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			{{short description|Herbicide}}
			{{cs1 config|name-list-style=vanc}}
	{{chembox		{{chembox
	| verifiedrevid = 413104052
	| Name = 2,4-Dichlorophenoxyacetic acid		| Name = 2,4-Dichlorophenoxyacetic acid
			| ImageFile1 = 2,4-Dichlorophenoxyacetic acid structure numbered.svg
	| ImageFile1_Ref = {{chemboximage|correct|??}}		| ImageFile1_Ref = {{chemboximage|correct|??}}
			| ImageSize1 = 210
	| ImageFile1 = 2,4-Dichlorophenoxyacetic acid structure.svg
	| ImageName1 = 2,4-Dichlorophenoxyacetic acid		| ImageName1 = 2,4-dichlorophenoxyacetic acid
	| ImageFile2 = 2,4-Dichlorophenoxyacetic acid Tubes.PNG		| ImageFile2 = 2,4-Dichlorophenoxyacetic-acid-3D-balls-2.png
			| ImageSize2 = 220
	| ImageName2 = 2,4-Dichlorophenoxyacetic acid in 3-D
	| IUPACName = (2,4-dichlorophenoxy)acetic acid		| ImageAlt2 = Ball-and-stick model of 2,4-dichlorophenoxyacetic acid
			| PIN = (2,4-Dichlorophenoxy)acetic acid
	| OtherNames = 2,4-D<br />hedonal<br />trinoxol
			| OtherNames = 2,4-D
	| Section1 = {{Chembox Identifiers
			|Section1={{Chembox Identifiers
			| ChEBI_Ref = {{ebicite|correct|EBI}}
	| ChEBI = 28854		| ChEBI = 28854
	| SMILES = Clc1cc(Cl)ccc1OCC(=O)O		| SMILES = Clc1cc(Cl)ccc1OCC(=O)O
Line 24:		Line 29:
	| StdInChIKey = OVSKIKFHRZPJSS-UHFFFAOYSA-N		| StdInChIKey = OVSKIKFHRZPJSS-UHFFFAOYSA-N
	| CASNo = 94-75-7		| CASNo = 94-75-7
	| CASNo_Ref = {{cascite|correct|CAS}}		| CASNo_Ref = {{cascite|correct|CAS}}
			| UNII_Ref = {{fdacite|correct|FDA}}
			| UNII = 2577AQ9262
	| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}		| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
	| ChemSpiderID = 1441		| ChemSpiderID = 1441
	| RTECS =		| RTECS =
	}}		}}
	| Section2 = {{Chembox Properties		|Section2={{Chembox Properties
	|C=8|H=6|Cl=2|O=3		| C=8 | H=6 | Cl=2 | O=3
	| MolarMass = 221.04 g/mol		| MolarMass = 221.04 g/mol
	| Appearance = white to yellow powder		| Appearance = white to yellow powder
	| Solubility = 900 mg/L (25 °C)		| Solubility = 900 mg/L
	| MeltingPt = 140.5 °C (413.5 K)		| MeltingPtC = 140.5
	| BoilingPt = 160 °C (0.4 mm Hg)		| BoilingPtC = 160
			| BoilingPt_notes = 0.4 mm Hg
	| pKa =		| pKa =
	}}		}}
	| Section3 = {{Chembox Structure		|Section3={{Chembox Structure
	| CrystalStruct =		| CrystalStruct =
	| Dipole =		| Dipole =
	}}		}}
	| Section7 = {{Chembox Hazards		|Section7={{Chembox Hazards
			| ExternalSDS =
	| ExternalMSDS =
			| GHSPictograms = {{GHS07}} {{GHS05}}
			| GHS_ref = <ref name="sigma">{{Sigma-Aldrich|supelco|id=49083|name=2,4-D|accessdate=2022-03-17}}</ref>
			| HPhrases = {{H-phrases|302|317|318|335|412}}
			| PPhrases = {{P-phrases|261|273|280|305+351+338}}
	| MainHazards =		| MainHazards =
	| FlashPt =		| FlashPt = nonflammable
			| FlashPt_ref = <ref name=PGCH/>
	| RPhrases =
			| PEL = TWA 10 mg/m<sup>3</sup><ref name=PGCH>{{PGCH|0173}}</ref>
	| SPhrases =
			| REL = TWA 10 mg/m<sup>3</sup><ref name=PGCH/>
			| IDLH = 100 mg/m<sup>3</sup><ref name=PGCH/>
			| LD50 = 500 mg/kg (oral, hamster)<br/>
			100 mg/kg (oral, dog)<br/>
			347 mg/kg (oral, mouse)<br/>
			699 mg/kg (oral, rat)<br/><ref>{{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 |access-date = 26 February 2015}}</ref>
	}}		}}
	| Section8 = {{Chembox Related		|Section8={{Chembox Related
	| OtherCpds = ], ]		| OtherCompounds = ], ]
	}}		}}
	}}		}}
	'''2,4-Dichlorophenoxyacetic acid''' (2,4-D) is a common systemic ] / ] used in the control of broadleaf weeds. It is the most widely used herbicide in the world, and the third most commonly used in North America.<ref></ref> 2,4-D is a synthetic ] (plant hormone), and as such it is often used in laboratories for plant research and as a supplement in plant ] media such as ].		'''2,4-Dichlorophenoxyacetic acid''' is an ] with the ] {{chem2|Cl2C6H3OCH2CO2H}}. It is usually referred to by its ] ] '''2,4-D'''.<ref>{{cite web |url=http://www.alanwood.net/pesticides/ |title=Compendium of Pesticide Common Names}}</ref> It is a systemic ] that kills most ] by causing uncontrolled growth, but most ] such as ], ] turf, and ] are relatively unaffected.
			2,4-D is one of the oldest and most widely available herbicides and ]s 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.
	==History==		==History==
			{{see also | List of multiple discoveries}}
			2,4-D was first reported in 1944 by Franklin D-Jones at the C. B. Dolge Company in Connecticut.<ref>{{cite journal |doi=10.1021/ja01851a601 |title=New Compounds. Some Chlorophenoxyacetic Acids |date=1941 |last1=Pokorny |first1=Robert |journal=Journal of the American Chemical Society |volume=63 |issue=6 |page=1768 }}</ref>
			The biological activity of 2,4-D as well as the similar hormone herbicides ], and ] were discovered during ], a case of ] by four groups working independently under wartime secrecy in the United Kingdom and the United States: William G. Templeman and associates at ] (ICI) in the UK; Philip S. Nutman and associates at ] in the UK; Franklin D. Jones and associates at the American Chemical Paint Company; and Ezra Kraus, John W. Mitchell, and associates at the ] and the ]. All four groups were subject to wartime secrecy laws and did not follow the usual procedures of publication and patent disclosure. In December 1942, following a meeting at the ] the Rothamsted and ICI workers pooled resources and Nutman moved to ] to join the ICI effort.<ref name=JH50>{{Cite book |title=Jealott's Hill: Fifty years of Agricultural Research 1928-1978 |editor-first=F.C. |editor-last1=Peacock |last=Allen |first=H.P. |display-authors=etal |chapter=Chapter 5: Selective herbicides |pages=35–41 |publisher=Imperial Chemical Industries Ltd. |year=1978 |isbn=0901747017 |chapter-url=https://archive.org/details/jealottshillfift0000peac/page/1}}</ref> The first scientific publication describing the 2,4-D structure and plant growth regulating activity was by Percy W. Zimmerman and Albert E. Hitchcock at the ],<ref>{{Cite journal|last1=Zimmerman|first1=Percy W.|last2=Hitchcock|first2=Albert E.|date=1942|title=Substituted phenoxy and benzoic acid growth substances and the relation of structure to physiological activity.|journal=Contrib. Boyce Thompson Institute|volume=12|pages=321–343}}</ref> who were not the original inventors. The precise sequence of early 2,4-D discovery events and publications has been discussed.<ref>{{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)0492.0.CO;2 |s2cid=85637273 }}</ref>
			William Templeman found that when ] (IAA), a naturally-occurring ], 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.<ref>{{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}}</ref> MCPA was discovered at about that time by his ICI group.<ref name=JH50/><ref name=Cobb>Andrew H. Cobb, John P. H. Reade. . Wiley-Blackwell; 2nd edition (October 25, 2010) {{ISBN|978-1405129350}}</ref>{{rp|Sec 7.1}}
	2,4-D was developed during World War II by a British team at ], under the leadership of ], aiming to increase crop yields for a nation at war.<ref>See the review article: J. H. Quastel, "2,4-dichlorophenoxyacetic acid (2,4-D) as a selective herbicide," ''Agricultural Control Chemicals'' (Washington, D.C.: American Chemical Society, 1950), Chapter 45, pages 244-249.</ref> When it was commercially released in ], it became the first successful selective herbicide and allowed for greatly enhanced weed control in ], ] (corn), ], and similar ] grass crops, because it only kills ] (broadleaf plants), leaving behind ] (grasses).
			In the USA, a similar 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-T), both ]s and ] of IAA. Robert Pokorny, an industrial chemist for the C.B. Dolge Company in ], published their synthesis in 1941.<ref>{{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}}</ref>
	===Genetically modified crops===
	] has demonstrated ] and ] resistance to 2,4-D due to insertion of a bacterial aryloxyalkanoate dioxygenase gene.<ref>Terry Wright, Guomin Shan, Terence Walsh, Justin Lira, Cory Cui, Ping Song, Meibao Zhang, Nicole Arnold, Gaofeng Lin, Kerrm Yau, Sean Russell, Robert Cicchillo, Mark Peterson, David Simpson, Ning Zhou, Jayakumar Ponsamuel, and Zhanyuan Zhang. 2010. Robust crop resistance to broadleaf and grass herbicides provided by aryloxyalkanoate dioxygenase transgenes. PNAS 107: 20240-20245. {{DOI|10.1073/pnas.1013154107}}</ref> This is intended as an alternative to ] crops due to the increasing prevalence of ] resistant weeds.
			2,4-D was not used as a chemical warfare agents during the war.<ref name=Cobb/>{{rp|Sec 7.1}} The ] were looking for a chemical to starve Nazi 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 tolerate 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 and wheat,<ref>{{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 |url-status= dead }}</ref> and in the 1950s it was registered in the United States to control size and enhance skin color in potatoes without affecting yields.<ref>{{cite journal |last1=Waterer |first1=D. |title=Influence of growth regulators on skin colour and scab diseases of red-skinned potatoes |journal=Canadian Journal of Plant Science |date=1 September 2010 |volume=90 |issue=5 |pages=745–753 |doi=10.4141/CJPS10055|doi-access=free }}</ref>
	==Mechanism of action==
	2,4-D is a synthetic ], which is a class of ]s. It is absorbed through the leaves and is translocated to the ]s 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 ] salt, but more potent ] versions exist as well.
			The first publication of 2,4-D's use as a selective herbicide came in 1944.<ref>{{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}}</ref><ref>{{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 | journal = Science | volume = 100 | issue = 2590| pages = 154–155 | doi = 10.1126/science.100.2590.154 | pmid = 17778584 | bibcode = 1944Sci...100..154H }}</ref> The ability of 2,4-D to control broadleaf weeds in turf was documented soon thereafter, in 1944.<ref>Mitchell JW, Davis FF and Marth PC (1944) Turf and weed control with plant growth regulators. ''Golfdom'' '''18''':34-38.</ref> 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 ]s (broadleaf plants), but not most ]s&nbsp;— narrowleaf crops, such as ], ] (corn), ], and similar ] grass crops.<ref name=Cobb/> At a time when labor was scarce and the need for increased food production was large, it literally "replaced the hoe".<ref name=Cobb/>{{rp|Sec 7.1}}
	==Manufacture==
	2,4-D is a member of the ] family of herbicides, which include:
	* ] (2,4,5-T)
	* ] (MCPA)
	* 2-(2-Methyl-4-chlorophenoxy)propionic acids (], MCPP)
	* 2-(2,4-Dichlorophenoxy)propionic acid (dichloroprop, 2,4-DP)
	* (2,4-Dichlorophenoxy)butyric acid (2,4-DB)
			2,4-D is one of the ingredients in ], an herbicide that was widely used during the ] and the ].<ref name=NPIC2/> However, ] (TCDD), a contaminant in the production of another ingredient in Agent Orange, ], was the cause of the adverse health effects associated with Agent Orange.<ref name=NPIC/><ref>{{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 |archive-date=2022-04-26 |archive-url=https://web.archive.org/web/20220426203157/https://www.epa.gov/ingredients-used-pesticide-products/24-d |url-status=dead }}</ref>
	2,4-D is manufactured from ] and ], which is itself produced by ] of ]. Alternatively, it may be produced by the chlorination of phenoxyacetic acid. The production processes creates several contaminants including ]s, ], and other ]s and their acids.<ref>{{cite web | url = http://www.inchem.org/documents/ehc/ehc/ehc29.htm | publisher = ] | title = 2,4-Dichlorophenoxyacetic Acid (2,4-D)}}</ref>
			In the 2000s, ] developed a new ] ] version of 2,4-D (2,4-D choline) that Dow included in its "Enlist Duo" herbicide along with ] and an agent that reduces drift; the choline salt form of 2,4-D is less volatile than 2,4-D.<ref name="yosemite.epa.gov"/><ref name=fleury>{{cite web |url=http://www.agannex.com/energy/enlist-weed-control-system-in-canada |first=Donna |last=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 |archive-url=https://web.archive.org/web/20140503232918/http://www.agannex.com/energy/enlist-weed-control-system-in-canada |archive-date=May 3, 2014 |url-status=dead }}</ref><ref>Josh Flint for Prairie Farmer. August 31, 2011 {{Webarchive|url=https://web.archive.org/web/20140504025154/http://farmprogress.com/story-dow-agrosciences-names-its-newest-herbicide-offering-duo-0-52677 |date=2014-05-04 }}</ref>
	===Dioxin impurities===
	Some preparations of 2,4-D are contaminated with ] due to the manufacturing process.<ref>{{cite web |url=http://www.inchem.org/documents/ehc/ehc/ehc84.htm |title=Dichlorophenoxyacetic acid, 2,4- (2,4-D): environmental aspects (EHC 84, 1989) |work=United Nations Environment Programme, the International Labour Organisation, and the World Health Organization |accessdate=}}</ref> ] (TCDD) is classified as "carcinogenic to humans" by ].<ref>{{cite journal |author=Hardell L, Walker MJ, Walhjalt B, Friedman LS, Richter ED |title=Secret ties to industry and conflicting interests in cancer research |journal=Am. J. Ind. Med. |volume=50 |issue=3 |pages=227–33 |year=2007 |month=March |pmid=17086516 |doi=10.1002/ajim.20357 |url=}}</ref>
			==Manufacture==
	Contamination is predominantly of the type with 2 or 3 chlorine atoms. Another form of dioxin, 2,7-dichlorodibenzo-p-dioxin (DCDD), an inevitable by-product of 2,4-D manufacturing, was found to be ] to dioxin ] in its toxic effect on the immunity of mice. TCDD received all the publicity while the DCDD component was largely forgotten. To this day, DCDD is not regulated or monitored by the EPA and PMRA, even though DCDD levels could be at much higher levels than TCDD. {{Citation needed|date=October 2008}} The typical smell of 2,4-D is the break-down product ], which is a suspected endocrine disrupter and possible carcinogen. 2,4-D is toxic to the liver at small dosages. Increases in liver function tests, jaundice, acute hepatitis, lobular and portal inflammation indicative of a toxic reaction, as well as permanent damage leading to cirrhosis in exposed golfers <ref>{{cite journal |author=Leonard C, Burke CM, O'Keane C, Doyle JS |title="Golf ball liver": agent orange hepatitis |journal=] |volume=40 |issue=5 |pages=687–8 |year=1997 |month=May |pmid=9203952 |doi= |url=http://gut.bmj.com/cgi/pmidlookup?view=long&pmid=9203952 |pmc=1027176}}</ref><ref>{{cite journal |author=Johnston S, McCusker G, Tobinson TJ |title='Golf ball liver': a cause of chronic hepatitis? |journal=] |volume=42 |issue=1 |pages=143 |year=1998 |month=January |pmid=9505901 |doi= 10.1136/gut.42.1.143a|url= |pmc=1726975}}</ref><ref></ref>
			2,4-D is a member of the ].<ref name=NPIC/> It is manufactured from ] and ], which is itself produced by ] of ]. Alternatively, it is produced by the chlorination of phenoxyacetic acid. The production processes may create several contaminants including di-, tri-, and ] isomers and ]s, as well as ].<ref name=IPCS>{{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|access-date= 2020-02-02}}</ref>
			]
			==Mode of action==
	The defoliant and herbicide ], used extensively throughout the ], contained 2,4-D. The controversies associated with the use of Agent Orange were associated with a contaminant (]) in the ] component.<ref></ref>
			2,4-D is a synthetic ] that induces uncontrolled growth and eventually death in susceptible plants.<ref>{{cite web |title=Synthetic Auxins - MSU Extension {{!}} Montana State University |url=https://www.montana.edu/extension/pubs/herbicideinjuryguide/Auxins.html |website=www.montana.edu |publisher=Montana State University Extension |access-date=29 December 2023}}</ref><ref name=Song>{{cite journal |doi=10.1111/jipb.12131 |title=Insight into the mode of action of 2,4-dichlorophenoxyacetic acid (2,4-D) as an herbicide |date=2014 |last1=Song |first1=Yaling |journal=Journal of Integrative Plant Biology |volume=56 |issue=2 |pages=106–113 |pmid=24237670 |doi-access=free }}</ref><ref name="invasive">{{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 |access-date=2015-11-01}}</ref> It is absorbed through the leaves and is translocated to the ]s 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 ] ], but more potent ] versions exist, as well.<ref>{{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|doi-access=free}}</ref>
			]'']]
	== Applications ==		== Applications ==
	2,4-D is primarily used as a herbicide.<ref>{{HPD|2530}}</ref> It is sold in various formulations under a wide variety of brand names. 2,4-D can be found in lawn herbicide mixtures such as "Weed B Gon MAX", "PAR III", "Trillion", "Tri-Kil", "Killex" and "Weedaway Premium 3-Way XP Turf Herbicide". All of these mixtures typically contain three active ingredients: 2,4-D, ] and ]. Over 1,500 herbicide products contain 2,4-D as an active ingredient.{{Citation needed|date=July 2010}}		2,4-D is primarily used as a selective ] that kills many terrestrial and aquatic broadleaf ]s, but not ]es. 2,4-D can be found in commercial lawn herbicide mixtures, which often contain other active ingredients including ] and ]. Over 1,500 herbicide products contain 2,4-D as an active ingredient.<ref>EPA Last revised March 30, 2007 {{webarchive |url=https://web.archive.org/web/20150910115620/http://www.epa.gov/teach/chem_summ/24D_summary.pdf |date=September 10, 2015 }}</ref>
			]
			A variety of sectors use products containing 2,4-D to kill weeds and unwanted vegetation. In agriculture, it was the first herbicide for selective killing of weeds but not crops. It has been used since 1945<ref>{{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 |access-date=2015-11-12}}</ref> to control broad-leafed weeds in pastures, orchards, and cereal crops such as corn, oats, rice, and wheat.<ref>{{cite web | last1=Harvey | first1=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 |access-date=2015-11-12}}</ref> 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.<ref>{{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 |access-date=2015-11-12}}</ref> The estimated use of 2,4-D in US agriculture is mapped by the US Geological Survey. In 2019, the latest date for which figures are available, this reached {{convert|45000000|lb|kg}} annually.<ref>{{cite web |url=https://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=2019&map=24D&hilo=L |title=Estimated Agricultural Use for 2,4-D, 2019 |author=US Geological Survey |date=2021-10-12 |access-date=2021-12-27 }}</ref>
			In domestic lawn and garden maintenance, 2,4-D is commonly used. 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.<ref name=efsa/>{{rp|35–36}} <ref>{{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 |access-date=2015-11-06 |archive-url=https://web.archive.org/web/20151102024718/http://www.24d.org/benefits/default.aspx |archive-date=2015-11-02 |url-status=dead }}</ref>
	2,4-D is most commonly used for:
	* Weed control in lawns and other turf
	* No-till burndown
	* Control of weeds and brush along fences and highway and railroad rights of way
	* Conifer release (control of broad-leaf trees in conifer plantings)
	* Grass hayfields and pastures
	* Cereal grains
	* Corn and sorghum (occasionally)
	* As a synthetic auxin analogue
			A 2010 monitoring study conducted in the US and Canada found that "current exposures to 2,4-D are below applicable exposure guidance values."<ref>{{cite journal|vauthors=Aylward LL, Morgan MK, Arbuckle TE, Barr DB, Burns CJ, Alexander BH, Hays SM|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}}</ref>
	2,4-D continues to be used, where legal, for its low cost. However, where municipal lawn pesticide bylaws exist, such as in Canada,<ref></ref> alternatives such as ] and ]-based products are increasingly being used to combat weeds.
			2,4-D has been used in laboratories for plant research as a supplement in plant ] media such as ] since at least 1962.<ref>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}}</ref> 2,4-D is used in plant cell cultures as a dedifferentiation (callus induction) hormone. It is classified as an auxin plant hormone derivative.<ref>{{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}}</ref>
	==Toxicity==
			==Health effects==
	{{see also|Health effects of pesticides|Pesticide poisoning}}		{{see also|Health effects of pesticides|Pesticide poisoning}}
			Men who work with 2,4-D are at risk for abnormally shaped sperm and thus ]; the risk depends on the amount and duration of exposure and other personal factors.<ref>NIOSH. Updated June 2014. </ref>
			===Acute toxicity===
			According to the U.S. ], "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."<ref name=EPAFAQ2014/> {{As of| 2005}} the ] or LD<sub>50</sub> determined in acute toxicity rat studies was 639&nbsp;mg/kg.<ref name=EPARED2005>, 2005. {{webarchive|url=https://web.archive.org/web/20080517130243/http://www.epa.gov/oppsrrd1/REDs/factsheets/24d_fs.htm |date=2008-05-17 }} EPA</ref>
			] has been used in acute poisoning, but evidence to support its use is poor.<ref>{{cite journal |vauthors=Roberts DM, Buckley NA |title=Urinary alkalinisation for acute chlorophenoxy herbicide poisoning |journal=Cochrane Database Syst Rev |issue=1 |pages=CD005488 |year=2007 |pmid=17253558 |doi=10.1002/14651858.CD005488.pub2 |editor1-last=Roberts |editor1-first=Darren M}}</ref>
	===Cancer risk===		===Cancer risk===
			The ] classifies 2,4-D as a possible ] to humans while the ] does not.<ref>{{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}}</ref><ref name=Lancet>{{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}}</ref> The ] (IARC), said 2,4-D was classified as "possibly carcinogenic to humans (]), based on inadequate evidence in humans and limited evidence in experimental animals".<ref>{{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 | access-date=14 February 2016}}</ref>
	Different organizations have taken different stances on 2,4-D's cancer risk. On August 8, 2007, the United States Environmental Protection Agency issued a ruling that stated that existing data does not support a conclusion that links human cancer to
	2,4-D exposure.<ref></ref> The International Agency for Research on Cancer (IARC) has classified 2,4-D among the phenoxy acid herbicides ] and ] as a class 2B carcinogen - possibly carcinogenic to humans.<ref>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.</ref> A 1995 panel of 13 scientists reviewing studies on the carcinogenicity of 2,4-D had divided opinions, but the predominant opinion was that it is possible that 2,4-D causes cancer in humans.<ref></ref>
	A 1990 study of ] in ], even when adjusting for exposure to other chemicals, found that 2,4-D exposure substantially increased the risk of ] (NHL).<ref></ref> A 2000 study of 1517 former employees of ] who had been exposed to the chemical in manufacturing or formulating 2,4-D found no significant increase in risk of mortality due to NHL following 2,4-D exposure, but did find an increase in risk of mortality due to ].<ref>{{cite web|title= C J Burnsa, K K Beardb, J B Cartmill, "Mortality in chemical workers potentially exposed to 2,4-dichlorophenoxyacetic acid (2,4-D) 1945-94: an update", ''Occupational and Environmental Medicine'', Vol. 58, pp. 24-30, 2001.|url=http://oem.bmj.com/cgi/content/abstract/58/1/24|work=|archiveurl=http://www.webcitation.org/5glwM8D7U|archivedate=2009-05-14|deadurl=no|accessdate=2009-05-08}}</ref>
			In June 2015 the ]'s ] confirmed its 1987 classification of 2,4-D as a possible carcinogen.<ref>{{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}}</ref><ref>Carey Gillam for Reuters. June 22, 2015 {{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 }}</ref>
	===Other===
	The ] determined in an acute toxicity rat study is 639&nbsp;mg/kg.<ref>US EPA 2,4-D Reregistration Eligiblity Decision, 2006</ref> Single oral doses of 5 and 30&nbsp;mg/kg body weight did not cause any acute toxic effects in human volunteers. This chemical has been associated with the risk of ].<ref>{{cite journal |author=Burns CJ, Beard KK, Cartmill JB |title=Mortality in chemical workers potentially exposed to 2,4-dichlorophenoxyacetic acid (2,4-D) 1945-94: an update |journal=Occup Environ Med |volume=58 |issue=1 |pages=24–30 |year=2001 |month=January |pmid=11119631 |pmc=1740039 |doi= 10.1136/oem.58.1.24|url=}}</ref>
			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.<ref name="autogenerated1">{{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 |access-date=2014-05-03}}</ref>
	The ] salt formulations can cause irreversible eye damage (]); ] formulations are considered non-irritating to the eyes.
			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.<ref name="pmid1820267">{{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 | pages= 213–22 | pmid=1820267 | doi= 10.1289/ehp.9196213| pmc=1568222 |display-authors=etal}}</ref>
	One study found that occupational exposure to 2,4-D caused male reproductive problems, including dead and malformed ].<ref>{{cite web|title= D. Lerda, R. Rizzi, "Study of reproductive function in persons occupationally exposed to 2,4-dichlorophenoxyacetic acid (2,4-D).", ''Mutation Research'', Vol. 262, No. 1, pp. 47-50. 1991.|url=http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=ENV&recid=2522252&q=%222%2C4-D%22&uid=1101926&setcookie=yes|work=|archiveurl=http://www.webcitation.org/5glwLknsa|archivedate=2009-05-14|deadurl=no|accessdate=2009-05-08}}</ref>
			In a prior 1987 report the IARC classified some chlorphenoxy herbicides including 2,4-D, ] and ] as a group as class 2B carcinogens - "possibly carcinogenic to humans".<ref> 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.</ref>
	Concerns regarding ] have been voiced with increased sensitivity to ] and thus concerns of increased risk of ] among those exposed.<ref>{{cite journal |author=Jones DC, Miller GW |title=The effects of environmental neurotoxicants on the dopaminergic system: A possible role in drug addiction |journal=Biochem. Pharmacol. |volume=76 |issue=5 |pages=569–81 |year=2008 |month=September |pmid=18555207 |doi=10.1016/j.bcp.2008.05.010 |url=}}</ref>
			2,4-D has been linked to lymphoma and bladder cancer in dogs.<ref>{{cite web |last1=Harveston |first1=Kate |title=Canine Cancers Linked to Lawn Care Chemicals |date=13 March 2019 |url=https://emagazine.com/canine-cancers-linked-to-lawn-care-chemicals/}}</ref>
	===Treatment===
	While ] has been used in acute poisonings, evidence to support its use is poor.<ref>{{cite journal |author=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=}}</ref>
			===Contaminants===
			A July 2013 ] investigation found elevated levels of ] in a generic version of 2,4-D, one of Australia's most widely used herbicides. Samples 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."<ref>{{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 2,4-D |publisher=Abc.net.au |date=22 July 2013 |access-date=2014-05-03}}</ref>
			==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 ], dichloroanisole, ] (6.9% of the TRR in milk), and ] (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.<ref name=efsa/>{{rp|21}}
	==Environmental behavior==		==Environmental behavior==
			Owing to the longevity and extent of use, 2,4-D has been evaluated several times by regulators and review committees.<ref>{{cite journal |doi=10.1016/j.envint.2017.10.020 |title=Potential impact of the herbicide 2,4-dichlorophenoxyacetic acid on human and ecosystems |date=2018 |last1=Islam |first1=Faisal |last2=Wang |first2=Jian |last3=Farooq |first3=Muhammad A. |last4=Khan |first4=Muhammad S.S. |last5=Xu |first5=Ling |last6=Zhu |first6=Jinwen |last7=Zhao |first7=Min |last8=Muños |first8=Stéphane |last9=Li |first9=Qing X. |last10=Zhou |first10=Weijun |journal=Environment International |volume=111 |pages=332–351 |pmid=29203058 }}</ref><ref>{{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 | journal = J Toxicol | volume = 2013 | page = 371610 | doi = 10.1155/2013/371610 | pmid = 23533401 | pmc = 3600329 | doi-access = free }}</ref><ref name=NYTdeny>Andrew Pollack for the New York Times. April 9, 2012 Quote: "The E.P.A. has reviewed the safety of 2,4-D several times, particularly with regard to an increased risk of cancer."</ref>
	Owing to the longevity and extent of use, 2,4-D is among the most thoroughly studied herbicides with respect to environmental properties. 2,4-D applied at 1.16&nbsp;lb/acre to bluegrass turf in a laboratory experiment had a half-life of ten days. Other studies found half-life figures between 1.5 and 16 days. Soil microbes are primarily responsible for its disappearance in soil. Studies in Alaska and Canada failed to detect leaching in 22 weeks or from spring to fall,<ref>Forest Service, (1984). Pesticide Background Statements, Vol. I Herbicides. United States Department of Agriculture, Agriculture Handbook No. 633.</ref> but 2,4-D has been included on the EPA list of compounds that are likely to leach from soil.
			2,4-D amine salts and esters are not persistent under most environmental conditions.<ref name=NPIC>National Pesticide Information Center </ref> The degradation of 2,4-D is rapid (half life of 6.2 days) in aerobic mineral soils.<ref name=EPARED2005/>{{rp|54}} 2,4-D is broken down by microbes in soil, in processes that involve ], cleavage of the acid side-chain, ], and ring opening. The ethyl hexyl form of the compound is rapidly hydrolyzed in soil and water to form the 2,4-D acid.<ref name=NPIC/> 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.<ref name=NPIC/>
	In aquatic environments microorganisms readily degrade 2,4-D and breakdown by sunlight is not a major reason for loss. Rates of breakdown increase with increased nutrients, sediment load and dissolved organic carbon. Under oxygenated conditions the half-life can be short, in the order of one week to several weeks. 2,4-D interferes with normal plant growth processes. Uptake of the compound is through leaves, stems and roots; however, it is, in general, nonpersistent. In one study when 2,4-D was applied to grass, there were 80 ppm at day zero, 45 ppm at 14 days, and 6 ppm at 56 days. Breakdown in plants is by a variety of biological and chemical pathways.<ref>National Research Council Canada (1978). Phenoxy Herbicides - Their Effects on Environmental Quality with Accompanying Scientific Criteria for 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD). Subcommittee on Pesticides and Related Compounds, NRC Associate Committee on Scientific Criteria for Environmental Quality, Ottawa, Canada.</ref>
			In aerobic aquatic environments, the half life is 15 days. In anaerobic aquatic environments 2,4-D is more persistent, with a half life of 41 to 333 days.<ref>{{cite journal |doi=10.1021/acsomega.8b02282 |title=Combined Toxicity of 2,4-Dichlorophenoxyacetic Acid and Its Metabolites 2,4-Dichlorophenol (2,4-DCP) on Two Nontarget Organisms |year=2019 |last1=Ju |first1=Zhen |last2=Liu |first2=Shu-Shen |last3=Xu |first3=Ya-Qian |last4=Li |first4=Kai |journal=ACS Omega |volume=4 |issue=1 |pages=1669–1677 |pmid=31459423 |pmc=6648169 }}</ref> 2,4-D has been detected in streams and shallow groundwater at low concentrations, in both rural and urban areas. Breakdown is pH dependent.<ref name=NPIC/> Some ester forms are highly toxic to fish and other aquatic life.<ref name=NPIC2>{{cite web|title=2,4-D General Fact Sheet|url=http://npic.orst.edu/factsheets/24Dgen.html|publisher=National Pesticide Information Center|access-date=7 October 2015}}</ref>
	A number of 2,4-D-degrading bacteria have been isolated and characterized from a variety of environmental habitats.<ref>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.</ref><ref>Suwa, Y., A.D. Wright, F. Fukimori, K.A. Nummy, R.P. Hausinger, W.E. Holben, and L.J. Forney. 1996. Characterization of a chromosomally encoded 2,4-dichlorophenoxyacetic acid alpha-ketoglutafate dioxygenase from Burkholderia sp. strain RASC. Applied and Environmental Microbiology 62: 2464-2469.</ref> Metabolic pathways for the compound’s degradation have been available for many years, and genes encoding 2,4-D ] have been identified for several organisms. As a result of the extensive ] on environmental behavior, physiology and genetics, 2,4-D was the first herbicide for which the bacteria actively responsible for ] degradation was demonstrated.<ref>Cupples, A.M. and G.K. Sims. 2007. Identification of In Situ 2,4-Dichlorophenoxyacetic Acid-Degrading Soil Microorganisms using DNA-Stable Isotope Probing. Soil Biology and Biochemistry 39: 232-238.</ref> 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.<ref>Radajewski, S., P. Ineson, N.R. Parekh, and J.C. Murrell. 2000. Stable-isotope probing as a tool in microbial ecology. Nature 403: 646-649.</ref> This advancement has been particularly beneficial for the study of soil microorganisms, since only a very small fraction of the thousands of species present in highly diverse soil bacterial communities can be isolated in pure culture.
			"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.<ref name=EPAFAQ2014>{{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|access-date=November 6, 2014|date=2014-09-22|archive-date=2022-04-26|archive-url=https://web.archive.org/web/20220426203157/https://www.epa.gov/ingredients-used-pesticide-products/24-d|url-status=dead}}</ref>{{date missing}}
	Despite its short half-life in soil and in aquatic environments, the compound has been detected in groundwater supplies in at least five States and in Canada.<ref>Howard, Philip H. Handbook of Environmental Fate and Exposure Data for Organic Chemicals. Lewis Publishers Chelsea, Michigan.</ref> It has also been detected in surface waters throughout the United States at very low concentrations.
			===Microbial breakdown===
	==Legal issues==
			A number of 2,4-D-degrading bacteria have been isolated and characterized from a variety of environmental habitats.<ref>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.</ref><ref>{{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 | journal = Applied and Environmental Microbiology | volume = 62 | issue = 7| pages = 2464–2469 |pmid=8779585 |pmc=168028 |doi=10.1128/AEM.62.7.2464-2469.1996 |bibcode=1996ApEnM..62.2464S }}</ref> Metabolic pathways for the compound's degradation have been available for many years, and genes encoding 2,4-D ] have been identified for several organisms. As a result of the extensive ] on environmental behavior, physiology, and genetics, 2,4-D was the first herbicide for which the bacteria actively responsible for ''] ''degradation were demonstrated.<ref>{{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 | journal = Soil Biology and Biochemistry | volume = 39 | pages = 232–238 | doi=10.1016/j.soilbio.2006.07.011}}</ref> 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.<ref>{{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 | journal = Nature | volume = 403 | issue = 6770| pages = 646–649 | doi=10.1038/35001054|pmid=10688198 |bibcode=2000Natur.403..646R |s2cid=4395764 }}</ref>
			==Regulation ==
	2,4-D has been evaluated by the European Union and included on its list of approved herbicides, stating inter alia that "the review has established that the residues arising from the proposed uses,
			]s were first set in the EU in 2002 and re-evaluated in 2011 by the ], which concluded that the codex maximum residue limits were "not expected to be of concern for European consumers".<ref name=efsa>{{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|doi-access=free}}</ref>{{rp|26}} The total chronic exposure represented less than 10% of the acceptable daily intake (ADI).<ref name=efsa/>{{rp|28}} 2,4-D is currently not approved for use on lawns and gardens in Denmark, Norway, Kuwait, and the Canadian provinces of Québec<ref>{{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 |access-date=2014-05-03}}</ref> and Ontario.<ref>{{cite web|url=http://www.ene.gov.on.ca/en/news/2009/030401.php |title=Ministry of the Environment &#124; Ontario.ca |publisher=Ene.gov.on.ca |access-date=2014-05-03}}</ref>{{Failed verification|date=June 2021}} 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.<ref name=gm>{{cite news|first=Barrie|last=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/|access-date=26 June 2015|work=The Globe and Mail|date=May 27, 2011}}</ref>
	consequent on application consistent with good plant protection practice, have no harmful effects on human or
	animal health."<ref></ref> Concern over 2,4-D is such that it is currently not approved for use on lawns and gardens in Sweden,<ref>http://sv.wikipedia.org/2,4-diklorfenoxiättiksyra</ref> Denmark, Norway, Kuwait and the Canadian provinces of Québec <ref>http://www.mddep.gouv.qc.ca/pesticides/permis-en/code-gestion-en/espace-vert.htm</ref> and Ontario.<ref>http://www.ene.gov.on.ca/en/news/2009/030401.php</ref> 2,4-D use is severely restricted in the country of Belize. In 2005, the United States Environmental Protection Agency approved the continued use of 2,4-D.<ref></ref> In Canada, the Pest Management Regulatory Agency (PMRA) has placed a condition of registration on 2,4-D such that the 2,4-D registrant(s) must provide the PMRA with a required developmental neurotoxicity study by September 20, 2009.<ref></ref> According to the PMRA, the due date of the study has since been extended to early 2010.
			In 2012, EPA denied the petition filed November 6, 2008, by the ] to revoke all tolerances and to cancel all registrations of 2,4-D. EPA stated that new study and EPA's comprehensive review confirmed EPA's previous finding that the 2,4-D tolerances are safe at anticipated exposure.<ref name=NYTdeny/><ref name="EPA4712Docket Folder Summary">{{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|access-date=September 12, 2012|format=Docket Folder Summary|date=April 7, 2012}}</ref><ref name=FR51812>{{cite journal|title=2,4-D; Order Denying NRDC's Petition To Revoke Tolerances|journal=]|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|access-date=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}}</ref> The estimated annual use of 2,4-D in US agriculture is mapped by the US Geological Service.<ref>{{cite web |url=https://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=2016&map=24D&hilo=L&disp=2,4-D |title=Estimated Agricultural Use for 2,4-D in the USA, 2016 |author=US Geological Survey |access-date=2020-02-15 }}</ref>
	==References==
	<references/>
			In October 2014, the US EPA registered ], 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.<ref name="yosemite.epa.gov">EPA Press Release. October 15, 2014 {{Webarchive|url=https://web.archive.org/web/20170804190154/https://yosemite.epa.gov/opa/admpress.nsf/bd4379a92ceceeac8525735900400c27/72fde554930f3f6985257d7200591180!OpenDocument |date=2017-08-04 }}</ref> 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.<ref>{{cite web|last=Vogt|first=Willie|date=January 26, 2016|title=Ninth Circuit Court denies move by EPA to vacate herbicide label|url=https://www.farmprogress.com/soybeans/federal-court-denies-move-epa-vacate-herbicide-label|access-date=2016-02-05|publisher=Farm Futures}}</ref><ref>{{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}}</ref>
	==External links==
	Government and academic references:
	*
	*
	*
	*
	* , Environmental Health Perspectives online 12. 8. 2009
	* Burns et al.: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1740039/?tool=pubmed
			On 21 August 2013, the ] (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.<ref>{{cite web|title=APVMA 2,4-D Review webpage|url=http://www.apvma.gov.au/products/review/current/2_4_d.php|publisher=APVMA|access-date=2014-06-06|archive-url=https://web.archive.org/web/20140606215228/http://www.apvma.gov.au/products/review/current/2_4_d.php|archive-date=2014-06-06|url-status=dead}}</ref> In July 2013 APVMA published their report findings.<ref>{{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|archive-url=https://web.archive.org/web/20140606215344/http://www.apvma.gov.au/products/review/docs/2-4-d-hve.pdf|archive-date=6 June 2014|access-date=25 August 2016}}</ref>
	Industry website:
	*
			==Genetically modified crops==
	Health and environmental references:
	*
	*
	*
			In 2010, ] published that it had created ]s made resistant to 2,4-D by insertion of a bacterial aryloxyalkanoate dioxygenase gene, ''aad1''.<ref>{{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|bibcode=2010PNAS..10720240W|doi-access=free}}</ref><ref name="ISAAAaad1" /><ref>Mark A. Peterson, Guomin Shan, Terence A. Walsh, and Terry R. Wright. ISB News Report,3 pages, May 2011, Research & Development, Dow AgroSciences, Indianapolis</ref>{{rp|1}} Dow intended it to be used as an alternative or complement to ] crops due to the increasing prevalence of ]-resistant weeds.<ref name="NYTDOWCORN">{{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|access-date=April 25, 2012|newspaper=The New York Times|date=April 25, 2012|first=Andrew|last=Pollack}}</ref>
			As of April 2014, ] and soybeans resistant to 2,4-D and glyphosate have been approved in Canada.<ref name=fleury/> In September 2014, the ] also approved Dow's maize and soybeans, and in October, the EPA registered the "Enlist Duo" herbicide containing 2,4-D and glyphosate.<ref name="yosemite.epa.gov"/><ref name=ISAAAaad1>ISAAA GM Approval Database . International Service for the Acquisition of Agri-biotech Applications (ISAAA), n.d. accessed February 27, 2015</ref><ref name=wired>{{cite magazine|first=Brandon|last=Keim|title=New Generation of GM Crops Puts Agriculture in a 'Crisis Situation'|url=https://www.wired.com/2014/09/new-gm-crops/|access-date=13 April 2015|magazine=Wired|publisher=Condé Nast|date=25 September 2014}}</ref>
			==See also==
			*]
			*]
			==References==
			{{reflist|30em}}
			==External links and further reading==
			{{commons category|2,4-Dichlorophenoxyacetic acid}}
			*
			* ] January, 2005
			* Review of the literature by Dow scientists Crit Rev Toxicol. Oct 2012
			* Pesticides Properties database entry for 2,4-D
			* on Pubchem
	{{Herbicides}}		{{Herbicides}}
	{{DEFAULTSORT:Dichlorophenoxyacetic Acid, 2,4-}}		{{Authority control}}
			{{DEFAULTSORT:Dichlorophenoxyacetic Acid, 2, 4-}}
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