A Working Group of the International Agency for Research on Cancer (IARC) convened in Lyon, France, June 5–12 to scrutinise the available knowledge base on the carcinogenicity of diesel engine exhaust, gasoline engine exhaust and some nitroarenes.1 Diesel and gasoline engine exhaust and nitroarenes were previously evaluated by IARC in 1989.2 For gasoline engine exhaust the classification remained Group 2B (‘possibly carcinogenic to humans’) as well as for seven of the nitroarenes. The newly evaluated nitroarene 3-nitrobenzanthrone was also added to this group. 6-Nitrochrysene and 1-nitropyrene were classified as 2A ‘Probably carcinogenic to humans’. 6-Nitrochrysene and 1-nitropyrene are important exposure markers for diesel exhaust since metabolites of these substances have been found in workers exposed to diesel exhaust.3–5 The most prominent outcome of the IARC evaluation meeting was the upgrade of the classification of diesel exhaust, now in Group 1 ‘Carcinogenic to humans’ with sufficient evidence for lung cancer and limited evidence for bladder cancer.

For diesel engine exhaust the change from Group 2A to Group 1 was primarily driven by new evidence from epidemiological studies in the mining and trucking industry. The most recent study performed in underground ‘non-metal mining’ included 12 315 miners from salt (sodium chloride), potash (potassium carbonate), trona (sodium carbonate), and limestone mines.6 ,7 Miners were exposed to relative high diesel exhaust exposure levels and had no or very low co-exposures to asbestos, silica, uranium and radon. Average intensity of respirable elemental carbon (REC) exposure, based on each individual's full work history at the study …