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2,4-Dichlorophenoxy acetic acid
DESIGNATIONS
CAS No.: 94-75-7
Registry name: 2,4-Dichlorophenoxyacetic acid
Chemical name: 2,4-Dichlorophenoxyacetic acid
Synonyms, Trade names: 2,4-D
Chemical name (German): 2,4-Dichlorphenoxyessigsäure
Chemical name (French): Acide 2,4-dichlorophénoxyacetique
Appearance: colourless, crystalline powder with musty odour
BASIC CHEMICAL AND PHYSICAL DATA
| 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 |
ORIGIN AND USE
Usage:
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.
Origin/derivation:
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.
Toxicity
| 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 | |
| Mammals: | ||
| 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.
ENVIRONMENTAL BEHAVIOUR
Water:
2,4-D esters are hydrolysed in surface water and groundwater
to form the appropriate acids.
Soil:
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)
ENVIRONMENTAL STANDARDS
| Medium/ acceptor | Sector | Country/ organ. | Status |
Value | Cat. | Remarks | Source |
| Water: | Drinkw | A | (L) |
50 µg/l | acc. DVGW, 1988 | ||
| Drinkw | CDN | (L) |
100 µg/l | MAC | acc. DVGW, 1988 | ||
| Drinkw | D | L |
100 µg/l | acc. DVGW, 1988 | |||
| Drinkw | EC | G |
100 µg/l | acc. DVGW, 1988 | |||
| Drinkw | USA | G |
100 µg/l | acc. RIPPEN, 1988 | |||
| Drinkw | WHO | G |
100 µg/l | acc. RIPPEN, 1988 | |||
| Surface | AUS | G |
4 µg/l | Protection of aquatic | acc. CES, 1985 | ||
| Surface | MEX | (L) |
0.1 mg/l | organisms (incl. deriv.), estuaries | acc. CES, 1985 | ||
| Surface | MEX | (L) |
0.01 mg/l | Coastal waters | acc. CES, 1985 | ||
| Air: | Workp | D | L |
10 mg/m3 | Incl. salts and esters | DFG, 1989 | |
| Workp | SU | (L) |
1 mg/m3 | acc. DVGW, 1988 | |||
| Workp | USA | (L) |
10 mg/m3 | TWA | acc. RIPPEN, 1989 | ||
| Foodstuffs: | WHO | G |
0.3 mg/(kg·d) | ADI | acc. RIPPEN, 1989 | ||
| D | (G)1) |
0.1 mg/(kg·d) | DTA | acc. DFG, 1986 | |||
| Citrus fruits | D | L |
2 mg/kg | acc. DVGW, 1988 | |||
| Other foodstuffs | D | L |
0.1 mg/kg | acc. DVGW, 1988 |
Note:
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 |
| Water: | |||
| 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 |
| Soil/sediment: | |||
| Sewage sludge | USA | 0.55-7,300 µg/kg (n = 55 of 223) | acc. RIPPEN, 1989 |
Assessment/comments
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.