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| Atrazine | |
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| IUPAC name | 1-chloro-3-ethylamino-5-isopropylamino-2,4,6-triazine |
| Other names | Atrazine See also synonyms |
| Identifiers | |
| CAS number | [1912-24-9] |
| SMILES |
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| Properties | |
| Molecular formula | C8H14ClN5 215.683477 g/mol |
| Appearance | colorless solid |
| Density | 1.187 g/cm³ |
| Melting point |
175 °C (448 K) |
| Boiling point |
200 °C (473 K) |
| Solubility in water | 0.007 g/100 mL (?°C) |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references |
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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.[1] 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.
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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.citation needed Atrazine is the most widely used herbicide in conservation tillage systems, which are designed to prevent soil erosion.
Biodegradation
The half-life of atrazine in soil is 13 to 261 days.[2] Atrazine biodegradation can occur by two known pathways:
1) Atrazine can be dechlorinated and then the other ring substituents are removed by amidohydrolases by the enzymes AtzA, AtzB and AtzC respectively. The end product, cyanuric acid, is used as a carbon and nitrogen source. The most characterized organism that performs this pathway is Pseudomonas sp. strain ADP.
2) The other mechanism involves dealkylation of the amino groups. In this mechanism dechlorination can be performed in the second step to eventually yield 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.[3][4]
Sorption of atrazine in soil determines the bioavailability to degradation, which is performed mostly by microbes. Low atrazine biodegradation rates are a product of low solubility and sorption to areas inaccessible by bacteria. The addition of surfactants increases the solubility, thereby increasing catalysis. Before use the surfactant must be evaluated for its effect on the environment, in addition its use as a preferential carbon and energy source must be evaluated. 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 although the optimum carbon and nitrogen availability is not known. It has been shown that inorganic nitrogen increases atrazine catabolism while organic nitrogen decreases it. Low concentrations of glucose can have the effect of decreasing bioavailability through formation of bound atrazine, while higher concentrations promote the catabolism of atrazine.[5]
The genes for enzymes AtzA-C have been found to be highly conserved in atrazine degrading organisms worldwide. This 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 mercury catabolism genes as well. This plasmid is conjugatable to Gram negative bacteria in the lab and could easily lead to the worldwide distribution with the amount of atrazine and mercury being produced. AtzA-C have also been found in a Gram positive bacterium, but chromosomally located.[6] This is not surprising due to the presence of insertion elements flanking each gene and the detection of these genes on different plasmids. Their configurations on these different plasmids suggest the insertion elements are involved in the assembly of this specialized catabolic pathway.[4] Two options exist for degradation of atrazine using microbes: bioaugmentation or biostimulation.[4]
Controversy
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It has been suggested that this article be split into articles entitled Atrazine controversy, accessible from a disambiguation page. () |
Atrazine has been banned in the European Union (EU). However, the EU scientific review stated, “It is expected that the use of atrazine, consistent with good plant protection practice, will not have any harmful effects on human or animal health or any unacceptable effects on the environment.”citation needed A very similar product to atrazine, called terbuthylazine, is used in the EU today.citation needed
Atrazine is one of the most widely used herbicides in the United States, with 76 million pounds of it applied each year.[8] It is probably the most commonly used herbicide in the world, and is used in about 80 countries worldwide.[9]
Experiments indicate that atrazine is a teratogen, causing demasculinization in male frogs even at low concentrations. Under the effects of atrazine, male frogs were found to have greatly increased occurrences of either malformed or testicular gonads which contain non-degenerate eggs.[10] The same study also found that atrazine causes male frogs' testosterone levels to dip below those of females.[9] Effects were however significantly reduced in high concentrations, as is consistent with other teratogens affecting the endocrine system, such as estradiol.citation needed
The 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.[11] 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.[12]
Atrazine in an endocrine disruptor.[13]
Young tadpoles undergoing organ morphogenesis were found to develop deformed hearts and impaired kidneys and digestive systems when exposed to atrazinecitation needed. Tissue malformation may be induced by ectopic programmed cell death, althrough a mechanism was not identified.[14]
Studies show that atrazine likely causes hormone disruption in humans as well as fish and amphibians.[15] In 2003, the EPA classified the herbicide as "not likely" to cause cancer in humans, stating it did "not find any results among the available studies that would lead us to conclude that a potential cancer risk is likely from exposure to atrazine."[16] After a 10-year science review, the EPA recommended atrazine's re-registration in October 2003.[17]
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."[18]
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." [19]
References
- ^ Jennifer Lee (2003-06-19). "Popular Pesticide Faulted for Frogs' Sexual Abnormalities", The New York Times.
- ^ Interim Reregistration Eligibility Decision for Atrazine, U.S. EPA, January, 2003.
- ^ Zeng Y, Sweeney CL, Stephens S, Kotharu P. (2004). Atrazine Pathway Map. Wackett LP. Biodegredation Database.
- ^ a b c Wackett LP, Sadowsky MJ, Martinez B, Shapir N (January 2002). "Biodegradation of atrazine and related s-triazine compounds: from enzymes to field studies". Appl. Microbiol. Biotechnol. 58 (1): 39–45. doi:. PMID 11831474.
- ^ Ralebitso TK, Senior E, van Verseveld HW (2002). "Microbial aspects of atrazine degradation in natural environments". Biodegradation 13: 11–19. doi:.
- ^ Cai B, Han Y, Liu B, Ren Y, Jiang S. (2003). "Isolation and characterization of an atrazine-degrading bacterium from industrial wastewater in China". Letters in Applied Microbiology 36: 272–276. doi:.
- ^ USGS Pesticide Use Maps
- ^ Walsh, Edward (2003-02-01). "EPA Stops Short of Banning Herbicide", Washington Post, pp. A14. Retrieved on 2007-04-27.
- ^ a b Briggs H. (April 15, 2002), Pesticide 'causes frogs to change sex'. BBC News. Retrieved on 2007-10-16.
- ^ Tyrone Hayes, Kelly Haston, Mable Tsui, Anhthu Hoang, Cathryn Haeffele, and Aaron Vonk (2003). "Atrazine-Induced Hermaphroditism at 0.1 ppb in American Leopard Frogs" (Free full text). Environmental Health Perspectives 111. doi:.
- ^ Weedkiller 'threatens frogs', BBC News
- ^ Hayes, TB (2004). "There Is No Denying This: Defusing the Confusion about Atrazine". Bioscience 54 (112): 1138–1149. doi:.
- ^ Mizota, K.; Ueda, H. (2006). "Endocrine Disrupting Chemical Atrazine Causes Degranulation through Gq/11 Protein-Coupled Neurosteroid Receptor in Mast Cells". Toxicological Sciences 90: 362. doi:. PMID 16381660.
- ^ Early Exposure To Common Weed Killer Impairs Amphibian Development
- ^ PLOS. Atrazine Activates Endocrine Gene Networks.
- ^ EPA Interim Reregistration Eligibility Decision (IRED), January 2003.
- ^ Revised EPA Interim Reregistration Eligibility Decsion (IRED), October 2003.
- ^ Triazine Cumulative Risk Assessment and Atrazine, Simazine, and Propazine Decisions, June 22, 2006, EPA.
- ^ 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.
Further reading
- Fan W, Yanase T, Morinaga H, et al (May 2007). "Atrazine-induced aromatase expression is SF-1 dependent: implications for endocrine disruption in wildlife and reproductive cancers in humans". Environ. Health Perspect. 115 (5): 720–7. doi:. PMID 17520059.
- Tyrone Hayes' page about his research on Atrazine: atrazinelovers.com
- Synonyms and brand names
Wikipedia content modification information:
- This page was last modified on 4 September 2008, at 19:15.
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