A novel synthetic erionite fibre radiolabelled with (57)Co

The aim was to produce a radiolabelled fibre suitable for long-term carcinogenesis studies. To this end, we have successfully synthesised erionite fibres by a method adapted to incorporate (57)Co into the crystal framework. Morphologically the fibres are straight, of median length 2.5 microm, with 11% of fibres > 8 microm long, and median width 0.32 microm. These values are comparable to natural Oregon erionite. Autoradiography confirmed that the (57)Co was associated with the fibres themselves. The stability of the radiolabel in vivo was examined by instilling 1 mg of synthetic erionite into the lungs of F-344 rats. About half of the thoracic content of (57)Co was cleared in the first week, and over the following 5 weeks the remainder was cleared slowly with a half-time of 120 days. After 6 weeks the urinary excretion of (57)Co was only 0.054% of the initial lung content per day. This represented fibre dissolution plus any leaching of (57)Co from the fibres. It can be concluded that the (57)Co is bound into the erionite fibres with sufficient stability in vivo for studying their effects in relation to translocation to the pleura.