PARAQUAT

OSHA comments from the January 19, 1989 Final Rule on Air Contaminants Project extracted from 54FR2332 et. seq. This rule was remanded by the U.S. Circuit Court of Appeals and the limits are not currently in force.

CAS: 4685-14-7; Chemical Formula:

OSHA’s former limit for paraquat was 0.5 mg/m³ as an 8-hour TWA, with a skin notation. The ACGIH has established a limit of 0.1 mg/m³ as an 8-hour TWA. The Agency proposed, and the final rule establishes, a permissible exposure limit of 0.1 mg/m³ TWA for this substance; the skin notation is retained. NIOSH (Ex. 8-47, Table N1) concurs. Paraquat refers to a group of compounds that are odorless, yellow solids. The principal compounds are: 1,1′-dimethyl-4,4′-bipyridinium; 1,1′-dimethyl-4,4′-bipyridinium bis (methyl sulfate); and 1,1′-dimethyl-4,4′-bipyridinium dichloride.

The toxicity of these compounds depends on the compound’s cationic moiety. Acute oral toxicity is reported as 30 mg/kg ion as cation for guinea pigs and 127 mg/kg ion for female rats, while the dermal LD(50) in rabbits is 240 mg/kg ion (Clark 1964, as cited in ACGIH 1986/Ex. 1-3, p. 456; Clark, McElligott, and Hurst 1966/Ex. 1-503; McElligott 1965, as cited in ACGIH 1986/Ex. 1-3, p. 456). Paraquat can penetrate broken skin after it has broken down the skin’s usual barriers (Swan 1969/Ex. 1-576; Clark, McElligott, and Hurst 1966/Ex. 1-503). By inhalation or intratracheal injection, paraquat is very toxic because of its irritant properties (Gage 1968/ Ex. 1-508). Rats exposed once for six hours to a concentration of 1 mg/m³ died if the aerosol contained particles with diameters of 3 to 5 microns (Gage 1968/Ex. 1-508). Rats exposed six hours/day for three weeks to the same aerosol at 0.4 mg/m³ exhibited signs of pulmonary irritation; no effects were observed for the same exposure regimen at 0.1 mg/m³ (Gage 1968/Ex. 1-508).

When the diameter of the particles in the aerosol are not of respirable size, toxicity is greatly reduced. The 4-hour LC(50) for rats is 6400 mg/kg, and dogs, rats, and guinea pigs tolerated three weeks of daily exposures to 100 mg/m³ without apparent pulmonary effect (although nosebleeds were observed) (Palazzolo 1965, as cited in ACGIH 1986/Ex. 1-3, p. 456).

Dietary administration, for 90 days, of doses ranging from 300 to 700 ppm showed dose-related effects ranging from pulmonary edema to intraalveolar hemorrhage and death (Kimbrough and Gaines 1970/Ex. 1-560).

Paraquat’s teratogenic potency in mice is low (Bus and Gibson 1975/Ex. 1-539), although 100 ppm administered in the drinking water of pregnant rats increased postnatal mortality significantly (Bus and Gibson 1975/Ex. 1-539).

In humans, 69 accidental deaths and 81 suicides were attributed to the effects of paraquat exposure up to 1972 (Chipman Chemicals 1972, as cited in ACGIH 1986/Ex. 1-3, p. 456). Bouletreau, Ducluzeau, Bui-Xuan et al. (1977/ Ex. 1-538) reported 31 cases of renal insufficiency, and a spray applicator was killed when he absorbed a lethal dose of inadequately diluted paraquat through the skin (Jaros 1978/Ex. 1-513). Workers using a 0.05- to 1-percent solution of paraquat developed skin and mucous membrane irritation but experienced no symptoms of systemic poisoning (Howard 1978/Ex. 1-512). Fugita, Suzuki, and Ochiai (1976, as cited in ACGIH 1986/Ex. 1-3, p. 456) reported five cases of reversible kerato-conjunctivitis, with corneal injury, after one month of exposure to paraquat. Only NIOSH commented on paraquat.

OSHA is establishing an 8-hour TWA limit of 0.1 mg/m³ for paraquat, with a skin notation. The Agency concludes that this limit will protect workers from the significant risk of skin, eye, and pulmonary irritation observed in animals exposed to aerosols of respirable size at levels below OSHA’s former PEL for paraquat. The Agency considers the irritant effects of paraquat to be material impairments of health. OSHA is retaining the skin notation for this substance because of its capacity to penetrate the skin.