A Practicable Measurement Strategy for Compliance Checking Number Concentrations of Airborne Nano- and Microscale Fibers

Abstract

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.

Towards health-based nano reference values (HNRVs) for occupational exposure: Recommendations from an expert panel

“…However, the threshold diameter to distinguish between rigid and non-rigid HARNs depends also on the material, and has up to now only been verified experimentally for carbon-based nanotubes or -fibers. Broßell et al ( Broßell et al, 2020 ) and Murphy et al ( Murphy et al, 2021 ) have reported a threshold diameter for the rigidity of CNTs to be above ~30 to 40 nm, while in the German Federal Institute for Occupational Safety and Health (BAuA) measurement strategy for nanosized fibers a cut-off diameter of 20 nm is used ( Meyer-Plath et al, 2020 ). This figure is based on data on MWCNTs, but includes a safety margin of about a factor of 16 for nanofibers for which no experimental data on their toxicity or rigidity is available ( Meyer-Plath et al, 2020 ).…”

Meta‐Analysis of Integrated Proteomic and Transcriptomic Data Discerns Structure–Activity Relationship of Carbon Materials with Different Morphologies

“…In particular, there is a lack of chronic in vivo toxicity studies for materials with diameters between 15 and 30 nm. [ 20 , 52 , 53 ] Therefore, the second step of the present work included an evaluation of the extent of alteration of HALLMARK pathways observed for materials with high aspect ratios but length and diameter smaller than that of Mitsui‐7 and 30 nm, respectively. In this regard, we detected that the cellular effect of the NM‐400 (NRCEW26) material resembles one of the rigid fibers, although its 11 nm diameter suggests it would behave like a tangled material.…”

Bloß kein zweites Asbest

“…in den vergangenen zwei Jahrzehnten wurden mit metho den der Nanotechnologie große Fortschritte bei der entwick lung neuer materialien erzielt. eine neue und vielfäl tige materialgruppe sind die auf Fulleren und Graphenstrukturen basierenden Kohlenstoffmaterialien, speziell die ein und mehrwandigen Kohlenstoff nanoröhren (Carbon Nanotubes, CNT [16,17]. ein solches Bruchverhalten entlang Faserrichtung zeigten bisher vornehmlich die kristallinen pechbasierten Carbonfasern.…”