Plant enzymatic activity as an indicator of nano-TiO2 exposure in rice ecosystems

Abstract

The widespread use of nano-titanium dioxide (nano-TiO₂) has raised concerns about its environmental impact, particularly in soil-plant systems. This study investigates the effects of nano-TiO₂ on rice (Oryza sativa cv. PB1121) growth and enzymatic activities, compared to bulk TiO₂, through a pot culture experiment. Eight doses of Ti were applied: six as soil treatments (0, 2.5, 5, 10, 25, and 50 mg Ti kg⁻¹) and two as foliar treatments (0.05 % and 0.1 %). Results showed that grain yield peaked at 25 mg Ti kg⁻¹ soil for both nano and bulk TiO₂, while a 0.05 % foliar spray outperformed by 0.1 %. Titanium accumulated mostly in roots, followed by straw and grains. Nano-TiO₂ significantly increased antioxidant enzyme activities—catalase (CAT), superoxide dismutase (SOD), guaiacol peroxidase, and ascorbate peroxidase (APX)—and lipid peroxidation (measured as malondialdehyde) in rice roots and shoots, indicating oxidative stress. The findings suggest that plant enzymatic activity serves as an early indicator of nano-TiO₂ exposure, making it a valuable biomarker for environmental monitoring. However, higher Ti doses may inhibit plant growth depending on Ti source and concentration. Further studies should examine the effects of nano-TiO₂ of different sizes, shapes, and charges on various crops and soil types to validate these results and assess the broader implications for agricultural and environmental health. This research highlights the dual potential of nano-TiO₂ as both a growth enhancer and a stress-inducing agent, emphasizing the need for careful management in agricultural applications.