Effects of phosphorylation of chrysotile on pleuropulmonary fibrogenicity and carcinogenicity.

As well as fibre size, fibre chemistry is a determinant of toxicity of mineral fibres. On these grounds, a few years ago, the asbestos industry in Québec developed a process to modify the surface chemistry of chrysotile asbestos by fixing phosphorous atoms. The pleuropulmonary fibrogenicity and carcinogenicity of the native and surface treated chrysotile, called chrysophosphate, were tested. Both products initiated similar pulmonary fibrogenicity in rats exposed by inhalation and sheep exposed by injection in the tracheal lobe. Tumour production in rats after long term inhalation or intrapleural injection was not different between chrysotile and chrysophosphate. These findings clearly show that modification of the phosphate surface of chrysotile fibres does not appear to alter the pleuropulmonary activities of the mineral, thus arguing against the earlier contention of less biological activity for chrysophosphate, a contention essentially based upon results of in vitro tests. This study strongly argues for in vivo testing of new fibrous materials before making definite conclusions about their biological activities.