Characterization of TiO2 NPs in Radish (Raphanus sativus L.) by Single-Particle ICP-QQQ-MS

Justyna Wojcieszek,Maciej Jarosz,Monika Asztemborska,Javier Jiménez-Lamana,Joanna Szpunar,Lena Ruzik

doi:10.3389/fenvs.2020.00100

Abstract

Titanium dioxide nanoparticles (TiO2 NPs) are increasingly used in a wide range of consumer products and industrial applications, causing their presence in the environment, where they can interact with plants including edible ones. In addition, the released TiO2 NPs can undergo chemical and physical transformations which may influence their potential toxicity. However, the study of TiO2 NPs in environmental samples by the technique offering the highest sensitivity, ICP-MS, is hampered by the presence of some elements (such as, e.g., Ca abundant in plant tissues) that cause polyatomic and/or isobaric interferences. This study proposed, for the first time, the use of a triple quadrupole ICP operating in tandem mass spectrometry and single particle mode (SP-ICP-QQQ-MS) to study the uptake, translocation and possible transformations of TiO2 NPs with two different nominal sizes in a model plant (Raphanus sativus L.). A careful optimization of the reaction cell conditions (O2 and H2 gas flows) allowed the reduction of background level and resulted in a significant increase of the sensitivity of the analysis, bringing size detection limits for TiO2 NPs down to 15 nm in ultrapure water and to 21 nm in a matrix containing 50 mg L-1 of Ca. In addition, an enzymatic digestion procedure was applied in order to extract intact nanoparticles from the tissues of plants treated with TiO2 NPs, followed by size characterization by SP-ICP-MS. The size distributions obtained in roots treated with TiO2 NPs suggested a preferential uptake of smaller nanoparticles. Results also revealed that the majority of TiO2 NPs were retained in roots. Additionally, no significant dissolution was observed, as well as no differences for nanoparticles found in roots and leaves, proving that radish is able to translocate intact TiO2 NPs up to above ground organs.

Highlights

With the fast development of nanotechnology over the past decade, there are more and more applications of nanomaterials in daily life, e.g., in many commercial and industrial products, medicine, electronics, and energy sectors
Optimization of H2 and O2 Gas Flows When working on SP-ICP-MS, special attention should be paid to the size limit of detection
The using of a triple-quadrupole ICP operating in tandem mass spectrometry and single-particle mode (SP-ICP-QQQ-MS) allowed the reduction in the background signal in plant matrices for monitoring the most sensitive isotope of titanium

Summary

Introduction

With the fast development of nanotechnology over the past decade, there are more and more applications of nanomaterials in daily life, e.g., in many commercial and industrial products, medicine, electronics, and energy sectors. TiO2 NPs occur in three different crystallographic forms: anatase and rutile (tetragonal) and, more rarely, brookite (orthorhombic) Among those three major polymorphs, anatase is extensively applied in commercial products due to its higher activity comparing to other forms, rutile is the more stable form (Chen and Mao, 2007; Zhang et al, 2015). TiO2 NPs are being used for many products such as plastics, paints, surface coatings, medical devices, cosmetics, and nanofertilizers (Hong et al, 2017) They are applied as food additives or in nutritional supplements, and oral exposure to TiO2 NPs may happen through the consumption of such products (Shakeel et al, 2016). TiO2 NPs account for about 70% of the total production volume of pigments worldwide and are in the top five NPs used in consumer products (Jafarizadeh-Malmiri et al, 2019; Dar et al, 2020)

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