DIOXATHION

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: 78-34-2; Chemical Formula: C₁₂H₂₆O₆P₂S₄

OSHA formerly had no permissible exposure limit for dioxathion. The ACGIH has a limit of 0.2 mg/m³ as an 8-hour TWA, with a skin notation. The proposed PEL was 0.2 mg/m³ as an 8-hour TWA, with a skin notation, and NIOSH (Ex. 8-47, Table N1) concurs with this limit, which is established in the final rule. Dioxathion is a nonvolatile, very stable, dark amber liquid.

The pesticide, dioxathion, contains both the cis- and trans-isomers of 2,3-p-dioxanedithiol; the cis-isomer is approximately four times as acutely toxic as the trans-isomer (ACGIH 1986/Ex. 1-3, p. 219). The oral LD(50) values reported for rats range from 23 to 118 mg/kg (with most values in the 23- to 64-mg/kg portion of the range); in dogs, oral LD(50)s range from 10 to 40 mg/kg. The LC(50) in rats is 1398 mg/m³; in mice, it is 340 mg/m³ (Hercules, Inc. 1973, as cited in ACGIH 1986/Ex. 1-3, p. 219). The percutaneous LD(50)s in rats and rabbits are reported to be 63 and 85 mg/kg, respectively (NIOSH 1983b, as cited in ACGIH 1986/Ex. 1-3, p. 219). Instillation of 0.1 ml dioxathion into the rabbit eye produces mild, transient conjunctivitis but no corneal damage (ACGIH 1986/Ex. 1-3, p. 219).

In subacute oral toxicity studies, the no-effect dose level in rats was reported to be 0.22 mg/kg/day; in dogs, a no-effect level of between 0.075 and 0.25 mg/kg/day was indicated (Frawley, Weir, Tusing et al. 1963/Ex. 1-317). The no-effect level in multigenerational studies of reproductive effects in rats was reported to be 10 ppm (Kennedy, Frawley, and Calandra 1973/Ex. 1-340).

Human volunteers who ingested 0.075 mg/kg/day of dioxathion had no symptoms related to plasma or blood cholinesterase activity, while those ingesting 0.15 mg/kg/day exhibited a slight decrease in plasma cholinesterase activity (Frawley, Weir, Tusing et al. 1963/Ex. 1-317). The World Health Organization has estimated an acceptable daily intake for man of 0.0015 mg dioxathion/kg (WHO 1967, as cited in ACGIH 1986/Ex. 1-3, p. 219). Other organophosphorus compounds have been demonstrated to produce levels of cholinesterase inhibition analogous to those produced by dioxathion (ACGIH 1986/Ex. 1-3, p. 219). Only NIOSH commented on this substance.

In the final rule, OSHA is establishing an 8-hour TWA PEL of 0.2 mg/m³ for dioxathion; the Agency is also establishing a skin notation for this substance. OSHA concludes that these limits will protect workers against the significant risk of metabolic effects associated with inhalation and oral exposure and with dermal penetration of this substance, which was formerly not regulated by OSHA. The Agency has determined that these limits will substantially reduce these significant risks; OSHA finds that the cholinesterase inhibition caused by exposure to dioxathion constitutes a material impairment of health.