Assessment of leaching potential of aldicarb and its metabolites using laboratory studies

The metabolites of pesticides can contaminate groundwater and pose a risk to human health when this water is used for drinking. This paper reports the results of a laboratory study on aldicarb and its main metabolites, aldicarb sulfone and aldicarb sulfoxide. Aldicarb and its metabolites showed K_oc values (6–31) which were lower than that of atrazine (55), indicating that they are very mobile in soil. They are less persistent than atrazine (DT₅₀ = 25 days), with DT₅₀ values from less than 1 day and up to 12 days. Aldicarb behaved as a non‐leacher, whereas its metabolites clearly showed the characteristics of leachers. Aged residue leaching experiments showed that aldicarb can occur at high concentrations in the leachate, together with its two metabolites. The leachate composition depends on the incubation time of the parent compound. Aldicarb and its metabolites can form various mixtures in groundwater on the basis of the time elapsing between the application of the insecticide and the first significant rainfall. This study confirms the characteristics of contaminants of aldicarb and especially its metabolites, as reported in the literature. © 2001 Society of Chemical Industry     

Residues of aldicarb and its main metabolites in the leaves of sugar beet plants

The residues of aldicarb and of its main metabolites (aldoxycarb, 2-mesyl-2-methylpropionitrile, and 2-mesyl-2-methylpropan-1-ol) were measured, by a gas-liquid chromatographic procedure, in the leaves of ripe sugar beet plants from cultures made by several farmers. The sugar beet plants had been grown in normal fields and treated at sowing with aldicarb at the usual rate of 1 kg ha^?1 in the form of ‘Temik’, the commercial formulation of aldicarb which contains 10% by weight of aldicarb. The samples of sugar beet plants were taken from three fields of different soil types. The residue concentrations, ranged in order of soil type, were: sandy loam > silt loam > clay.     

The metabolism of [14C]aldicarb in the leaves of sugar beet plants

Sugar beet plants were grown in the field, after in-furrow application of [¹⁴C]aldicarb (3 kg of aldicarb ha^?1) at planting. The ripe sugar beet plants were harvested, and the blades and petioles of the leaves were analysed separately. In the whole leaves, 15% of the ¹⁴C (all the percentages of ¹⁴C are relative to the total ¹⁴C incorporated into the whole leaves) was insoluble in ethanol+ water (1+1 by volume), 31% was organo-soluble (and thus unconjugated in the leaves), and 54% was water-soluble (mainly conjugated to plant constituents). The weights and concentrations (as aldicarb equivalents) of various identified metabolites of aldicarb, incorporated into the leaves, were determined; no aldicarb, as such, was detected.     

Aldicarb sulfoxidation by plant root extracts

Soybean root homogenates were found to oxidize aldicarb to aldicarb sulfoxide. Fractionation of soybean root homogenate indicates that the enzyme(s) which oxidize aldicarb to the sulfoxide are largely (63%) in the 25,000g supernatant. In vitro studies of the 25,000g supernatant showed a linear reaction rate at 24 and 34°C for periods of up to 2 and 1 hr, respectively, at the pH optimum of 5.5. Bean and soybean root 25,000g supernatants were the most active on a per milligram of protein basis followed by corn, sorghum, barley, and tomato (8–27 nmol/mg of protein/hr). A 140-fold purification of soybean root aldicarb sulfoxidase was achieved. In vitro studies indicated that methomyl, methiocarb, phorate, Counter, fensulfothion, fenthion, Nemacur, EPTC, vernolate, carboxin, dl-methionine, l-cysteine, l-methionyl-l-serine, thiodiglycolic acid, lipoic acid, thiourea, and thioacetic acid when present at a 10:1 ratio with aldicarb significantly inhibited soybean root aldicarb sulfoxidation.     

Residue analysis of butocarboxim and aldicarb applied in a drip-irrigated peach grove by the HPLC post-column fluorogenic labeling technique

The new high-performance liquid chromatography (HPLC) post-column fluorogenic labeling technique was used for the analysis of residues of butocarboxim, aldicarb and their sulfoxide and sulfone metabolites in peach leaves and fruits. In order to simplify the procedure, the different metabolites were separated by column chromatography during the cleanup process and the residues were determined by HPLC employing an aqueous methanol solvent in the isocratic mode. The limit of detection for the two insecticides was 0.1 μg/g in the leaves and 0.02 μg/g in the fruit. Aldicarb (10% granular formulation) and butocarboxim (50% E.C. diluted 1:5 with water) were applied to the soil in a drip-irrigated peach grove, by placement under one dripper on one side of each tree. The insecticides were taken up by the tree and distributed almost equally on both sides of the tree. The concentration of the insecticides was somewhat lower in the younger leaves. Residue levels of 0.4 to 0.9 μg/g were detected in the fruits at harvest, 10 and 18 days after the last treatment. Based on the results from the field experiment it was concluded that one of the advantages of drip irrigation was that it enabled adequate control of the green leafhopper (Asymmetrasca decedens) throughout the summer with relatively low dosages of systemic insecticides.     

Distribution of the radioactivity in sugar beet plants treated with [14C]aldicarb

Sugar beet plants were grown in the field, after in-furrow application of [¹⁴C]aldicarb (3 kg of aldicarb ha^?1) at planting. Some plants (the growing plants) were harvested 99 days after sowing and the rest (the ripe plants) 196 days after sowing. The percentages of the weights of [¹⁴C]aldicarb equivalents (the total aldicarb plus aldicarb sulphoxide and sulphone, plus all the other metabolites of [¹⁴C]aldicarb which contain ¹⁴C, expressed as aldicarb equivalents) incorporated into the beet plants, relative to the weight applied to the soil, were 2.8 and 1.8, respectively for the growing and ripe plants. The concentrations of [¹⁴C]aldicarb equivalents (mg kg^?1 fresh weight) in the growing and ripe plants, respectively were: blades of the external leaves, 3.16 and 0.93; blades of the internal leaves, 0.63 and 0.68; petioles of the external leaves, 0.51 and 0.26; petioles of the internal leaves, 0.15 and 0.05; crowns, 0.14 and 0.15; roots, 0.16 and 0.13. The proportions of the extractable aldicarb plus aldicarb sulphoxide and aldicarb sulphone determined by gas-liquid chromatography (expressed as aldicarb equivalents) relative to [¹⁴C]aldicarb equivalents, in the external and internal leaf blades of the growing beets, were 56 and 60%, respectively; these values declined to 25 and 19%, respectively in the ripe plants. The proportion was 21 % or less in all other parts of the growing and ripe plants.     

Transformation of aldicarb sulfoxide and aldicarb sulfone in four water-saturated sandy subsoils

The transformation of aldicarb sulfoxide and aldicarb sulfone was studied in incubations with water-saturated subsoils under simulated field conditions at 10°C. The subsoils were collected at four locations from beneath the water table at a depth of 2.5 to 3.5 m. In three of the subsoils, the half-life of sulfoxide, incubated at concentrations of 0.14-0.17 mg litre^?1, ranged from 0.7 to 2.8 years. At higher concentrations (8-13 mg litre^?1), its half-life ranged from 3.4 to 6.4 years. At the lower concentration, a large fraction of sulfoxide was transformed into sulfone. The rates of transformation of the sulfone at the lower concentration in the three subsoils corresponded to half-lives of 3.3 to 8.1 years, but in only one subsoil was a significant transformation rate (half-life 6.7 years) measured at the higher concentration during the 2.3-year incubation period. The half-lives at the lower concentrations were more like those in field studies, and perhaps would still underestimate transformation rates under field conditions. After a year, 2.5-15% of the higher sulfoxide and sulfone doses had been trapped as [¹⁴C] carbon dioxide. In the fourth subsoil, with more anaerobic conditions, the half-life of sulfoxide at both concentrations was less than 0.02 year and that of sulfone was about 0.04 year. Four or five radio-labelled transformation products could be traced in this subsoil and about half of the dose of both compounds was trapped as [¹⁴C] carbon dioxide.     

固相萃取液相色谱串联质谱法测定生姜中涕灭威及其代谢产物

建立了固相萃取-液相色谱串联质谱法测定生姜基质中涕灭威及其代谢产物涕灭威亚砜、涕灭威砜的分析方法。试样经乙腈提取,氨基SPE小柱净化后,采用多反应监测（MRM）正离子模式检测,外标法定量。实验结果表明：3种目标物在10ng/mL到50ng/mL质量浓度范围内呈现良好的线性,方法的检出限均为2μg/kg,3个加标水平下平均回收率在72～94%之间。该方法准确、灵敏、重现性好,可用于生姜样品中涕灭威及其代谢产物涕灭威亚砜、涕灭威砜的实际检测。     

Foliar residues and toxicity to Aphis citricola of three systemic insecticides applied to the soil in a citrus grove

A study was made of the accumulation of aldicarb, ethiofencarb and dimethoate in citrus leaves and fruit; the toxicity of these insecticides to the spirea aphid (Aphis citricola Van der Goot) was also studied. The effectiveness of the treatments was affected mainly by the rate of accumulation of the toxicant in the leaves. At 18 g a.i. per tree, the greatest residues found in the leaves were 106, 12.2 and 1.3 μg 8^?1 fresh weight for aldicarb, ethiofencarb and dimethoate, respectively. The concentration in mature leaves was very similar to that in young leaves. The residue levels in the mature fruits were much lower than in the leaves. The main components of the residues in the leaves were aldicarb sulphoxide [2-methyl-2-(methylsulphinyl)- propionaldehyde O-methylcarbamoyloxime], dimethoate, omethoate and ethiofencarb sulphoxide [2-(ethylsulphinylmethyl)phenyl methylcarbamate]. A laboratory study with synthetic diets showed similar toxicity for all three insecticides, whereas in detached leaves, or when taken up by citrus trees, ethiofencarb was the least toxic to the aphids.     

Leaching of aldicarb and thiofanox,and their uptake in soils by sugarbeet plants

The leaching of aldicarb and thiofanox in soils (sandy loam, silt loam and sandy clay loam), and their uptake by sugarbeet plants were studied. Three irrigation levels were maintained: half, normal and double dose. The residues were determined as the sum of the insecticidal metabolites (parent compound + sulphoxide+ sulphone) for both pesticides. Leaching was greatly influenced by the amount of water added and the soil type. Under normal conditions, leaching seemed to proceed very slowly, keeping the chemicals available for uptake by the root systems for a long time. The concentration of insecticide in the leaves was highest in beets grown on sandy loam and lowest in those grown on sandy clay loam. The quantity of irrigation did not influence the residue concentration in the leaves greatly, although its influence was obvious on the total residue present (μg per plant). Increasing the water dose always resulted in a higher total residue, and a greater plant weight. The breakdown in the soils was directly related to the water dose. The experiments show that thiofanox was more stable than aldicarb and was taken up by sugarbeet to a greater extent.     

The importance of pH in food selection by the tobacco whitefly,Bemisia tabaci

The tobacco whitefly,Bemisia tabaci Gennadius, was found to differentiate between pH values at the leyel of 0.25. It had a clear preference for media with pH values of 6.0 to 7.25 offeredin vitro, in both choice and no-choice situations, when “resting whiteflies” or survival was measured. The whiteflies showed a clear preference for a sucrose concentration of 15%. The addition of 10% sucrose to buffers at various pH values did not change the pattern of their pH preference. Inin vivo experiments whiteflies preferred old cotton leaves (120 days) to younger leaves (60 days). The pH of old leaves was 6.8 while that of young leaves was 5.9. These results may explain the fact that whiteflies attacked cotton plants in commercial fields only late in the season, when the pH values of the cotton leaves exceeded pH 6.     

棉花主要抗虫次生物质与其对绿盲蝽抗性的关系

系统研究了不同供试棉花品种(系)对绿盲蝽的抗性水平,并在室内采用香草醛法和高效液相色谱法分别测定了缩合单宁、黄酮类化合物和萜烯类化合物的含量,以明确棉花主要抗虫次生物质与其对绿盲蝽抗性的关系.结果表明,不同棉花品种(系)在不同生长期及不同组织中次生代谢物质含量存在一定差异;苗期顶叶中缩合单宁、总萜烯类化合物和总杀实夜蛾素含量与棉花对绿盲蝽抗性存在显著正相关性,蕾期顶叶和棉蕾中芸香苷含量与棉花对绿盲蝽抗性具有显著正相关性,铃期棉铃中槲皮素、异槲皮苷含量与棉花对绿盲蝽抗性呈现显著负相关性.田间缩合单宁、芸香苷、总萜烯类化合物和总杀实夜蛾素含量高的棉花品种(系)可以在一定程度上减轻或抑制绿盲蝽的危害,而另外两种黄酮类物质槲皮素和异槲皮苷则有利于绿盲蝽的发生危害.     

The metabolism of cypermethrin in plants: The conjugation of the cyclopropyl moiety

The metabolism of the pyrethroid insecticide cypermethrin ([S,R,]-α-cyano-3-phenoxybenzyl-(1R,1S,cis,trans)-2,2-dimethyl-3-(2′,2′-dichlorovinyl)cyclopropane carboxylate), I, has been examined in lettuce plants grown and treated twice under outdoor conditions with ¹⁴C-cyclopropyllabeled material. The application rate at each treatment was equivalent to 0.3 kg/ha. At harvest, 21 days after the last application, the plants contained mainly unchanged cypermethrin (33% of the total radiolabel present) and polar materials (54%) which were shown to be conjugates of trans-2(2′,2′-dichlorovinyl)-3,3-dimethylcyclopropane carboxylic acid (II). One of these was identified as the β,d-glucopyranose ester. In separate experiments the uptake and metabolism of the acid (II) in cotton leaves were examined in the laboratory and the acid was shown to be readily converted into a mixture of the β,d-glucopyranose ester, an acidic derivative of this, and disaccharide derivatives including the glucosylarabinose ester and the glycosylxylose ester. Subsequently, cotton leaves were exposed to solutions of these individual conjugates, and interconversions between these metabolites were observed.     

The metabolism of [14C]aldicarb in the root of sugar beet plants

Sugar beet plants were grown in the field, after in-furrow application of [¹⁴C]- aldicarb (3 kg of aldicarb ha^?1) at planting. The ripe sugar beet plants were harvested, and the roots were analysed. The roots were fractionated according to a procedure similar to the normal beet-sugar manufacturing process. Expressed as a proportion of the total radioactivity incorporated into the root, the pulp contained 29.7%, the lime cake 9.7%, the crystallised sugar 17.7% (which gave, with the radioactivity found in the sugar in the molasses, a total of 20.7% of the radioactivity in the total sugar), and the molasses, 42.9%. A part of the labelled carbon from the radio- active aldicarb and its metabolites had thus been metabolised and incorporated into sugar molecules. Except for the radioactivity in the sugar and in the lime cake from the processing, the proportion of radioactive non-conjugated organosoluble compounds was very low (2.6%), and perhaps partially corresponded to the very low amount of aldoxycarb (aldicarb sulphone) in the root (less than 0.001 mg of [¹⁴C]-aldicarb equivalents kg^?1 fresh weight). Hydrolysis of the molasses yielded free radioactive 2-methyl-2-(methylsulphinyl)propan-1-ol (3.1%), 2-mesyl-2-methyl-propan-I-ol (8.9%) and 2-mesyl-2-methylpropionic acid (12.0%) which had been conjugated to plant constituents in the root. The corresponding concentrations (expressed as mg of [¹⁴C]aldicarb equivalents kg^?1 fresh weight of root) were 0.004, 0.011, and 0.016, respectively. No aldicarb, aldicarb sulphoxide or aldoxycarb (nor the corresponding nitrile, generated from aldicarb during the fractionation procedure) was liberated by the hydrolysis, indicating the absence of conjugates of these compounds in the root.     

Control of Aphis fabae on broad beans (Vicia faba) by the systemic action of gamma-bhc,thionazin and aldicarb

The in-row application of aldicarb granules at 2 lb active ingredient (a.i.)/acre (2·24 kg/ha) at sowing gave complete control of Aphis fabae Scop. on broad beans (Vicia faba L. cv. Seville) up to 7 days before harvest and resulted in a three-fold increase in yield compared with a similar thionazin treatment. Bean plants grown from seeds which were soaked in a gamma-BHC solution at 20 ppm for 24 h prior to planting were protected from this aphid for most of the growing season almost as effectively as with the thionazin treatment. A thin-layer chromatography method was developed for the determination in plants and soil of aldicarb and its two major toxic metabolites, the sulphoxide and sulphone. Gas-liquid chromatography was used to monitor the declining levels of gamma-BHC and thionazin, and simultaneous bioassays were made with Aphis fabae on excised leaf discs from the crop. Analysis of the bean seeds and pods at harvest 90 days after sowing indicated no detectable gamma-BHC, less than 0·01 ppm of thionazin and approximately 0·09 ppm total residue of aldicarb sulphone and sulphoxide. Approximately 22% and 13% of the applied aldicarb, in the form of sulphone and sulphoxide but not the parent compound, remained in the top 6 in (152 mm) of soil at the end of 2 and 4 months respectively. Toxicity studies with Aphis fabae, Acyrthosiphon pisum Harris, and Megoura viciae Buck showed an increasing sensitivity in that order to gamma-BHC at 1 ppm in bean plants. Acute toxicity investigations with feeding Aphis fabae indicated an increasing sensitivity in the order of gamma-BHC < aldicarb sulphone < aldicarb sulphoxide < thionazin < aldicarb. Despite the high acute toxicity of thionazin to Aphis fabae it gave low protection against aphids, possibly owing to its relatively short persistence in both plants and soil when compared with aldicarb.     

In vitro inhibition of α-amylase and protease by nematocides in Cicer arietinum L

The in vitro effects of four systemic nematocides, i.e., aldicarb, carbofuran, oxamyl, and phorate, on the α-amylase and protease activities in Cicer arietinum has been revealed. All four nematocides markedly inhibited the activities of both the enzymes, with a general tendency of increased inhibition with corresponding increase in the concentrations of the nematocides. There was complete inhibition of α-amylase activity by the highest concentration (500 μM) of aldicarb and carbofuran, while oxamyl at the same concentration showed the same effects on protease activity. The lowest concentration (10 μM) was almost ineffective.     

Acetylcholinesterase of Aphis citricola: Properties and significance in determining toxicity of systemic organophosphorus and carbamate compounds

In apterous adults of the spirea aphid, Aphis citricola van der Goot, the optimum conditions for determining acetylcholinesterase (AChE) activity consist of reaction mixture of 0.1 M phosphate buffer (pH 7.5), 10^?3M acetylthiocholine (ASCh), and enzyme extract equivalent to 80 ± 3 μg protein incubated for 15 min at 30°C. The K_m value for ASCh (6.7 × 10^?5M) was much lower than that of butyrylthiocholine (BuSCh) (1.25 × 10^?2M). The enzyme activity was almost completely inhibited by 10^?6M paraoxon or 10^?5M eserine and was 84% inhibited by 10^?5M BW284C51 (a specific AChE inhibitor). DTNB was found to inhibit the enzyme activity and was therefore added at the end of the reaction. AChE activity of A. citricola was inhibited in vitro and in vivo by dimethoxon > dimethoate, and aldicarb sulfoxide > aldicarb > aldicarb sulfone. The in vivo effect correlates well with the toxicity level of the various toxicants. A neurotoxicity index which combines both mortality and in vivo inhibition of the aphid AChE activity is suggested as a measure for determining the toxicity of organophosphorus and carbamate compounds toward aphids.     

棉花叶片茸毛性状与绿盲蝽抗性的关系

为明确棉花叶片茸毛性状与其对绿盲蝽抗性的关系,于2008-2009年连续两年系统研究了不同供试棉花品种(系)对绿盲蝽的抗性水平,并在室内测定了棉花中脉和叶片上茸毛的类型、密度和长度.结果表明,不同棉花品种(系)对绿盲蝽的抗性水平存在差异;且不同棉花品种(系)叶片各类型茸毛密度和茸毛长度分别表现显著差异(P<0.05);叶片茸毛密度与棉花对绿盲蝽的抗性呈显著负相关(y=3.5482-0.0007x1-0.0089x2,R2=0.5741,P=0.0007),叶片茸毛类型和茸毛长度与棉花对绿盲蝽的抗性没有显著相关性.选育叶片无毛或少毛的棉花品种(系)可用于棉花绿盲蝽的治理.     

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

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-¹⁴C]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 [¹⁴C]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-¹⁴C]DBSC in the cotton plant.