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Abstract
Background and objectives: A comprehensive time-to-tumor analysis of the 16 dose groups which received intratracheal instillations of “respirable granular bio-durable particles without known significant specific toxicity” (GBP) in a large carcinogenicity study with rats should be conducted.
Methods: The primary lung tumors were mathematically treated as observed in an incidental context (non-fatal occult tumors), based on biological observations and on the fact that lifetime was not considerably reduced even in groups with high tumor frequency. Maximum likelihood estimates of the parameters of time-to-tumor multistage Weibull models were calculated.
Results: Retained dust volume is a highly significantly better dose measure than instilled dust mass, where particle size is taken into account; there is no empirical support for a dose threshold from this study.
Conclusions: Carcinogenicity studies with intratracheal instillation can lead to results that are relevant for the assessment of relative carcinogenic potencies of particles. A dose threshold for GBP is not supported.
For this paper, data were used that were generated in a large animal experiment conducted in the 1990s by F. Pott and M. Roller as employees of the Medical Institute of Environmental Hygiene at the Heinrich-Heine-University, Duesseldorf, Germany. Parts of previous evaluations of the study were supported by the Federal Institute of Occupational Safety and Health (BAuA), Dortmund, Germany.
Disclosure: The author declares no conflict of interest.
The specific analyses for the present paper and the preparation of the manuscript were done by the author (Advisory Office for Risk Assessment) without financial support.