Titanium dioxide (TiO2) pigment is a non-toxic, particulate material in widespread use and found in everyone's daily life. The particle size of the anatase or rutile crystals are optimised to produce a pigment that provides the best possible whiteness and opacity. The average particle size is intentionally much larger than the 100 nm boundary of the EU nanomaterial definition, but the TiO2 pigment manufacturing processes results in a finite nanoscale content fraction. This optically inefficient nanoscale fraction needs to be quantified in line with EU regulations. In this paper, we describe the measurement procedures used for product quality assurance by three TiO2 manufacturing companies and present number-based primary particle size distributions (PSDs) obtained in a round-robin study performed on five anatase pigments fabricated by means of sulfate processes in different plants and commonly used worldwide in food, feed, pharmaceutical and cosmetic applications. The PSDs measured by the three titanium dioxide manufacturers based on electron micrographs are in excellent agreement with one another but differ significantly from those published elsewhere. Importantly, in some cases, the PSDs result in a different regulatory classification for some of the samples tested. The electron microscopy results published here are supported by results from other complementary methods including surface area measurements. It is the intention of this publication to contribute to an ongoing discussion on size measurements of TiO2 pigments and other particulate materials and advance the development of widely acceptable, precise, and reproducible measurement protocols for measuring the number-based PSDs of particulate products in the size range of TiO2 pigments.

Billions Europe Ltd Winder House Kingfisher Way Stockton on Tees TS18 3EX United Kingdom

Global Special Analytics Venator Germany GmbH Dr Rudolf Sachtleben Str 4 47198 Duisburg Germany

R and D PRECHEZA nábř Dr Edvarda Beneše 1170 24 750 02 Přerov Czech Republic

Research Services KRONOS INT Inc Peschstr 5 51737 Leverkusen Germany

TRONOX Pigment UK Ltd Laporte Road Stallingborough North East Lincolnshire DN40 2PR United Kingdom

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EUR-Lex - 32022H0614(01) - EN - EUR-Lex. [ Mar 6; 2024 ]. Available from: https://eur-lex.europa.eu/legal-content/DE/TXT/?uri=CELEX:32022H0614%2801%29.

JRC Publications Repository: Towards a review of the EC Recommendation for a definition of the term "nanomaterial" Part 2: Assessment of collected information concerning the experience with the definition. [ Mar 6; 2024 ]. Available from: https://publications.jrc.ec.europa.eu/repository/handle/JRC91377.

JRC Publications Repository: Identification of nanomaterials through measurements. [ Mar 6; 2024 ]. Available from: https://publications.jrc.ec.europa.eu/repository/handle/JRC118158.

Hodoroaba V-D, Mielke J. NanoDefine Technical Report D3.1. Wageningen, Netherlands: NanoDefine Consortium; 2014.

Uusimäki T, Hallegot P. NanoDefine Technical Report D2.4. Wageningen, Netherlands: NanoDefine Consortium; 2016.

Gilliland D. NanoDefine Technical Report D2.3. Wageningen, Netherlands: NanoDefine Consortium; 2016.

EFSA Panel on Food Additives and Flavourings (FAF) Younes M, Aquilina G, Castle L, Engel K-H, Fowler P, Frutos Fernandez M J, Fürst P, Gundert-Remy U, Gürtler R, et al. EFSA J. 2021;19:e06585. doi: 10.2903/j.efsa.2021.6585. PubMed DOI PMC

Verleysen E, Waegeneers N, Brassinne F, De Vos S, Jimenez I O, Mathioudaki S, Mast J. Nanomaterials. 2020;10(3):592. doi: 10.3390/nano10030592. PubMed DOI PMC

Geiss O, Bianchi I, Senaldi C, Bucher G, Verleysen E, Waegeneers N, Brassinne F, Mast J, Loeschner K, Vidmar J, et al. Food Control. 2021;120:107550. doi: 10.1016/j.foodcont.2020.107550. PubMed DOI PMC

Geiss O, Ponti J, Senaldi C, Bianchi I, Mehn D, Barrero J, Gilliland D, Matissek R, Anklam E. Food Addit Contam, Part A. 2020;37:239–253. doi: 10.1080/19440049.2019.1695067. PubMed DOI

EFSA Panel on Food Additives and Flavourings (FAF) Younes M, Aquilina G, Castle L, Engel K-H, Fowler P, Frutos Fernandez M J, Gürtler R, Gundert-Remy U, Husøy T, et al. EFSA J. 2019;17:e05760. doi: 10.2903/j.efsa.2019.5760. PubMed DOI PMC

Winkler J. Titanium Dioxide. Germany: Vincentz Network; 2019. DOI

JRC Publications Repository: Basic comparison of particle size distribution measurements of pigments and fillers using commonly available industrial methods. [ Mar 6; 2024 ]. Available from: https://publications.jrc.ec.europa.eu/repository/handle/JRC92531.

Test No. 125: Nanomaterial Particle Size and Size Distribution of Nanomaterials | OECD Guidelines for the Testing of Chemicals, Section 1: Physical-Chemical properties | OECD iLibrary. [ Mar 6; 2024 ]. Available from: https://www.oecd-ilibrary.org/environment/test-no-125-nanomaterial-particle-size-and-size-distribution-of-nanomaterials_af5f9bda-en. DOI

Todorov V, Filzmoser P. J Stat Software. 2009;32(3):1–47. doi: 10.18637/jss.v032.i03. DOI

Mozhayeva D, Engelhard C. J Anal At Spectrom. 2020;35:1740–1783. doi: 10.1039/c9ja00206e. DOI

Laborda F, Bolea E, Jiménez-Lamana J. Trends Environ Anal Chem. 2016;9:15–23. doi: 10.1016/j.teac.2016.02.001. DOI

ISO 20427:2023 - Pigments and extenders — Dispersion procedure for sedimentation-based particle sizing of suspended pigment or extender with liquid sedimentation methods. [ Mar 6; 2024 ]. Available from: https://www.iso.org/standard/80236.html.

Babick F, Stintz M, Koch T. Powder Technol. 2018;338:937–951. doi: 10.1016/j.powtec.2018.07.052. DOI

Gómez Tena M P, Gilabert J, Machí C, Zumaquero E, Toledo J. Relationship between the specific surface area parameters determined using different analytical techniques; Qualicer 2014 – 13th World Congress on Ceramic Tile Quality; 2014. https://www.qualicer.org/recopilatorio/ponencias/pdfs/56%20POSTER%20ING.pdf .

Theissmann R, Kluwig M, Koch T. Beilstein J Nanotechnol. 2014;5:1815–1822. doi: 10.3762/bjnano.5.192. PubMed DOI PMC

ISO 787-24:1985 - General methods of test for pigments and extenders, Part 24: Determination of relative tinting strength of coloured pigments and relative scattering power of white pigments – Photometric methods. [ Mar 6; 2024 ]. Available from: https://www.iso.org/standard/5104.html.

Gesenhues U. Chem Eng Technol. 2001;24:685–694. doi: 10.1002/1521-4125(200107)24:7<685::aid-ceat685>3.0.co;2-1. DOI

R version 4.2.1. Vienna, Austria: R Foundation for Statistical Computing; 2022. Available from: https://www.R-project.org/

Delignette-Muller M L, Dutang C. J Stat Software. 2015;64(4):1–34. doi: 10.18637/jss.v064.i04. DOI

Wickham H. ggplot2: Elegant Graphics for Data Analysis. New York, NY, U.S.A.: Springer; 2016. ((Use R!)). DOI