Biochar-mediated transformation of titanium dioxide nanoparticles concerning TiONPs-biochar interactions, plant traits and tissue accumulation to cell translocation.

Titanium dioxide nanoparticles (TiONPs) application in variety of commercial products would likely release these NPs into the environment. The interaction of TiONPs with terrestrial plants upon uptake can disturb plants functional traits and can also transfer to the food chain members. In this study, we investigated the impact of TiONPs on wheat (Triticum aestivum L.) plants functional traits, primary macronutrients assimilation, and change in the profile of bio-macromolecule. Moreover, the mechanism of biochar-TiONPs interaction, immobilization, and tissue accumulation to cell translocation of NPs in plants was also explored. The results indicated that the contents of Ti in wheat tissues was reduced about 3-fold and the Ti transfer rate (per day) was reduced about 2 fold at the 1000 mg L exposure level of TiONPs in biochar amended exposure medium. Transmission electron microscopy (TEM) with elemental mapping confirmed that Ti concentrated in plant tissues in nano-form. The interactive effect of TiONPs + biochar amendment on photosynthesis related and gas exchange traits was observed at relatively low TiONPs exposure level (200 mg L), which induced the positive impact on wheat plants proliferation. TiONPs alone exposure to wheat also modified the plant's bio-macromolecules profile with the reduction in the assimilation of primary macronutrients, which could affect the food crop nutritional value and quality. X-ray photoelectron spectroscopy (XPS) chemical analysis of biochar + TiONPs showed an additional peak, which indicated the binding interaction of NPs with biochar. Moreover, Fourier-transform infrared (FTIR) spectroscopy confirmed that the biochar carboxyl group is the main functionality involved in the bonding process with TiONPs. These findings will help for a mechanistic understanding of the role of biochar in the reduction of NPs bioavailability to primary producers of the terrestrial environment.