OSHA formerly had an 8-hour TWA limit of 0.1 mg/m3, with a skin notation, for phosdrin (mevinphos). The ACGIH has a TLV-TWA of 0.01 ppm (0.1 mg/m3) and a TLV-STEL of 0.03 ppm (0.3 mg/m3), also with a skin notation. The proposal retained the 8-hour TWA of 0.1 mg/m3 and added a STEL of 0.3 mg/m3; the skin notation was retained. NIOSH (Ex. 8-47, Table N1) concurred with these limits, which are established in the final rule. Phosdrin is a colorless liquid. The commercial product is a mixture of cis- and trans-isomers that have a yellow color.
The acute oral LD(50) of phosdrin is 4 to 8 mg/kg for male mice and 6 to 8 mg/kg for female rats (Shell Chemical Corporation 1956, as cited in ACGIH 1986/Ex. 1-3, p. 412). Phosdrin is a cholinesterase inhibitor and has been reported to cause slight plasma cholinesterase depression but no decrease in brain cholinesterase activity in rats fed 2 to 5 ppm. The compound may be absorbed dermally and by inhalation or ingestion; the action of the compound is direct and immediate (Cleveland and Treon 1961/Ex. 1-476). The dermal LD(50) in rats has been reported to be 4.5 mg/kg (Gaines 1969/Ex. 1-320). Chronic feeding of rats demonstrated a minimal lethal dose of between 100 and 200 ppm. Cholinesterase activity decreased continually when sublethal doses were administered until a maximum reduction in RBC cholinesterase activity of 25 percent was achieved on the 27th day of the administration of 1.5 to 20 mg doses (Huelse and Federspil 1975/Ex. 1-959).
In industry, the primary hazards associated with exposure to phosdrin are absorption of phosdrin through the skin, lung, and mucous membranes, which causes liver damage (Natoff 1970/Ex. 1-966). Phosdrin intoxication is reported to occur in humans, with accompanying symptoms of headache, visual distortion, weakness, cramps, diarrhea, pain, and respiratory distress. Severe exposure may cause convulsions; in one reported case, some symptoms (anxiety, depression, vertigo, and nystagmus) persisted for as long as four months (Zavon, as cited in ACGIH 1986/Ex. 1-3, p. 412). Only NIOSH commented on this substance.
In the final rule, OSHA is retaining the 8-hour TWA PEL of 0.1 mg/m3 and adding a STEL of 0.3 mg/m3 for phosdrin; the skin notation is retained. These limits are based on analogy to the toxicity of parathion. The Agency concludes that these limits will protect workers against the significant risk of cholinesterase inhibition and hepatic injury, which constitute material health impairments that result from the absorption of phosdrin through the skin and mucous membranes and from exposure by the inhalation and oral routes. OSHA finds that these limits will substantially reduce these significant risks.