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Despite compelling reports on asbestos-like pathogenicity, regulatory bodies have been hesitant to implement fiber number-based exposure limits for biodurable nanoscale fibers. One reason has been the lack of a practicable strategy for assessing airborne fiber number concentrations. Here, a method is proposed, detailed and tested for compliance checking concentrations of airborne nano- and microscale fibers. It relies on Poisson statistical significance testing of the observed versus a predicted number of fibers on filters that have sampled a known volume of aerosol. The prediction is based on the exposure concentration to test. Analogous to the established counting rules for WHO-fibers, which use a phase contrast microscopy-related visibility criterion of 200 nm, the new method also introduces a cut-off diameter, now at 20 nm, which is motivated by toxicological findings on multi-walled carbon nanotubes. This cut-off already reduces the workload by a factor of 400 compared to that necessary for imaging, detecting and counting nanofibers down to 1 nm in diameter. Together with waiving any attempt to absolutely quantify fiber concentrations, a compliance check at the limit-of-detection results in an analytical workload that renders our new approach practicable. The proposed method was applied to compliance checking in 14 very different workplaces that handled or machined nanofiber-containing materials. It achieved detecting violations of the German benchmark exposure level of 10,000 nanofibers per cubic meter.

Introduction Because of their unique physico-chemical properties, CNTs have attracted a great deal of research interest and have many promising industrial applications. However, this also increases the exposure potential for workers, raising the need to understand their hazard for an effective occupational health and safety management. CNTs can induce lung inflammation, granuloma formation, fibrosis and cancer in rodents; in particular, MWCNTs are known to induce in vitro markers of remodelling and fibrosis. CNTs greatly vary in length, thickness, rigidity, aspect ratio, surface defects and reactivity, with a remarkable contribution of synthesis methods and posttreatments. Thus, CNTs are not a single substance, but a heterogeneous family of materials that elicit different biological responses and, thus, are associated with different hazard levels not simply ascribable to the fibre paradigm. Methods Cell models representative of the airway barrier were challenged with MWCNT preparations endowed with different physico-chemical properties, evaluating endpoints such as viability, expression of pro-inflammatory markers, nitric oxide production, epithelial barrier competence, clonogenic activity, genotoxicity. Epithelial-mesenchymal transition (EMT) was also assessed as an early event leading to fibrosis and, possibly, involved in neoplastic transformation. Results Only long MWCNTs promoted EMT and caused frustrated phagocytosis. On the other hand, MWCNT agglomeration led to contact-mediated focal epithelial damage and impaired barrier functionality in vitro. Functionalization with carboxyl or amino groups modified the quantity and type of proteins adsorbed and, hence, the interaction with cells. Discussion These findings may contribute to safe-by design manufacturing of MWCNT. Importantly, all the endpoints evaluated represent MIEs than can be combined to construct putative AOPs, associated with disease onset and progression. It is therefore concluded that the knowledge of the physicochemical properties associated to the MIEs of different adverse outcomes is a prerequisite for the toxicological profile of a MWCNT preparation.

Es wird eine Methode vorgestellt, um Sicherheitsaspekte von Prozessen zu untersuchen, mit denen metallische faserverstärkte Verbundwerkstoffe hergestellt und bearbeitet werden. Ziel ist, zu anwendungssicheren Prozessen zu gelangen, indem Gefahren gesundheitsgefährdender Stäube möglichst frühzeitig identifiziert und geeignete Schutzmaßnahmen ausgewählt werden. In der hier untersuchten Anwendung wurden Komposite aus Kupfer (Cu) mit Kohlenstoffnanoröhren (carbon nanotubes, CNTs) oder Kohlenstoffnanofasern (carbon nanofibers, CNFs) hergestellt und bearbeitet. Sie profitieren als elektrische Leiter und thermisch leitfähige Kontaktmaterialien von den Eigenschaften der zugesetzten Kohlenstoffmaterialien. Es kamen zum einen verknäulte CNTs mit Durchmessern von ca. 20 nm zum Einsatz, zum anderen rigide CNFs mit Durchmessern von ca. 100 nm. Für beide Fasertypen wurde zunächst im Labor die Staubungsneigung des trockenen Pulvers bestimmt, indem der Staub, der in einem Vibro-Fluidisierungsprozess entsteht, morphologisch charakterisiert, klassifiziert und quantifiziert wurde. Zur Bestimmung der Faserexposition von Beschäftigten erfolgte im Anschluss die Messung der luftgetragenen Faseranzahlkonzentrationen an den Arbeitsplätzen. Dabei kam ein neues Messverfahren für Aerosole aus nanoskaligen Fasern zur Anwendung, das derzeit durch ein Projekt der Deutschen Gesetzlichen Unfallversicherung e. V. (DGUV) validiert wird.