IARC carcinogens reported in cigarette mainstream smoke and their calculated log P values

Cigarette smoke is a complex aerosol of minute liquid droplets (termed the particulate phase) suspended within a mixture of gases (CO2, CO, NOx, etc.) and semi-volatile compounds. The International Agency for Research on Cancer (IARC) has classified a number of the chemical constituents reported in cigarette mainstream smoke (MS) as carcinogens. Previously, we published a series of historical reviews reporting that 11 IARC Group 1 (known human), nine Group 2A (probable human) and 48 Group 2B (possible human) carcinogens have been observed in MS. Here, we expand the list of IARC classified carcinogens from 68 to 81 compounds (11 Group 1, 14 Group 2A and 56 Group 2B) reported in MS. A number of the IARC compounds reported in MS are found in the vapor phase including three Group 1, eight Group 2A and 18 Group 2B constituents. Several IARC MS compounds are found in both the vapor and particulate phases including two in Group 1, one in Group 2A and one in Group 2B. Forty-eight IARC MS carcinogens are found in the particulate phase only. Lipophilicity, as determined by the base 10 logarithm of the calculated octanol–water partition coefficient and denoted as Clog P, is reported for each of the 71 non-metallic MS IARC carcinogens. Clog P correlates with a number of biological activities including in vitro mutagenicity and carcinogenicity in rodents, and in the absence of any additional toxicological or epidemiological data, a high log P compound is more likely to be carcinogenic than a low log P compound.