2,4-Dichlorophenoxyacetic acid

{{chembox | Name = 2,4-Dichlorophenoxyacetic acid | ImageFile1 = 2,4-Dichlorophenoxyacetic acid structure numbered.svg | ImageClass1 = skin-invert-image | ImageFile1_Ref = {{chemboximage|correct|??}} | ImageSize1 = 210 | ImageName1 = 2,4-dichlorophenoxyacetic acid | ImageFile2 = 2,4-Dichlorophenoxyacetic-acid-3D-balls-2.png | ImageClass2 = bg-transparent | ImageSize2 = 220 | ImageAlt2 = Ball-and-stick model of 2,4-dichlorophenoxyacetic acid | PIN = (2,4-Dichlorophenoxy)acetic acid | OtherNames = 2,4-D |Section1={{Chembox Identifiers | ChEBI_Ref = {{ebicite|correct|EBI}} | ChEBI = 28854 | SMILES = Clc1cc(Cl)ccc1OCC(=O)O | PubChem = 1486 | KEGG_Ref = {{keggcite|correct|kegg}} | KEGG = C03664 | InChI = 1/C8H6Cl2O3/c9-5-1-2-7(6(10)3-5)13-4-8(11)12/h1-3H,4H2,(H,11,12) | InChIKey = OVSKIKFHRZPJSS-UHFFFAOYAM | ChEMBL_Ref = {{ebicite|correct|EBI}} | ChEMBL = 367623 | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChI = 1S/C8H6Cl2O3/c9-5-1-2-7(6(10)3-5)13-4-8(11)12/h1-3H,4H2,(H,11,12) | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = OVSKIKFHRZPJSS-UHFFFAOYSA-N | CASNo = 94-75-7 | CASNo_Ref = {{cascite|correct|CAS}} | UNII_Ref = {{fdacite|correct|FDA}} | UNII = 2577AQ9262 | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID = 1441 | RTECS = }} |Section2={{Chembox Properties | C=8 | H=6 | Cl=2 | O=3 | MolarMass = 221.04 g/mol | Appearance = white to yellow powder | Solubility = 900 mg/L | MeltingPtC = 140.5 | BoilingPtC = 160 | BoilingPt_notes = 0.4 mm Hg | pKa = }} |Section3={{Chembox Structure | CrystalStruct = | Dipole = }} |Section7={{Chembox Hazards | ExternalSDS = [http://www.inchem.org/documents/icsc/icsc/eics0033.htm ICSC 0033] | GHSPictograms = {{GHS07}} {{GHS05}} | GHS_ref = <ref name="sigma">{{Sigma-Aldrich|supelco|id=49083|name=2,4-D|accessdate=March 17, 2022}}</ref> | HPhrases = {{H-phrases|302|317|318|335|412}} | PPhrases = {{P-phrases|261|273|280|305+351+338}} | MainHazards = | FlashPt = nonflammable | FlashPt_ref = <ref name=PGCH/> | PEL = TWA 10 mg/m3<ref name=PGCH>{{PGCH|0173}}</ref> | REL = TWA 10 mg/m3<ref name=PGCH/> | IDLH = 100 mg/m3<ref name=PGCH/> | LD50 = 500 mg/kg (oral, hamster) 100 mg/kg (oral, dog) 347 mg/kg (oral, mouse) 699 mg/kg (oral, rat) <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 = December 4, 2014 |access-date = February 26, 2015}}</ref> }} |Section8={{Chembox Related | OtherCompounds = 2,4,5-T, Dichlorprop }} }}

'''2,4-Dichlorophenoxyacetic acid''' is an organic compound with the chemical formula {{chem2|C8H6Cl2O3}}. It is usually referred to by its ISO common name '''2,4-D'''.<ref>{{cite web |url=http://www.alanwood.net/pesticides/ |title=Compendium of Pesticide Common Names}}</ref> It is a systemic herbicide that kills most broadleaf weeds by causing uncontrolled growth, but most grasses such as cereals, lawn turf, and grassland are 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.

==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 name=":0">{{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 |bibcode=1941JAChS..63.1768P }}</ref> The biological activity of 2,4-D as well as the similar hormone herbicides 2,4,5-T, and MCPA were discovered during World War II, 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 (ICI) 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. In December 1942, following a meeting at the Ministry of Agriculture the Rothamsted and ICI workers pooled resources and Nutman moved to Jealott's Hill 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=0-901747-01-7 |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 Zimmerman and Albert Hitchcock at the Boyce Thompson Institute,<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)049[0290:ITBTMD]2.0.CO;2 |s2cid=85637273 }}</ref>

William Templeman found that when indole-3-acetic acid (IAA), a 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.<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">{{Cite book |last=Cobb |first=Andrew H. |url=https://books.google.com/books?id=hVK4vrpma2YC |title=Herbicides and Plant Physiology |last2=Reade |first2=John P. H. |date=June 9, 2011 |publisher=John Wiley & Sons |isbn=978-1-4443-2249-1 |language=en}}Andrew H. Cobb, John P. H. Reade. [https://books.google.com/books?id=hVK4vrpma2YC Herbicides and Plant Physiology]. Wiley-Blackwell; 2nd edition (October 25, 2010) {{ISBN|978-1405129350}}</ref>{{rp|Sec 7.1}}

In the United States, 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-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.<ref name=":0" />

2,4-D was not used as a chemical warfare agent during the war.<ref name=Cobb/>{{rp|Sec 7.1}} The Allies of World War II 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= November 23, 2015 |archive-url= https://web.archive.org/web/20111207192448/http://www.plantsciences.ucdavis.edu/plantsciences/features/fall2010_rotator/weeds3_weed_crop.htm |archive-date= December 7, 2011 }}</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=September 1, 2010 |volume=90 |issue=5 |pages=745–753 |doi=10.4141/CJPS10055|doi-access=free }}</ref>

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 |url=https://archive.org/details/sim_science_1944-08-18_100_2590/page/154 | 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 dicotyledons (broadleaf plants), but not most monocotyledons — narrowleaf crops, such as wheat, maize (corn), rice, and similar cereal 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}} Its effectiveness, together with its non-corrosive, non-explosive and seemingly non-irritating or poisonous qualities, led to it being considered the best all-around herbicide by 1946.<ref>{{Cite book |url=http://archive.org/details/sim_consumer-reports_1947?q=Fertilizer |title=Consumer Reports 1947 |publisher=Consumers Union of U.S., Inc. |year=1947 |pages=375 |language=English}}https://archive.org/details/sim_consumer-reports_1947/page/374/mode/2up?q=Fertilizer Consumer Reports 1947 Buying Guide, p. 375.</ref>

2,4-D is one of the ingredients in Agent Orange, an herbicide that was widely used during the Malayan Emergency and the Vietnam War.<ref name=NPIC2/> 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.<ref name=NPIC/><ref name="EPAFAQ2014" />

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.<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 }}</ref><ref>{{Cite web |last=Flint |first=Josh |date=August 31, 2011 |title=Dow AgroSciences Names Its Newest Herbicide Offering Enlist Duo |url=http://farmprogress.com/story-dow-agrosciences-names-its-newest-herbicide-offering-duo-0-52677 |url-status=dead |archive-url=https://web.archive.org/web/20140504025154/http://farmprogress.com/story-dow-agrosciences-names-its-newest-herbicide-offering-duo-0-52677 |archive-date=May 4, 2014 |publisher=Prairie Farmer}}</ref>

==Manufacture== 2,4-D is a member of the phenoxy family of herbicides.<ref name=NPIC/> It 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 may create several contaminants including di-, tri-, and tetrachlorodibenzo-''p''-dioxin isomers and ''N''-nitrosamines, as well as monochlorophenol.<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= February 2, 2020}}</ref> right|thumb|Containers of 2-4 D herbicide, ca. 1947

==Mode of action== 2,4-D is a synthetic auxin 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 |url-status=dead |archive-url=https://web.archive.org/web/20231229173921/https://www.montana.edu/extension/pubs/herbicideinjuryguide/Auxins.html |archive-date=December 29, 2023 |access-date=December 29, 2023 |website=www.montana.edu |publisher=Montana State University Extension}}</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 |bibcode=2014JIPB...56..106S }}</ref><ref name="invasive">{{cite web |date=April 2001 |title=Weed Control Methods Handbook: 2,4-D |url=http://www.invasive.org/gist/products/handbook/10.24-d.pdf |url-status=live |archive-url=https://web.archive.org/web/20160304113140/http://www.invasive.org/gist/products/handbook/10.24-d.pdf |archive-date=March 4, 2016 |access-date=November 1, 2015 |website=invasive.org |publisher=University of Georgia Center for Invasive Species and Ecosystem Health}}</ref> 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.<ref name="Song" />

[[File:Lantana 2-4-D effect close up.jpg|right|thumb|Effect of 2-4-D foliar application on ''Lantana'']]

== Applications == 2,4-D is primarily used as a selective herbicide that kills many terrestrial and aquatic broadleaf weeds, but not grasses. 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.<ref>{{Cite web |title=EPA Chemical Summary: 2,4-Dichlorophenoxyacetic Acid (2,4-D) |url=http://www.epa.gov/teach/chem_summ/24D_summary.pdf |url-status=dead |archive-url=https://web.archive.org/web/20150910115620/http://www.epa.gov/teach/chem_summ/24D_summary.pdf |archive-date=September 10, 2015}}</ref> thumb|Estimated use of 2,4-D in the USA to 2019 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 |last=Ganzel |first=Bill |title=Herbicides – 2,4-D & Its Cousins |url=http://www.livinghistoryfarm.org/farminginthe40s/pests_03.html |url-status=dead |archive-url=https://web.archive.org/web/20151112095835/http://www.livinghistoryfarm.org/farminginthe40s/pests_03.html |archive-date=November 12, 2015 |access-date=November 12, 2015 |publisher=Wessels Living History Farm}}</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. |date=February 1947 |title=2,4-D as a Weed Killer |url=http://ucanr.edu/repository/fileaccess.cfm?article=100374&p=MSQYWZ&CFID=82966751&CFTOKEN=41384002 |url-status=live |archive-url=https://web.archive.org/web/20151208153136/http://ucanr.edu/repository/fileaccess.cfm?article=100374&p=MSQYWZ&CFID=82966751&CFTOKEN=41384002 |archive-date=December 8, 2015 |access-date=November 12, 2015 |publisher=University of California at Berkeley}}</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 |date=September 2008 |title=Fall Weed Control - FAQs |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 |url-status=dead |archive-url=https://web.archive.org/web/20151208160444/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 |archive-date=December 8, 2015 |access-date=November 12, 2015 |publisher=Saskatchewan Ministry of Agriculture}}</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=October 12, 2021 |access-date=December 27, 2021 }}</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=November 6, 2015 |archive-url=https://web.archive.org/web/20151102024718/http://www.24d.org/benefits/default.aspx |archive-date=November 2, 2015 }}</ref>

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|bibcode=2010EnvHP.118..177A }}</ref>

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.<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>

==Health effects== {{see also|Health effects of pesticides|Pesticide poisoning}} 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.<ref>{{cite web |title=The Effects of Workplace Hazards on Male Reproductive Health |url=https://www.cdc.gov/niosh/docs/96-132/ |url-status=dead |archive-url=https://web.archive.org/web/20170506045837/https://www.cdc.gov/niosh/docs/96-132/ |archive-date=May 6, 2017 |publisher=NIOSH}}</ref>

===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."<ref name=EPAFAQ2014/> {{As of| 2005}} the median lethal dose or LD50 determined in acute toxicity rat studies was 639 mg/kg.<ref name=EPARED2005>[https://web.archive.org/web/20050910221958/http://www.epa.gov/oppsrrd1/REDs/24d_red.pdf US EPA 2,4-D Reregistration Eligibility Decision], 2005. [http://www.epa.gov/oppsrrd1/REDs/factsheets/24d_fs.htm Associated RED Fact sheet] {{webarchive|url=https://web.archive.org/web/20080517130243/http://www.epa.gov/oppsrrd1/REDs/factsheets/24d_fs.htm |date=May 17, 2008 }} EPA</ref>

Urinary alkalinisation 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 |article-number=CD005488 |year=2007 |pmid=17253558 |doi=10.1002/14651858.CD005488.pub2 |editor1-last=Roberts |editor1-first=Darren M}}</ref>

===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.<ref>{{cite web|url=https://pubchem.ncbi.nlm.nih.gov/compound/2_4-dichlorophenoxyacetic_acid#section=NIOSH-Toxicity-Data|archive-url=https://web.archive.org/web/20150529110140/http://pubchem.ncbi.nlm.nih.gov/compound/2_4-dichlorophenoxyacetic_acid#section=NIOSH-Toxicity-Data|archive-date=May 29, 2015|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 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".<ref>{{cite web | title=IARC Monographs evaluate DDT, lindane, and 2,4-D | date=June 23, 2015 | url=https://www.iarc.fr/en/media-centre/pr/2015/pdfs/pr236_E.pdf | access-date=February 14, 2016}}</ref>

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.<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 [https://www.msn.com/en-us/news/us/who-unit-finds-24-d-herbicide-possibly-causes-cancer-in-humans/ar-AAbYBtV 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=June 23, 2015 }}</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 |archive-url=https://archive.today/20120801064011/http://www.epa.gov/fedrgstr/EPA-PEST/2007/August/Day-08/p15109.htm |archive-date=August 1, 2012 |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=May 3, 2014}}</ref>

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 |bibcode=1991EnvHP..96..213I |display-authors=etal}}</ref>

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".<ref>[http://monographs.iarc.fr/ENG/Monographs/suppl7/Suppl7-48.pdf 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.</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=March 13, 2019 |url=https://emagazine.com/canine-cancers-linked-to-lawn-care-chemicals/}}</ref>

===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. 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=July 22, 2013 |access-date=May 3, 2014}}</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 dichlorophenol, dichloroanisole, 4-chlorophenoxyacetic acid (6.9% of the TRR in milk), and 2,4-dichlorophenol (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== 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 |bibcode=2018EnInt.111..332I }}</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 | article-number = 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 [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."</ref>

2,4-D amine salts and esters are not persistent under most environmental conditions.<ref name=NPIC>National Pesticide Information Center [http://npic.orst.edu/factsheets/2,4-DTech.pdf NPIC 2,4-D Technical Fact Sheet]</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 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.<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 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 |doi-access=free|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=October 7, 2015}}</ref>

"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=https://www.epa.gov/ingredients-used-pesticide-products/24-d|website=www2.epa.gov|publisher=EPA|access-date=November 6, 2014|date=September 22, 2014|archive-date=April 26, 2022|archive-url=https://web.archive.org/web/20220426203157/https://www.epa.gov/ingredients-used-pesticide-products/24-d|url-status=live}}</ref>{{date missing}}

===Microbial breakdown=== 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 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.<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 |issue=1 | pages = 232–238 | doi=10.1016/j.soilbio.2006.07.011|bibcode=2007SBiBi..39..232C }}</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 == 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".<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|page=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=April 3, 2005 |access-date=May 3, 2014}}</ref> and Ontario.<ref>{{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 |access-date=May 3, 2014}}</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=June 26, 2015|work=The Globe and Mail|date=May 27, 2011}}</ref>

In 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 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=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|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=February 15, 2020 }}</ref>

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.<ref name="yosemite.epa.gov">EPA Press Release. October 15, 2014 [https://archive.today/20150227132207/http://yosemite.epa.gov/opa/admpress.nsf/bd4379a92ceceeac8525735900400c27/72fde554930f3f6985257d7200591180!OpenDocument 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] [https://www.epa.gov/ingredients-used-pesticide-products/registration-enlist-one-and-enlist-duo EPA Documents: Registration of Enlist Duo]</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=February 5, 2016|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 = February 5, 2016}}</ref>

On August 21, 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.<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=June 6, 2014|archive-url=https://web.archive.org/web/20140606215228/http://www.apvma.gov.au/products/review/current/2_4_d.php|archive-date=June 6, 2014}}</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=June 6, 2014|access-date=August 25, 2016}}</ref>

==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''.<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=November 23, 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. [http://www.isb.vt.edu/news/2011/May/Aryloxyalkanoate-Dioxygenase-Transgenes.pdf 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</ref>{{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.<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, genetically modified maize and soybeans resistant to 2,4-D and glyphosate have been approved in Canada.<ref name=fleury/> 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.<ref name="yosemite.epa.gov"/><ref name=ISAAAaad1>ISAAA GM Approval Database [http://www.isaaa.org/gmapprovaldatabase/gene/default.asp?GeneID=88&Gene=aad-1 GM Approval Database Genes List, Gene: aad1]. 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=April 13, 2015|magazine=Wired|publisher=Condé Nast|date=September 25, 2014}}</ref>

==References== {{reflist|30em}}

==External links and further reading== {{commons category}} * [https://www.cdc.gov/niosh/npg/npgd0173.html CDC - NIOSH Pocket Guide to Chemical Hazards] * [https://web.archive.org/web/20110521045015/http://www.sierraclub.ca/national/programs/health-environment/pesticides/2-4-D-overview.pdf Overview of the toxic effects of 2,4-D] Sierra Club Canada January 2005 * [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3483058/ "Review of 2,4-dichlorophenoxyacetic acid (2,4-D) biomonitoring and epidemiology"] Review of the literature by Dow scientists Crit Rev Toxicol. Oct 2012 * [http://sitem.herts.ac.uk/aeru/ppdb/en/Reports/4.htm PPDB] Pesticides Properties database entry for 2,4-D * [https://pubchem.ncbi.nlm.nih.gov/compound/1486 2,4-D] on Pubchem {{Herbicides}}

{{DEFAULTSORT:Dichlorophenoxyacetic Acid, 2, 4-}} Category:Chloroarenes Category:Auxinic herbicides Category:Phenoxyacetic acids Category:Acetic acids Category:Plant growth regulators Category:IARC Group 2B carcinogens Category:Systemic herbicides Category:Group 4 herbicides