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May 1994

Documentation for Immediately Dangerous To Life or Health Concentrations (IDLHs)


CAS number: 94–75–7

NIOSH REL: 10 mg/m3 TWA

Current OSHA PEL: 10 mg/m3 TWA

1989 OSHA PEL: Same as current PEL

1993-1994 ACGIH TLV: 10 mg/m3 TWA

Description of Substance: White to yellow, crystalline, odorless powder.

LEL:. Noncombustible Solid

Original (SCP) IDLH: 500 mg/m3

Basis for original (SCP) IDLH: The chosen IDLH has been estimated from oral data, because no useful data on acute inhalation toxicity are available. NIOSH [1976] cited a dog oral LD50 of 100 mg/kg [Seabury 1963]. Dudley and Thapar [1972] estimated that the LD50 for humans was between 80 and 800 mg/kg.

Short-term exposure guidelines: None developed


Lethal dose data:








Adjusted LD

Derived value




Cabral et al. 1979

Seabury 1963

Senczuk and Pogorzelska 1980

Sine 1993













3,500 mg/m3

700 mg/m3

2,429 mg/m3

4,893 mg/m3

350 mg/m3

70 mg/m3

243 mg/m3

489 mg/m3

Human data: It has been reported that the lethal oral dose ranges from 80 to 800 mg/kg [Dalgaard-Mikkelsen and Poulsen 1962; Dudley and Thapar 1972]. [Note: Oral doses of 80 to 800 mg/kg are equivalent to a worker being exposed to about 3,700 to 37,000 mg/m3 for 30 minutes, assuming a breathing rate of 50 liters per minute and 100% absorption.]


Revised IDLH: 100 mg/m3

Basis for revised IDLH: No inhalation toxicity data are available on which to base an IDLH for 2,4-D. Therefore, the revised IDLH for 2,4-D is 100 mg/m3 based on acute oral toxicity data in humans [Dalgaard-Mikkelsen and Poulsen 1962; Dudley and Thapar 1972] and animals [Seabury 1963]. This may be a conservative value due to the lack of relevant acute inhalation toxicity data for workers.


1. Cabral JRP, Raitano F, Mollner T, Bronczyk S, Shubik P [1979]. Acute toxicity of pesticides in hamsters. Toxicol Appl Pharmacol 48:A192 [Abstract].

2. Dalgaard-Mikkelsen SV, Poulsen E [1962]. Toxicology of herbicides. Pharmacol Rev 14:225-250.

3. Dudley AW Jr, Thapar NT [1972]. Fatal human ingestion of 2,4-D, a common herbicide. Arch Pathol 94:270-275.

4. NIOSH [1976]. AG68250. Acetic acid, (2,4-dichlorophenoxy)-. In: Registry of toxic effects of chemical substances, 1976 ed. Cincinnati, OH: U.S. Department of Health, Education, and Welfare, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health, DHEW (NIOSH) Publication No. 76-191, p. 21.

5. Seabury JH [1963]. Toxicity of 2,4-dichlorophenoxyacetic acid for man and dog. Arch Environ Health 7:202-209.

6. Senczuk W, Pogorzelska H [1980]. Budowa chemiczna a toksykodynamiczne wlasciwosci pochodnych kwasow fenoksykarboksylowych. Roczniki Panstwowego Zakladu Higieny 31:373-377 (in Polish).

7. Sine C, ed. [1993]. 2,4-D. In: Farm chemicals handbook '93, p. C102.

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