Carbamates methomyl

Fig. 28.2. Reproduced from Figs. 1 and 2 of Ref. [49]. Currents generated by electrodes 17 h after exposure to pesticides, (a) Electrodes exposed to an or-gano-phosphate, malathion and a commercial formulation of it, Maldison. Maldison diluted to the recommended dose (RD) contains 6.1 mM malathion. (b) Electrodes exposed to a carbamate, methomyl and a commercial formulation of it, Lannate. Lannate diluted to the RD contains 2.2. mM methomyl. A is a multiple of the RD or 6.1 mM malathion or 2.2 mM methomyl.

Environmental. The A/-methylcarbamates generally are biodegradable and of low soil persistence with half-Hves for carbaryl and aldicarb of 1—2 weeks and of carbofuran of 1—4 months. Certain carbamates are highly toxic to birds with oral LD qS for mallard, eg, pheasant, in mg/kg carbofuran, 0.40, 4.2 mexacarbate, 3.0, 4.5 and methomyl, 16, 15 compared to carbaryl >2000. Fish toxicity of carbamates is generally low, but these compounds are extremely toxic to bees. In cases of human poisoning, atropine is a specific antidote. 

Oxime carbamates are not directly amenable to gas chromatography (GC) because of their high thermal instability, which often leads to their breakdown at the injection port or in the column during analysis. Analysis of oxime carbamates by GC with sulfur detection or flame photometric detection involves oxidation of the intact insecticides or alkaline hydrolysis to form the more volatile but stable oxime compound. Enzymatic techniques have been reported for the analysis of these compounds. Enzyme-linked immunosorbent assay (ELISA) has been used to determine aldicarb and its sulfone and sulfoxide metabolites and methomyl in water, soil, and sediment samples. 

Oxime carbamates are generally applied either directly to the tilled soil or sprayed on crops. One of the advantages of oxime carbamates is their short persistence on plants. They are readily degraded into their metabolites shortly after application. However, some of these metabolites have insecticidal properties even more potent than those of the parent compound. For example, the oxidative product of aldicarb is aldicarb sulfoxide, which is observed to be 10-20 times more active as a cholinesterase inhibitor than aldicarb. Other oxime carbamates (e.g., methomyl) have degradates which show no insecticidal activity, have low to negligible ecotoxicity and mammalian toxicity relative to the parent, and are normally nondetectable in crops. Therefore, the residue definition may include the parent oxime carbamate (e.g., methomyl) or parent and metabolites (e.g., aldicarb and its sulfoxide and sulfone metabolites). The tolerance or maximum residue limit (MRL) of pesticides on any food commodity is based on the highest residue concentration detected on mature crops at harvest or the LOQ of the method submitted for enforcement purposes if no detectable residues are found. For example, the tolerances of methomyl in US food commodities range from 0.1 to 6 mg kg for food items and up to 40 mg kg for feed items. ... 

The first recommended soil method for oxime carbamates is the method of Honing et al. by HPLC/MS. The LOQ of the method, specifically for aldicarb, methomyl, and oxamyl, is 0.05mgkg. Soil (lOg) is Soxhlet extracted for 16h with acetone-dichloromethane (1 1) using double-thickness cellulose extraction thimbles (80 X 22-mm i.d.). Prior to extraction, the Soxhlet system and the thimbles are cleaned for 14 h by refluxing with methanol. The extracts are removed and concentrated nearly to dryness in a rotary evaporator operating at 35 °C evaporation to dryness... 

Base hydrolysis kinetic data are reported for ppb solutions of carbofuran,3-OH carbofuran, methomyl and oxamyl. The results are compared with those reported previously for aldicarb, aldlcarb sulfoxide, and aldicarb sulfone. Second order reaction rate constants, k, have been calculated and range from 169 liter mln mole for oxamyl to 1.15 liter mln mole for aldicarb. The order for rate of base hydrolysis is as follows oxamyl >3-hydroxycarbofuran >aldicarb sulfone v- carbofuran >aldicarb sulfoxide > methomyl -v aldicarb. The activation energy for the base hydrolysis of carbofuran was measured to be 15.1 +0.1 kcal mole , and is similar to the value previously reported for aldicarb sulfone. Rapid detoxification of aldicarb, a representative oxime carbamate pesticide, by in situ hydrolysis on reactive ion exchange beds is reported. 

Materials. Aldicarb standards were obtained from the United States Environmental Protection Agency (USEPA), Quality Assurance Section and from Union Carbide Corporation. Crystalline samples of carbofuran and 3-hydroxycarbofuran were supplied by the Agricultural Chemical Group of FMC Corporation. Reference standards of methomyl (99% pure) and oxamyl (99% pure) were obtained from USEPA. HPLC grade methanol was purchased from Burdick and Jackson, Inc. Methylene chloride used for bulk extractions of the carbamate pesticides in solution was recovered, distilled and reused. Analytical reagent grade chemicals and solvents were used in all experiments. Doubly distilled deionized water was used for solution rate studies. Deionized distilled water (DDW) was used for dilutions in reactive ion exchange experim ts., , ... 

A third important carbamate is aldicarb or Temik , an insecticide and nematocide for potato and vegetable crops. This chemical has been foimd in water wells in 11 states above the 1 ppm EPA safety threshold, barring use in some locales in 1982. According to Union Carbide, one manufacturer, humans can safely ingest 500 ppb. But it is one of the most acutely toxic pesticides registered by the EPA. A fourth carbamate insecticide is methomyl. 

Carbamates (carbaryl, benomyl, carbofuran, aldicarb, methomyl). Symptoms of exposure were nausea, dizziness, b listers, dermatitis, malaise, sweating, tearing, breathing difficulty, and chest tightness. Usually, incidents have occurred within 1 to 2 days after application except for aldicarb (up to 4 days after application). 

Methomyl, (m-s- butylphenylmethyl carbamate) Dichloromethane Gas liquid chromatography [313,314]... 

Similarly, on-column methylation has been applied to carbamate pesticides containing an active N-H group. Wien and Tanaka (41) showed that N-aryl carbamates are methylated on-column with tri-methylanilinium hydroxide-methanol to give the intact N-methyl and N-aryl derivatives. On the other hand N-methyl, 0-aryl carbamates such as carbaryl or carbofuran yielded only the methyl ethers of their respective phenols. This work has now been extended to sulfur-containing carbamates such as methomyl, methio-carb, aldicarb, etc. (42-43). Here the oxime hydrolysis products of these carbamates are chromatographed as the 0-methyl oximes. 

Resistance genes can be dominant, recessive, incompletely dominant, or incompletely recessive. Resistance to carbamates and organophosphates is usually dominant or incompletely dominant. Resistance to DDT, Bt, and spinosyns is usually recessive. Resistance to dieldrin is usually incompletely dominant. Resistance to pyrethroids is usually incompletely recessive. As shown in Figure 10.1 and 10.2, diamondback moth resistance to per-methrin was inherited as an incompletely recessive, autosomal factor, whereas resistance to methomyl was inherited as an incompletely dominant, autosomal factor. In cases of monofactorial inheritance of resistance to insecticides, the degree of dominance (D) in the progeny can be calculated, as described by Stone (1968), as follows ... 

Cross-resistance refers to a situation in which a strain that becomes resistant to one insecticide automatically develops resistance to other insecticides to which it has not been exposed. For example, selection of a strain of Spodoptera littoralis with fenvalerate resulted in a 33-fold increase in tolerance to fenvalerate. The resistant strain also showed resistance to other pyrethroids (11- to 36-fold) and DDT (lower than for the pyrethroids). Exposure of Cidex qninquefasciatus to fenitrothion resulted in the development of resistance to the carbamate insecticide propoxur. Similarly, selection of a housefly strain with permethrin resulted in a 600-fold increase in resistance to permethrin. The resistant strain also showed resistance to methomyl, DDT, dichlorvos, and naled (Hassall, 1990). 

Cotton is one of the crops most heavily reliant upon insecticide use. Although Bt cotton has been introduced in some areas, insecticide sprays remain as important components of cotton pest management programs. In some areas of the cotton belt, the majority of applications are made by aircraft. Issues which have been of regulatory concern in recent years include pest resistance associated with the frequent sprays, beneficial insect effects, worker exposure, and spray drift impacts on surfrice water quality. Products currently in use include organophosphates such as azinphos-methyl, methyl parathion, acephate, and disulfoton, pyrethroids such as lambda-cyhalodirin and carbamates such as methomyl. 

Most recently, there have been incidents in the USA where food has been intentionally contaminated with chemical insecticides. Not surprisingly, children were affected in these incidents. One incident occurred in 1998, where a restaurant s salt supply was contaminated with methomyl, a carbamate insecticide. It was reported that five children became ill after eating the insecticide-contaminated food (Buchholz et al, 2002). In another incident that occurred in 2003, approximately 200 pounds of ground beef were contaminated at a grocery store in Michigan with an insecticide called Black Leaf 40. Approximately 90 people (age range 1-76 years) became ill after ingesting the contaminated beef... 

Caibamate pesticides are used as insecticide, acaricide, and herbicide. Various subclasses can be distinguished. Aryl V-methyl carbamates (1), such as caibaiyl, carbofuran, propoxur, and oxime V-methyl carbamates(2), such as aldicaib, methomyl, oxamyl, have most widely been studied. LC-MS is the method-of-choice for carbamates, since their thermal lability prohibits GC analysis. 

The most important inhibitors of CarbEs are organo-phosphorus insecticides (malathion, parathion, para-oxon, methyl parathion, EPN, and others), nerve agents (DFP, soman, sarin, tabun, and VX) and carbamate insecticides (carbofuran, carbaryl, aldicarb, propoxur, oxamyl, methomyl, and others). Organo-phosphorus toxicants inhibit CarbEs irreversibly by phosphorylation and carbamates inhibit CarbEs reversibly by carbamylation similar to the basic mechanism (i.e., acylation of the active site) ... 

Methomyl exerts toxicity by inhibiting acetylcholinesterase. As with other carbamate insecticides, acetylcholinesterase inhibition is much less persistent than with organophosphate intoxication. 

Carbamates of acyclic hydroximidates and thiolhydroximidates have been reported to exhibit insecticidal and nematicidal activity (1-5). Included among these are the commercial materials methomyl and oxamyl. Derivatives of monocyclic thiolhydroximidates have also been described ( ). We wish to report a series of carbamates of bicyclic hydroximidates, thiolhydroximidates, and amidoximes which exhibit broad activity as insecticides and nematicides (7). 

Carbamates, first synthesized in the 1930s and commercialized in the 1960s, constitute the most recently developed class of anticholinesterase insecticides. Developed to replace the more dangerous CH and OP insecticides, their toxic principle derived from the effects on humans of the Calabar bean used in the West African trial by ordeal (Ecobichon 1997). Carbamates inhibit nervous tissue cholinesterases, but less irreversibly than OP insecticides, resulting in reduced toxicity (Ecobichon 1997). Common carbamate names include carbaryl, methomyl, and maneb. 

Cross enhancement was observed between carbofuran and all the aryl methylcarbamates examined except furathiocarb. The behaviour of the oximino methylcarbamates (aldicarb, methomyl, oxamyl) was more variable. Both aldicarb and cloethocarb enhanced soils showed cross enhancement to carbofuran and oxamyl. The chlorpropham enhanced soil was not cross enhanced to carbofuran. The carbamate enhanced soils were not cross enhanced to butylate, EPTC or phorate. 

The U.S.A., through the National Pesticide Survey, " which was organized by the Environmental Protection Agency (US-EPA), established a fist of compounds based on the amount used (>7000 Tons), water solubility (>30 mg/1), and hydrolysis half-life (>25 weeks). The list includes some carbamate pesticides (e.g., aldicarb, propoxur, carbaryl, carbofuran, methiocarb, methomyl, oxamyl, cycloate, butylate, propham, and swep) and various derivatives (e.g., aldicarb sulphone, aldicarb sulphoxide, and 3-hidroxycarbofiiran). In Europe, a list of priority pollutants including pesticides was established in order to protect the environment from the adverse ecological impact of these compounds. ... 

Carbamates, such as aldicarb, carbaryl, methomyl, or terbucarb — Carbamates have the following general structure ... 

Certain carbamates, such as, aldicarb and methomyl are classified by the U.S. EPA under Restricted Use Pesticides (RUP) because of their high acute toxicity to humans. Such RUP may only be purchased and used by certified applicators. Also, several carbamates are designated by the U.S. EPA as class P acutely toxic hazardous wastes. These compounds listed below in Table 45.1 are regulated under the category of discarded commercial chemical products, off-specification species, container residues and spills thereof. 

Methomyl (S-melhyl N[(melhylcarbamoyl)oxy] Ihioaceljmidale, Lannate, Nudrin [CAS 16752-77-5]) A carbamate-type cholinesterase inhibitor (see p 291). 

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