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The Galson Blog

Edward Stuber CIH


New REL for TiO2

A recently released NIOSH guidance document on handling titanium dioxide (TiO2) powders in the workplace recommend separate occupational exposure limits for the same material based on particle size. Distinct exposure limits for distinct size fractions is on its way. Move over respirable and inhalable - nanpoparticles are here to stay.

In recent years new toxicity data on the adverse pulmonary effects of exposure to TiO2 indicated (according to NIOSH) the need for revised risk management recommendations including recommended exposure limits (RELs) for fine (defined as primary particle diameters >100 nm) and ultrafine or nanoscale (defined as primary particle diameters <100 nm) TiO2.

NIOSH recommended two mass occupational exposure limits for the two size fractions of TiO2: 2.4 mg/m3 for fine particles and 0.3 mg/m3 for ultrafine or nanoscale particles. In addition, NIOSH declassified fine particles of TiO2 as a potential occupational carcinogen due to the lack of sufficient animal or epidemiologic data to support such a classification, but it found sufficient data from animal studies to maintain this classification for nanoscale particles of TiO2.

The main difference in exposure assessment in workplaces handling TiO2 is the need to differentiate not just by chemical composition but also by size. NIOSH recommends measuring personal exposure concentrations to fine and nanoscale TiO2 with NIOSH Method 0600. If respirable exposure levels to TiO2 are higher than 0.3 mg/m3 (REL for nanoscale TiO2), then additional characterization by electron microscopy is required to determine the particle size and the percentage of ultrafine and fine TiO2 so that the appropriate RELs can be applied.

The full guidance document can be found here:http: //

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