Reevaluating the carcinogenicity of ortho-toluidine: a new conclusion and its implications

Regul Toxicol Pharmacol. 1992 Dec;16(3):301-17. doi: 10.1016/0273-2300(92)90010-7.


The aromatic amine ortho-toluidine has been recognized by IARC as an animal carcinogen for the past decade. Three recent epidemiological studies of worker populations have now implicated this chemical as a human bladder carcinogen. In a study by E. Ward, A. Carpenter, S. Markowitz, D. Roberts, and W. Halperin ((1991), J. Natl. Cancer Inst. 83, 501-506), workers definitely exposed to ortho-toluidine for at least 10 years experienced a Standardized Incidence Ratio (SIR) of 27.2 (90% CI = 11.8-53.7). The other major exposure was to aniline, which significant epidemiological studies have failed to confirm as a human carcinogen. In retrospect, studies by G. F. Rubino, G. Scansetti, G. Piolatto ((1982) Environ. Res. 27, 241-254) and M. J. Stasik ((1988) Int. Arch. Occup. Environ. Health 60, 21-24) also support the hypothesis that ortho-toluidine is a human bladder carcinogen. Animal studies of both ortho-toluidine and its possible confounders in these epidemiological investigations further confirm this hypothesis. When evaluated in a suitably comprehensive way, according to the traditional standards for assessing causality outlined by A. B. Hill ((1977) A Short Textbook of Medical Statistics, pp. 288-294, Lippincott, Philadelphia) the evidence that ortho-toluidine causes human bladder cancer has become much more conclusive. In this case, animal tests have proven a good predictor of human carcinogenicity.

Publication types

  • Research Support, U.S. Gov't, P.H.S.
  • Review

MeSH terms

  • Animals
  • Carcinogenicity Tests
  • Carcinogens / toxicity*
  • Humans
  • Occupational Exposure
  • Toluidines / adverse effects
  • Toluidines / toxicity*
  • Urinary Bladder Neoplasms / chemically induced


  • Carcinogens
  • Toluidines
  • 2-toluidine