DICROTOPHOS

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: 141-66-2; Chemical Formula: C₈H₁₆NO₅P

Previously, OSHA had no limit for dicrotophos; the ACGIH has a TLV of 0.25 mg/m³ TWA, with a skin notation, for this brown liquid with a mild ester odor. The proposed PEL was 0.25 mg/m³, with a skin notation; NIOSH (Ex. 8-47, Table N1) concurs that this limit is appropriate. The final rule establishes an 8-hour TWA of 0.25 mg/m³ and a skin notation.

Dicrotophos is a cholinesterase inhibitor (ACGIH 1986/Ex. 1-3, p. 193). The acute oral LD(50) in rats is reported as 22 mg/kg, and the percutaneous LD(50) in rabbits is 224 mg/kg (Stanford Research Institute 1962, as cited in ACGIH 1986/Ex. 1-3, p. 193). Another study reports the oral LD(50) in rats as 16 to 21 mg/kg and the dermal LD(50) in the same species as 42 mg/kg (Gaines 1969/Ex. 1-320). Two-year feeding studies in rats given 0, 1, 10, or 100 ppm dicrotophos showed no detectable effects at the 1-ppm concentration. At the higher concentrations, decreased body weights (as compared with those of controls) and cholinesterase inhibition were observed (Woodard Research Corporation 1967, as cited in ACGIH 1986/Ex. 1-3, p. 193). Dietary studies in dogs showed both plasma and erythrocyte cholinesterase inhibition at a 16-ppm concentration, but no significant ill effects at concentrations of 0, 0.16, or 1.6 ppm (Woodard Research Corporation 1967, as cited in ACGIH 1986/Ex. 1-3, p. 193). Studies of vapor inhalation in male rats have shown that transient illness occurred after a one-hour exposure to 910 mg/m³ of technical dicrotophos, and to 2620 mg/m³ or 2120 mg/m³ of 38-percent dicrotophos (Kettering Laboratories 1965, as cited in ACGIH 1986/Ex. 1-3). Dicrotophos does not cause demyelinization in chickens (Tunstall Laboratory 1965 and Kettering Laboratory 1963, both as cited in ACGIH 1986/Ex. 1-3, p. 193), and it is metabolized in a fashion similar to mono-microtophos (Menzer and Casida 1965/Ex. 1-986). Only NIOSH commented on dicrotophos.

The proposed PEL was based on the data described above and, in part, by analogy with other cholinesterase-inhibiting substances. In the final rule, OSHA is establishing an 8-hour TWA permissible exposure limit of 0.25 mg/m³, with a skin notation, for dicrotophos. The Agency concludes that this limit will protect workers from the material impairments of health, such as cholinesterase inhibition, potentially associated with inhalation, ingestion, and dermal exposure to this substance at the levels formerly permitted by the absence of a limit. OSHA has determined that these limits will substantially reduce this significant risk.