Atrazine

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Name = Atrazine
ImageFile = Atrazin.png ImageName = Atrazine
ImageFile1 = Atrazine-3D-balls.png ImageName1 = Atrazine
IUPACName = 1-chloro-3-ethylamino-5-isopropylamino-2,4,6-triazine
OtherNames = Atrazine
See also [http://www.chemindustry.com/chemicals/521112.html synonyms]
Section1 = Chembox Identifiers
SMILES = ClC1=NC(NC(C)C)=NC(NCC)=N1
CASNo = 1912-24-9
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C=8|H=14|Cl=1|N=5
Appearance = colorless solid
Density = 1.187 g/cm³
Solubility = 0.007 g/100 mL (?°C)
MeltingPt = 175 °C (448 K)
BoilingPt = 200 °C (473 K)
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Atrazine, 2-chloro-4-(ethylamine)-6-(isopropylamine)-s-triazine, an organic compound consisting of an s-triazine-ring is a widely used herbicide. Its use is controversial due to its effects on nontarget species, such as on amphibians.cite news | author = Jennifer Lee | title = Popular Pesticide Faulted for Frogs' Sexual Abnormalities | date = 2003-06-19 | publisher = The New York Times | url = http://query.nytimes.com/gst/fullpage.html?res=9A05E6DB1138F93AA25755C0A9659C8B63] Like many commercial products, it is sold under numerous trade names. Although banned in the European Union, it is one of the most widely used herbicides in the U.S. with 77 million lb applied in 2003.

Uses

Atrazine is used to stop pre- and post-emergence broadleaf and grassy weeds in major crops by binding to the plastoquinone-binding protein in photosystem II, inhibiting electron transport. Atrazine and its derivatives are also used in many industrial processes, including the production of some dyes and explosives.Fact|date=June 2008 Atrazine is the most widely used herbicide in conservation tillage systems, which are designed to prevent soil erosion.

Its effect on yields has been estimated from 6% to 1%, with 3-4% being the conclusion of an extensive review.Frank Ackerman. (2007). " [ase.tufts.edu/gdae/Pubs/rp/EconAtrazine.pdf The Economics of Atrazine] . "Int J Occup Environ Health] .]

Biodegradation

The half-life of atrazine in soil is 13 to 261 days. [ [http://www.epa.gov/oppsrrd1/REDs/atrazine_combined_docs.pdf Interim Reregistration Eligibility Decision for Atrazine] , U.S. EPA, January, 2003.] Atrazine biodegradation can occur by two known pathways:

1) Atrazine can be dechlorinated followed by removal the other ring substituents via amidohydrolases by the enzymes AtzA, AtzB, and AtzC. The end product is cyanuric acid. The best characterized organism that performs this pathway is "Pseudomonas" sp. strain ADP.

2) The other pathway involves dealkylation of the amino groups. Subsequent dechlorination yields cyanuric acid. The end result is 2-chloro-4-hydroxy-6-amino-1,3,5-triazine, which currently has no known path to further degradation. This path occurs in "Pseudomonas" species and a number of bacteria. [Zeng Y, Sweeney CL, Stephens S, Kotharu P. (2004). Atrazine Pathway Map. Wackett LP. Biodegredation Database.] cite journal |author=Wackett LP, Sadowsky MJ, Martinez B, Shapir N |title=Biodegradation of atrazine and related s-triazine compounds: from enzymes to field studies |journal=Appl. Microbiol. Biotechnol. |volume=58 |issue=1 |pages=39–45 |year=2002 |month=January |pmid=11831474 |doi= 10.1007/s00253-001-0862-y|url=]

Atrazine degrades in soil by the action microbes. Rates of biodegradation affected by atrazine's low solubility , thus surfactants increase the accelerate degradation. Atrazine itself is a poor energy source due to the highly oxidized carbons in the ring. It is catabolized as a carbon and nitrogen source in limiting environments. Inorganic nitrogen accelerates atrazine catabolism whereas organic nitrogen decreases it. Low concentrations of glucose can decrease the bioavailability, whereas higher concentrations promote the catabolism of atrazine. [cite journal | author = Ralebitso TK, Senior E, van Verseveld HW | year = 2002 | title = Microbial aspects of atrazine degradation in natural environments | journal = Biodegradation | volume = 13 | pages = 11–19 | doi = 10.1023/A:1016329628618]

The genes for enzymes AtzA-C have been found to be highly conserved in atrazine-degrading organisms worldwide. The prevalence of these genes could be due to the mass transfer of AtzA-C on a global scale. In "Pseudomonas sp". ADP, the Atz genes are located non-contiguously on a plasmid with the genes for mercury catabolism. This plasmid is conjugatable to Gram negative bacteria in the laboratory and could lead to the worldwide distribution, in view of the extensive release of of atrazine and mercury. AtzA-C have also been found in a Gram positive bacterium but are chromosomally located. [cite journal | author = Cai B, Han Y, Liu B, Ren Y, Jiang S. | year = 2003 | title = Isolation and characterization of an atrazine-degrading bacterium from industrial wastewater in China | journal = Letters in Applied Microbiology | volume = 36 | pages = 272–276 | doi = 10.1046/j.1472-765X.2003.01307.x] The insertion elements flanking each gene suggests that they are involved in the assembly of this specialized catabolic pathway. Two options exist for degradation of atrazine using microbes: bioaugmentation or biostimulation.

Controversy

Atrazine was banned in the European Union (EU) in 2004 because of its persistent groundwater contamination In the United States, however, atrazine is one of the most widely used herbicides, with 76 million pounds of it applied each year. [cite news | last = Walsh | first = Edward | title = EPA Stops Short of Banning Herbicide | pages = A14 | publisher = Washington Post | date = 2003-02-01 | url = | accessdate = 2007-04-27 ] It is probably the most commonly used herbicide in the world, and is used in about 80 countries worldwide. Its endocrine effects, possible carcinogenic effect, and epidemiological connection to low sperm levels in men has led several researchers to call for banning it in the US.

It is a teratogen, causing demasculinization in male frogs even at low concentrations, [cite journal | author= Tyrone Hayes, Kelly Haston, Mable Tsui, Anhthu Hoang, Cathryn Haeffele, and Aaron Vonk | title=Atrazine-Induced Hermaphroditism at 0.1 ppb in American Leopard Frogs | url = http://www.ehponline.org/members/2003/5932/5932.html | format = Free full text | journal= Environmental Health Perspectives | year=2003 | volume=111 | pages= | doi=10.1289/ehp.5932] and an estrogen disruptor. [cite journal | author = Mizota, K.; Ueda, H. | year = 2006 | url = http://toxsci.oxfordjournals.org/cgi/content/full/90/2/362#BDY | doi = 10.1093/toxsci/kfj087 | journal = Toxicological Sciences | title = Endocrine Disrupting Chemical Atrazine Causes Degranulation through Gq/11 Protein-Coupled Neurosteroid Receptor in Mast Cells | volume = 90 | pages = 362 | pmid = 16381660] Male frogs affected by atrazine could reach testosterone levels below females.Briggs H. (April 15, 2002), [http://news.bbc.co.uk/1/hi/sci/tech/1930658.stm Pesticide 'causes frogs to change sex'] . "BBC News". Retrieved on 2007-10-16.]

The U.S. Environmental Protection Agency (EPA) and its independent Scientific Advisory Panel (SAP) examined all available studies on this topic — including Hayes' work — and concluded that there is "currently insufficient data" to determine if atrazine affects amphibian development. Hayes, formerly part of the SAP panel, resigned in 2000 to continue studies independently. [ [http://news.bbc.co.uk/2/hi/science/nature/2379383.stm Weedkiller 'threatens frogs'] , BBC News] Hayes notes that all of the studies that failed to conclude that atrazine caused hermaphroditism were plagued by poor experimental controls and were funded by Syngenta, the company that produces the chemical. [cite journal | author = Hayes, TB | year = 2004 | title = There Is No Denying This: Defusing the Confusion about Atrazine | journal = Bioscience | volume = 54 | issue = 112 | pages = 1138–1149 | doi = 10.1641/0006-3568(2004)054 [1138:TINDTD] 2.0.CO;2] In 2006 the U.S. EPA considered re-registration of Atrazine final when it issued a cumulative risk assessments on the triazine herbicides, and concluded that they posed "no harm that would result to the general U.S. population, infants, children or other...consumers." [ [http://www.epa.gov/oppsrrd1/cumulative/triazine_fs.htm Triazine Cumulative Risk Assessment and Atrazine, Simazine, and Propazine Decisions] , June 22, 2006, EPA.] A former scientist working for the Minnesota Pollution Control Agency believes he was fired for attempting to testify against atrazine. [Davidson C. (2007). [http://www.tcdailyplanet.net/node/7292 Whistleblower Wotzka, legislators and researcher put Atrazine back in spotlight] . "Twin Cities Daily Planet".]

As reported in February 2008, young tadpoles undergoing organ morphogenesis were found to develop deformed hearts and impaired kidneys and digestive systems when exposed to atrazine. Tissue malformation may be induced by ectopic programmed cell death, althrough a mechanism was not identified. [ [http://www.sciencedaily.com/releases/2008/04/080416091015.htm Early Exposure To Common Weed Killer Impairs Amphibian Development ] ]

Toxicity

According to Extension Toxicology Network, "The oral LD₅₀ 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 and greater than 3000 mg/kg in rats. 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." [ [http://extoxnet.orst.edu/pips/atrazine.htm 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.]

References

Further reading

*
* Tyrone Hayes' page about his research on Atrazine: [http://atrazinelovers.com/ atrazinelovers.com]
* [http://www.chemindustry.com/chemicals/521112.html Synonyms and brand names]