Immediately Dangerous to Life or Health Concentrations (IDLH)
CAS number: 56–38–2
NIOSH REL: 0.05 mg/m3 TWA [skin]
Current OSHA PEL: 0.1 mg/m3 TWA [skin]
1989 OSHA PEL: Same as current PEL
1993-1994 ACGIH TLV: 0.1 mg/m3 TWA [skin]
Description of substance: Pale-yellow to dark-brown liquid with a garlic-like odor.
LEL: . . Unknown
Original (SCP) IDLH: 20 mg/m3
Basis for original (SCP) IDLH: No useful data on acute inhalation toxicity are available on which to base the IDLH for parathion. If the IDLH were estimated from the statement by AIHA  that “the minimum lethal oral dose for humans has been estimated as ranging from less than 10 mg to 120 mg [Bidstrup 1950; Grob 1950; Hayes 1963],” then an IDLH of 5 mg/m3 would be chosen. This appears to be far too conservative, however, because ACGIH  noted that workers regularly exposed to 2 to 15 mg/m3, with an average concentration of 8 mg/m3, exhibited only a 25% decrease in cholinesterase levels [Kay et al. 1952]. The chosen IDLH, therefore, has been estimated from the female rat oral LD50 of 3 mg/kg cited by ACGIH .
Short-term exposure guidelines: None developed
ACUTE TOXICITY DATA:
Lethal concentration data:
|Deichmann et al. 1952
Deichmann et al. 1952
Izmerov et al. 1982
Lethal dose data:
|Adjusted LD||Derived value|
|Eto et al. 1966
Kenaga & Morgan 1978
Kenaga & Morgan 1978
Nishizawa et al. 1961
von Dozent et al. 1955
Weiss and Orzel 1967
Human data: Workers regularly exposed to 2 to 15 mg/m3 (average of 8 mg/m3) exhibited only a 25% decrease in cholinesterase levels [CDC 1956]. The minimum lethal oral dose has been reported to range from 0.17 to 1.471 mg/kg [Arena 1970; CDC 1956; Hartley and Kidd 1986]. [Note: An oral dose ranging from 0.17 to 1.471 mg/kg is equivalent to a worker being exposed to about 8 to 69 mg/m3 for 30 minutes, assuming a breathing rate of 50 liters per minute and 100% absorption.]
|Revised IDLH: 10 mg/m3
Basis for revised IDLH: The revised IDLH for parathion is 10 mg/m3 based on chronic inhalation toxicity data in humans [CDC 1956]. This may be a conservative value due to the lack of relevant acute toxicity data in humans exposed to concentrations above 10 mg/m3.
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