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The structure, composition, and dimensions of TiO2 and ZnO nanomaterials in commercial sunscreens

Abstract

TiO2 and ZnO nanomaterials are widely used to block ultraviolet radiation in many skin care products, yet product labels do not specify their dimensions, shape, or composition. The absence of this basic information creates a data gap for both researchers and consumers alike. Here, we investigate the structural similarity of pigments derived from actual sunscreen products to nanocrystals which have been the subject of intense scrutiny in the nanotoxicity literature. TiO2 and ZnO particles were isolated from eight out of nine commercial suncare products using three extraction methods. Their dimension, shape, crystal phase, surface area, and elemental composition were examined using transmission and scanning electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller (BET) specific surface area analysis, energy dispersive X-ray and inductively coupled plasma optical emission spectroscopy. TiO2 pigments were generally rutile nanocrystals (dimensions ~25 nm) with needle-like or near-spherical shapes. ZnO pigments were wurtzite rods with a short axes less than 40 nm and longer dimensions often in excess of 100 nm. We identify two commercial sources of TiO2 and ZnO nanocrystals whose physical and chemical features are similar to the pigments found in sunscreens. These particular materials would be effective surrogates for the commercial product and could be used in studies of the health and environmental impacts of engineered nanomaterials contained in sunscreens.

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Notes

  1. We use the term “suncare product” to refer broadly to any product that offers sun protection. Recent trends have made sun protection commonplace in personal care products ranging from shampoo to moisturizer. The term sunscreens is limited to those products whose primary function is to block UV radiation.

  2. We took 8.2 wt% as an average level for sunscreen pigment content that was estimated based on range of weight fraction of TiO2 and ZnO (1.9–14.5 wt%) in sun protection products in four popular retail stores in the US (CVS, Target, Wal-Mart and Walgreens on September 26th and 27th of 2009).

  3. In the US alone, taking estimates of market size provided by Datamonitor and assuming roughly 23% of the suncare products use inorganic agents, there are about 142 tons of TiO2 and ZnO that enter the environment (supporting information) (Datamonitor 2009a, b).

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Acknowledgments

This work was supported by the Center for Biological and Environmental Nanotechnology (EEC-0647452) through NSF, the Shared Equipment Authority instrumentation at Rice University and in part through the collaboration with Consumer’s Union.

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Correspondence to Vicki L. Colvin.

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Lewicka, Z.A., Benedetto, A.F., Benoit, D.N. et al. The structure, composition, and dimensions of TiO2 and ZnO nanomaterials in commercial sunscreens. J Nanopart Res 13, 3607 (2011). https://doi.org/10.1007/s11051-011-0438-4

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  • DOI: https://doi.org/10.1007/s11051-011-0438-4

Keywords

  • Sunscreen
  • Nanomaterial
  • TiO2
  • ZnO
  • Ultraviolet blocking
  • Health and safety implications