Toxicological investigations on the respirable fraction of silicon carbide grain products by the in vitro vector model

Abstract

Increased lung cancer incidence with workers at the production site of crude silicon carbide (SiC) using the Acheson process has been reported. Several agents derived from the process were discussed as causative factors. Recently concern had been expressed about the presence of cleavage fragments (CFs) in commercial products fulfilling the WHO criteria for fibers. This study has focused on the toxicological significance of such CFs. The test samples were respirable fractions of five different commercial samples of SiC grains. The CF content (scanning electron microscopy) was in the range 17–493 fibers/µg. Crystalline silica and whiskers could not be detected. Quartz DQ12, cristobalite, SiC whisker, UICC crocidolite and electrocorundum were used as control reference samples. Biological activity was assessed with the in vitro vector model (VM) on ex vivo rat and guinea pig alveolar macrophages (AMs). The dose range of the VM is derived from calculated AM loads from intratracheal instillation experiments and confirmed by measured AM loads from inhalation studies on alumina monohydrate particles with low biological activity: ≤120 pg/AM. The response of the references was clearly different from that of the SiC grains which yielded low toxicity overall. However, the parameter reactive oxygen species secreted by AMs was elevated at the higher SiC doses, but not related to the CF content of these samples. Our data showed that CFs seem to have no biological relevance. This is in agreement with results from recent studies in which no carcinogenic activity had been demonstrated for CFs.

• Cleavage fragments
• in vitro toxicity
• silicon carbide, vector model