The current OSHA limit for tetramethyl lead (TML) is 0.075 mg/m3 TWA, with a skin notation, while the ACGIH has recommended a TLV of 0.15 mg/m3, measured as Pb and with a skin notation. There is no NIOSH REL for TML. Tetraethyl lead is a colorless liquid, which may be dyed blue, orange, or red; it has a slight musty odor.
In establishing the previous TLV of 0.15 mg/m3, the ACGIH cited the work of de Treville, Wheeler, and Sterling (1962/Ex. 1-310), who reported that tetramethyl lead is about three times more volatile than tetraethyl lead and thus results in airborne TML levels that are about three times higher than those for TEL. Despite the heavier TML exposure of employees, urinary lead levels were not significantly different from the urinary lead levels of employees exposed to TEL. The ACGIH concluded that a 0.075 mg/m3 TLV for TML, identical to the TLV recommended at the time for TEL, should furnish an adequate margin of safety. The revised TLV of 0.15 mg/m3 was based on a personal communication by Linch (1968, as cited in ACGIH 1986/Ex. 1-3, p. 563), who reported that exposure to 0.179 mg/m3 tetramethyl lead was not associated with a significant increase in urinary lead levels.
NIOSH concurs (Ex. 8-47, Table N1) that the retention of the Agency's 0.075 mg/m3 limit is appropriate, and no other comments on TML were received. Based on the same reasoning as that described above in connection with tetraethyl lead, OSHA is not increasing its existing TWA limit for TML; the skin notation for TML is also retained.