OSHA formerly had an 8-hour TWA limit of 5 ppm, with a skin notation, for nitrotoluene. The ACGIH has a TLV-TWA of 2 ppm, also with a skin notation. The proposed PEL was 2 ppm as an 8-hour TWA, with a skin notation, and NIOSH concurred with this limit (Ex. 8-47, Table N1). The final rule establishes an 8-hour TWA PEL for nitrotoluene of 2 ppm and retains the skin notation. The ortho- and meta-isomers of nitrotoluene are yellow liquids; the para-isomer is also yellow, but exists in crystalline form.
Nitrotoluene is one of the aromatic nitrogen compounds that may cause methemoglobin formation. Linch (1974/Ex. 1-747) has studied the nitrotoluene isomers and reported that they have relatively low emiagenic potential; he considered nitrotoluene comparable to aniline in its toxic effects (Linch 1974/Ex. 1-747). Cases of poisoning as a result of exposure to nitrotoluene are rare (von Oettingen 1941/Ex. 1-874). Only NIOSH commented on this substance.
In the final rule, OSHA establishes an 8-hour TWA limit of 2 ppm and retains the skin notation for nitrotoluene. The Agency concludes that this limit will protect workers against the significant risk of methemoglobinemia, a material health impairment that is associated with exposure to this substance; the skin notation is retained because of nitrotoluene's capacity to penetrate the skin.