OSHA formerly had a limit of 1 ppm TWA (6 mg/m3) for p-nitroaniline (PNA), with a skin notation. The ACGIH has a limit of 3 mg/m3 TWA, with a skin notation. OSHA proposed to reduce the former 8-hour TWA of 1 ppm (equivalent to 6 mg/m3) to 3 mg/m3, and to retain the skin notation. NIOSH (Ex. 8-47, Table N1) concurred that these limits were appropriate, and they are established in the final rule. para-Nitroaniline usually exists in the form of yellow needles.
p-Nitroaniline is readily absorbed through the skin and is a strong methemoglobin-forming agent; prolonged exposure can cause liver damage (ACGIH 1986/Ex. 1-3, p. 430). Anderson (1946/Ex. 1-1049) reported several cases of PNA-poisoning among shipboard workers assigned to clean up a p-nitroaniline spill; one man with a history of liver disease became jaundiced and died, and the other exposed workers became cyanotic and complained of headache, sleepiness, weakness, and respiratory distress (Anderson 1946/Ex. 1-1049). It has also been reported that children who ingested p-nitroaniline that was contained in wax crayons subsequently became ill (Rieders and Brieger 1953/Ex. 1-798).
Several investigators (Anderson 1946/Ex. 1-1049; Gupta 1953, Fairhall 1957j, both as cited in ACGIH 1986/Ex. 1-3, p. 430; Linch 1974/Ex. 1-747) have concluded that the nitroanilines are more hazardous than aniline, and, on this basis, the ACGIH has recommended a TWA limit for PNA that is lower than the limit for aniline (ACGIH 1986/Ex. 1-3, p. 430). Only NIOSH submitted comments on p-nitroaniline.
In the final rule, OSHA is establishing a PEL of 3 mg/m3 (8-hour TWA) for p-nitroaniline and is retaining the skin notation. The Agency concludes that this limit will protect workers against the significant risk of methemoglobinemia and liver damage, both of which constitute material health impairments that are associated with exposure to PNA at levels above 3 mg/m3. The Agency is retaining the skin notation because this substance is readily absorbed through the skin in toxic amounts.