Paraquat

CAS number: 1910–42–5

NIOSH REL: 0.1 mg/m³ (respirable dust) TWA [skin]

Current OSHA PEL: 0.5 mg/m³ (respirable dust) TWA [skin]

1989 OSHA PEL: 0.1 mg/m³ (respirable dust) TWA [skin]

1993-1994 ACGIH TLV: 0.1 mg/m³ (respirable dust) TWA,

0.5 mg/m³ (total dust) TWA

Description of substance: Yellow solid with a faint, ammonia-like odor.

LEL: . Noncombustible Solid

Original (SCP) IDLH: 1.5 mg/m³

Basis for original (SCP) IDLH: The chosen IDLH is based on the statements by Gage [1968] that “after single exposures the LC₅₀ appears to be a function of the duration and of the concentration; in the rat the lethal concentration-time product is about 6 micrograms/liter-hour. Guinea pigs and male mice are about as sensitive as rats. Female mice are less sensitive. The dog can tolerate a concentration-time product of 25 micrograms/liter-hour without ill effects.”

Short-term exposure guidelines: None developed

ACUTE TOXICITY DATA:

Lethal concentration data:

Species	Reference	LC50	LCLo	Time	Adjusted 0.5-hr LC (CF)	Derived value
Respirable dust G. pig	Gage 1968	3 mg/m3	-----	30 min	3.0 mg/m3 (1.0)	0.30 mg/m3
Respirable dust Mouse	Gage 1968	3 mg/m3	-----	30 min	3.0 mg/m3 (1.0)	0.30 mg/m3
Respirable dust Rat	Gage 1968	-----	1 mg/m3	6 hr	2.3 mg/m3 (2.3)	0.23 mg/m3
Nonrespirable dust Rat	Palazzolo 1965	-----	6,400 mg/m3	4 hr	12,800 mg/m3 (2.0)	1,280 mg/m3

Lethal dose data:

Species	Reference	Route	LD50 (mg/kg)	LDLo (mg/kg)	Adjusted LD	Derived value
Rat Mouse Dog G. pig	Bailey & White 1965 Barabas et al. 1981 Iyakuhin 1979 Murray &Gibson 1972	oral oral oral oral	57 120 25 22	----- ----- ----- -----	399 mg/m3 840 mg/m3 175 mg/m3 154 mg/m3	40 mg/m3 84 mg/m3 18 mg/m3 15 mg/m3

Human data: It has been stated that the high acute inhalation toxicity of paraquat is dependent wholly on the size of the particulate, with respirable sizes (i.e., <5 micrometer mass median diameter) found to be 5 to 6 times more toxic than nonrespirable dusts [McElligo 1965]. It has been reported that under paraquat spraying conditions particle sizes appear to be nonrespirable [Swan 1969].

Revised IDLH: 1 mg/m3 Basis for revised IDLH: The revised IDLH for paraquat is 1 mg/m3 based on the acute inhalation toxicity data for respirable particulate in animals [Gage 1968]. This is a conservative value if the occupational exposure is totally to nonrespirable size particles of paraquat since respirable aerosols are much more toxic [McElligo 1965; Swan 1969].

REFERENCES:

1. Bailey GW, White JL [1965]. Herbicides: a compilation of their physical, chemical, and biological properties. Residue Reviews 10:97-102.

2. Barabas K, Vigh L, Horvath I, Szabo L, Matkovics B [1981]. Effects of paraquat in vivo on fatty acids of mouse and guinea pig tissues. Gen Pharmacol 12:225-227.

3. Gage JC [1968]. Toxicity of paraquat and diquat aerosols generated by a size-selective cyclone: effect of particle size distribution. Br J Ind Med 25:304-314.

4. Iyakuhin Kenkyu (Study of Medical Supplies) [1979]; 10:520-522 (in Japanese).

5. McElligo TF [1965]. Industrial hygiene research lab report IHR/172. Alderly Park, Macclesfield, Cheshire, England: Imperial Chemicals Industries, Ltd. [From ACGIH [1991]. Paraquat. In: Documentation of the threshold limit values and biological exposure indices. 6th ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists, pp. 1159-1161.]

6. Murray RE, Gibson JE [1972]. A comparative study of paraquat intoxication in rats, guinea pigs and monkeys. Exp Molec Pathol 17:317-325.

7. Palazzolo RF [1965]. Report to Imperial Chemical Industries, Ltd. Alderly Park, Macclesfield, Cheshire, England. [From ACGIH [1991]. Paraquat. In: Documentation of the threshold limit values and biological exposure indices. 6th ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists, pp. 1159-1161.]

8. Swan AAB [1969]. Exposure of spray operators to paraquat. Br J Ind Med 26:322-329.