Atrazine
Atrazine is a chlorinated herbicide of the triazine class. It is used to prevent pre-emergence broadleaf weeds in crops such as maize, soybean and sugarcane, and also in turf landscaping, such as golf courses and residential lawns. Its use significantly increases crop yields. 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. Its use is controversial and highly regulated.
, atrazine was the most common pesticide found in drinking water in the U.S.
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.Atrazine has a dramatic positive impact on crop yields. 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. 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.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 a large number of mammalian proteins.
Degradation
Atrazine remains in soil for a matter of months 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. Atrazine rapidly degrades in the presence of reduced iron-bearing soil clays, such as ferruginous smectites.Irradiation with 254 nm degrades atrazine.
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.
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.Cancer
In 2025, IARC updated the classification of atrazine to be "probably carcinogenic to humans". 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".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". It recommended proper study design for further investigation. As required by the EPA, two experiments were conducted under Good Laboratory Practices 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, delays in sexual development in female rats, and decreased birth weight.
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 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. 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.In Canada, the PMRA allowed the product's registration unchanged in 2015. For context, the EU's ban was based on a pollutant level of 0.1 μg/L and the U.S. drinking water standard is 3 μg/L, the Canadian standard is 2.32 μg/L.