RESPIRABLE INDUSTRIAL FIBRES: DEPOSITION, CLEARANCE AND DISSOLUTION IN ANIMAL MODELS

This paper examines the available experimental and theoretical results describing deposition and clearance of mineral fibres inhaled by animals and humans in order to define the limits which these mechanisms impose on the relevance of animal experiments in the assessment of potential human health risks. Direct experimental data for deposition of spherical particles are extended by examination of the physical processes and by some limited experimental data for fibres. This shows that alveolar deposition efficiency (in rat and in man) is sufficiently similar for particles and fibres with aerodynamic diameters less that 5 microns for rats to be a relevant model for airborne dusts in this size range. Inter-species differences in mechanical clearance are substantial, with clearance being faster in the rat than in man, and this is a factor which should be considered in interpreting animal toxicity studies. The durability of fibres in the biochemical conditions of the lung may be more important over the longer lifespan of humans.