Contribution of polycyclic aromatic hydrocarbons and nitro-derivatives to the carcinogenic impact of diesel engine exhaust condensate evaluated by implantation into lungs of rats

Diesel exhaust condensate was seperated by a liquid-liquid distribution into a hydrophilic ( I; about 25 per cent by weight of the total condensate) and a hydrophobic part ( II; about 75 per cent-wt.). To evaluate the carcogenicity, the proportionately dosed fractions have been implanted into the lungs of Osborne Mendel rats and compared with several doses of benzo[a)pyrene and the vehicle, a mixture of trioctanoin plus beeswax. Only the hydrophobic part which contained polycycl ic aromatic compounds ( PAC) resulted in 5 malignant tumors in a group of 35 animals. In addition, the hydrophobic part was seperated by column chromatograpy on Sephadex LH 20 and subsequently on silica gel into several fractions, such as non-aromatic compounds plus PAC with 2 and 3 rings ( IIa; 72 per cent-wt of the total condensate), polycyclic aromatic compounds ( PAH) with 4 and more rings (IIb; 0.8 per cent-wt) polar PAC (IIc; 1.1 per cent-wt) and nitro-PAH ( IId; 0.7 per cent). PAH consisting of 4 and mor e rings ( IIb) were were found to be the most p otent subfraction and provoked when proportionately dosed 6 carcinomas in a group of 35 rats. Only a low contribution to the carcinogenicity was observed by the subfraction of nitro-PAH (IId) which produced 1 carcinama/35 rats. The polar PAC (IIc) and the fraction of non-aromatic plus PAC with 2 and 3 rings (II2), although the main subfraction (72 per cent-wt of the total condensate) did not provoke any tumors. The reconstitution potency as the unfractionated hydrophobics (II), provoking 7 carcinoma in 35 rats. It may be concluded from these findings that most of the carcinogenicity of diesel exhaust originates from the PAH consisting of 4 and more rings.