Occupational exposure during handling and loading of halloysite nanotubes – A case study of counting nanofibers

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

*Corresponding author for this work

    Research output: Contribution to journalJournal articleResearchpeer-review

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    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 μgm−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.
    Original languageEnglish
    Pages (from-to)153-160
    Publication statusPublished - 2018


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