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2,4,5-trichlorophenoxy acetic acid
DESIGNATIONS
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
BASIC CHEMICAL AND PHYSICAL DATA
| 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 |
ORIGIN AND USE
Usage:
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.
Origin/derivation:
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
2,4,5-T.
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) |
Toxicity
| Mammals: | ||
| 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 |
| Birds: | ||
| 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 |
| Plants: | ||
| Cress seeds: | ED50 0.02 ppm | acc. RIPPEN, 1989 |
| Winter rye seeds: | ED50 8.3 ppm (72h) | acc. RIPPEN, 1989 |
Note:
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.
ENVIRONMENTAL BEHAVIOUR
Water:
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.
Air:
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.
Soil:
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.
Half-life:
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.
ENVIRONMENTAL STANDARDS
| Medium/ acceptor |
Sector | Country/ organ. | Status | Value |
Cat. | Remarks | Source |
| Water: | Surface | EC | L |
0.001 mg/l |
1) | acc. DVGW, 1988 | |
| Surface | EC | L |
0.0025 mg/l |
2) | acc. DVGW, 1988 | ||
| Surface | EC | L |
0.005 mg/l |
3) | acc. DVGW, 1988 | ||
| Drinkw | A | 10 mg/l |
acc. DVGW, 1988 | ||||
| Drinkw | D | L |
0.1 mg/l |
acc. DVGW, 1988 | |||
| Drinkw | EC | L |
0.1 mg/l |
acc. DVGW, 1988 | |||
| Air: | Workp | D | L |
10 mg/m3 |
MAK | acc. DFG, 1994 | |
| Workp | USA | (L) |
10 mg/m3 |
TWA | acc. RIPPEN, 1989 | ||
| Foodstuffs: | D | G |
0.03 mg/kg.d |
ADI | TCDD: <0.01 mg/kg.d | DFG, 1986 | |
| D | L |
2 mg/kg |
4) | Forest fungi | acc. DVGW, 1988 | ||
| D | L |
0.05 mg/kg |
4) | Vegetable foodstuffs | acc. DVGW, 1988 |
Notes:
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 | Value |
Source |
| Foodstuffs: | |||
| 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 |
Assessment/comments
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.