From sun cream and paint to the food chain? The case of titanium dioxide nanoparticles

04-06-2021

#WORLDENVIRONMENTDAY Titanium dioxide (TiO2) is in many consumer products. Scientists at the ESRF are assessing its prevalence in its nanoparticle form in crops and its potential risk.

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An increasing amount of consumer products used in everyday life, such as toothpaste, sunscreen, paint or even sprinkles used to decorate cakes, contain titanium dioxide (TiO2). In many cases, the interest of this material lays in its white appearance, which results from its excellent light-scattering properties.

However, the World Health Organization classifies TiO2 as carcinogen when inhaled and the European Food Safety Agency has recently proposed to ban its use as a food additive (E171).

The reality is that because it is so used, it inevitably reaches waste water treatment plants, where sludge is made as a by-product. This sludge is often used in agricultural practices as a source of important nutrients (nitrogen and phosphorus).

Castillo Michel and collaborators have been studying the fate of TiO2 in the plants and soils for more than a decade: “Despite the likely extensive spread of TiO2 nanoparticles in the environment, quantitative information and its eco-toxicological consequences are under study” .

At the ESRF’s beamlines, especially ID21 and ID16B, where they use micro X-ray fluorescence, micro X-ray absorption near-edge spectroscopy and nano-tomography, Castillo and his collaborators track the amount of TiO2 in sludge, soils and different parts of the plants.   They started by adding TiO2 nanoparticles in soils and then monitored in the lab a cucumber plant growing on them. “We found TiO2 in practically all the parts of the plant, including the fruit”, explains Castillo. It was the proof of concept that the beamlines can effectively track the fate of these nanoparticles.

Recently, the researchers have studied Alfalfa sprouts, very often used in salads but also given to cows as food, taken from a field in Mexico. They have also found TiO2  in their edible part, confirming Castillo’s hypothesis that the material may accumulate in plants in their natural environment.

The repercussions of this are still unknown. “Our motivation for this research is to gage how or whether this is actually impacting our soils and crops”, he says. Today, the concentration of some elements in the sludge used in agricultural fields is regulated. For example, there is a limit for cadmium , as cadmium in high concentrations can be harmful for human health. “We aim to provide answers and propose solutions, so if research shows that TiO2 in its nanoparticle form  harmful, then some kind of regulation of its concentration in the sludge could be the solution to limit it reaching the food chain”, concludes Castillo.

With the new Extremely Brilliant Source, detection limits and spatial resolution have been substantially improved, and they will enable Castillo and his collaborators to study the journey of nanoparticles at lower – and hitherto undetectable – doses that more accurately portray the real environment.

References:

Muccifora, S., et al, Nanomaterials 202111(4), 921.

Servin, A., et al, Environmental Science and Technology, 47(20), 11592-11598.

Servin, A., et al, Environmental Science and Technology 46 (14), 7637- 7643.

Bakshi, M. et al,  Journal of Hazardous Materials, Volume 369, 5 May 2019, 191-198.

Text by Montserrat Capellas Espuny

Video by Montserrat Capellas Espuny and Mark McGee.

Top image: Alfalfa sprouts.