DIQUAT

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: 85-00-7; Chemical Formula: C₁₂H₁₂Br₂N₂

Previously, OSHA had no PEL for diquat. The ACGIH has a limit of 0.5 mg/m³ TWA for these yellow crystals. The proposed PEL was 0.5 mg/m³ as an 8-hour TWA, and NIOSH (Ex. 8-47, Table N1) concurs with this limit. The final rule establishes 0.5 mg/m³ as the 8-hour TWA PEL for diquat.

In most species, the acute oral toxicity of diquat is similar to that of paraquat and ranges from 100 to 400 mg/kg in rats, mice, rabbits, and dogs. Cows experience more severe toxic effects, with an acute oral LD(50) of 30 mg/kg. The 24-hour percutaneous LD(50) in rabbits is greater than 400 mg cation/kg; no skin irritation or other ill effects were demonstrated at this level (Clark and Hurst 1970/Ex. 1-135; Rowe and Wright 1965, as cited in ACGIH 1986/Ex. 1-3, p. 222). Rats fed 1000 ppm daily (about 50 mg/kg/day) for two years survived; reduced food intake and growth were the only consequences observed. At 500 ppm (about 25 mg/kg/day), the only ill effect observed was a pathologic change in the eye. A dietary level of 10 ppm (about 0.5 mg/kg/day) for two years did not induce cataract formation, but cataracts do occur at higher levels, with pathology observed at the 500-ppm level; one in four animals demonstrated complete corneal opacity in one or both lenses after six months at the 1000-ppm level. Cataract formation requires prolonged exposure and is not induced by single high-level exposures (ACGIH 1986/Ex. 1-3, p. 222).

Unlike paraquat, diquat does not produce lung damage in exposed humans or animals. Acute poisoning may produce nonspecific respiratory distress as well as other nonspecific signs of poisoning. In humans, accidental ingestion has produced less toxic reactions than those associated with paraquat ingestion (Orepoulos and McEvoy 1969/Ex. 1-429). OSHA received no comments, other than NIOSH’s, on diquat.

In the final rule, OSHA is establishing an 8-hour PEL of 0.5 mg/m³ TWA for diquat. The Agency concludes that this limit will protect against the significant risk of ocular damage, which constitutes a meterial health impairment that is associated with chronic exposure at levels above the new PEL.