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|Molar mass||269.767 g/mol|
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Alachlor is an herbicide from the chloroacetanilide family. It is an odorless, white solid. The greatest use of alachlor is for control of annual grasses and broadleaf weeds in crops. It is the second most widely used herbicide in the United States. Use of alachlor as a herbicide is banned in the European Union.
Its mode of action is elongase inhibition, and inhibition of geranylgeranyl pyrophosphate (GGPP) cyclisation enzymes, part of the gibberellin pathway. It is marketed under the trade names Alanex, Bronco, Cannon, Crop Star, Intrro, Lariat, Lasso, Micro-Tech and Partner.
The largest use of alachlor is as a herbicide for control of annual grasses and broadleaf weeds in crops, primarily on corn, sorghum and soybeans. It is the second most widely used herbicide in the United States, with particularly heavy use on corn and soybeans in Illinois, Indiana, Iowa, Minnesota, Nebraska, Ohio and Wisconsin.
Alachlor mixes well with other herbicides. It is marketed in mixed formulations with atrazine, glyphosate, trifluralin and imazaquin. It is a selective, systemic herbicide, absorbed by germinating shoots and by roots. Its mode of action is elongase inhibition, and inhibition of geranylgeranyl pyrophosphate (GGPP) cyclisation enzymes, part of the gibberellin pathway. Stated more simply, it works by interfering with a plant's ability to produce protein and by interfering with root growth.
It is most commonly available as microgranules containing 15% active ingredients (AI), or emulsifiable concentrate containing 480 g/ litre of AI. Homologuation in Europe requires a maximum dose of 2,400 g per hectare of AI, or 5 litres/hectare of emulsifiable concentrate or 17 kg/ha of microgranules. The products are applied as either pre-drilling, soil incorporated or pre-emergence.
The United States Environmental Protection Agency (EPA) classifies the herbicide as toxicity class III - slightly toxic. The Maximum Contaminant Level Goal (MCLG) for Alachlor is zero, to prevent long-term effects. The Maximum Contaminant Level (MCL) for drinking water is two parts per billion (2 ppb).
The EPA cited the following long-term effects for exposures at levels above the MCL in drinking water exposed to runoff from herbicide used on row crops: slight skin and eye irritation; at lifetime exposure to levels above the MCL: potential damage to liver, kidney, spleen; lining of nose and eyelids; cancer. The major source of environmental release of alachlor is through its manufacture and use as a herbicide. Alachlor was detected in rural domestic well water by EPA's National Survey of Pesticides in Drinking Water Wells. EPA's Pesticides in Ground Water Database reports detections of alachlor in ground water at concentrations above the MCL in at least 15 U.S. states.
Alachlor is a controlled substance under Australian law and is listed as a Schedule 7 (Dangerous Poison) substance. Access, use and storage are strictly controlled under state and territory law. Since 2006, use of alachlor as a herbicide has been banned in the European Union.
In "a judgment that could lend weight to other health claims against pesticides," in January, 2012 a French court found Monsanto, which manufactures Lasso, liable for chemical poisoning of a French farmer in 2004. In 2015 a French appeals court upheld the ruling and ordered the company to "fully compensate" the grower.
Alachlor exhibits moderate sorption in soil, ranging from 43-209 mL/g. Photodegradation is a minor contributor to alachlor fate. Degradation in soil appears to be largely biologically mediated, and produces multiple metabolites. The half life in aerobic soil ranges from about 6 to 15 days and is considerably shorter under anaerobic conditions. One possible explanation for the short anaerobic half life is the observation that alachlor is rapidly transformed under anoxia to up to 14 degradation products in the presence of iron-bearing ferruginous smectites. The iron in such minerals can be used by certain soil bacteria as an electron acceptor when soils are flooded, thus the process of herbicide transformation by reduced clay is thought to be microbially mediated. Similar observations have been reported for the herbicides trifluralin and atrazine.
Alachlor is often used in high school chemistry classrooms as a reactant in demonstrations such as the combustion of magnesium. Alachlor can be used as a substitution for methane gas in such an experiment when gas is not available.
- "Consumer Factsheet on: ALACHLOR" (PDF). National Primary Drinking Water Regulations. United States Environmental Protection Agency (EPA. Retrieved 4 September 2015. Cite error: Invalid
<ref>tag; name "Consumer_Factsheet_on:_ALACHLOR" defined multiple times with different content (see the help page).
- Thomas D. Boyer, Michael Peter Manns, Arun J. Sanyal, David Zakim (1990). "Zakim and Boyer's Hepatology: A Textbook of Liver Disease". Saunders, 1990. p. 486. Retrieved 4 September 2015.
- Arnold P. Appleby, Franz Müller, Serge Carpy “Weed Control“ in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a28_165
- Cornell Herbicide Profile
- "EXTOXNET PIP - ALACHLOR". orst.edu. Retrieved 17 May 2015.
- "e-phy". Ministère de l'agriculture, de l'agroalimentaire (in French). Retrieved 30 April 2013.
- US EPA Consumer Factsheet
- "Poisons Standard 2013". comlaw.gov.au. Retrieved 17 May 2015.
- Douet, Marion (13 February 2012). "Monsanto guilty of chemical poisoning in France". Reuters. Retrieved 30 April 2013.
- "French court confirms Monsanto liable in chemical poisoning case". Reuters. 2015-09-11. Retrieved 2015-09-15.
- Vencill, W.K. 2002. WSSA herbicide handbook (8th edition). Weed Science Society of America. Lawrence, KS, USA. ISBN 1-891276-33-6.
- Xu, J., J. W. Stucki, J. Wu, J. Kostka, and G. K. Sims. 2001. Fate of atrazine and alachlor in redox-treated ferruginous smectite. Environmental Toxicology & Chemistry 20: 2717-2724.
- Kappa, Bromide 2013. Substitutions for methane gas in high school combustion demonstrations.