Names | |
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Preferred IUPAC name 3,5-Dimethyl-4-(methylsulfanyl)phenyl methylcarbamate | |
Other names Mercaptodimethur Mesurol | |
Identifiers | |
3D model (JSmol) | |
1881431 | |
ChEBI | |
ChEMBL | |
ChemSpider | |
ECHA InfoCard | 100.016.357 |
EC Number |
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KEGG | |
MeSH | Methiocarb |
PubChem CID | |
UNII | |
CompTox Dashboard (EPA) | |
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Properties | |
C11H15NO2S | |
Molar mass | 225.312 |
Appearance | Colourless crystals |
Density | 1.25 g cm−3 |
Melting point | 118.5 °C (245.3 °F; 391.6 K) |
Boiling point | 311 °C (592 °F; 584 K) (degrades at 300 °C or 572 °F or 573 K) |
0.027 g L−1 | |
Solubility in Xylene | 20 g L−1 |
Solubility in Acetone | 144 g L−1 |
Solubility in Ethyl acetate | 87 g L−1 |
Solubility in 1-Octanol | 31 g L−1 |
log P | 3.18 |
Vapor pressure | .015 mPa |
Henry's law constant (kH) | .12 mPa m3 mol−1 |
Hazards | |
Occupational safety and health (OHS/OSH): | |
Main hazards | Skin irritant, neurotoxin |
Flash point | Not highly flammable |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Methiocarb is a carbamate pesticide (an acetylcholinesterase inhibitor) which is used as an insecticide, [1] [2] bird repellent, [3] acaricide [2] and molluscicide [2] since the 1960s. Methiocarb has contact and stomach action on mites and neurotoxic effects on molluscs. Seeds treated with methiocarb also affect birds. Other names for methiocarb are mesurol [4] and mercaptodimethur.
Due to its toxicity, methiocarb approval as a plant protection product has been withdrawn by the EU effective 2020. [5]
The carbamate functional group in methiocarb can be cleaved by cholinesterase to result in the carbamate, which binds to the cholinesterase, and the phenol.
Methiocarb (3) is synthesised by Bayer from 4-methylthio-3,5-xylenol (1) and methyl isocyanate (2). [6] The xylenol (1) will act as the nucleophile in this reaction attacking the partially positively charged carbon in the isocyanate (2).
Methiocarb acts by acetylcholinesterase inhibition. [1] The product of the cleavage of the carbamate group of methiocarb is methylcarbamic acid which is bound to cholinesterase after the reaction. The normal function of cholinesterase is to cleave the acetyl-choline bond which results in the binding of acetic acid to cholinesterase which is a fast reversible reaction. The carbamic acid also reversibly binds but the hydrolysis of the bond is slower and therefore the acid inhibits the function of cholinesterase which results in elevated acetylcholine levels. In comparison: organophosphates inhibit irreversibly and will therefore inhibit the acetylcholinesterase even more.[ citation needed ]
In addition to its cholinergic effects, methiocarb has been found to be an endocrine disruptor, acting as an estrogen, antiandrogen, and aromatase inhibitor. [7]
Methiocarb is biotransformed in the liver mainly by sulfoxidation. This can happen to methiocarb itself but also to the phenol group which is cleaved from methiocarb by choline-esterase. In some cases this same sulfur can be oxidised once more to give the sulfone. A minor pathway that occurs is the hydroxylation of the N-methyl. [8] [9]
Methiocarb can be taken up through different routes. The most common for humans is up take through the skin or as an aerosol, because of its use as a pesticide in agriculture. For insects and birds this would be by the oral route. The NOAEL's of these routes have been determined as follows: For the oral route, the NOAEL is set to 3.3 mg/kg per day for rats, based on a 2-year study. For absorption through the skin the NOAEL is set to 150 mg/kg per day for rabbits, based on the reduction of food consumption. [8]
When methiocarb is fed to rats at a dose of 50 ppm, it gives a reduction of brain cholinesterase by 14% and 5% in males and females respectively. When methiocarb is administered as an aerosol to rats, the highest concentration (96 mg/m3 in solvent) showed signs of involuntary muscle contraction (tremors). These signs weren't observed in the other groups. The brain acetylcholine esterase is reduced in comparison to the solvent controls, to 61% and 74% for males and females respectively. There were no changes in organ weight. The NOAEL was determined to be 6 mg/m3 based on the reduction of brain acetylcholine esterase activity. [8]
To determine the distribution of methiocarb through the body carbon-14 ([14C]) labeled methiocarb studies have been performed on rats. About 8 hours after IP injection of [14C]methiocarb more than 20 is present in the kidneys, 14 in the lungs, 14 in the heart, 6 in the body fat and 26 in the red blood cells. All the numbers are a measure of the radioactivity in dpm x 103/g of dried tissue. 30 Minutes after treatment gave, for all tissues except bodyfat, much higher values indicating that elimination takes place shortly after injection. Also, an increase in all tissues except the red blood cells has been observed between 2 and 4 hours after injection. This indicates that after two hours redistribution takes place shortly followed by elimination. This radioactivity study only measured the [14C] so the compound could already be metabolized to different compounds with different toxicities, which is not indicated in this study. [10]
Exposure | Acute toxicity |
---|---|
Dermal LD50(mg/kg bodyweight) | |
Rabbit | >2000 [8] |
Rat | >200 [8] |
Inhalation (1 hour) LC50(mg/m3) | |
Rat | 1200 [8] |
Intraperitoneal LD50(mg/kg bodyweight) | |
Mouse | 6 [8] |
Oral LD50(mg/kg bodyweight) | |
Dog | 10 [8] |
Guinea Pig | 40 [8] |
Mouse | 25 [8] |
Rat | 30 [8] |
In rats the cholinesterase activity fell down to 50 percent of the control values in 27 days where the dose applied in their diet was 2 mg/ kg bw in the first three days and 4 mg/kg bw for the next 24 days. No abnormal clinical signs were observed. [8] [11] In rabbits methiocarb was applied to the skin to a group of ten at doses of 0, 60, 150 or 375 mg/kg bw per day for 6 h/day. Two out of ten rabbits with the low dose did not survive and with the high dose had a reduced food consumption. Cholinesterase activity was reduced in males with a high dose at 14 and 21 days of treatment. There were no intergroup differences observed in cholinesterase activity among females. The erythrocyte acetylcholinesterase activity is apparently not inhibited in a dose-related fashion. The duration of the study was 24 days. [8] [12]
In mice, a one-year study of 50 males and 50 females was performed. The mice received diets containing methiocarb at doses of 0, 15, 43 and 130 mg/kg bw per day in males and 0, 20, 57, and 170 mg/kg bw per day in females. Food consumption, behaviour and mortality rate were not affected at any dose. At one month the decrease in plasma acetylcholinesterase activity was the highest and the smallest reductions were observed at 24 months. Brain acetylcholinesterase activity was also lowered, more in males than in females. [8] [13] [14] In rats a two-year study of 60 rats was performed. The rats received diets containing 0, 3.3, 9.3 and 29 mg/kg bw per day for males and 0, 5, 14, and 42 mg/kg bw per day for females. Food consumption, behaviour and mortality rate were not affected at any dose. The total protein concentrations were raised at higher doses of methiocarb. The plasma acetylcholinesterase activity was lowered at the high dose at day one and from eight weeks onwards in males and at day one and 1, 2, 4 and 13 weeks in females. No brain acetylcholinesterase activity was observed. [8] [15] [16]
Because methiocarb is widely used as an insecticide on crops, environmental risks were also studied to establish safety risks for human health. The metabolism of methiocarb in plants, soil and water have been proposed from radiolabeled [14C]methiocarb studies. In plants, the major metabolites were methiocarb sulfoxide and methiocarb sulfoxide phenol. Environmental fate in water and soil has been determined from the metabolites formed by anaerobic as well as aerobic degradation, photolysis, adsorption and leaching of methiocarb. In soil the half life of methiocarb sulfone phenol is 20 days, methiocarb sulfoxide phenol is 2 days, methiocarb 1.5 days and methiocarb sulfoxide 6 days. Methiocarb is mainly metabolized to methiocarb phenol and minor to methiocarb sulfoxide and methiocarb sulfoxide phenol. Also after 217 days no methiocarb or metabolites are present anymore in the soil. This is because a lot of gets metabolized to CO2. In water, no methiocarb was present already after 32 days. The half life of methiocarb in water is strongly pH dependent but at pH 7 the half life is about 28 days. [17]
Methiocarb is used as toxin for different purposes. It ranges from snails, insects, rodents and even as a bird repellent. As an insecticide it is effective for thrips and has a low dose that is lethal for these animals. The LC99,99 for suspension concentrate is 0.34 g/L and for the wettable powder it is 2.30, which is a bit too much for effective use. [18]
For the use as a molluscicide methiocarb is effective, but at a high dose. In a research with E. vermiculata, methiocarb showed to be the most effective as topical applicant (although DMSO was used as a solvent). The LD50 is 414 μg per snail and the LD99,99 is roughly estimated 1400 μg per snail for methiocarb. In comparison to methomyl which was more effective, with its LD50 was 90 μg per snail. Which is a lot lower than the LD50 of methiocarb. [19]
As snail bait methiocarb has the same effectiveness as methomyl for 1% (mass percent) and 2%. but the LC50 of methiocarb is higher than the one of methomyl. 0.93:0.31. They both reached an average mortality of 85%, by the use of 2% methiocarb/methomyl bait. [19]
In another comparison study (with Monacha obstructa ) between methiocarb and methomyl. Methomyl showed again to be more effective. The LD50 in this study were 12 μg per snail for methomyl and 27 μg per snail for methiocarb. These compound were topically applied on the snails and these compounds were first dissolved in 95% ethanol and diluted with water to make the concentrations. [20]
As an avian repelled to protect fruit, methiocarb was in one research not effective. The birds still damaged the figs. This happened because the methiocarb was sprayed on the fruit. The birds pinched the fruits or peeled the skin of the fruit and ate the meat of the figs. In that manner these birds are very little or not exposed to the repellent. [21]
In another study with quelea, it was investigated if methiocarb had an adverse effect on the food choice. It showed that when quelea ate seeds with methiocarb, the next time they would choose some other food. This shows that methiocarb can be effective as a bird repellent. [22]
In one study methiocarb is shown to be not very effective against mice as a rodenticide. In the first field trial, snail pellets of methiocarb were spread across the land and killed almost 23% of the initial mice population in one night, but the population did not decrease (probably because of reinvasion of the neighbouring land). There hasn't been searched for carcasses after that, but birds were seen scavenging on carcasses. In the second field trial, grain was covered in methiocarb and strychnine and it showed a mortality rate of 40% for methiocarb and 90% for strychnine. Although methiocarb seems to be effective at first. Mice develop an aversion for the methiocarb, which makes it not very effective as rodenticide. [23]
Methiocarb is a plant protection agent and while suicide with these type of toxins is rare, there is one case reported of a suicide with methiocarb. An 80-year-old woman in Germany killed herself by drinking a bottle of Mesurol. The red/pink fluid was on her clothes, face, and hands (probably because of the vomiting) and in the gastrointestinal tract as in the respiratory tract. The toxicological examination showed that the methiocarb uptake wasn't completed and the concentration of methiocarb and its metabolite in the urine was low. This is due to the short duration of exposure. Elevated concentration of methiocarb may be the result of post-mortem uptake, but it could also be the post-mortem redistribution of methiocarb and metabolites from the gastrointestinal tract. The conclusion of the toxicological examination was death by acute poisoning of methiocarb. [24]
The amount of methiocarb in the stomach is calculated to compare it with the LD50 of rats. The amount of methiocarb is estimated to have been 6.1 gram (by a stomach volume of 1L). The weight of this woman was 53 kg. That would make 115 mg/kg bw. When compared to the LD50 for rats, which is 30 mg/kg, it is reasonable to say that this woman died of poisoning from methiocarb. Bear in mind that this is only the amount of methiocarb found in the stomach and that the rest was already methiocarb distributed through the body. [24]
Matrix | Concentration of methiocarb | Semiquantative detection of methiocarb-metabolite† | Concentration ratio methiocarb/metabolite |
---|---|---|---|
Stomach | 6100 μg/mL | 65 μg/mL | 94:1 |
Liver | 25 μg/g | 10 μg/g | 2.5:1 |
Kidney | 11 μg/g | Not detected | - |
Heart blood | 4.0 μg/mL | 3.6 μg/g | 1.1:1 |
Femoral vein blood | Not detected | 12 μg/mL | - |
Brain | 2.5 μg/g | Not detected | - |
Bile | 2.0 μg/g | Not detected | - |
Urine | 1.9 μg/mL | 1.5 μg/mL | 1.3:1 |
†Semiquantitative analysis was performed by the approximation of similar extinction coefficients of mercaptodimethur and its metabolite descarbamoylmercaptodimethur at wavelength 200 nm. [24]
Carbofuran is a carbamate pesticide, widely used around the world to control insects on a wide variety of field crops, including potatoes, corn and soybeans. It is a systemic insecticide, which means that the plant absorbs it through the roots, and from there the plant distributes it throughout its organs where insecticidal concentrations are attained. Carbofuran also has contact activity against pests. It is one of the most toxic pesticides still in use.
Carbaryl is a chemical in the carbamate family used chiefly as an insecticide. It is a white crystalline solid previously sold under the brand name Sevin, which was a trademark of the Bayer Company. The Sevin trademark has since been acquired by GardenTech, which has eliminated carbaryl from most Sevin formulations. Union Carbide discovered carbaryl and introduced it commercially in 1958. Bayer purchased Aventis CropScience in 2002, a company that included Union Carbide pesticide operations. Carbaryl was the third-most-used insecticide in the United States for home gardens, commercial agriculture, and forestry and rangeland protection. As a veterinary drug, it is known as carbaril (INN).
Imidacloprid is a systemic insecticide belonging to a class of chemicals called the neonicotinoids which act on the central nervous system of insects. The chemical works by interfering with the transmission of stimuli in the insect nervous system. Specifically, it causes a blockage of the nicotinergic neuronal pathway. By blocking nicotinic acetylcholine receptors, imidacloprid prevents acetylcholine from transmitting impulses between nerves, resulting in the insect's paralysis and eventual death. It is effective on contact and via stomach action. Because imidacloprid binds much more strongly to insect neuron receptors than to mammal neuron receptors, this insecticide is more toxic to insects than to mammals.
Chlorfenvinphos is an organophosphorus compound that was widely used as an insecticide and an acaricide. The molecule itself can be described as an enol ester derived from dichloroacetophenone and diethylphosphonic acid. Chlorfenvinphos has been included in many products since its first use in 1963. However, because of its toxic effect as a cholinesterase inhibitor it has been banned in several countries, including the United States and the European Union. Its use in the United States was discontinued in 1991.
Ethion (C9H22O4P2S4) is an organophosphate insecticide. It is known to affect the neural enzyme acetylcholinesterase and disrupt its function.
Demeton-S-methyl is an organic compound with the molecular formula C6H15O3PS2. It was used as an organothiophosphate acaricide and organothiophosphate insecticide. It is flammable. With prolonged storage, Demeton-S-methyl becomes more toxic due to formation of a sulfonium derivative which has greater affinity to the human form of the acetylcholinesterase enzyme, and this may present a hazard in agricultural use.
Aldicarb is a carbamate insecticide which is the active substance in the pesticide Temik. It is effective against thrips, aphids, spider mites, lygus, fleahoppers, and leafminers, but is primarily used as a nematicide. Aldicarb is a cholinesterase inhibitor which prevents the breakdown of acetylcholine in the synapse. Aldicarb is considered "extremely hazardous" by the EPA and World Health Organization and has been banned in more than 100 countries. In case of severe poisoning, the victim dies of respiratory failure.
Azinphos-methyl (Guthion) is a broad spectrum organophosphate insecticide manufactured by Bayer CropScience, Gowan Co., and Makhteshim Agan. Like other pesticides in this class, it owes its insecticidal properties to the fact that it is an acetylcholinesterase inhibitor. It is classified as an extremely hazardous substance in the United States as defined in Section 302 of the U.S. Emergency Planning and Community Right-to-Know Act, and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.
Phosmet is a phthalimide-derived, non-systemic, organophosphate insecticide used on plants and animals. It is mainly used on apple trees for control of codling moth, though it is also used on a wide range of fruit crops, ornamentals, and vines for the control of aphids, suckers, mites, and fruit flies.
Dinoseb is a common industry name for 6-sec-butyl-2,4-dinitrophenol, a herbicide in the dinitrophenol family. It is a crystalline orange solid which does not readily dissolve in water. Dinoseb is banned as an herbicide in the European Union (EU) and the United States because of its toxicity.
Demeton, sold as an amber oily liquid with a sulphur like odour under the name Systox, is an organophosphate derivative causing irritability and shortness of breath to individuals repeatedly exposed. It was used as a phosphorothioate insecticide and acaricide and has the chemical formula C8H19O3PS2. Although it was previously used as an insecticide, it is now largely obsolete due to its relatively high toxicity to humans. Demeton consists of two components, demeton-S and demeton-O in a ratio of approximately 2:1 respectively. The chemical structure of demeton is closely related to military nerve agents such as VX and a derivative with one of the ethoxy groups replaced by methyl was investigated by both the US and Soviet chemical-weapons programs under the names V-sub x and GD-7.
Carbophenothion also known as Stauffer R 1303 as for the manufacturer, Stauffer Chemical, is an organophosphorus chemical compound. It was used as a pesticide for citrus fruits under the name of Trithion. Carbophenothion was used as an insecticide and acaricide. Although not used anymore it is still a restricted use pesticide in the United States. The chemical is identified in the US as an extremely hazardous substance according to the Emergency Planning and Community Right-to-Know Act.
Carbosulfan is an organic compound adherent to the carbamate class. At normal conditions, it is brown viscous liquid. It is not very stable; it decomposes slowly at room temperature. Its solubility in water is low but it is miscible with xylene, hexane, chloroform, dichloromethane, methanol and acetone. Carbosulfan is used as an insecticide. The European Union banned use of carbosulfan in 2007.
Sulfotep (also known as tetraethyldithiopyrophosphate and TEDP) is a pesticide commonly used in greenhouses as a fumigant. The substance is also known as Dithione, Dithiophos, and many other names. Sulfotep has the molecular formula C8H20O5P2S2 and belongs to the organophosphate class of chemicals. It has a cholinergic effect, involving depression of the cholinesterase activity of the peripheral and central nervous system of insects. The transduction of signals is disturbed at the synapses that make use of acetylcholine. Sulfotep is a mobile oil that is pale yellow-colored and smells like garlic. It is primarily used as an insecticide.
Ethoprophos (or ethoprop) is an organophosphate ester with the formula C8H19O2PS2. It is a clear yellow to colourless liquid that has a characteristic mercaptan-like odour. It is used as an insecticide and nematicide and it is an acetylcholinesterase inhibitor.
Triamiphos (chemical formula: C12H19N6OP) is an organophosphate used as a pesticide and fungicide. It is used to control powdery mildews on apples and ornamentals. It was discontinued by the US manufacturer in 1998.
Triazofos is a chemical compound used in acaricides, insecticides, and nematicides.
Ethiofencarb is a carbamate insecticide which is useful in controlling aphids on hard and soft fruits and some vegetables. It is not as dangerous as organophosphorous pesticides, but is considered highly toxic to humans in the UK, moderately toxic under US EPA classification, and highly toxic to aquatic life.
EPN is an insecticide of the phosphonothioate class. It is used against pests such as European corn borer, rice stem borer, bollworm, tobacco budworm, and boll weevil.
Cadusafos is a chemical insecticide and nematicide often used against parasitic nematode populations. The compound acts as a acetylcholinesterase inhibitor. It belongs the chemical class of synthetic organic thiophosphates and it is a volatile and persistent clear liquid. It is used on food crops such as tomatoes, bananas and chickpeas. It is currently not approved by the European Commission for use in the EU. Exposure can occur through inhalation, ingestion or contact with the skin. The compound is highly toxic to nematodes, earthworms and birds but poses no carcinogenic risk to humans.
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