Previously, OSHA had no limit for diazinon. The ACGIH has a TLV-TWA of 0.1 mg/m3, with a skin notation. The proposed PEL was an 8-hour TWA of 0.1 mg/m3, with a skin notation; NIOSH concurs that these limits are appropriate (Ex. 8-47, Table N1). The final rule establishes a 0.1-mg/m3 PEL, with a skin notation, for diazinon. Pure diazinon is a colorless liquid, but the technical grade is pale yellow to dark brown in color and has a faint odor.
Gaines (1960/Ex. 1-319) reports the acute oral LD(50) for male and female rats to be 108 and 76 mg/kg, respectively. Other reports set the acute oral LD(50)s in rats, guinea pigs, and rabbits at 76 to 150, 240 to 320, and 130 mg/kg, respectively (Association of American Pesticide Control Officials, Inc. 1969, as cited in ACGIH 1986/Ex. 1-3, p. 172). Studies from Hazleton Laboratories (1965, as cited in ACGIH 1986/Ex. 1-3, p. 172) and Radeleff (1958/Ex. 1-434) have shown much greater susceptibility to diazinon in birds and calves, with the oral LD(50) being less than 10 mg/kg in some instances. The dermal LD(50) in rabbits is 400 mg/kg (RTECS 1983-84). However, susceptibility to repeated doses is relatively consistent among species, with dogs showing signs of poisoning at 9.3 mg/kg per day and rats showing complete inhibition of red blood cell cholinesterase and marked inhibition of brain cholinesterase at 50 mg/kg/day (Bruce, Howard, and Elsea 1955/Ex. 1-585). Monkeys were poisoned at 5 mg/kg/day (Woodard, Woodard, and Cronin 1968/Ex. 1-458). Chronic feeding studies in rats have shown no chronic toxicity at 10, 100, and 1000 ppm. For many mammals, diazinon is less toxic than parathion (ACGIH TLV-TWA of 0.1 mg/m3), although this is not true under some circumstances (ACGIH 1986/Ex. 1-3, p. 172).
In humans, Hayes (1963/Ex. 1-982) reports that two patients were poisoned by a dermal diazinon dosage of about 1.1 mg/kg; however, Gassman (1957/Ex. 1-901) reports no ill effects from an accidental ingestion of 30 mg/kg. One man received a dose of 250 mg/kg and recovered after treatment, which included gastric lavage (Bockel 1967, as cited in ACGIH 1986/Ex. 1-3, p. 172). In tests, Geigy (1966, as cited in ACGIH 1986/Ex. 1-3, p. 172) found that a series of doses of 0.05 mg/kg/day for 28 days produced plasma cholinesterase inhibition, and it has been suggested that the no-effect level for cholinesterase inhibition in humans is 0.02 mg/kg/day. Skin absorption of diazinon occurs readily, and overexposures are associated with weakness, headache, blurred vision, salivation, sweating, nausea, vomiting, diarrhea, abdominal cramps, slurred speech, and moist rales in the lungs (ACGIH 1986/Ex. 1-3, p. 172).
In the final rule, the Agency is establishing an 8-hour TWA PEL of 0.1 mg/m3, with a skin notation, for diazinon. OSHA concludes that these limits will protect exposed workers from the significant risk of cholinesterase inhibition, weakness, headache, nausea, vomiting, as well as the other symptoms and signs of diazinon poisoning, which together consitute material health impairments that are associated with exposures at levels above the new PEL.