Occupational Exposure to Carbon Nanotubes and Nanofibers

A.7.1 Particle CharacteristicsBoth types of CNF were vapor grown, but obtainedfrom different sources. In Murray et al. [2012], theCNF was supplied by Pyrograf Products, Inc. Thechemical composition was 98.6% wt. elemental carbonand 1.4% wt. iron. CNF structures were 80 to160 nm in diameter, and 5 to 30 µm in length. Thespecific surface area (SSA) measured by BET was 35-45 m 2 /g; the effective SSA was estimated as ~21 m 2 /g[Murray et al. 2012]. In DeLorme et al. [2012], theCNF was supplied by Showa Denko KK, Tokyo,Japan. The chemical composition was >99.5% carbon,0.03% oxygen and < 0.003% iron. CNF structureswere 40-350 nm (158 nm average) in diameterand 1-14 µm in length (5.8 µm average). The BETSSA was 13.8 m 2 /g [DeLorme et al. 2012].A.7.2 Experimental Designand AnimalsThe species and route of exposure also differed inthe two studies. In Murray et al. [2012], six femaleC57BL/6 mice (8-10 wk of age, 20.0 + 1.9 g bodyweight) were administered a single dose (120 µg) ofCNF by pharyngeal aspiration [Murray et al. 2012];mice were examined at 1, 7, and 28 days post-exposure.In DeLorme et al. [2012], female and maleCrl:CD Sprague Dawley rats (5 wk of age) were exposedto CNF by nose-only inhalation at exposureconcentrations of 0, 0.54, 2.5, or 25 mg/m 3 (6 hr/d,5 d/wk, 13 wk). The rats were examined 1-d afterthe end of the 13-wk exposure and 3 months postexposure.Body weights were reported as: 252 g +21.2 female; 520 g + 63.6 male (unexposed controls,1-d post-exposure); 329 g + 42.2 female; 684g + 45.8 male (unexposed controls, 3 mo. post-exposure)[DeLorme et al. 2012].A.7.3 Lung ResponsesIn mice, the lung responses to CNF included pulmonaryinflammation (polymorphonuclear lymphocytes,PMNs, measured in bronchioalveolarlavage fluid, BALF); PMN accumulation in CNFexposedmice was 150-fold vs. controls on day 1.NIOSH CIB 65 • Carbon Nanotubes and NanofibersBy day 28 post-exposure, PMNs in BALF of CNFexposedmice had decreased to 25-fold vs. controls.Additional lung effects included increased lungpermeability (elevated total protein in BALF), cytotoxicity(elevated lactate dehydrogenase, LDH),which remained significantly elevated compared tocontrols at day 28 post-exposure. Oxidative damage(elevated 4-hydroxynonenol, 4-HNE, and oxidativelymodified proteins, i.e., protein carbonyls)was significantly elevated at days 1 and 7, but notat day 28. Collagen accumulation at day 28 postexposurewas 3-fold higher in CNF-exposed micevs. controls by biochemical measurements. Consistentwith the biochemical changes, morphometricmeasurement of Sirius red-positive type I and IIIcollagen in alveolar walls (septa) was significantlygreater than controls at day 28 post-exposure[Murray et al. 2012].In rats, the respiratory effects observed in the De-Lorme et al. study [2012] were qualitatively similarto those found in the Murray et al study [2012]. Thewet lung weights were significantly elevated comparedto controls in male rats at 25 mg/m 3 CNF andin female rats at 2.5 and 25 mg/m 3 CNF at 1-daypost-exposure; lung weights remained elevated ineach sex in the 25 mg/m 3 exposure group at 3 mo.post-exposure. Histopathologic changes at 1 daypost-exposure included inflammation in the terminalbronchiolar and alveolar duct region in the2.5 and 25 mg/m 3 exposure groups, and interstitialthickening with type II pneumocyte proliferationin the 25 mg/m 3 exposure group. Cell proliferationassays confirmed increased cell proliferation in thathighest dose group in the subpleural, parenchymaland terminal bronchiolar region; the subpleuralproliferation in this dose group did not resolve inthe females by the end of the 3 month recovery period.Cell proliferation appeared to resolve in malesafter a 3 month recovery period but numerically remainedhigher in the parenchyma and subpleuralregions. Histopathologic evidence of inflammationand the presence of fiber-laden macrophageswere reported to be reduced but still present in thehigh dose group after a 3 month recovery period.Inflammation within the alveolar space (as measuredby PMN levels in BALF) was statistically sig-139