Notes

Write a note in this area. It's really easIn June 2015 the World Health Organization's (WHO) International Agency for Research on Cancer (IARC) confirmed its 1987 classification of 2,4-D as a possible carcinogen.[26][27]

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.[28]

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.[29]

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".[30]

Contaminants[edit]
A July 2013 Four Corners investigation found elevated levels of dioxins in a generic version of 2,4-D, one of Australia's most widely used herbicides. One scientist said the product tested by Four Corners, which was imported from China, had "one of the highest dioxin readings for 2,4-D in the last 10 to 20 years, and could pose potential health risks."[31]

Metabolism[edit]
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 and into dichloroanisole and 4-chlorophenoxyacetic acid. (6.9% of the TRR in milk) and 2,4-dichlorophenol13 (5% of the TRR in milk; 7.3% of the TRR in eggs and 4% of the TRR in chicken liver). Residue levels in kidney were the highest.[16]:21

Environmental behavior[edit]
Owing to the longevity and extent of use, 2,4-D has been evaluated several times by regulators and review committees.[32][33]

2,4-D amine salts and esters are not persistent under most environmental conditions.[9] The degradation of 2,4-D is rapid (half life of 6.2 days) in aerobic mineral soils.[24]: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.[9] 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.[9]

In aerobic aquatic environments, the half life is 15 days, while in anaerobic aquatic environments, 2,4-D was moderately persistent to persistent (half life of = 41 to 333 days). 2,4-D has been detected in streams and shallow groundwater at low concentrations, in both rural and urban areas. Breakdown is pH dependent.[9]

"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.[23][date missing]

Microbial breakdown[edit]
A number of 2,4-D-degrading bacteria have been isolated and characterized from a variety of environmental habitats.[34][35] 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 was demonstrated.[36] 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.[37]

degrading soil bacteria. FEMS Microbiology Ecology 29: 45-58.
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[1]

External links and further reading[edit]
Wikimedia Commons has media related to 2,4-Dichlorophenoxyacetic acid.
CDC - NIOSH Pocket Guide to Chemical Hazards
Overview of the toxic effects of 2,4-D Sierra Club Canada January, 2005
"Review of 2,4-dichlorophenoxyacetic acid (2,4-D) biomonitoring and epidemiology" Review of the literature by Dow scientists Crit Rev Toxicol. Oct 2012
[hide] v t e
Pest control: herbicides
Anilides/anilines
acetochlor alachlor asulam benfluralin butachlor diethatyl diflufenican dimethenamid flamprop metazachlor metolachlor pendimethalin pretilachlor propachlor propanil trifluralin
Aromatic acids
aminopyralid chloramben clopyralid dicamba picloram pyrithiobac quinclorac quinmerac
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cacodylic acid copper arsenate DSMA MSMA
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2,4-D 2,4-DB dichlorprop fenoprop MCPA MCPB 2,4,5-T
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Quaternary
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Jump up ^ Dibbisa D., Egigu M.C., Muthuswamy M. (2016). "Delaying Postharvest Ripening of Tomato (Lycopersicon Esculenthum Mill.) by using 2,D-Dichlorophenoxy Acetic Acid". International Journal of Current Research and Review. 8 (2): 65.
Categories: ChloroarenesAuxinic herbicidesPhenol ethersAcetic acidsPlant growth regulatorsIARC Group 2B carcinogens
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