Very little is known about the in vivo toxicity of inhaled double-walled carbon nanotubes (DWCNTs). In the present study, we compared the pulmonary toxicity of DWCNT to MWCNT-7, a well-known multi-walled carbon nanotube. Rats were divided into six groups: untreated, vehicle, low-dose DWCNT, high-dose DWCNT, low-dose MWCNT-7, and high-dose MWCNT-7. The test materials were administered by intra-tracheal intra-pulmonary spraying (TIPS) every other day for 15 days: the low-dose and high-dose groups were administered final total doses of 0.25 and 0.50 mg/rat of the test material. The animals were sacrificed 1 and 6 weeks after the final TIPS administration. Six weeks after the final TIPS administration, rats administered MWCNT-7 had high levels of macrophage infiltration into the lung with dense alveolar wall fibrous thickening throughout the lung; significant elevation of lactate dehydrogenase activity, alkaline phosphatase activity, and total protein concentration in the bronchioalveolar lavage fluid; an increase in the pulmonary cell PCNA index; slightly elevated levels of 8-OHdG DNA adducts in lung tissue DNA; a small but significant increase in protein concentration in the pleural cavity lavage fluid and an increase in the visceral mesothelial cell PCNA index. None of these parameters was increased in rats administered DWCNT. The primary lesion in rats administered DWCNT was scattered formation of granulation tissue containing internalized DWCNT fibers. Our data indicate that DWCNT has lower pulmonary and pleural toxicity than MWCNT-7.Electronic supplementary materialThe online version of this article (10.1007/s00204-018-2336-3) contains supplementary material, which is available to authorized users.

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