Tumorigenicity of cellulose fibres injected into the peritoneal cavity

Cellulose fibres, along with many other organic fibres are durable, and therefore, if inhaled, have the potential to persist within the lung. Persistent fibres may cause disease. This report describes the effects of injecting high purity cellulose fibres into the abdominal cavity of rats. This assay is used to investigate the potential of fibres to produce cancer in rats. Crocidolite asbestos was used as a positive control and saline (used to suspend the fibres for injection) as a negative control. Four doses, from 1 million to 1000 million fibres (defined as fibres longer than 5 urn) were tested for each fibre type.The two higher doses of crocidolite asbestos caused greatly reduced survival compared to the saline controls. With cellulose there was a much less marked effect on survival. In the highest dose cellulose group, multiple large nodules (granulomas) and widespread adhesions (bands of new tissue connecting organs to each other and to the abdominal wall) were present in all animals. Granulomas were not observed in the 109 fibre crocidolite group. More than 80% of animals in the 108 and 109 crocidolite asbestos groups had mesotheliomas, a type of tumour sometimes found in the lungs of people exposed to asbestos. By contrast there were only two animals in the cellulose groups with mesothelioma tumours, one in the 107 and one in the 108 groups. However, nine (18%) of the 109 cellulose group had another type of malignant tumour called a sarcoma. This tumour type is not usually associated with fibres in this animal model.This study has demonstrated that high doses of cellulose fibres are carcinogenic when injected into the abdominal cavity of rats.