Toxicology of calcium silicate insulating materials. Final report on MOD contract NCS 361/71364

Inhalation studies were undertaken to test the effects on rats of the calcium silicate insulation products Caposil 16, Newtherm 800 and Paratemp AF. Groups of 48 animals were treated with dust,generated from each material at a respirable concentration of 10 mg/m3 of air for one year. The size range of the dust particles was similar to that found during dockyard usage of the materials. Forty-eight control animals were maintained in the same type of dusting chamber but received only filtered air. After the 12 month dusting period the majority of the animals were allowed to live out their normal life span. The dusted animals showed no signs of ill health until they reached an advanced age and the survival times and body weights for both control and dusted groups were similar. In most animals the only response to dust inhalation was the accumulation of dust-containing macrophages in the lung tissue but these declined substantially in number after the end of dusting and few remained in old animals. All haematological parameters were within normal published ranges for both dusted and control animals although the white cell levels from all the dusted groups were raised compared to the controls. The only type of pathological pulmonary lesion found in the study that appeared related to dust inhalation was the formation of a few small silicotic lesions in the lungs and lymph nodes of animals treated with Newtherm 800. While only two pulmonary neoplasms and one peritoneal mesothelioma were produced in this study, figures too low to indicate any dust association, a number of small benign lesions, similar in histological pattern to mesotheliomas were found in association with the tunica viginalis of nine animals. Since six of these occurred in the group treated with Paratemp AF as compared to two with Caposil 16 and one in the controls, a possible association with this dust was indicated. However, these differences were not statistically significant and the lesions did not appear to affect the health of the animals in any way. The study produced,ao evidence that inhaled dust (at a respirable concentration of 10 mg/m ) from Newtherm 800, Paratemp AF, or Caposil 16 affected the survival or health of laboratory rats. A comparison of the biological effects of the three calcium silicate insulation materials with a series of asbestos and other mineral fibre dusts subjected to similar testing by the Institute of Occupational Medicine is included in the report.