Atrazine ( ) is a chlorinated herbicide of the triazine class. It is used to prevent pre-emergence broadleaf weeds in crops such as maize (corn), soybean and sugarcane, and also in turf landscaping, such as golf courses and residential lawns. Atrazine is one of the most widely used herbicides in the United States, Canada, Australia, and Brazil, but has been banned in other countries including in the European Union and the Gulf Cooperation Council.
In general, use of this herbicide is controversial and often highly regulated.
, atrazine was the most common pesticide found in drinking water samples collected in the U.S.Gilliom RJ et al. US Geological Survey The Quality of Our Nation's Waters: Pesticides in the Nation's Streams and Ground Water, 1992–2001 March 2006, Revised February 15, 2007
Uses Atrazine is an herbicide that is used to stop pre- and post-emergence broadleaf and grassy weeds in crops such as sorghum, maize, sugarcane, lupins, pine, and eucalypt plantations, and triazine-tolerant canola. In the United States as of 2014, atrazine was the second-most widely used herbicide after glyphosate, with of it applied each year, nearly identical to its usage in 1974, of 76.8 million pounds.
Corn yields has been estimated to increase from 1% to 8%. In another study looking at combined data from 236 university corn field trials from 1986 to 2005, atrazine treatments showed an average increase of (~) than alternative herbicide treatments.Fawcett, Richard S. "Twenty Years of University Corn Yield Data: With and Without Atrazine ", North Central Weed Science Society , 2008 Effects on sorghum yields have been estimated to be as high as 20%, owing in part to the absence of alternative weed control products that can be used on sorghum.
Chemistry and biochemistry Atrazine was invented in 1958 in the Geigy laboratories as the second of a series of 1,3,5-triazines. (dead link 22 June 2022)
Atrazine is prepared from cyanuric chloride, which is treated sequentially with ethylamine and isopropylamine. Like other triazine herbicides, atrazine functions by binding to the plastoquinone-binding protein in photosystem II, which animals lack. Plant death results from starvation and oxidative damage caused by breakdown in the electron transport process. Oxidative damage is accelerated at high light intensity.
Atrazine has been found to act as an agonist of the G protein-coupled estrogen receptor 1. Atrazine has been shown to bind covalently to (chemically react with) a large number of mammalian proteins.
Degradation
Atrazine remains in soil for a matter of months (although in some soils can persist to at least four years) and can migrate from soil to groundwater; once in groundwater, it degrades slowly. The low rates of biodegradation are attributed to atrazine's low solubility. It has been detected in groundwater at high levels in some regions of the U.S. where it is used on some crops and turf. The U.S. Environmental Protection Agency expresses concern regarding contamination of surface waters (lakes, rivers, and streams). Atrazine rapidly degrades in the presence of reduced iron-bearing soil clays, such as ferruginous smectites.
Irradiation with 254 nm (ultraviolet light) degrades atrazine.Felix de Lima et al, "Photolytic Degradation of Herbicide Atrazine by Radiation Ultraviolet (UVC): An Application of Green Chemistry" , Chemical Science International Journal 17(3): 1-10, 2016
Biodegradation Atrazine biodegradation occur by two pathways:
Hydrolysis of the C-Cl bond is followed by the ethyl and isopropyl groups, catalyzed by the hydrolase enzymes called AtzA, AtzB, and AtzC. The end product of this process is cyanuric acid, itself unstable with respect to ammonia and carbon dioxide. The best characterized organisms that use this pathway are of Pseudomonas sp. strain ADP. Dealkylation of the amino groups gives 2-chloro-4-hydroxy-6-amino-1,3,5-triazine, the degradation of which is unknown. This path also occurs in Pseudomonas species, as well as a number of bacteria.
A common pathway for atrazine degradation involves the intermediate cyanuric acid, which can serve as a nitrogen source for aerobic microorganisms. Some aerobic atrazine degraders have been shown to use the compound for growth under anoxia in the presence of nitrate as an electron acceptor,
The genes for enzymes AtzA-C are highly conserved in atrazine-degrading organisms. The insertion elements flanking each gene suggest that they are involved in the assembly of this specialized catabolic pathway.
Toxicology According to Extension Toxicology Network in the U.S., "The oral median Lethal Dose or for atrazine is 3090 mg/kg in rats, 1750 mg/kg in mice, 750 mg/kg in rabbits, and 1000 mg/kg in hamsters. The dermal LD50 in rabbits is 7500 mg/kg. The 1-hour inhalation LC50 is greater than 0.7 mg/L in rats. The 4-hour inhalation LC50 is 5.2 mg/L in rats." The maximum contaminant level is 0.003 mg/L and the reference dose is 0.035 mg/kg/day.Pesticide Information Profile: Atrazine , Extension Toxicology Network (Cooperative Extension Offices of Cornell University, Oregon State University, the University of Idaho, and the University of California at Davis and the Institute for Environmental Toxicology, Michigan State University), June 1996.
Carcinogenicity In 2025, IARC updated the classification of atrazine to be "probably carcinogenic to humans" (Group 2A). A 2011 study that tracked 57,310 licensed American pesticide applicators over 13 years concluded that "there was no consistent evidence of an association between atrazine use and any cancer site".Beane Freeman, Laura E. (2011) Atrazine and Cancer Incidence Among Pesticide Applicators in the Agricultural Health Study (1994–2007) . Environmental Health Perspectives.
General reproductive health Studies suggest it is an endocrine disruptor, an agent that can alter the natural hormonal system.
Some studies have been complicated by poor reproducibility conflicts of interest, and accusations of retribution.
The U.S. EPA's Scientific Advisory Panel examined relevant studies and concluded in 2010, "atrazine does not adversely affect amphibian gonadal development based on a review of laboratory and field studies".Atrazine Updates: Amphibians , April 2010, EPA. It recommended proper study design for further investigation. As required by the EPA, two experiments were conducted under Good Laboratory Practices (GLP) and were inspected by EPA and German regulatory authorities, concluding 2009 that "long-term exposure of larval X. laevis to atrazine at concentrations ranging from 0.01 to 100 μg/L does not affect growth, larval development, or sexual differentiation".
Atrazine may affect reproduction of minnows.
A 2011 review of the mammalian reproductive toxicology of atrazine jointly conducted by the World Health Organization and the Food and Agriculture Organization of the United Nations concluded that atrazine was not teratogenic. Reproductive effects in rats and rabbits were only seen at doses that were toxic to the mother. Observed adverse effects in rats included fetal resorption in rates (at doses ≥50 mg/kg per day), delays in sexual development in female rats (at doses ≥30 mg/kg per day), and decreased birth weight (at doses ≥3.6 mg/kg per day).
A 2014 systematic review, funded by atrazine manufacturer Syngenta, assessed its relation to reproductive health problems. The authors concluded that the quality of most studies was poor and without good quality data, the results were difficult to assess, though it was noted that no single category of negative pregnancy outcome was found consistently across studies. The authors concluded that a causal link between atrazine and adverse pregnancy outcomes was not warranted due to the poor quality of the data and the lack of robust findings across studies. Syngenta was not involved in the design, collection, management, analysis, or interpretation of the data and did not participate in the preparation of the manuscript.
Aquatic impacts and regulation According to the U.S. EPA, the maximum allowable atrazine concentration in drinking water is 3 μg/L. This level was established in 2011 and remains in place in 2025.
Because it is pervasive in run-off, its impact on aquatic life has been scrutinized. A Natural Resources Defense Council report from 2009 said that the EPA is ignoring atrazine contamination in surface and drinking water in the central United States. Atrazine has a negative impact on aquatic life.
In 2010, the Australian Pesticides and Veterinary Medicines Authority (APVMA) tentatively concluded that environmental atrazine "at existing levels of exposure" was not affecting amphibian populations in Australia consistent with the 2007 U.S. EPA findings.Chemicals in the News: Atrazine, Australian Pesticides and Veterinary Medicines Authority, Original June 30, 2010, Archived by Internet Archive July 4, 2010 APVMA responded to Hayes' 2010 published paper, that his findings "do not provide sufficient evidence to justify a reconsideration of current regulations which are based on a very extensive dataset".
Regulatory action
Its use was banned in the European Union in 2004.European Commission. 2004/248/EC: Commission Decision of 10 March 2004 concerning the non-inclusion of atrazine in Annex I to Council Directive 91/414/EEC and the withdrawal of authorisations for plant protection products containing this active substance (Text with EEA relevance) (notified under document number C(2004) 731) Danny Hakimfeb for the New York Times. February 23, 2015. A Pesticide Banned, or Not, Underscores Trans-Atlantic Trade Sensitivities
In Canada, the PMRA allowed the product's registration to remain unchanged in 2015. For context, the EU's ban was based on a maximum acceptable pollutant level of 0.1 μg/L. The U.S. drinking water standard is 3 μg/L; the Canadian standard is 5 μg/L.
Legal actions In 2012, Syngenta, an atrazine manufacturer, was the defendant in a class-action lawsuit concerning the levels of atrazine in human water supplies. Syngenta agreed to pay $105 million to reimburse more than one thousand water systems for "the cost of filtering atrazine from drinking water". The company denied all wrongdoing.City of Greenville v. Syngenta Crop Protection, Inc., and Syngenta AG Case No. 3:10-cv-00188-JPG-PMF , accessed August 23, 2013Clare Howard for Environmental Health News. June 17, 2013 Special Report: Syngenta's campaign to protect atrazine, discredit critics.
See also Pesticides in the United States – Atrazine Endocrine disruptor Simazine
References
External links Atrazine- PubChem(National library of medicine) - atrazine Atrazine Fact Sheet - National Pesticide Information Center - Atrazine Fact Sheet Atrazine - CDC - NIOSH Pocket Guide to Chemical Hazards