Atmosphere in urban areas may be polluted by a number of combustion sources, including industries, vehicle traffic, and residential heating. Traffic police constitute a group of workers that is highly exposed to urban pollutants, especially those from motor vehicle exhaust. We conducted a biomonitoring study to simultaneously measure in 34 nonsmoking police officers and in 36 nonsmoking office workers, as referents, the individual benzo(a)pyrene [B(a)P] exposure using personal samplers and the formation of DNA adducts in peripheral WBCs using 32P-postlabeling techniques. Our results show that the police officers were exposed to significantly higher levels of B(a)P than were referents (P < 0.0001). No seasonal variation of the atmospheric levels of B(a)P was found throughout the year. The median relative adduct labeling x 10(-8) values of the controls and exposed police officers were 0.94 (range, 0.1-3.7) and 1.3 (range, 0.1-5.5), respectively, using the nuclease P1 technique. Although the DNA adduct levels of police officers were globally higher than those of referents (P < 0.05), the difference was entirely due to the summer difference [median values 0.80 (range, 0.1-1.8) and 2.8 (range, 0.7-5.5), respectively (P < 0.001)]. In winter, the DNA adduct levels were substantially identical, and in midseason, there was only a very small increase in police officers, with respect to controls (statistically not significant). Moreover, a more significant seasonal variation of bulky aromatic DNA adduct levels was observed in WBC DNA samples of police officers (P < 0.05) compared to those of referents. The seasonal variation of bulky aromatic adduct levels could be correlated with the reported seasonal variation of aryl hydrocarbon hydroxylase inducibility in human lymphocytes.