The primary aims of the study were to detect differences of the carcinogenicity of granular dusts on the rat lung after intratracheal instillation and to find out the optimal metric for the carcinogenic potency. 16 of the 19 dusts constituted a group for which no specific toxicity was detected, and which seemed not has been essential for their carcinogenicity. Therefore, these dusts were defined as granular bio-durable particles without known significant specific toxicity (GBP; in German: GBS) in the frame of this carcinogenicity experiment. 12 of the 16 GBP were classified as fine dusts (GBP-F) and 4 as ultrafine dusts (GBP-UF).

The most important results and conclusions: All 16 GBP produced lung tumours, mostly dose-dependently and many more than expected. The GBP volume in connection with particle size turned out to be the most adequate dose metric for the carcinogenicity of GBP. The 4 GBP-UF were 2½ times more effective than the 4 "small" GBP-F (mean diameter 0.09 - 0.2 µm), and 8 times more effective than the 8 "large" GBP-F (mean diameter 1.8 - 4.0 µm). The present state of knowledge fulfils the criteria for the classification of GBP in the EU category 2 of carcinogenic substances.