Tumours in mice after subcutaneous injection of automobile exhaust condensates

Automobile exhaust condensate (AEC), either mixed with benzo[a]pyrene (BaP) or suspended or dissolved in tricaprylin, was injected subcutaneously into NMRI mice in a series of experiments. The addition of AEC decreased the incidence of tumours which developed with 30, 90 and 270 microgram BaP. Reduction of tumour incidence was proportional to the amount of AEC added. With an injection of 10 microgram BaP, the latent period was greatly increased when AEC was added, but the occurrence of tumours was the same. Components of AEC appear to inactivate BaP, at least temporarily. In further experiments AEC and nine fractions thereof were injected subcutaneously into mice. The fraction comprising only polycyclic aromatic hydrocarbons (PAH) induced the highest incidence of tumours. In contrast, when it was administered in combination with other fractions the PAH fraction was less active. Application of the products of further fractionation of PAH showed that polycyclic compounds with seven or more rings can also induce tumours in this model.