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2,4-Dichlorophenoxy acetic acid


CAS No.: 94-75-7
Registry name: 2,4-Dichlorophenoxyacetic acid
Chemical name: 2,4-Dichlorophenoxyacetic acid
Synonyms, Trade names:
Chemical name (German):
Chemical name (French):
Acide 2,4-dichlorophénoxyacetique
colourless, crystalline powder with musty odour


Empirical formula: C8H6Cl2O3
Rel. molecular mass: 221.04 g
Density: 1.563 g/cm3
Boiling point: 160°C at 50 Pa
Melting point: 140.5°C
Vapour pressure: <10-5 Pa
Solvolysis/solubility: in water:0.55 g/l

in olive oil 0.5 g/l, in benzene 6 g/l, in acetone 850 g/l


2,4-D, its salts and esters are used as a herbicide to combat broad-leafed plants in particular. The quantity applied is generally between 0.3 and 4.5 kg/ha. They are frequently used together with other herbicides. Besides MCPA (2-methyl-4-chlorophenoxyacetic acid), 2,4-D is one of the most widespread herbicides used in the cultivation of grain. The butyl esters of 2,4-D and 2,4,5-T were used by the USA in the Vietnam War with the designation "Agent Orange" to defoliate the forests of Southern Vietnam.

Probably no known natural sources. 2,4-D is produced by the chlorination of phenol and subsequent conversion with chloroacetic acid. The technical product may contain between 0.1 and 0.6 % of chlorophenols and traces of polychlorinated dibenzodioxins and dibenzofurans.

Production figures:
Worldwide approx. 100,000 t/a; EC (1980) 15,000-20,000 t; USA (1976) 17,000 t

Emission figures (estimated):
All the 2,4-D produced is released into the environment. In addition, 2,4-D is formed following hydrolysis as metabolite of the acid esters used as herbicides.


Humans: LD50 80 mg/kg, oral acc. RIPPEN, 1989
LDLo 50-500 mg/kg, oral acc. RIPPEN, 1989
TCLo 0.01 mg/l, inhalation acc. RIPPEN, 1989
Mouse LD50 360-368 mg/kg, oral acc. DFV, 1986
Rat LD50 375-1200 mg/kg, oral acc. DFV, 1986
LD50 1,500 mg/kg, dermal acc. RIPPEN, 1989
Rabbit LD50 800 mg/kg, oral acc. RIPPEN, 1989
LD50 > 1,600 mg/kg, dermal acc. RIPPEN, 1989
Dog LD50 100 mg/kg, oral acc. RIPPEN, 1989
Birds: LD50 540 mg/kg acc. RIPPEN, 1989
Aquatic organisms:
Golden orfe LC50 250 mg/l acc. RIPPEN, 1989
Rainbow trout LC50 1.1 mg/l (96h) (free acid) acc. PERKOW, 1985
LC50 100 mg/l (96h) (diethylamine salt) acc. PERKOW, 1985
Young rainbow trout LC50 0.022-0.033 mg/l (96 h) acc. RIPPEN, 1989
Water flea (Daphnia magna) LC50 > 100 mg/l (48 h) acc. RIPPEN, 1989
Algae EC50 50 mg/l (10 d, inhibited growth) acc. RIPPEN, 1989
Other organisms:
Earthworm LC50 10-100 mg/cm2, application (48 h) acc. RIPPEN, 1989
Actinomycetes EC50 160-184 mg/kg acc. RIPPEN, 1989
Soil fungi EC80 75-128 mg/kg acc. RIPPEN, 1989

Characteristic effects:

Humans/mammals: Carcinogenic effect still under dispute; proven teratogenity in rats. 2,4-D can be resorbed through the gastro-intestinal tract and via the skin (2,4-D ester also via the lungs). It acts on the central and peripheral nervous system (spasms and paralysis) as well as the motor activity and intervenes in the intermediary carbohydrate metabolism. 2,4-D absorbed orally is rapidly excreted without being transformed and is not stored in the body (DVGW, 1988). Severe eye irritation, slight skin irritation.

Plants: 2,4-D interferes with the metabolism of the plant, e.g. in the nucleic-acid metabolism.


2,4-D esters are hydrolysed in surface water and groundwater to form the appropriate acids.

2,4-D, in particular the alkali and amine salts, is extremely mobile in soil on account of its high water solubility. There is thus the possibility of groundwater being polluted by seepage water.

Degradation, decomposition products, half-life:
UV transformation in water results in products similar to humic acid via chlorophenols and polyphenols. 2,4-dichlorophenol has been detected under anaerobic conditions in sediment and in aquatic organisms whereas 4-chlorophenol has been discovered (as an intermediate product) in digested sludge.

Half-lives: 4-29 d in soil, roughly 5 d in plants (depending on type). The persistence of 2,4-D in surface water or groundwater would appear to be subject to considerable fluctuation depending on the season. The data vary between complete degradation within 36 days and a loss of only 8 % after 78 days in a laboratory experiment. RIPPEN (1989) quotes half-lives in surface water of between < 12 up to 50 days.

Food chain:
Bioaccumulation in algae (chlorella fusca)


Medium/ acceptor Sector Country/ organ.


Value Cat. Remarks Source
Water: Drinkw A


50 µg/l     acc. DVGW, 1988
Drinkw CDN


100 µg/l MAC   acc. DVGW, 1988
Drinkw D


100 µg/l     acc. DVGW, 1988
Drinkw EC


100 µg/l     acc. DVGW, 1988
Drinkw USA


100 µg/l     acc. RIPPEN, 1988
Drinkw WHO


100 µg/l     acc. RIPPEN, 1988
Surface AUS


4 µg/l   Protection of aquatic acc. CES, 1985
Surface MEX


0.1 mg/l   organisms (incl. deriv.), estuaries acc. CES, 1985
Surface MEX


0.01 mg/l   Coastal waters acc. CES, 1985
Air: Workp D


10 mg/m3   Incl. salts and esters DFG, 1989
Workp SU


1 mg/m3     acc. DVGW, 1988
Workp USA


10 mg/m3 TWA   acc. RIPPEN, 1989
Foodstuffs:   WHO


0.3 mg/(kg·d) ADI   acc. RIPPEN, 1989


0.1 mg/(kg·d) DTA   acc. DFG, 1986
Citrus fruits   D


2 mg/kg     acc. DVGW, 1988
Other foodstuffs   D


0.1 mg/kg     acc. DVGW, 1988


1) "Toxicology" Working Party of German Research Association
Usage banned for example in Czechoslovakia and Sweden; restricted in Great Britain.

Comparison/reference values

Medium/origin Country Value Source
Drinking water (1983) USA 0.04 µg/l acc. RIPPEN, 1989
Rhine (km 865, 1978)   < 0.01 µg/l acc. RIPPEN, 1989
Surface water (1983) USA 100 µg/l, (max.) acc. RIPPEN, 1989
Drain water under forest D 2000 µg/l (appl. 4.5 kg/ha, ester) acc. RIPPEN, 1989
Sewage sludge USA 0.55-7,300 µg/kg (n = 55 of 223) acc. RIPPEN, 1989


The relatively high mobility of 2,4-D implies a hazard to water - including groundwater - in the area of application. This should be considered if the water resource is to serve the drinking water supply. As can be seen from the quoted standards, the assessments of the toxicity of 2,4-D differ widely. The figures for drinking water vary by three orders of magnitude.

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