INVESTIGATIONS ON HEALTH-RELATED PROPERTIES OF 2 SEPIOLITE SAMPLES

Published ip injection studies have shown different biological behavio r of different sepiolite samples. There was no evidence for carcinogen ic potential of sepiolite from Vicalvaro, Spain, whereas a high tumor incidence was reported for sepiolite from Finland. The low biological activity of the sepiolite from Vicalvaro, compared to the Finnish samp le, could be caused by low in vivo persistence or by the short length of the fibers, or both. In this study a further sepiolite sample, obta ined as a commercial sample originating from China, was investigated T his sample contained a higher fraction of fibers longer than 5 mu m, c omparable to the Finnish sepiolite sample. The fraction of fibers with a length > 5 mu m was 0.12 and 2.2% for the Vicalvaro and Chinese sep iolite, respectively. For the fiber fraction longer than 8 mu m, the c orresponding values were 0.0045 and 0.82%. The in vivo persistence of the sepiolite samples from China and Vicalvaro was analyzed after intr atracheal instillation of 2 mg in female Wistar rats. Fiber retention in the lungs was analyzed by transmission electron microscopy at diffe rent sacrifice dates up to 12 months after application. For the Vicalv aro sepiolite, a splining of fiber bundles was found during retention time in the lung. Therefore, no half-time of the fiber clearance could be calculated from the number of fibers. The decrease of the calculat ed retained fiber mass was faster for the Vicalvaro sepiolite (T-1/2 = 89 days) compared to the Chinese sepiolite (T-1/2 = 129 days). For 2 or 3 rats per group, at sacrifice dale 12 months after ip injection, t he lung was investigated by histopathology. The main difference betwee n both treatment groups was a more pronounced fibrotic response in the Chinese sepiolite-treated rats compared to those treated with Vicalva ro sepiolite. It is concluded that both the higher fraction of long se piolite fibers and the slower elimination rate of the fiber mass in th e Chinese sample were important factors for the different biological r eaction in comparison with Vicalvaro sepiolite.