FENAMIPHOS

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: 22224-92-6; Chemical Formula: C₁₃H₂₂NO₃PS

OSHA formerly had no limit for fenamiphos. The ACGIH has a TLV-TWA of 0.1 mg/m³ for this substance, with a skin notation. The proposed PEL was 0.1 mg/m³, with a skin notation; NIOSH (Ex. 8-47, Table N1) concurs, and this limit is established in the final rule, along with a skin notation. Fenamiphos is a tan-colored, waxy solid.

Fenamiphos is a cholinesterase inhibitor that produces both central and peripheral cholinergic reactions (WHO 1975, as cited in ACGIH 1986/Ex. 1-3, p. 265). The acute oral LD(50) values reported for fenamiphos are 2 to 19 mg/kg in rats, 22 mg/kg in mice, 56 to 100 mg/kg in guinea pigs, 10 to 17 mg/kg in rabbits, and approximately 10 mg/kg in cats and dogs. Acute dermal LD(50) values are 72 to 154 mg/kg in rats and 178 to 225 mg/kg in rabbits. One- and four-hour exposures of rats to fenamiphos aerosols resulted in LC(50) values of 110 to 175 mg/m³ and 91 to 100 mg/m³, respectively. Rabbits exhibited no dermal or eye irritation (WHO 1975 and Loeser and Kimmerle 1971, both as cited in ACGIH 1986/Ex. 1-3, p. 265).

Rats exposed to fenamiphos aerosol at concentrations of 0.03, 0.25, or 3.5 mg/m³ of air for three weeks exhibited no symptoms. At 3.5 mg/m³, rats showed significant depression of plasma cholinesterase; 0.25 mg/m³ was the highest no-effect concentration observed (Kimmerle 1982c, as cited in ACGIH 1986/Ex. 1-3, p. 265). Two-year feeding studies of dogs (at levels of 0.5, 1.0, and 10 ppm) and rats (at levels of 3, 10, and 30 ppm) revealed no treatment-related toxic or oncogenic effects or tissue changes at a dietary level of 10 ppm; no-observed-effect levels were 3 ppm for the rat and 1 ppm for the dog (WHO 1975, as cited in ACGIH 1986/Ex. 1-3, p. 265). Studies of rabbits and rats showed no embryotoxic or teratogenic effects, and results of a three-generation study in rats showed that fenamiphos had no effect on reproduction (WHO 1975, as cited in ACGIH 1986/Ex. 1-3, p. 265). Studies of mice have also shown no mutagenic effects, and a study of chickens demonstrated no delayed neurotoxic effects (WHO 1975 and Loeser and Kimmerle 1971, both as cited in ACGIH 1986/Ex. 1-3, p. 265). Fenamiphos is metabolized rapidly to sulfoxide and sulfone derivatives and is excreted primarily in the urine, as demonstrated in absorption tests of the skin and the digestive and respiratory tracts of rats and cows (Waggoner and Khasawinah 1974/Ex. 1-579).

There are no reports of human poisonings caused by exposure to fenamiphos, and no quantitative data are available relating adverse health effects to measurable airborne concentrations of fenamiphos. NIOSH submitted the only comment on fenamiphos.

In the final rule, OSHA is establishing a PEL for this substance of 0.1 mg/m³ TWA to protect against the significant risk of anticholinesterase effects presented by exposure to this substance at the levels formerly permitted by the absence of an OSHA limit. A skin notation is also established based on the evidence of systemic toxicity via percutaneous absorption of fenamiphos. The Agency concludes that these limits will substantially reduce these risks; OSHA finds that cholinesterase inhibition constitutes a mat