DISULFOTON

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: 298-04-4; Chemical Formula: C₈H₁₉O₂PS₃

OSHA formerly had no exposure limit for disulfoton. The ACGIH has a limit of 0.1 mg/m³ TWA for this substance. The proposed PEL for disulfoton was 0.1 mg/m³ as an 8-hour TWA; the final rule establishes this limit and adds a skin notation. Pure disulfoton is an oily, colorless liquid; the technical grade is a brown liquid.

The acute toxicity of disulfoton is very high by all laboratory-tested routes of administration. For weanling rats, the intraperitoneal LD(50) is reported to be 5.4 mg/kg; for adult rats, it is 9.4 mg/kg (Brodeur and Dubois 1963/Ex. 1-718). The acute dermal LD(50) is 6 mg/kg for adult female rats and 25 mg/kg for adult male rats (Gaines 1969/Ex. 1-320). The acute oral LD(50)s for male and female rats are reported as 6.8 mg/kg and 2.3 mg/kg, respectively (Brodeur and Dubois 1964/Ex. 1-1015). Rats have demonstrated an acquired tolerance for disulfoton (Brodeur and Dubois 1964/Ex. 1-1015).

Metabolically, disulfoton is highly fat-soluble, and the compound apparently interferes with mixed-function oxidase activity in the same manner shown to be the case for parathion; with respect to median lethal doses, parathion and disulfoton are similar (Stevens et al. 1973, as cited in ACGIH 1986/Ex. 1-3, p. 226).

NIOSH (Ex. 8-47, Table N2) noted that OSHA had inadvertently omitted the skin notation for the proposed limit for disulfoton. NIOSH points out that the studies described above for this substance clearly demonstrate that disulfoton “is almost as toxic via the skin as when administered internally,” and further, that the 1986 ACGIH Documentation (Ex. 1-3, p. 226) includes a skin notation for this substance. On the basis of these comments, OSHA is including a skin notation for disulfoton in the final rule. With the exception of NIOSH, no commenter submitted evidence to the record on disulfoton.

In the final rule, OSHA is establishing an 8-hour TWA PEL for disulfoton of 0.1 mg/m³, with a skin notation. The Agency concludes that this limit will prevent the significant risk of acute toxicity and metabolic injury, which are material impairments of health that are associated with exposures at levels above the new PEL. The skin notation is included to protect workers against the dermal toxicity that has been demonstrated in animal tests.