Respirable industrial fibres: pathology in animal models

This paper discusses the general efficacy of the rat as a model for studying the pathogenicity of respirable fibres in humans. Rats show differences in lung structure from man and these could influence the pulmonary response to some degree, but they do develop interstitial fibrosis, carcinoma and mesothelioma when exposed to respirable fibres and these same types of lesions are found in fibre-exposed humans. Because of the importance of long fibres in causing pathological change, a substantial number of long respirable fibres must be used in inhalation studies if the relative pathogenicity of different fibre types is to be assessed. From data on the fibre burden in human disease and information on build-up of fibres in rat studies in a range of different fibres, a 1 year exposure to a cloud of 200 fibres ml-1 minimum, preferably more, is recommended. The rate of dissolution of the fibres within the lung milieu will be an an important factor in determining the pathogenicity. Many questions remain unanswered as to the mechanism of lung pathogenicity caused by respirable fibres particularly in the areas of durability, fibre shape, fibre surface chemistry and the exact mechanism, at the cellular level whereby fibres can cause pathological change. The use of rat inhalation studies, properly conceived and designed, remain a key approach whereby these questions can be answered.