Carcinogenicity studies after interperitoneal injection of two types of stone wool fibres in rats

A summary is given of the pathology results after intraperitoneal (i.p.) injection in rats of insulation wool HT, representing the new biosoluble types. The pathology results are compared with a previously conducted i.p. study with traditional stone wool D6 (with similar chemical composition to MMVF21). The HT fibre is characterized by a relatively high content of aluminium and a relatively low content of silica compared to MMVF21. HT has a high in vitro dissolution rate at pH 4.5, a relatively low dissolution rate at pH 7.5 and is less biopersistent than the MMVF21 fibre. Female Wistar rats received a dose of 2 × 109 WHO HT fibres by i.p. injection. The fibres had been size-selected to be largely rat respirable. The negative control group was exposed to saline. Following exposure, the animals were maintained until survival in one group fell below 20%. At this time, all animals were killed. All animals were subjected to a necropsy examination; any gross abnormalities observed at necropsy were subjected to histopathological examination. In addition, histopathology was carried out on a predefined list of tissues. The incidences of lesions and survival in the control and fibre dosed animals were compared using appropriate statistical methods to determine whether the dosed animals showed adverse effects on survival or a positive carcinogenic response. The main protocol for the previously conducted study with D6 (MMVF21) was similar, but the animals were maintained as long as they survived, and the WHO fibre dose was lower. The results of the comparative study showed a marked difference in the i.p. pathogenicity of D6 (MMVF21) and HT in terms of their carcinogenic potential. D6 (MMVF21) caused a statistically significant increase of mesotheliomas in the peritoneal cavity compared to the negative control, but the HT fibre did not cause any mesotheliomas or any increase in other tumour types.