title: Structural defects play a major role in the acute lung toxicity of multiwall carbon nanotubes: physicochemical aspects.
abstract: Carbon nanotubes (CNT) have been reported to elicit toxic responses in vitro and in vivo, ascribed so far to metal contamination, CNT length, degree of oxidation, or extent of hydrophilicity. To examine how structural properties may modulate the toxicity of CNT, one preparation of multiwall CNT has been modified (i) by grinding (introducing structural defects) and subsequently heating either in a vacuum at 600 degrees C (causing reduction of oxygenated carbon functionalities and reduction of metallic oxides) or in an inert atmosphere at 2400 degrees C (causing elimination of metals and annealing of defects) and (ii) by heating at 2400 degrees C in an inert atmosphere and subsequently grinding the thermally treated CNT (introducing defects in a metal-deprived carbon framework). The presence of framework and surface defects, metals, and oxygenated functionalities was monitored by means of a set of techniques, including micro-Raman spectroscopy, adsorption calorimetry, X-ray photoelectron spectroscopy, inductively coupled plasma mass spectrometry, and atomic emission spectroscopy. Contrary to traditional toxicants, such as asbestos, CNT may quench rather than generate oxygenated free radicals. The potential of the modified CNT to scavenge hydroxyl radicals was thus evaluated by means of electron spin resonance spectroscopy (spin trapping). The original ground material exhibited a scavenging activity toward hydroxyl radicals, which was eliminated by heating at 2400 degrees C but restored upon grinding. This scavenging activity, related to the presence of defects, appears to go paired with the genotoxic and inflammatory potential of CNT reported in the companion paper. Thus, defects may be one of the major factors governing the toxic potential of CNT.
authors.affiliation: Dipartimento di Chimica IFM, Interdepartmental Center G. Scansetti for Studies on Asbestos and other Toxic Particulates, Universita degli Studi di Torino, Torino, Italy.
authors.forename: Ivana
authors.initials: I
authors.lastname: Fenoglio
authors.forename: Giovanna
authors.initials: G
authors.lastname: Greco
authors.forename: Maura
authors.initials: M
authors.lastname: Tomatis
authors.forename: Julie
authors.initials: J
authors.lastname: Muller
authors.forename: Encarnacion
authors.initials: E
authors.lastname: Raymundo-Piñero
authors.forename: François
authors.initials: F
authors.lastname: Béguin
authors.forename: Antonio
authors.initials: A
authors.lastname: Fonseca
authors.forename: Janos B
authors.initials: JB
authors.lastname: Nagy
authors.forename: Dominique
authors.initials: D
authors.lastname: Lison
authors.forename: Bice
authors.initials: B
authors.lastname: Fubini
mesh_terms: D000208:Acute Disease; D000327:Adsorption; D055598:Chemical Phenomena; D016166:Free Radical Scavengers / Q000737:chemistry; D006801:Humans; D017665:Hydroxyl Radical / Q000737:chemistry; D008171:Lung Diseases / Q000139:chemically induced*; D037742:Nanotubes, Carbon / Q000737:chemistry* / Q000633:toxicity*; D010084:Oxidation-Reduction; D010316:Particle Size; D013499:Surface Properties; D013696:Temperature; D014835:Volatilization; D014867:Water / Q000737:chemistry
chemical_list: D016166:Free Radical Scavengers; D037742:Nanotubes, Carbon; D014867:Water; D017665:Hydroxyl Radical