Variations in the carcinogenicity of mineral fibres

An intraperitoneal injection assay system in laboratory rats was used to examine the relative carcinogenicity of five asbestiform dusts of chrysotile origin and two of amosite origin. Twenty-five milligram suspensions of dust were injected into each of 32 rats for each treatment and the animals subsequently monitored for the development of tumours. The intraperitoneal route was shown to provide a useful assay of the tumour-producing potential of particulate materials, with an increased sensitivity when compared with intrapleural inoculation methods. The results showed that the chrysotile samples tended to be more carcinogenic than the amosite preparations and some of the possible reasons for this are discussed. It was concluded, from estimations of particle size using the scanning electron microscope, that relative fibre length did not provide a useful measure of the carcinogenicity of the seven dusts, owing in part to problems arising from the preparation of realistic, representative, samples for microscopy.