The fate of titanium nanoparticles in natural environments
In a study published in August 2021 in the Journal of Hazardous Materials, scientists from IPGP and LNE studied the evolution of titanium nanoparticle concentrations in the surface waters of three catchment areas over the course of a year, in order to gain a better understanding of the environmental factors, both natural and anthropogenic, that influence the fate of these nanoparticles in the critical zone, and more specifically in aquatic environments.
Titanium, and more specifically titanium dioxide TiO2, has been widely used in industry for decades, notably as a pigment or bleaching agent. More recently, nanoparticulate forms of titanium dioxide are also increasingly used in the cosmetics, food and energy industries.
Substantial quantities of titanium from human activities are thus found in terrestrial and aquatic ecosystems, and it is therefore important to determine the fate of these discharges.
But such measures are difficult to implement in natural environments. Firstly, because nanoparticles are difficult to detect and quantify instrumentally, and because they interact with their environment, making it more difficult to detect their different forms. On the other hand, titanium is also naturally present in surface water as a result of soil erosion, which differs according to the use of the soil, thus also varying the quantity of titanium naturally present.
It is therefore important to study the overall biogeochemical cycle of titanium in ecosystems in order to better assess the impact of anthropogenic nanoparticles on natural environments.
In a study published in August 2021 in the Journal of Hazardous Materials, scientists from the IPGP, the University of Paris and the Laboratoire National de Métrologie et d’Essais (LNE) sampled surface water from three catchment areas with different land uses over the course of a year: one predominantly forested, the second agricultural and the third urban.
By measuring the concentrations of TiO2 in these samples and the changes in concentrations over time, the team showed that soil use had an impact on the concentration of nanoparticles, that the type of soil, associated with the use made of it, also plays a role in the speciation of titanium (i.e. the way in which it can form complexes with other constituents present in the environment) and also that the concentration of TiO2 varied seasonally.
Using an original analysis method, single particle inductively coupled plasma mass spectrometry (sp-ICPMS), the researchers detected an average of 910 million TiO2 nanoparticles per litre of water, with a predominance of objects with an average size of 40 nm. They also found that twice as many TiO2 nanoparticles were exported from the agricultural catchment as from the urban catchment.
By showing how natural environmental factors and those linked to human activities (soil type, season, quantity of dissolved organic matter, agricultural activity, urban density) affect the fate of titanium nanoparticles in aquatic environments, this study provides new constraints on how titanium nanoparticles evolve and interact with their environment, as well as a better understanding of the parameters that control the biogeochemical cycles of titanium, and more broadly of other nanoparticles present in ecosystems.
This study received financial support from the Île-de-France region via DIM Analytics, the PIREN-Seine interdisciplinary research programme and the IdEx Université de Paris.
Ref : Jia-Lan Wang, Enrica Alasonati, Paola Fisicaro, Marc F. Benedetti, Titanium nanoparticles fate in small-sized watersheds under different land-uses, Journal of Hazardous Materials, Volume 422, 2022, 126695, ISSN 0304-3894, https://doi.org/10.1016/j.jhazmat.2021.126695.
