection and foliage treatment. Both carbamates were readily translocated to all plant parts following stem injection, but translocation following leaf application was restricted to within the leaf. In cotton plants, the dibutylaminosulfenyl derivative was easily hydrolyzed to form carbofuran which, in turn, was oxidized at the 3-position of the ring and the N -methyl group. These oxidized metabolites were then converted to plant conjugates. Major metabolites were carbofuran and 3-hydroxy-carbofuran followed by 3-keto-carbofuran phenol and N -hydroxymethyl-carbofuran. Five minor metabolites also were detected. In corn plants, the dibutylaminosulfenyl derivative gave the same metabolites, although the metabolism rate was significantly slower in corn relative to cotton. Overall, the results showed that there were no fundamental differences in the metabolism of the morpholinosulfenyl and dibutylaminosulfenyl derivatives. The stability of both carbamate derivatives in different solvent systems also was investigated.

Inhibition of sterol 14α-demethylation in Botrytis cinerea by the novel imidazole-1-carboxylate fungicides

Abstract The effect of the novel imidazole-1-carboxylates (1-(4-substituted phenoxymethyl)-2,2-dimethylpropyl imidazole-1-carboxylates), which have a carbonyl group linking to the 1-position of imidazole, on growth and sterol biosynthesis in Botrytis cinerea was studied. The present fungicidal compounds severely suppressed the mycelial growth of B. cinerea with a concomitant decrease in the ergosterol level and the accumulation of 14α-methyl sterols, indicating inhibition of sterol 14α-demethylase. The 14α-demethylation is well known to be catalyzed by cytochrome P450-dependent monooxygenase, which gives type II spectral changes by interacting with 14α-demethylation inhibitors such as prochloraz. Imidazole-1-carboxylates produced type II spectra with rat liver P450. These results demonstrate that the inhibition of 14α-demethylation is the mode of action of the present azole fungicides.

Metabolism of dibutyl-14C-labeled dibutylaminosulfenyl derivative of carbofuran in the cotton plant

Abstract The fate of the di- n -butylaminosulfenyl moiety in 2,3-dihydro-2,2-dimethyl-7-benzofuranyl (di- n -butylaminosulfenyl)(methyl)carbamate (DBSC or Marshal) was studied in the cotton plant at 1, 3, 6, and 10 days following foliage treatment with [ di-n-butylamino - 14 C]DBSC. Dibutylamine and two major radioactive metabolites were obtained following extraction of the plant tissue with a methanol-buffer containing N -ethylmaleimide (NEM), a sulfhydryl scavenger which was added to prevent the cleavage of the NS bond during the workup procedure. The most adundant radioactive material recovered from plants was identified as a product arising from the reaction between NEM and dibutylamine. Extraction of plant tissue with straight methanol-buffer solution or with methol-buffer containing other sulfhydryl scavengers resulted in 57–86% of the applied radioactivity being recovered as dibutylamine in the organosoluble fraction. When [ 14 C]dibutylamine was applied to cotton leaves, most of the radioactivity, i.e., 96% of the total recovered radioactivity, was found in the organosoluble fraction as dibutylamine. Dibutylamine is the major metabolite of [ di-n-butylamino - 14 C]DBSC in the cotton plant.

A High-Performance Liquid Chromatographic Method for Determination of Benfuracarb and Carbofuran Residues in Soil and Water

土壌中ならびに水中におけるベンフラカルブおよびその主要分解物であるカルボフランの残留分析法を確立した. 土壌試料中のベンフラカルブおよびカルボフランは, アセトニトリルで抽出後, ジクロロメタンに転溶した. 抽出物をシリカゲルカラムクロマトグラフィーにより精製後, 逆相カラムを用いた高速液体クロマトグラフィーにより定量した. ベンフラカルブおよびカルボフランの検出限界はそれぞれ0.04および0.02ppmであり, 回収率は77～92, 90～100%であった. 水田水中のベンフラカルブおよびカルボフランは, ジクロロメタンで抽出し, ベンフラカルブは, 逆相, カルボフランは順相の高速液体クロマトグラフィーにより, それぞれ定量した. ベンフラカルブおよびカルボフランの検出限界はともに0.001ppmであり, 回収率はそれぞれ94～96, 94～97%であった. 脱塩水の場合には, 試料を直接逆相の高速液体クロマトグラフに注入することにより両化合物を定量した.