Nano scale particles are receiving increasing attention worldwide due to the properties
that might be fundamentally distinct of dissolved materials or microscopic particles
for many applications. Nano scale particles are characterized by size ranging from
1 to 100 nm extent at least in one dimension. Nano scale particles of titanium dioxide
(nTiO₂) are becoming more prevalent in the environment as a consequence of their large-scale
industrial utilization. The nTiO₂ particles are known in two crystalline form: rutil
and anatase, where rutile is a nanoparticle in two dimensions, whereas anatase is
in all three dimensions. Although the European Food Safety Authority (EFSA) has updated
the safety assessment of titanium dioxide (E 171) in the past years that nTiO₂ as
a food additive colourant is not considered being safe. In spite, data are scarce
on the environmentel effect and phytotoxicity of nTiO₂ crystalline forms. This study
aims to evaluate the potential phytotoxicity of TiO₂ nanoparticles specifically the
anatase and rutile crystalline form, on bread wheat (Triticum aestivum). Since accumulation
of nTiO₂ particles in a high density means an additional risk, we were also aimed
to model the effect of accumulation. Manufactured nTiO₂ particles (anatase and rutile;
NTA-20-S25-01 and NTR-20-02, respectively) were applied on wheat seedlings at three
leaves stage in a concentration range from 50 to 3000 ppm. Experiments were performed
in hydroponics as short (1-2 days) and long term (14 days) exposure. Physiological
responses: status of the photosynthetic apparatus, malondialdehyde (MDA) content,
activity of antioxidative enzymes (ascorbate peroxidase activity; catalase) were analyzed
together with element mapping by X-ray fluorescence (XRF) imaging. Data emphasize
that anatase was nottoxic, while rutile showed toxic effects only at higher concentrations,
connected with the increase in the Ti-Kα XFR signal. Importantly, high MDA levels
and reduced photosynthetic efficiency were shown under high rutile exposure, pointing
to oxidative damage and reduced photosynthetic efficiency. These outcomes illustrate
the need to differentiate between nanoparticle types in assessing environmental impacts.
Follow-up studies can highlight the ecological impacts of nTiO₂ particles through
the investigation of long-term exposure effects linked to those nanoparticles, molecular
responses, and soil-plant interactions.
This work was supported by the grant K-135607 of NKFIH, Hungary. Á.S. was supported
by the János Bolyai Scholarship of the Hungarian Academy of Sciences (BO-00113-23-8).
XRF imaging facility was granted by the European Structural and Investment Funds (VEKOP-2.3.3-15-2016-00008).
We kindly thank the technical support of Sándorné Pardi
