p-TOLUIDINE

OSHA comments from the January 19, 1989 Final Rule on Air Contaminants Project extracted from 54FR2332 et. seq. This rule was remanded by the U.S. Circuit Court of Appeals and the limits are not currently in force.

CAS: 106-49-0; Chemical Formula: CH₃C₆H₄NH₂

OSHA had no former PEL for p-toluidine. OSHA proposed establishing a 2-ppm PEL, with a skin notation, and these limits are established in the final rule. The ACGIH considers this substance a suspected human carcinogen and has given it a classification of A2 (ACGIH 1986/Ex. 1-3). p-Toluidine is a white solid.

One study investigates the carcinogenic potential of lifetime exposure to p-toluidine in experimental animals (Weisburger, Russfield, Homburger et al. 1978/Ex. 1-535). Male and female mice were exposed to p-toluidine in the diet for a total of 18 months. During the first six months of the experiment, mice were exposed to 1000 or 2000 mg p-toluidine/kg diet. As a result of the weight loss that occurred in mice exposed to the 2000 mg/kg diet dose, the concentrations of p-toluidine were reduced to 500 and 1000 mg/kg diet during the last 12 months of exposure. The rate of food consumption by the animals was not reported and was assumed to be 3 g/day. Thus, the average doses of p-toluidine received during the 18-month exposure were calculated to be 80 and 160 mg/kg body weight per day (Weisburger, Russfield, Homburger et al. 1978/Ex. 1-535).

For both the low and high dietary doses of p-toluidine, a significant increase in the incidence of hepatomas was observed. The incidence of tumors in the control, 80, and 160 mg/kg/day groups were 3/38, 10/38, and 12/35, respectively. The same study (Weisburger, Russfield, Homburger et al. 1978/Ex. 1-535) showed negative results in male rats exposed to two doses of p-toluidine in the diet for 18 months (1000- and 2000-mg/kg diet).

Risk estimate for p-toluidine. To assess the quantitative risk of p-toluidine’s carcinogenicity, OSHA used the Weisburger et al. (1978/Ex. 1-535) data which, despite some limitations (e.g., changes in dose levels during the experiment and the absence of data concerning the amount of food animals consumed during the exposure period), were considered adequate for risk assessment purposes.

The maximum likelihood estimates (MLE) of excess cancers per 1,000 workers over an occupational lifetime and the 95-percent upper-bound estimates were obtained by using a linearized multistage model (GLOBAL83). These values are summarized in Table C15-8. This table shows the number of cancer deaths potentially associated with working lifetime exposure to 20, 5, or 2 ppm p-toluidine.

OSHA concludes, as Table C15-8 shows, that workers exposed to p-toluidine, which was formerly not regulated by OSHA, are at significant risk of developing hepatomas; an effect that the Agency considers a material impairment of health. For example, the MLE at 20 ppm is 112 excess cancer deaths per 1,000 workers exposed over a working lifetime. Promulgating a PEL of 2 ppm will substantially reduce this significant risk. According to this scenario, a 90-percent reduction in excess cancer deaths will be achieved by establishing the 2-ppm limit. The risks existing at the former uncontrolled level are clearly significant. NIOSH (Ex. 8-47, Table N6B) judged the evidence on p-toluidine sufficient to warrant a separate 6(b) rulemaking. OSHA is establishing an 8-hour TWA limit of 2 ppm for p-toluidine in the final rule; a skin notation is included to protect against percutaneous absorption of this substance.