OSHA formerly had a limit of 15 mg/m3 TWA for ronnel. The ACGIH has a TLV-TWA of 10 mg/m3 for this white, noncombustible powder. The proposed PEL was 10 mg/m3 as an 8-hour TWA; NIOSH (Ex. 8-47, Table N1) concurs with this limit, and it is established in the final rule.
Ronnel is an indirect cholinesterase inhibitor that affects the blood plasma rather than the red cell acetylcholinesterase (Plapp and Casida 1958a/Ex. 1-657). The acute oral LD(50) for rats is reported as 1250 and 2630 mg/kg for males and females, respectively. The oral LD(50) in dogs is greater than 500 mg/kg (McCollister, Oyen, and Rowe 1959/Ex. 1-594). Two-year dietary studies of rats fed up to 50 mg/kg/day showed no effect on growth rate, food consumption, survival, or hematopoesis (McCollister, Oyen, and Rowe 1959/Ex. 1-594). In a study by Gladenko and Stuk (1972, as cited in ACGIH 1986/Ex. 1-3, p. 513), albino rats developed clinical symptoms of motor irritation, tremor, increased auditory and tactile sensitivity, lacrimation, and salivation within two weeks of exposure at levels between 164 and 328 mg/kg; some animals died during the latter part of the study. At exposures below 16.4 mg/kg, no ill effects were observed (Gladenko and Stuk 1972, as cited in ACGIH 1986/Ex. 1-3, p. 513). A two-year feeding study in dogs exposed at 10 mg/kg showed no ill effects except cholinesterase depletion (Worden, Noel, and Mawdesley-Thomas 1972/Ex. 1-583).
Patch tests of 50 human subjects showed that ronnel has no skin-sensitizing potential (McCollister, Oyen, and Rowe 1959/Ex. 1-594). Only NIOSH submitted comments on this substance.
In the final rule, OSHA is establishing an 8-hour TWA limit of 10 mg/m3 for ronnel. The Agency concludes that this limit will protect workers against the significant risk of cholinergic effects associated with exposure to this substance. OSHA has determined that this limit will substantially reduce this significant risk, and that cholinesterase inhibition constitutes a material health impairment.