Carcinogenicity and mutagenicity of the shale-oil produced in the Estonian Kiviter retort.

Skin painting experiments in CC57Bl mice showed that the total oil (TO) obtained by thermal processing of lump oil shale in the high capacity 'Kiviter' retort containing 56 ppm benzo[a]pyrene (BP) and diluted with benzene (66.6%) induced skin tumours in five out of 60 effective mice--in three mice squamous-cell papillomas and in two mice carcinomas. The light fraction (230-350 degrees C) of this oil and the laboratory residue (82 ppm BP) of the latter failed to induce skin tumours. An industrial residue of a blend of shale oils containing 590 ppm BP induced in 10 mice papillomas and in three mice carcinomas, gave a positive response in the Ames assay and also induced chromosome aberrations and sister chromatid exchanges. The laboratory residue and light fraction were clearly mutagenic in the Ames assay and positive responses were also obtained with the basic and neutral fractions and a polynuclear aromatics fraction.