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Occupational exposure during handling and loading of halloysite nanotubes - a case study of counting nanofibers

: Koivisto, Antti Joonas; Bluhme, Anders Brostrøm; Kling, Kirsten Inga; Fonseca, Ana Sofia; Redant, Emile; Andrade, Flavia; Hougaard, Karin Sørig; Krepker, Maksym; Prinz, Ofer Setter; Segal, Ester; Holländer, Andreas; Jensen, Keld Alstrup; Vogel, Ulla; Koponen, Ismo Kalevi

Fulltext urn:nbn:de:0011-n-4907791 (1.3 MByte PDF)
MD5 Fingerprint: 95dfa5d4f77cf414e758946c398cd3b9
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Created on: 7.11.2019

NanoImpact 10 (2018), pp.153-160
ISSN: 2452-0748
European Commission EC
H2020; 720815; NanoPack
Journal Article, Electronic Publication
Fraunhofer IAP ()

Halloysite nanotubes (HNTs) are abundant naturally-occurring hollow aluminosilicate clay mineral fibers with a typical diameter < 100 nm and an aspect ratio of up to 200. Here we assessed the potential inhalation exposure to HNTs in an industrial research laboratory. Inside a fume hood, ten times 100 g of HNTs were poured at rate of 0.5 kg min−1, which increased concentrations from the background level up to 2900 cm−3 and 6.4 μm2 cm−3. Inside the fume hood, the respirable mass concentration was 143 μg m−3 including background particles. Outside the fume hood we did not measure elevated concentrations. We classified 1895 particles according to their length and aspect ratio. Five particles were in aspect ratio > 3 and in length > 2 μm. These particles were agglomerated and/or aggregated particles where the longest individual fiber was 2 μm in length. The occupational exposure limits for refractory mineral fibers vary from 0.1 to 2 fibers cm−3. Following standard protocols for fiber analysis, detection of 0.1 fibers cm−3 would require analysis on 4 × 104 images when the filter loading is good. Thus, the fiber sampling and quantification procedures needs to be improved significantly if nanofibers <100 nm in diameter are included in regulatory exposure assessment. Due to very limited toxicological information of HNTs we recommend avoiding inhalation exposure.