METHYL DEMETON

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: 8022-00-2; Chemical Formula: C₆H₁₅O₃PS₂

OSHA formerly had no limit for methyl demeton. The ACGIH has a TLV-TWA limit of 0.5 mg/m³, with a skin notation. The proposed PEL was 0.5 mg/m³, with a skin notation, and NIOSH (Ex. 8-47, Table N1) concurs. The final rule establishes an 8-hour TWA of 0.5 mg/m³, and a skin notation, for methyl demeton. Methyl demeton is an oily, colorless to pale-yellow liquid with an unpleasant odor.

Methyl demeton is reported to have an oral LD(50) value of 40 to 65 mg/kg for the thiolo isomer and 150 to 250 mg/kg for the thiono isomer. Both isomers form sulfoxide or sulfone, with an oral LD(50) similar to that of the parent compounds (Dubois and Plzak 1962/Ex. 1-629; Heath and Vandekar 1965, Klimmer and Plaff 1955, both as cited in ACGIH 1986/Ex. 1-3, p. 388). In solution or storage, methyl demeton may form alkyl sulfonium compounds of very high intravenous toxicity and an oral LD(50) of 10 to 20 mg/kg. Dermal toxicity is reported to be moderate, with an LD(50) of approximately 400 mg/kg (Heath and Vandekar 1965, as cited in ACGIH 1986/Ex. 1-3, p. 388). OSHA received only one comment, from NIOSH, on methyl demeton.

In humans, methyl demeton causes changes in intraocular pressure, and acute poisonings produce nausea, headache, dizziness, vomiting, and hyperemia of the nasal mucosa. Chronic exposure causes hyperemia of the respiratory organs and inner ear irritation (Dugel’nyy 1970; Rasuleva 1970, both as cited in ACGIH 1986/Ex. 1-3, p. 388).

OSHA is establishing an 8-hour TWA for methyl demeton of 0.5 mg/m³, with a skin notation. The Agency concludes that this limit will protect workers from the significant risk of ocular and nasal irritation, pulmonary effects, and cholinesterase inhibition, all of which constitute material impairment of health and are associated with exposure to this substance at levels above the new limit.