Contents - Previous - Next

2,4,5-trichlorophenoxy acetic acid


CAS No.: 93-76-5
Registry name: 2,4,5-Trichlorophenoxy acetic acid
Chemical name: Acetic acid, (2,4,5-trichlorophenoxy)
Synonyms, Trade names: 2,4,5-T
Chemical name (German): 2,4,5-Trichlorphenoxyessigsäure, 2,4,5-T
Chemical name (French): 2,4,5-trichlorophénoxy acide acétique,
Appearance: colourless to white, musty smelling crystals


Empirical formula: C8H5Cl3O3
Rel. molecular mass: 255.49 g
Density: 1.803 g/cm3 at 20°C
Boiling point: above 200°C decomposition
Melting point: 157-158°C (acid); 113-115°C (triethanolamine salt)
Vapour pressure: 0.7 x 10-6 Pa at 25°C
Solvolysis/solubility: in water: 280 mg/l at 25°C
in diethylether: 234 g/l;
in toluene: 7.3 g/l;
in xylene: 6.1 g/l;
soluble in isopropyl alcohol;
the alkali and amine salts of 2,4,5-T are readily soluble in water, whereas the esters are virtually insoluble in water but soluble in mineral oils


2,4,5-T is used in forestry and in agriculture as a systemic herbicide (for eradication of undergrowth etc.). The US military used it during the defoliation campaigns in Vietnam (mixture of 2,4,5-T and 2,4-D). These mixtures contained a significant amount of TCDD, which caused severe illnesses. 2,4,5-T as a salt or ester is generally applied in combination with other phenoxy acids. Its usage is restricted in Germany.

2,4,5-T is produced synthetically by the reaction of 2,4,5-trichlorophenol, chloroacetic acid and sodium hydroxide. Lindane production residues are also useful for the 2,4,5-T synthesis.

The technical product contains 2.9% dichloromethoxyphenoxyacetic acid, 0.6% dichlorophenoxyacetic acid, 0.4% bis(2,4,5-trichlorophenoxy)acetic acid and < 0.5 mg/kg TCDD (dioxin). As of 1981, manufacturers guarantee a TCDD content of < 0.01 mg/kg (DFG, 1986). There are about 400 products which contain

Production figures:

Worldwide (1992, estimated) 1,000 - 3,000 t (RIPPEN, 1989)
USA (1968) 27,000 t (RIPPEN, 1989)
USA (1979) <1,000 t (RIPPEN, 1989)
USA (1985) banned (RIPPEN, 1989)
D (1977) 1,800 t (RIPPEN, 1989)
D (1984) no further production  
EC (1980) 1,000 t (RIPPEN, 1989)


Rat: LD50 500 mg/kg, oral acc. PERKOW, 1989
Rat: LD50 >5000 mg/kg, dermal acc. PERKOW, 1989
Rat: LD50 300-800 mg/m3, oral acc. RIPPEN, 1989
Rat: LC50 0.83 mg/l, inh. (4 h) acc. RIPPEN, 1989
Mouse: LD50 389 mg/kg, oral acc. RIPPEN, 1989
Dog: LD50 100 mg/kg, oral acc. RIPPEN, 1989
Guinea pig: LD50 380 mg/kg, oral acc. RIPPEN, 1989
Chicken: LD50 310 mg/kg, oral acc. RIPPEN, 1989
Aquatic organisms:
Rainbow trout: LC50 0.98 mg/l, semistat. (96 h) acc. RIPPEN, 1989
Striped sawfish: LC50 15 mg/l (96 h) acc. RIPPEN, 1989
Carp: LC50 0.87 mg/l (48 h) acc. RIPPEN, 1989
Golden orfe: LC50 530 mg/l (48 h) acc. RIPPEN, 1989
Cress seeds: ED50 0.02 ppm acc. RIPPEN, 1989
Winter rye seeds: ED50 8.3 ppm (72h) acc. RIPPEN, 1989

Comprehensive toxicity data for various species of animal can be found in DFG (1986).

Characteristic effects:

Humans/mammals: 2,4,5-T considerably irritates the eyes, and the skin. Skin resorption is likely. Chronic exposure causes impairment of the liver function, changes in behaviour and nerve damage. Chloracne is frequently encountered because of the contamination with chlorophenols and TCDD. The teratogenic effect is attributed to contamination with TCDD and not to the pure 2,4,5-T.

The no-effect level in the most sensitive type of animal (mice) is 20 mg/kg (DFG, 1986).

2,4,5-T is found to be slightly mutagenic and teratogenic. There are not enough facts to definitely attest cancerogenic effects.

Plants: 2,4,5-T is an effective defoliant. Plants (and in particular dicotyledons) absorb 2,4,5-T through their leaves and metabolise the substance. Numerous metabolic processes are impaired. The direct effect sometimes takes the form of problems with passive permeability, but is also reflected by increased oxygen formation and greater growth. 2,4,5-T also acts as decoupler for the respiratory chain.


There is moderate sorption of 2,4,5-T on organic suspended matter and on sediments. It forms a film on the water's surface and is photolytically decomposed. Residues may be leached into the groundwater.

In hot climates, a considerable amount of the quantity applied is subject to evaporation. In the atmosphere, 2,4,5-T is either subject to photolytic decomposition or washed out by precipitation. The estimated half-life is about 1 day.

In soil, 2,4,5-T is either microbially degraded or it evaporates into the atmosphere. The majority of the herbicide remains in the topsoil (up to depths of 10 cm) due to the moderate mobility in soil. Considerable amounts are taken from the soil by plants.

More than 90% of the 2,4,5-T in soil is degraded within 70 days and 99% within one year (WEGLER, 1982). According to RIPPEN (1989), the "detoxification time" is, however, 270 days (extrapolated). A half-life in soil between 2 and 10 weeks is reported (DFG, 1986). In damp loam (application of 0.6 - 3.4 kg/ha) the substance can still be detected after 2-5 weeks. No further degradation takes place after 7 days in sewage treatment plants under aerobic conditions. The half-life in grass is 17 days.

Degradation, decomposition products:
Above 500°C, the substance is thermally destroyed and TCDD is formed. In an acid milieu, it is stable. In soil, degradation is mainly due to microorganisms; degradation to form CO2 is accelerated by humic substances and fulvic acids. 2,4,5-trichlorophenol forms in anaerobic sediments and during photolysis in the presence of humic substances. 2,4,5-T is transformed into chlorophenols, polyphenols, quinones and products similar to humic acids.

Combination effects:
Synergism with TCDD (> 1.5 ppm) is assumed (RIPPEN, 1989). Subcutaneous injections of lindane, phenobarbital or DDT over a period of several days accelerate the 2,4,5-T metabolism.


Sector Country/ organ. Status


Cat. Remarks Source
Water: Surface EC


0.001 mg/l

  1) acc. DVGW, 1988
Surface EC


0.0025 mg/l

  2) acc. DVGW, 1988
Surface EC


0.005 mg/l

  3) acc. DVGW, 1988
Drinkw A  

10 mg/l

    acc. DVGW, 1988
Drinkw D


0.1 mg/l

    acc. DVGW, 1988
Drinkw EC


0.1 mg/l

    acc. DVGW, 1988
Air: Workp D


10 mg/m3

MAK   acc. DFG, 1994
Workp USA


10 mg/m3

TWA   acc. RIPPEN, 1989
Foodstuffs:   D


0.03 mg/kg.d

ADI TCDD: <0.01 mg/kg.d DFG, 1986


2 mg/kg

4) Forest fungi acc. DVGW, 1988


0.05 mg/kg

4) Vegetable foodstuffs acc. DVGW, 1988


1) For drinking water treatment in each case: A1 for simple physical treatment and sterilisation
2) For drinking water treatment in each case: A2 for normal physical/chemical treatment and sterilisation
3) For drinking water treatment in each case: A3 for physical and refined chemical treatment, oxidation, adsorption and sterilisation
4) Order Governing Maximum Amounts of Pesticide, as at 1984

Usage banned in Italy since 1970; likewise in Holland, Norway, Sweden and the USA.

The TCDD level permitted in the Federal Republic of Germany must not exceed 0.005 mg/kg technical active substance (DFG, 1986).

The use of 2,4,5-T is restricted in Germany in the vicinity of surface water (Order Governing Use of Pesticides, as at 1986: use by aircraft and rail vehicles banned, as is utilisation on areas of open land not set aside for agriculture or gainful horticulture).

All 2,4,5-T formulations have been banned since 1985.

Comparison/reference values

Medium/origin Country


Coot/muscle in contaminated areas  

<1.34 ppm

acc. RIPPEN, 1989
Coot/fat in contaminated areas  

<30 ppb

acc. RIPPEN, 1989
Foliage (n=37) SF

0.1-30 ppm

acc. RIPPEN, 1989
Mushrooms (n=26) SF

<0.02-1.8 ppm

acc. RIPPEN, 1989
Berries (n=32) SF

0.07-15 ppm

acc. RIPPEN, 1989


The epidemiological investigations performed to date indicate only a minor risk of cancer and species-specific and dosage-dependent teratogenic effects in certain animals. These results cannot however be projected onto humans. To avoid TCDD formation, 2,4,5-T residues must not be incinerated. If applied as a herbicide, the drift of the fogs should be watched.

Contents - Previous - Next