“2,4-Dichlorophenoxyacetic acid”的意思、由来-开放百科全书

2,4-Dichlorophenoxyacetic acid (usually called 2,4-D) is an organic compound with the chemical formula C₈H₆Cl₂O₃. It is a systemic herbicide which selectively kills most broadleaf weeds by causing uncontrolled growth in them, but leaves most grasses such as cereals, lawn turf, and grassland relatively unaffected.

2,4-D is one of the oldest and most widely available herbicides and defoliants in the world, having been commercially available since 1945, and is now produced by many chemical companies since the patent on it has long since expired. It can be found in numerous commercial lawn herbicide mixtures, and is widely used as a weedkiller on cereal crops, pastures, and orchards. Over 1,500 herbicide products contain 2,4-D as an active ingredient.

Applications

2,4-D is primarily used as a selective herbicide which kills many terrestrial and aquatic broadleaf weeds, but not grasses. It acts by mimicking the action of the plant growth hormone auxin, which results in uncontrolled growth and eventually death in susceptible plants.^[5] Because it was discovered in the 1940s, a patent no longer governs the manufacture and sale of 2,4-D, and any company is free to produce it. Thus, it is sold in various formulations under a wide variety of brand names.^[5] 2,4-D can be found in commercial lawn herbicide mixtures, which often contain other active ingredients including mecoprop and dicamba. Over 1,500 herbicide products contain 2,4-D as an active ingredient.^[6]

A wide variety of different sectors uses products containing 2,4-D to kill weeds and unwanted vegetation. In agriculture, it was the first herbicide found to be capable of selectively killing weeds but not crops. It has been used since 1945^[7] to control broad-leafed weeds in pastures, orchards, and cereal crops such as corn, oats, rice, and wheat.^[8] Cereals, in particular, have excellent tolerance to 2,4-D when it is applied before planting. 2,4-D is the cheapest way for farmers to control winter annual weeds by spraying in the fall, often at the lowest recommended rate. This is particularly effective before planting beans, peas, lentils, and chickpeas.^[9]

In domestic lawn and garden maintenance, 2,4-D is commonly used for weed control in lawns and other turf. It is used to kill unwanted weeds such as dandelions, plantain, clover, and chickweed. In forestry, it is used for stump treatment, trunk injection, and selective control of brush in conifer forests. Along roadways, railways, and power lines, it is used to control weeds and brush which might interfere with safe operation and damage equipment. Along waterways, it is used to control aquatic weeds that might interfere with boating, fishing, and swimming or clog irrigation and hydroelectric equipment. It is often used by government agencies to control the spread of invasive, noxious, and non-native weed species and prevent them from crowding out native species, and also to control many poisonous weeds such as poison ivy and poison oak.^[16]{{rp|35–36}} ^[10]

A 2010 monitoring study conducted in the US and Canada found that "current exposures to 2,4-D are below applicable exposure guidance values."^[11]

2,4 D has been used in laboratories for plant research as a supplement in plant cell culture media such as MS medium since at least 1962.^[12] 2,4-D is used in plant cell cultures as a dedifferentiation (callus induction) hormone. It is classified as an auxin plant hormone derivative.^[13]

Health effects

Men who work with 2,4-D are at risk for abnormally shaped sperm and thus fertility problems; the risk depends on the amount and duration of exposure and other personal factors.^[14]

Acute toxicity

According to the U.S. Environmental Protection Agency, "The toxicity of 2,4-D depends on its chemical forms, including salts, esters, and an acid form. 2,4-D generally has low toxicity for humans, except certain acid and salt forms can cause eye irritation. Swimming is restricted for 24 hours after application of certain 2,4-D products applied to control aquatic weeds to avoid eye irritation."^[22] {{As of| 2005}} the median lethal dose or LD₅₀ determined in acute toxicity rat studies was 639 mg/kg.^[15]

Cancer risk

The International Agency for Research on Cancer classifies 2,4-D as a possible carcinogen to humans while the United States Environmental Protection Agency does not.^[17]^[18] The International Agency for Research on Cancer (IARC), said 2,4-D was classified as "possibly carcinogenic to humans (Group 2B), based on inadequate evidence in humans and limited evidence in experimental animals".^[19]

In June 2015 the World Health Organization's International Agency for Research on Cancer confirmed its 1987 classification of 2,4-D as a possible carcinogen.^[20]^[21]

On August 8, 2007, the EPA issued a ruling that existing data do not support a link between human cancer and 2,4-D exposure.^[22]

A 1995 panel of 13 scientists reviewing studies on the carcinogenicity of 2,4-D had divided opinions. None of the scientists thought the weight of the evidence indicated that 2,4-D was a "known" or "probable" cause of human cancer. The predominant opinion indicated that it is possible that 2,4-D can cause cancer in humans, although not all of the panelists believed the possibility was equally likely: one thought the possibility was strong, leaning toward probable, and five thought the possibility was remote, leaning toward unlikely. Two panelists believed it unlikely that 2,4-D can cause cancer in humans.^[23]

In a prior 1987 report the IARC classified some chlorphenoxy herbicides including 2,4-D, MCPA and 2,4,5-T as a group as class 2B carcinogens - "possibly carcinogenic to humans".^[24]

Contaminants

A July 2013 Four Corners investigation found elevated levels of dioxins in a generic version of 2,4-D, one of Australia's most widely used herbicides. One scientist said the product tested by Four Corners, which was imported from China, had "one of the highest dioxin readings for 2,4-D in the last 10 to 20 years, and could pose potential health risks."^[25]

Metabolism

When radioactively labeled 2,4 D was fed to livestock, 90% or more of the total radioactive residue (TRR) was shed in urine unchanged or as conjugated forms of 2,4-D. A relatively small portion of 2,4 D was metabolized into dichlorophenol, dichloroanisole, 4-chlorophenoxyacetic acid (6.9% of the TRR in milk), and 2,4-dichlorophenol13 (5% of the TRR in milk; 7.3% of the TRR in eggs and 4% of the TRR in chicken liver). Residue levels in kidney were the highest.^[16]{{rp|21}}

Environmental behavior

Owing to the longevity and extent of use, 2,4-D has been evaluated several times by regulators and review committees.^[26]^[27]

2,4-D amine salts and esters are not persistent under most environmental conditions.^[28] The degradation of 2,4-D is rapid (half life of 6.2 days) in aerobic mineral soils.^[15]{{rp|54}} 2,4-D is broken down by microbes in soil, in processes that involve hydroxylation, cleavage of the acid side-chain, decarboxylation, and ring opening. The ethyl hexyl form of the compound is rapidly hydrolyzed in soil and water to form the 2,4-D acid.^[28] 2,4-D has a low binding affinity in mineral soils and sediment, and in those conditions is considered intermediately to highly mobile, and therefore likely to leach if not degraded.^[28]

In aerobic aquatic environments, the half life is 15 days, while in anaerobic aquatic environments, 2,4-D was moderately persistent to persistent (half life of = 41 to 333 days). 2,4-D has been detected in streams and shallow groundwater at low concentrations, in both rural and urban areas. Breakdown is pH dependent.^[28] Some ester forms are highly toxic to fish and other aquatic life.^[29]

"The ester forms of 2,4-D can be highly toxic to fish and other aquatic life. 2,4-D generally has moderate toxicity to birds and mammals, is slightly toxic to fish and aquatic invertebrates, and is practically nontoxic to honeybees" per EPA.^[30]{{date missing}}

Microbial breakdown

A number of 2,4-D-degrading bacteria have been isolated and characterized from a variety of environmental habitats.^[31]^[32] Metabolic pathways for the compound’s degradation have been available for many years, and genes encoding 2,4-D catabolism have been identified for several organisms. As a result of the extensive metadata on environmental behavior, physiology, and genetics, 2,4-D was the first herbicide for which the bacteria actively responsible for in situ degradation were demonstrated.^[33] This was accomplished using the technique of DNA-based stable isotope probing, which enables a microbial function (activity), such as degrading a chemical, to be linked with the organism’s identity without the need to culture the organism involved.^[34]

Regulation

Maximum residue limits were first set in the EU in 2002 and re-evaluated in 2011 by the European Food Safety Authority, which concluded that the codex maximum residue limits were "not expected to be of concern for European consumers".^[35]{{rp|26}} The total chronic exposure represented less than 10% of the acceptable daily intake (ADI).^[35]{{rp|28}}

Concern over 2,4-D is such that it is currently not approved for use on lawns and gardens in Denmark, Norway, Kuwait, and the Canadian provinces of Québec^[36] and Ontario.^[37] 2,4-D use is severely restricted in the country of Belize. In 2008, Dow AgroScience, LLC, sued the Canadian government for allowing Quebec to ban 2,4-D, but settled in 2011.^[38]

In 2005, the US EPA approved the continued use of 2,4-D.^[15] On July 10, 2013, the Pest Management Regulatory Agency in Canada updated the re-evaluation notice of 2,4-D, stating that the 2,4-D registrants had provided it with required data and deemed them acceptable.^[39] On April 18, 2012, EPA denied the petition filed November 6, 2008, by the Natural Resources Defense Council to revoke all tolerances and to cancel all registrations of 2,4-D. EPA stated that recent new study and EPA’s comprehensive review confirmed EPA’s previous finding that the 2,4-D tolerances are safe at anticipated exposure.^[27]^[40]^[41]

In October 2014, the US EPA registered Enlist Duo, an herbicide containing the less volatile 2,4-D choline salt, glyphosate, and an antidrift agent, for use in six states: Illinois, Indiana, Iowa, Ohio, South Dakota, and Wisconsin.^[42] In November 2015, the EPA attempted to withdraw its own approval of Enlist Duo, as a result of legal actions against both the agency and Dow by two U.S. groups. However, while it was implied that the approval was "gone" because of the action, in fact, Enlist Duo was still approved pending a decision by the courts. On January 25, 2016, the US Ninth Circuit Court of Appeals denied EPA's motion to vacate its Enlist Duo registration. Dow stated the product would be available in 15 US states and Canada for the 2016 crop season.^[43]^[44]

On 21 August 2013, the Australian Pesticides and Veterinary Medicines Authority (APVMA) banned selected 2,4-D high volatile ester (HVE) products due to their environmental hazards. HVE 2,4-D products had already been banned in Europe and North America for 20 years; low volatile ester products continue to be available in Australia and worldwide.^[45] In July 2013 APVMA published their report findings.^[46]

Mode of action

2,4-D is a synthetic auxin, which is a class of plant hormones. It is absorbed through the leaves and is translocated to the meristems of the plant. Uncontrolled, unsustainable growth ensues, causing stem curl-over, leaf withering, and eventual plant death. 2,4-D is typically applied as an amine salt, but more potent ester versions exist, as well.^[47]

Manufacture

2,4-D is manufactured from chloroacetic acid and 2,4-dichlorophenol, which is itself produced by chlorination of phenol. Alternatively, it is produced by the chlorination of phenoxyacetic acid. The production processes create several contaminants including di-, tri-, and tetrachlorodibenzo-p-dioxin isomers and

Genetically modified crops

In 2010, Dow published that it had created genetically modified soybeans made resistant to 2,4-D by insertion of a bacterial aryloxyalkanoate dioxygenase gene, aad1.^[49]^[67]^[50]{{rp|1}} Dow intended it to be used as an alternative or complement to Roundup Ready crops due to the increasing prevalence of glyphosate-resistant weeds.^[51]

As of April 2014, genetically modified maize and soybeans resistant to 2,4-D and glyphosate have been approved in Canada.^[70] In September 2014, the USDA also approved Dow's maize and soybeans, and in October, the EPA registered the "Enlist Duo" herbicide containing 2,4-D and glyphosate.^[42]^[52]^[53]

History

The discovery of 2,4-D as well as the similar hormone herbicides 2,4,5-T, and MCPA occurred during World War II and was a case of multiple discovery by four groups working independently under wartime secrecy in the United Kingdom and the United States: William G. Templeman and associates at Imperial Chemical Industries in the UK; Philip S. Nutman and associates at Rothamsted Research in the UK; Franklin D. Jones and associates at the American Chemical Paint Company; and Ezra Kraus, John W. Mitchell, and associates at the University of Chicago and the United States Department of Agriculture. All four groups were subject to wartime secrecy laws and did not follow the usual procedures of publication and patent disclosure. The first scientific publications about these herbicides were by other workers who were not the original discovers, so the exact order of discovery is a matter of some debate.^[54]

William Tempelman found that when indole-3-acetic acid (IAA), the naturally occurring auxin, was used at high concentrations, it could stop plant growth. In 1940, he published his finding that IAA killed broadleaf plants within a cereal field.^[55] The related compound, MCPA, was discovered at about the same time by other UK scientists.^[56]{{rp|Sec 7.1}}

The search for an acid with a longer half life, i.e., a metabolically and environmentally more stable compound, led to 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), both phenoxy herbicides and analogs of IAA. Robert Pokorny, an industrial chemist for the C.B. Dolge Company in Westport, Connecticut, published their synthesis in 1941.^[57]

Both compounds were developed as part of a clandestine wartime effort to create chemical warfare agents for use in World War II; although 2,4-D was not used this way during the war.^[56]{{rp|Sec 7.1}} Britain and the United States were looking for a chemical to starve Germany and Japan into submission by killing their potato and rice crops, but 2,4-D was found to be ineffective for that purpose, because both crops are tolerant of it. Within a year after the war ended, 2,4-D was commercially released as an herbicide to control broadleaf weeds in grain crops such as rice,^[58] and in the 1950s it was registered in the United States to control size and enhance skin colour in potatoes without affecting yields.^[59]

The first publication of 2,4-D's use as a selective herbicide came in 1944.^[60]^[61] The ability of 2,4-D to control broadleaf weeds in turf was documented soon thereafter, in 1944.^[62] Starting in 1945, the American Chemical Paint Company brought 2,4-D to market as an herbicide called "Weedone". It revolutionized weed control, as it was the first compound that, at low doses, could selectively control dicotyledons (broadleaf plants), but not most monocotyledons — narrowleaf crops, such as wheat, maize (corn), rice, and similar cereal grass crops.^[56] At a time when labor was scarce and the need for increased food production was large, it literally "replaced the hoe".^[56]{{rp|Sec 7.1}}

2,4-D is one of the ingredients in Agent Orange, an herbicide that was widely used during the Vietnam War.^[29] However, 2,3,7,8-Tetrachlorodibenzodioxin (TCDD), a contaminant in the production of another ingredient in Agent Orange, 2,4,5-T, was the cause of the adverse health effects associated with Agent Orange.^[28]^[63]

In the 2000s, Dow AgroSciences developed a new choline salt version of 2,4-D (2,4-D choline) that Dow included in its "Enlist Duo" herbicide along with glyphosate and an agent that reduces drift; the choline salt form of 2,4-D is less volatile than 2,4-D.^[42]^[64]^[65]

See also

References

1. ^{{cite web|url=http://www.chemindustry.com/chemicals/0607119.html |title=ChemIndustry site |publisher=Chemindustry.com |date= |accessdate=2014-05-03}}
2. ^¹²{{Sigma-Aldrich|id=49083|name=2,4-D|accessdate=2017-05-06}}
3. ^¹²³{{PGCH|0173}}
4. ^{{cite web |url = https://www.cdc.gov/niosh/idlh/94757.html |title = 2,4-D |publisher = National Institute for Occupational Safety and Health |date = 4 December 2014 |accessdate = 26 February 2015}}
5. ^¹{{cite web|url=http://www.invasive.org/gist/products/handbook/10.24-d.pdf |title=Weed Control Methods Handbook: 2,4-D |publisher=University of Georgia Center for Invasive Species and Ecosystem Health |website=invasive.org |date= April 2001 |accessdate=2015-11-01}}
6. ^EPA Last revised March 30, 2007 EPA Chemical Summary: 2,4-Dichlorophenoxyacetic Acid (2,4-D) {{webarchive |url=https://web.archive.org/web/20150910115620/http://www.epa.gov/teach/chem_summ/24D_summary.pdf |date=September 10, 2015 }}
7. ^{{cite web |url=http://www.livinghistoryfarm.org/farminginthe40s/pests_03.html | title= Herbicides – 2,4-D & Its Cousins |publisher=Wessels Living History Farm |first=Bill |last=Ganzel |accessdate=2015-11-12}}
8. ^{{cite web | last=Harvey | first=W.A. | last2=Robblns | first2=W.W. |url=http://ucanr.edu/repository/fileaccess.cfm?article=100374&p=MSQYWZ&CFID=82966751&CFTOKEN=41384002 | title= 2,4-D as a Weed Killer |publisher=University of California at Berkeley |date=February 1947 |accessdate=2015-11-12}}
9. ^{{cite web |url=http://www.agriculture.gov.sk.ca/adx/aspx/adxGetMedia.aspx?DocID=2686,339,14661,14613,81,1,Documents&MediaID=6006&Filename=Fall+Weed+Control+-+FAQs+-+Printer+Friendly.pdf | title= Fall Weed Control - FAQs |publisher=Saskatchewan Ministry of Agriculture |date=September 2008 |accessdate=2015-11-12}}
10. ^{{cite web |url=http://www.24d.org/benefits/default.aspx |title=2,4-D Benefits |publisher=The Industry Task Force II on 2,4-D Research Data |date=2015 |accessdate=2015-11-06 |archive-url=https://web.archive.org/web/20151102024718/http://www.24d.org/benefits/default.aspx |archive-date=2015-11-02 |dead-url=yes |df= }}
11. ^{{cite journal|vauthors=Aylward LL, Morgan MK, Arbuckle TE, Barr DB, Burns CJ, Alexander BH, Hays SM|url=http://ehp.niehs.nih.gov/0900970/|title=Biomonitoring data for 2,4-dichlorophenoxyacetic acid in the United States and Canada: interpretation in a public health risk assessment context using Biomonitoring Equivalents|journal=Environmental Health Perspectives|date=February 2010|volume=118|issue=2|pages=177–81|doi=10.1289/ehp.0900970|pmc=2831914|pmid=20123603}}
12. ^Murashige, T. and F. Skoog. A revised medium for rapid growth and bioassays with tobaccotissue cultures. Physiol. Plantarum 1962. 15:473-97. in: {{cite journal|vauthors=Sharp WR, Gunckel JE|title=Physiological Comparisons of Pith Callus With Crown-Gall and Genetic Tumors of Nicotiana glauca, N. langsdorffii, and N. glauca-langsdorffii Grown in Vitro. II. Nutritional Physiology.|journal=Plant Physiology|date=July 1969|volume=44|issue=7|pages=1073–9|pmc=396217|pmid=16657160|doi=10.1104/pp.44.7.1073}}
13. ^{{Cite book|title = Plant Cell Biotechnology|last = Endreb|first = Rudolf|publisher = Springer|year = 1994|isbn = 978-0-387-56947-5|location = Germany|pages = 17, 18}}
14. ^NIOSH. Updated June 2014. [https://www.cdc.gov/niosh/docs/96-132/ The Effects of Workplace Hazards on Male Reproductive Health]
15. ^¹²US EPA 2,4-D Reregistration Eligibility Decision, 2005. Associated RED Fact sheet {{webarchive|url=https://web.archive.org/web/20080517130243/http://www.epa.gov/oppsrrd1/REDs/factsheets/24d_fs.htm |date=2008-05-17 }} EPA
16. ^{{cite journal |vauthors=Roberts DM, Buckley NA |title=Urinary alkalinisation for acute chlorophenoxy herbicide poisoning |journal=Cochrane Database Syst Rev |volume= |issue=1 |pages=CD005488 |year=2007 |pmid=17253558 |doi=10.1002/14651858.CD005488.pub2 |url= |editor1-last=Roberts |editor1-first=Darren M}}
17. ^{{cite web|url=https://pubchem.ncbi.nlm.nih.gov/compound/2_4-dichlorophenoxyacetic_acid#section=NIOSH-Toxicity-Data|title=2,4-Dichlorophenoxyacetic acid|last=Pubchem|website=pubchem.ncbi.nlm.nih.gov}}
18. ^{{cite journal|last1=Loomis|first1=Dana|title=Carcinogenicity of lindane, DDT, and 2,4-dichlorophenoxyacetic acid|journal=The Lancet Oncology|date=June 22, 2015|volume=16|issue=8|pages=891–892|doi=10.1016/s1470-2045(15)00081-9|pmid=26111929}}
19. ^{{cite web | title=IARC Monographs evaluate DDT, lindane, and 2,4-D | date=23 June 2015 | url=https://www.iarc.fr/en/media-centre/pr/2015/pdfs/pr236_E.pdf | accessdate=14 February 2016}}
20. ^{{cite journal|last1=Loomis|first1=Dana|last2=Guyton|first2=Kathryn|last3=Grosse|first3=Yann|last4=El Ghissasi|first4=Fatiha|last5=Bouvard|first5=Véronique|last6=Benbrahim-Tallaa|first6=Lamia|last7=Guha|first7=Neela|last8=Mattock|first8=Heidi|last9=Straif|first9=Kurt|title=Carcinogenicity of lindane, DDT, and 2,4-dichlorophenoxyacetic acid|journal=The Lancet Oncology|date=August 2015|volume=16|issue=8|pages=891–892|doi=10.1016/S1470-2045(15)00081-9|pmid=26111929}}
21. ^Carey Gillam for Reuters. June 22, 2015 WHO unit finds 2,4-D herbicide 'possibly' causes cancer in humans {{Webarchive|url=https://web.archive.org/web/20150623144109/http://www.msn.com/en-us/news/us/who-unit-finds-24-d-herbicide-possibly-causes-cancer-in-humans/ar-AAbYBtV |date=2015-06-23 }}
22. ^{{cite web|url=http://www.epa.gov/fedrgstr/EPA-PEST/2007/August/Day-08/p15109.htm |title=EPA: Federal Register: 2,4-D, 2,4-DP, and 2,4-DB; Decision Not to Initiate Special Review |publisher=Epa.gov |date=August 8, 2007 |accessdate=2014-05-03}}
23. ^{{cite journal| last=Ibrahim |first=MA|author2=Bond, GG|author3= Burke, TA|author4= Cole, P|author5= Dost, FN|author6= Enterline, PE| title=Weight of the evidence on the human carcinogenicity of 2,4-D. | journal=Environ Health Perspect | year= 1991 | volume= 96 | issue= | pages= 213–22 | pmid=1820267 | doi= 10.1289/ehp.9196213| pmc=1568222 |display-authors=etal}}
24. ^Chlorphenoxy Herbicides (Group 2B) in IARC monographs on the evaluation of carcinogenic risks to humans: An updating of IARC Monographs volumes 1 to 42. Supplement 7, WHO, Lyon, France 1987.
25. ^{{cite web|author=Four Corners By Janine Cohen |url=http://www.abc.net.au/news/2013-07-22/four-corners-dangerous-dioxins/4833848 |title=Four Corners investigation finds dangerous dioxins in widely used herbicide 24D |publisher=Abc.net.au |date=22 July 2013 |accessdate=2014-05-03}}
26. ^{{cite journal | author = von Stackelberg K. A | year = 2013 | title = Systematic Review of Carcinogenic Outcomes and Potential Mechanisms from Exposure to 2,4-D and MCPA in the Environment | url = | journal = J Toxicol | volume = 2013 | issue = | page = 371610 | doi = 10.1155/2013/371610 | pmid = 23533401 | pmc = 3600329 }}
27. ^¹Andrew Pollack for the New York Times. April 9, 2012 [https://www.nytimes.com/2012/04/10/business/energy-environment/epa-denies-request-to-ban-24-d-a-popular-weed-killer.html?_r=0 E.P.A. Denies an Environmental Group’s Request to Ban a Widely Used Weed Killer] Quote: "The E.P.A. has reviewed the safety of 2,4-D several times, particularly with regard to an increased risk of cancer."
28. ^¹²³⁴⁵National Pesticide Information Center NPIC 2,4-D Technical Fact Sheet
29. ^¹{{cite web|title=2,4-D General Fact Sheet|url=http://npic.orst.edu/factsheets/24Dgen.html|publisher=National Pesticide Information Center|accessdate=7 October 2015}}
30. ^¹{{cite web|title=Ingredients Used in Pesticide Products 2,4-D|url=http://www2.epa.gov/ingredients-used-pesticide-products/24-d|website=www2.epa.gov|publisher=EPA|accessdate=November 6, 2014|date=2014-09-22}}
31. ^Cavalca, L., A. Hartmann, N. Rouard, and G. Soulas. 1999. Diversity of tfdC genes: distribution and polymorphism among 2,4-dichlorophenoxyacetic acid degrading soil bacteria. FEMS Microbiology Ecology 29: 45-58.
32. ^{{cite journal |author1=Suwa Y. |author2=Wright A.D. |author3=Fukimori F. |author4=Nummy K.A. |author5=Hausinger R.P. |author6=Holben W.E. |author7=Forney L.J. | year = 1996 | title = Characterization of a chromosomally encoded 2,4-dichlorophenoxyacetic acid alpha-ketoglutafate dioxygenase from Burkholderia sp. strain RASC | url = | journal = Applied and Environmental Microbiology | volume = 62 | issue = 7| pages = 2464–2469 |pmid=8779585 |pmc=168028 }}
33. ^{{cite journal |author1=Cupples A.M. |author2=Sims G.K. | year = 2007 | title = Identification of In Situ 2,4-Dichlorophenoxyacetic Acid-Degrading Soil Microorganisms using DNA-Stable Isotope Probing | url = | journal = Soil Biology and Biochemistry | volume = 39 | issue = | pages = 232–238 | doi=10.1016/j.soilbio.2006.07.011}}
34. ^{{cite journal |author1=Radajewski S. |author2=Ineson P. |author3=Parekh N.R. |author4=Murrell J.C. | year = 2000 | title = Stable-isotope probing as a tool in microbial ecology | url = | journal = Nature | volume = 403 | issue = 6770| pages = 646–649 | doi=10.1038/35001054|pmid=10688198 |bibcode=2000Natur.403..646R }}
35. ^¹²³{{cite journal|author=European Food Safety Authority|title=Review of the existing maximum residue levels (MRLs) for 2,4-D according to Article 12 of Regulation (EC) No 396/2005|journal=EFSA Journal|date=November 2011|volume=9|issue=11|pages=2431|doi=10.2903/j.efsa.2011.2431}}
36. ^{{cite web|url=http://www.mddep.gouv.qc.ca/pesticides/permis-en/code-gestion-en/espace-vert.htm |title=The Pesticides Management Code - Protecting the environment and health in our green spaces |publisher=Mddep.gouv.qc.ca |date=2005-04-03 |accessdate=2014-05-03}}
37. ^{{cite web|url=http://www.ene.gov.on.ca/en/news/2009/030401.php |title=Ministry of the Environment | Ontario.ca |publisher=Ene.gov.on.ca |date= |accessdate=2014-05-03}}
38. ^{{cite news|author1=BARRIE MCKENNA|title=Deal confirms government's right to ban 'cosmetic' pesticides, minister says|url=https://www.theglobeandmail.com/news/national/deal-confirms-governments-right-to-ban-cosmetic-pesticides-minister-says/article581189/|accessdate=26 June 2015|work=The Globe and Mail|date=May 27, 2011}}
39. ^{{cite web|url=http://www.hc-sc.gc.ca/cps-spc/pubs/pest/_decisions/rev2013-02/index-eng.php |title=Health Canada Pest Management Regulatory Agency Re-evaluation Update 2,4-D REV2013-02 |publisher=Hc-sc.gc.ca |date= 2013-06-13|accessdate=2014-05-03}}
40. ^{{cite web|title=Petition to Revoke All Tolerances and Cancel All Registrations for the Pesticide 2,4-Dichlorophenoxyacetic Acid (2,4-D); Notice of Availability|url=http://www.regulations.gov/#!docketDetail;dct=FR+PR+N+O+SR;rpp=25;po=0;D=EPA-HQ-OPP-2008-0877|work=Docket ID: EPA-HQ-OPP-2008-0877 Agency: EPA|publisher=United States Environmental Protection Agency|accessdate=September 12, 2012|format=Docket Folder Summary|date=April 7, 2012}}
41. ^{{cite journal|title=2,4-D; Order Denying NRDC's Petition To Revoke Tolerances|journal=Federal Register|date=April 18, 2012|volume=77|issue= 75 (Wednesday, April 18, 2012)|pages=23135–23158|url=http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2008-0877-0446|accessdate=September 12, 2012|format=Order|quote=Petitions to Revoke Tolerances; Denials: Natural Resources Defense Council, 2,4-dichlorophenoxyacetic acid (2-4D) Document ID: EPA-HQ-OPP-2008-0877-0446 Document Type: Rule Docket ID: EPA-HQ-OPP-2008-0877}}
42. ^¹²EPA Press Release. October 15, 2014 EPA Announces Final Decision to Register Enlist Duo, Herbicide Containing 2, 4-D and Glyphosate/Risk assessment ensures protection of human health, including infants, children EPA Documents: Registration of Enlist Duo
43. ^{{cite web | url = http://farmfutures.com/story-ninth-circuit-court-denies-move-epa-vacate-herbicide-label-0-136737 | last = Vogt | first = Willie | title = Ninth Circuit Court denies move by EPA to vacate herbicide label | date = January 26, 2016 | publisher = Farm Futures | access-date = 2016-02-05 }}{{Dead link|date=March 2019 |bot=InternetArchiveBot |fix-attempted=yes }}
44. ^{{cite web | url = http://www.agcanada.com/daily/u-s-court-upholds-enlist-duo-registration | title = U.S. court upholds Enlist Duo registration | date = January 29, 2016 | publisher = AGCanada.com | access-date = 2016-02-05}}
45. ^{{cite web|title=APVMA 2,4-D Review webpage|url=http://www.apvma.gov.au/products/review/current/2_4_d.php|publisher=APVMA}}
46. ^{{cite web|url=http://www.apvma.gov.au/products/review/docs/2-4-d-hve.pdf|title=Annex to the APVMA's Preliminary Review Findings (Environment) Part 1 2,4-D Esters Volume 1 Review Summary April 2006 |publisher=APVMA|date=July 2013|archiveurl=https://web.archive.org/web/20140606215344/http://www.apvma.gov.au/products/review/docs/2-4-d-hve.pdf|archivedate=6 June 2014|accessdate=25 August 2016}}
47. ^{{cite journal|vauthors=Song Y|title=Insight into the mode of action of 2,4-dichlorophenoxyacetic acid (2,4-D) as an herbicide|journal=Journal of Integrative Plant Biology|date=February 2014|volume=56|issue=2|pages=106–13|doi=10.1111/jipb.12131|pmid=24237670}}
48. ^{{cite web | url = http://www.inchem.org/documents/ehc/ehc/ehc29.htm | publisher=UNEP, WHO ILO| author= International Programme on Chemical Safety| title = 2,4-Dichlorophenoxyacetic Acid (2,4-D)| date=1984|accessdate= 22 June 2010}}
49. ^{{cite journal|last1=Wright|first1=TR|last2=Shan|first2=G|last3=Walsh|first3=TA|last4=Lira|first4=JM|last5=Cui|first5=C|last6=Song|first6=P|last7=Zhuang|first7=M|last8=Arnold|first8=NL|last9=Lin|first9=G|last10=Yau|first10=K|last11=Russell|first11=SM|last12=Cicchillo|first12=RM|last13=Peterson|first13=MA|last14=Simpson|first14=DM|last15=Zhou|first15=N|last16=Ponsamuel|first16=J|last17=Zhang|first17=Z|title=Robust crop resistance to broadleaf and grass herbicides provided by aryloxyalkanoate dioxygenase transgenes|journal=Proceedings of the National Academy of Sciences of the United States of America|date=23 November 2010|volume=107|issue=47|pages=20240–5|doi=10.1073/pnas.1013154107|pmc=2996712|pmid=21059954}}
50. ^Mark A. Peterson, Guomin Shan, Terence A. Walsh, and Terry R. Wright. Utility of Aryloxyalkanoate Dioxygenase Transgenes for Development of New Herbicide Resistant Crop Technologies ISB News Report,3 pages, May 2011, Research & Development, Dow AgroSciences, Indianapolis
51. ^{{cite news|title=Dow Weed Killer, Nearing Approval, Runs Into Opposition|url=https://www.nytimes.com/2012/04/26/business/energy-environment/dow-weed-killer-runs-into-opposition.html|accessdate=April 25, 2012|newspaper=The New York Times|date=April 25, 2012|author=Andrew Pollack}}
52. ^¹ISAAA GM Approval Database GM Approval Database Genes List, Gene: aad1. International Service for the Acquisition of Agri-biotech Applications (ISAAA), n.d. accessed February 27, 2015
53. ^{{cite news|author1=Brandon Keim|title=New Generation of GM Crops Puts Agriculture in a ‘Crisis Situation’|url=https://www.wired.com/2014/09/new-gm-crops/|accessdate=13 April 2015|work=Wired|publisher=Condé Nast.|date=25 September 2014}}
54. ^{{cite journal|last=Troyer|first=James|year=2001|title=In the beginning: the multiple discovery of the first hormone herbicides|journal=Weed Science|volume=49|issue=2|pages=290–297|doi=10.1614/0043-1745(2001)049[0290:ITBTMD]2.0.CO;2}}
55. ^{{cite journal|last1=Templeman|first1=W. G.|last2=Marmoy|first2=C. J.|title=The effect upon the growth of plants of watering with solutions of plant-growth substances and of seed dressings containing these materials|journal=Annals of Applied Biology|date=November 1940|volume=27|issue=4|pages=453–471|doi=10.1111/j.1744-7348.1940.tb07517.x}}
56. ^¹²³Andrew H. Cobb, John P. H. Reade. [https://books.google.com/books?id=hVK4vrpma2YC&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false Herbicides and Plant Physiology]. Wiley-Blackwell; 2nd edition (October 25, 2010) {{ISBN|978-1405129350}}
57. ^{{Cite journal|last1=Pokorny|first1=Robert|title=New Compounds. Some Chlorophenoxyacetic Acids|journal=Journal of the American Chemical Society|date=June 1941|volume=63|issue=6|pages=1768|doi=10.1021/ja01851a601}}
58. ^{{cite web |title= The weed-crop connection |publisher= University of California at Davis |url= http://www.plantsciences.ucdavis.edu/plantsciences/features/fall2010_rotator/weeds3_weed_crop.htm |access-date= 2015-11-23 |archive-url= https://web.archive.org/web/20111207192448/http://www.plantsciences.ucdavis.edu/plantsciences/features/fall2010_rotator/weeds3_weed_crop.htm |archive-date= 2011-12-07 |dead-url= yes |df= }}
59. ^{{Cite journal |last1= Waterer |first1=D | last2=Roy |first2=D | last3=Szaroz |first3=P |title=Potential to use Plant Growth Regulators to Enhance the Appearance of Red-Skinned Potatoes |publisher = University of Saskatchewan|year=2009}}
60. ^{{Cite book | doi=10.1021/ba-1950-0001.ch045|chapter = 2,4-Dichlorophenoxyacetic Acid (2,4-D) as a Selective Herbicide|title = Agricultural Control Chemicals| volume=1| pages=244–249|series = Advances in Chemistry|year = 1950|last1 = Quastel|first1 = J. H.| isbn=978-0-8412-2442-1}}
61. ^{{cite journal |vauthors=Hamner CL, Tukey HB | year = 1944 | title = The Herbicidal Action of 2,4 Dichlorophenoxyacetic and 2,4,5 Trichlorophenoxyacetic Acid on Bindweed | url = http://www.sciencemag.org/content/100/2590/154.full.pdf | journal = Science | volume = 100 | issue = 2590| pages = 154–155 | doi = 10.1126/science.100.2590.154 | pmid = 17778584 | bibcode = 1944Sci...100..154H }}
62. ^Mitchell JW, Davis FF and Marth PC (1944) Turf and weed control with plant growth regulators. Golfdom 18:34-38.
63. ^{{cite web|title=Ingredients Used in Pesticide Products: 2,4-D |url=http://www2.epa.gov/ingredients-used-pesticide-products/24-d |publisher=United States Environmental Protection Agency (EPA) |access-date=24 October 2015|date=2014-09-22 }}
64. ^¹{{cite web| url=http://www.agannex.com/energy/enlist-weed-control-system-in-canada | author=Donna Fleury |title=Enlist weed control system in Canada. A new tool for managing hard to control and resistant weeds |publisher=AG Annex |date=April 2014| access-date=May 3, 2014}}
65. ^Josh Flint for Prairie Farmer. August 31, 2011 Dow AgroSciences Names Its Newest Herbicide Offering Enlist Duo