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

Asmus Meyer-Plath,Nico Dziurowitz,Barbara Katrin Simonow,Daniela Wenzlaff,Doris Perseke,Daphne Bäger,Sabine Plitzko,Carmen Thim

doi:10.3390/atmos11111254

Asmus Meyer-Plath, Nico Dziurowitz + Show 6 more

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https://doi.org/10.3390/atmos11111254

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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.

Highlights

Fibrous particles can induce long-term inflammation and disease if they are respired into the alveolar region of the lung and are neither dissolved in lung fluids nor removed by lung clearance mechanisms due to their fiber morphology
Such a high-volume flow rate as 6 L/min could only be used at very clean workplaces to avoid overloading the filter samples with generally ubiquitous microscale dust particles
Testing compliance of workplace atmospheres with the benchmark concentration value of 10,000 World Health Organization (WHO) /m that was published in the German TRGS 527 [13] for WHO-analogue fibers down to 1 nm diameter is still a challenge due to the impracticably high analytical effort stated above

Summary

Introduction

Fibrous particles can induce long-term inflammation and disease if they are respired into the alveolar region of the lung and are neither dissolved in lung fluids nor removed by lung clearance mechanisms due to their fiber morphology This epidemiologically substantiated observation has been formulated as the so-called fiber pathogenicity paradigm [1,2]. In light of the history of asbestos and asbestos-related diseases [3], it is of utmost importance for human health to detect, assess and control excessive concentrations of respirable biopersistent airborne fibers For such an assessment, several measurement strategies, categorization concepts and counting rules have been developed internationally, mainly focusing on the availability of analytical techniques and on the industrial relevance of fibers of toxicological concern.

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