Significance of particle size of benzo(a)pyrene for the induction of respiratory tract tumours in hamsters

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Abstract
To study the role of particle size of benzo (a) pyrene (BP) in the induction of respiratory tract tumours, goups of hamsters were given 52 weekly intratracheal instillations of fine (77% < 5.2 μm; 3% < 1.3 μan) or coarse (77 y 42 μm; 0% < 10 μm) BP particles suspended in gelatin‐0.9% NaCl solution. Both the fine and coarse particles were given at two different dose levels, viz., 0.5 and 1.0 mg BP/instillation. Another group of hamsters received 52 weekly intratracheal instillations each consisting of 1.0 mg BP particles of a wide size range (90% y 50 μm; 3% < 5.0 μm) suspended in 0.9% NaCl solution without gelatin. The retention of BP in the respiratory tract was studied in separate groups of hamsters receiving a single instillation of BP particles of the different size ranges. Coarse BP particles cleared less rapidly from the lungs and induced a much stronger tumour response in the respiratory tract than did fine BP particles. These findings demonstrated the crucial significance of particle size for the effectiveness of BP as a respiratory tract carcinogen. No appreciable differences in site of tumour formation were observed between treatment with fine and coarse BP particles, which led to the conclusion that the size of the particles did not play an important role in determining the location of the induced respiratory tract tumours. The elimination rate of the BP particles with a wide size range appeared to be in between those of the fine and the coarse particles. The tumour response found after administration of the BP particles of wide size range was very similar to that obtained with the high dose of coarse BP particles.