e-mail: jcummins@uwo.ca
Atrazine is an herbicide registered in the United States for the control of broadleaf weeds and some grassy weeds. Atrazine is currently used on corn (field and sweet), sorghum, sugarcane, wheat (where application is to wheat stubble on fallow land following wheat harvests; wheat is not the target crop), guava, macadamia nuts, orchard grass and hay, range grasses, and southern turf grasses. Atrazine is most widely used on corn followed by use on sorghum and sugarcane. Atrazine is registered for use on range grasses for the establishment of permanent grass cover on rangelands and pastures under the Conservation Reserve Program (CRP) in four states: OK, NE, TX, and OR. The CRP is administered by the U.S. Department of Agriculture (USDA). There are prohibitions against grazing on these CRP lands, and cutting the grasses for hay, except in national emergencies, such as severe drought. There are also "right-of-way" uses with grazing restrictions. Atrazine is also registered for use on the following nonagricultural use sites: lawns, golf courses, and sod farms.(1). Worldwide, atrazine is a leading agricultural chemical and so extensively used that it has identified as a significant pollutant in surface water, groundwater, offshore and atmosphere worldwide.
Atrazine is a herbicide that inhibits photosynthesis by inhibiting photosystem II . Many atrazine mutations have begun to appear in weeds and this resistance is predominantly based on detoxifying atrazine initially binding it to glutathione(2) a method used by naturally resistant corn (3). Efforts have been made to select or produce atrazine resistant mutants of crops such as soybean that is difficult to rotate with atrazine treated corn or resistant potato is selected to allow use of atrazine in weed control. Most of the crop plant mutants had impaired productivity(4). In potato an atrazine binding protein of photosystem II was mutated and was resistant to the herbicide without impaired productivity (5). Transgenic potato bearing a complex of human cytochrome p450 genes was found to be resistant to atrazine and was a proposed crop for phytoremediation of chemically polluted croplands (6)! The cytochrome p450 enzymes are very important in metabolism of man made chemicals, they both inactivate many carcinogens and in some instances activate pollutants to form carcinogens. Atrazine is used worldwide but its continued application is hampered by appearance of atrazine tolerant weeds.
Atrazine is a threatening pollutant through its effect on disrupting endocrine hormone metabolism. Frogs were found to be demasculinized or even hermaphroditic after being exposed at low ecologically relevant doses of the herbicide (7). Atrazine reduced olfactory-,mediated endocrine functions in salmon at levels commonly observed in water pollution (8). Atrazine inhibited testosterone production in prepubertal rats (9). The impact of atrazine on endocrine disruption is very alarming. A study of aquatic ecosystems concluded that a single universal maximum on atrazine in catchments does not provide adequate environment and suggests flexible limits be set (10). However, it may be far more reasonable to discuss eliminating further atrazine input into the aquatic environment.
The International Agency for Research on Cancer determined that there is sufficient evidence for the carcinogenicity of atrazine in animals and inadequate evidence of the carcinogenicity of atrazine in humans (11). The United States Environmental Protection Agency (EPA) concluded that the cancer studies showing atrazine carcinogenic in animals were not applicable to human but EPA made minor adjustments to the regulatory framework for atrazine based on the elevated pollution by that herbicide (12). Recently atrazine was found to potentiate arsenic toxicity in human cells (13) a result that causes concern over in areas where drinking water is polluted with both toxins. Even though cancer has been a focus of regulatory action on the herbicide impacts such as the intrauterine growth retardation observed in communities atrazine polluted drinking water supplies (14) should not have been given slight consideration. It is worth mentioning that the emphasis of the high level regulators appears to have been that the burden of proof is biased towards absolute evidence that human cancer is caused by the herbicide and such proof cannot be forthcoming until humans are used as experimental animals.
The report on endocrine disruption (7) includes references showing that atrazine can be present in parts per million in agricultural run-off and can reach 40 parts per billion in precipitation. The global impact of atrazine is staggering, alon with the references mentioned above significant atrazine pollution has been found in the Lio-He and Yangtse rivers of China (15) and a review of the atmospheric dispersion of atrazine shows impact of the herbicide in isolated areas of the globe (16). The global impact of atrazine is staggering and cries out for prompt action.
Prompt action to limit further pollution from atrazine may be delayed by the development of “super weeds” volunteer crops or weds that develop multiple herbicide tolerance by pollen exchange between commercial varieties. Some authorities and government regulators advise that herbicides such as atrazine should be used to control superweeds. For example an Agbiotech Infosource newsletter of Ag-West Biotech comments” This is what happened on an Alberta farm in the late 1990s. Producers planted three different kinds of herbicide resistant canola in nearby fields. The pollen from the canola flowers drifted on the wind or was carried by insects from field to field. This mixed the genes for resistance to RoundupTM as well as two other broad-spectrum herbicides, LibertyTM and PursuitTM. In following years, it was discovered that some of the volunteer canola plants in these fields could survive a spraying of any of the three herbicides. However, even in this case, the volunteer canola was hardly a "superweed". As Dr. McHughen points out, Roundup ReadyTM is only resistant to Roundup(tm) herbicide. Other herbicides will kill it as easily as any other weeds, and this holds true of all herbicide-resistant crops.” The recommendation by companies , government regulators and academe that the solution to “super weeds” is more and stronger herbicide and widespread deployment of a globally polluting herbicide such as atrazine seems to be a form of lunacy.
References
1..US Environmental protection Agency “OVERVIEW OF ATRAZINE RISK ASSESSMENT” May 2, 2002 Reregistration Branch 3, Health Effects division, Office of Pesticides Programs A
2. DePrado,R,Lopez-Martinez,N, and Gonzalez-Gutierrez,J “”Identification of two mechanisms of atrazine resistance in Setaria faberi and Setaria viridius biotypes” 2000 Pesticide Biochemistry and Physiology 67,114-24
3. Cherifi,M,Ravelton,M,Picciocchi,A,Ravanel,P and Tissut,M “Atrazine metabolism in corn seedlings” 2001 Plant PhysiolBiochem 39,665-72
4.Frey,J “Genetic flexibility of plant chloroplasts” 1998 Nature 398, 115-6
5. Smeda,R,Hasegawa,P,Goldborough,P,Singh,N and Weller,S “A serine to threonine substitution in the triazine herbicide-binding protein in potato cells results ih atrazine rtesistance without impairing productivity” 1993 Plant Physiol 103,911-7
6.Inui,H,Kodama,T,Ohkawa,Y and Ohkawa,H “Herbicide metabolism and cross tolerance in transgenic potato plants co-expressing human CYP1A1,CYP2B6, and CYP2C19” 2000 Pesticide Biochemistry and physiology 66,116-29
7. Hayes,T,Collins,A,Lee,M,Mendoza,M,Noriega,N,Stuart,A and Vonk,A “Hermaphroditic, demasculinized frogs after exposure to the herbicide atrazine at low ecologically relevant doses” 2002 Proc. Natnl.Acad Sci USA 99,5476-80
8. Moore,A and Lower,N “The impact of two pesticides on olfactory-mediated endocrine function in mature male Atlantic salmon” 2001 Comparative Biochemistry and Physiology Part B 129,269-76
9.Friedman,A “Atrazine inhibition of testosterone production in rat males following prepubertal exposure” 2002 Reproductive Toxicology 16, 275-9
10. Graymore,M.,Stagnitti,F and Allison,G “Impacts of atrazine on equatic ecosystems” 2001 Environment International 26,483-95
11. International Agency for Research on Cancer “Overall Evaluations of Carcinogenicity to Humans 6-Chloro-N-ethyl-N¢-(1-methylethyl)-1,3,5-triazine-2,4-diamine” VOL.: 73 (1999) (p. 59)
12. UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REVISED HUMAN HEALTH RISK ASSESSMENT Atrazine April 16, 2002 Reregistration Branch 3 Health Effects Division Office of Pesticide Programs
13. Tchounwou,P,Wilson,B,Ishaque,A and Schneider,J “Atrazine potentiation of arsenic trioxide-induced cytotoicity and gene expression in human liver carcinoma cells (HepG2)” 2001 Molecular and cellular Biochemistry 222, 49-59
14. Munger R; Isacson P; Hu S; Burns T; Hanson J; Lynch CF; Cherryholmes K; Van Dorpe P; Hausler WJ Jr “Intrauterine growth retardation in Iowa communities with herbicide-contaminated drinking water supplies” 1997 Environ Health Perspect, 105,308-14
15.Gfrerer,M,Martens,D,Gawik,B,Wenzi,T,Zhang,A,Quan,X,Cheng,S,Chen,J,Platzer,B,Lankmayr,E and Kettrup,A “Triazines in the aquatic systems of the eastern Chinese Rivers Liao-He and Yangtse” 2002 Chemosphere 455-66
16.Dijk,H and Guicherit,R. “”Atmospheric dispersion of current use pesticides: A review of the evidence from monitoring studies” 1999 Water, Air and Soil Pollution 115,21-70
17. Ag-West Biotech Inc.” WHAT MAKES A WEED?” AGBIOTECH INFOSOURCE Issue 58 October, 2000 Published by Ag-West Biotech Inc. http://www.agwest.sk.ca/e_infosrc.shtml
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