LAUSR

Carbon nanotubes (CNTs) are nanomaterials that can be inhaled by employees during production or handling. One CNT, Mitsui-7 (MWNT-7), has been classified by the International Agency for Research on Cancer as “possibly carcinogenic to humans”. In addition, there is a proposal coming from the risk assessment committee of ECHA to classify all fibres with dimension’s compatible with the “Fibre Paradigm” (FP), as carcinogenic. However, there is a lack of clarity regarding the fibres that do not fill the criteria of the FP. In this study, we compared Mitsui-7, compatible with the FP criteria, to a CNT, NM-403, too short and thin to fill this principle. We exposed Sprague Dawley female rats deficient for p53 (GMO), or wild type (WT), by intratracheal instillation to these two CNTs. The animals (GMO and WT) were exposed once a week for 4 consecutive weeks to 0.25 mg/rat of CNT and were sacrificed 3 days and 8 months after the last instillation. Exposure to both CNTs induced acute lung inflammation, which persisted after 8 months in the lungs of rats only exposed to NM-403. On the top of a persistent inflammation, NM-403 also stimulated hyperplasic changes in the rat lungs, which can be considered as a precursor stage for neoplasia. However, no adenoma nor carcinoma was detected. The hyperplasia was significantly more pronounced in the GMO rats. The results suggest that CNT not filling the criteria of the FP can cause persistent inflammation and pre-neoplastic changes. Their safety should be addressed with caution.