Methomyl toxicity

Gupta, R. C., Goad, J. T and Kadel. W. L. (1994). Enei y related metabolic alterations in diaphragm muscle resulting from acute methomyl toxicity. Heurotoxicology 15, 321-330. 

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. 

Insecticide methomyl is a very toxic pesticide and is highly soluble in water (57.9 g/1). It has a low sorption affinity to soil and can cause groundwater and surface water contamination in agricultural areas. Solubilities of methomyl in different solvents are in methanol 1000 g/1, in aceton 730 g/1, in ethanol 420 g/1, in isopropanol 220 g/1, in toluene 30 g/1. 

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. ... 

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. 

As In the case of the examples given in Tables I and III, the N-thiocarbamate derivatives were generally equal to the parent methylcarbamate in toxicity to house flies, particularly after taking into consideration Increase in molecular weights. Except for the methomyl and oxan l derivatives, substantial improvement in mosquito larvlcldal activity again appeare d to be a function of the lipophilic properties of the derivative. With the exception of the oxanyl derivatives, the data clearly indicate that the N-thiocarbamate derivatives are markedly less toxic to the white mouse than the parent methylcarbamate. Since... 

Methomyl, a highly toxic compound in the EPA s toxicity class I, is a restricted insecticide. 

Methomyl Chlorophenoxy compounds Chronic toxicity, mutagenicity... 

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. 

In a 2 year feeding study in dogs, the no-observed-adverse-effect level was 5 mg kg day . Methomyl is not teratogenic or a reproductive toxicant. 

Because of its rapid biotransformation, methomyl does not tend to cause cumulative toxicity. However, repeated, frequent exposures could lead to cumulative inhibition of cholinesterase, resulting in flu-like symptoms including weakness, loss of appetite, and myalgia. 

Methomyl is highly toxic to birds (oral LD50 in quail was 24-34 mg kg 28 mg kg in chickens, and 10-45 mg kg in other species). Methomyl is... 

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. 

The spectrum of action of methomyl is similar to that of aldicarb (37), but its toxicity to warm-blooded organisms is lower the lDj for rats being 26 mg/kg. 

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. 

Thlodicarb is a new insecticide being marketed by Union Carbide as Larvin for the control of insects on cotton. Thiodicarb is metabolized in the rat to acetamide, acetonitrile, CO, methomyl, and methomyl metabolites. No illnesses have been reported among applicators or field workers coming in contact with this carbamate insecticide. Thiodicarb is somewhat more persistent on crops than methomyl and is less toxic dermally in rabbit studies. The dermal dose-CliE response study showed that a dose of 33 mg/kg produced 50% ChE inhibition 24 hr. after the application of the dose, while a dose of 87 mg/kg of thiodicarb did not produce more inhibition than a dose of 44 mg/kg. The poor solubility of this carbamate in water/lipid most likely prevented the absorption of additional quantities of thiodicarb, thereby reducing its toxicity. Thiodicarb was found in lower concentrations in skin than either parathion or carbaryl during the percutaneous absorption studies. The concentrations in plasma. 

Bayer CropScience, LLC Institute, West Virginia, United States A runaway chemical reaction during startup of the methomyl unit resulted in explosion, fire, and release of toxic gas Two fatalities eight injuries destruction of equipment Reduction in technical advisors without ensuring their knowledge was retained elsewhere on staff capital project personnel unfamiliar with control system and process 4,5... 

Farre, M. et al.. Analysis and toxicity of methomyl and ametiyn after biodegradation. Anal. Bioanal. Chem., 373, 704,2002. 

Carbamates include aldicarb, methiocarb, methomyl, carbofuran, ben-diocarb and oxamyl. Although they are broad-spectrum insecticides, with moderate toxicity and persistence, they rarely bioaccumulate or cause major environmental impacts [25],... 

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