Sorption of Fulvic Acids onto Titanium Dioxide Nanoparticles Extracted from Commercial Sunscreens: ToF-SIMS and High-Dimensional Data Analysis

Narjes Tayyebi Sabet Khomami,Stefan Kunz,Allan Philippe,Alexander Welle

doi:10.3390/coatings12030335

Narjes Tayyebi Sabet Khomami, Stefan Kunz + Show 2 more

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https://doi.org/10.3390/coatings12030335

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Abstract

Titanium dioxide nanoparticles (n-TiO2) are common ingredients of sunscreens and are often released into surface waters during usage. Once released, the surface chemistry of n-TiO2 changes by interacting with dissolved organic matter (DOM). In previous studies, these interactions were investigated using model n-TiO2 and; therefore, do not account for the complex composition of the coating of n-TiO2 aged in sunscreens. Taking advantage of a mild extraction method to provide more realistic nanoparticles, we investigated the potentials of time of flight-secondary ion mass spectrometry (ToF-SIMS) combined with high-dimensional data analysis to characterize the sorption of fulvic acids, as a model for DOM, on titanium dioxide nanoparticles extracted from ten different commercial sunscreens (n-TiO2 ⸦ sunscreen). Clustering analysis confirmed the ability of ToF-SIMS to detect the sorption of fulvic acids. Moreover, a unique sorption pattern was recognized for each n-TiO2 ⸦ sunscreen, which implied different fractionation of fulvic acids based on the initial specifications of nanoparticles, e.g., size, coating, etc. Furthermore, random forest was used to extract the most important fragments for predicting the presence of fulvic acids on the surface of n-TiO2 ⸦ sunscreen. Finally, we evaluate the potential of ToF-SIMS for characterizing the sorption layer.

Highlights

Accepted: 28 February 2022Nanoparticulate inorganic UV filters are being increasingly used in sunscreens as an alternative to organic UV filters with reported detrimental effects on aqueous environments [1]
We showed here that ToF-SIMS provides enough information to detect natural coatings and to account for small differences between sunscreen samples
The results demonstrate that the extracted TiO2 nanoparticles of each sunscreen react differently with fulvic acids, which are composed of a mixture of several compounds

Summary

Introduction

Accepted: 28 February 2022Nanoparticulate inorganic UV filters are being increasingly used in sunscreens as an alternative to organic UV filters with reported detrimental effects on aqueous environments [1]. N-TiO2 occurs naturally in three crystalline structures: rutile, anatase, and brookite; rutile is the most common and stable form of this pigment [3]. These particles are utilized in sunscreens since they reflect and absorb UV photons, and their ability to protect against UV exposure is directly related to particle size [4]; n-TiO2 have UVB (290–320 nm) and UVA (320–400 nm) protection; the absorption spectrum shifts to a predominantly UVB spectrum as the particle size decreases [5]. Meyer et al [7] made a systematic review about ecological impacts of recreational activities in water bodies, concluding that the concentration of UV-filters in lakes generally increases in the summer months.

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