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: 114-26-1; Chemical Formula: C11H15NO2

OSHA had no former limit for propoxur. The ACGIH has established an 8-hour TLV-TWA of 0.5 mg/m3 for this white, odorless, crystalline compound. The proposed PEL was 0.5 mg/m3 as an 8-hour TWA; NIOSH (Ex. 8-47, Table N1) concurs with this limit, and the final rule establishes it.

The oral LD(50)s in male and female rats are 83 and 86 mg/kg, respectively; for both sexes, the dermal LD(50) is greater than 2400 mg/kg (Gaines 1969/Ex. 1-320). Dietary studies in rats at levels of 7.5 mg/kg/day for 28 days or at 800 ppm for three months produced no adverse effects (Association of American Pesticide Control Officials, Inc. 1966/Ex. 1-1011). Rats were exposed to propoxur concentrations of 5, 7, 18.7, or 31.7 mg/m3 six hours/day, five days/week for 12 weeks; animals in the high-dose group showed depressed red blood cell and brain cholinesterase levels, and plasma cholinesterase was depressed by as much as 20 to 30 percent (Association of American Pesticide Control Officials, Inc. 1966/Ex. 1-1011).

In humans, a few cases of mild propoxur poisoning have been reported among sprayers of this insecticide and among residents of propoxur-treated homes (Vandekar, Hedayat, Plestina, and Ahmady 1968/Ex. 1-679). In a study of human volunteers, a single oral dose of 1.5 mg/kg propoxur caused a depression in red blood cell cholinesterase and gastrointestinal symptoms that disappeared two hours after ingestion. Oral doses of 0.75 to 1.0 mg/kg produced no symptoms but did depress erythrocyte cholinesterase (Vandekar, Plestina, and Wilhelm 1971/Ex. 1-680). The only comment on this substance was submitted by NIOSH.

In the final rule, OSHA is establishing an 8-hour TWA of 0.5 mg/m3 for propoxur. The Agency concludes that this limit will protect workers against the significant risk of cholinesterase inhibition associated with exposure to this substance at the levels formerly permitted by the absence of any OSHA limit. OSHA finds that cholinesterase inhibition is a material health impairment.

Page last reviewed: September 28, 2011