Effects of different surface-coated nTiO2 on full-grown carrot plants: Impacts on root splitting, essential elements, and Ti uptake.

The production and environmental release of surface-modified titanium dioxide nanoparticles (nTiO2) have increased. Hence, crops may be directly exposed to the nTiO2 in soil. In this study, we grew carrots in soils amended with pristine, hydrophilic and hydrophobic surface-coated nTiO2 at 100, 200, and 400 mg kg-1 until full-plant maturity. The content of Ti in plant secondary roots treated with different nTiO2 at 400 mg kg-1 was in the order of hydrophobic > hydrophilic > pristine treatments, with values of 140.1, 100.5, and 64.3 mg kg-1, respectively. The fresh biomass of the taproot was significantly decreased by all nTiO2 forms at 400 mg kg-1 by up to 56 %, compared to control. Pristine nTiO2 at 100 mg kg-1 enhanced the fresh weight of leaves by 51 % with respect to control. Remarkably, an abnormal increase of taproot splitting was found in plants treated with all nTiO2 forms. In carrots treated with the surface-coated nTiO2, the accumulation of Ca, Mg, Fe, and Zn increased in leaves; but Mg, Mn, and Zn decreased in taproots. These results suggest that future regulation of nTiO2 release into soils should consider its surface coating properties since the phytotoxicity effects depend on nTiO2 outer structure.