Current assessment of the carcinogenic hazard of diesel exhaust

Diesel exhaust consists of gases, vapors, and soot, which consists of a carbon matrix with adsorbed organic compounds, inorganic salts, and metals. The carcinogenic hazard of organic extracts of diesel soot has long been known, and concern for human carcinogenesis was elevated during the late 1970s by new mutageniciry data and the anticipated increase in diesel use in the U.S. By the mid‐1980s, inhalation bioassays proved diesel soot to be a pulmonary carcinogen in heavily exposed rats, and epidemiology suggested a small increase in lung cancer in heavily exposed occupations. Evidence that organic compounds might not be the cause of the rat lung tumor response as previously assumed and the need to select a dose equivalence term for estimating unit risk values for human cancer led to recent studies which demonstrated that nearly organic‐free carbon black is equally carcinogenic to diesel soot in rats. Recent cancer risk estimates by EPA have used unit risk values calculated from rat studies using the dose ...