Simultaneous reduction of arsenic and lead bioaccumulation in rice (Oryza sativa L.) by nano-TiO2: a mechanistic study

Abstract

Heavy metals with opposite charges (e.g., arsenic and lead) generally have opposite environmental behaviors. Nano-enabled strategies to concurrently inhibit their accumulation in crops remain elusive. Here, nano-TiO₂ with an anatase (NAT) or rutile (NRT) structure or bulk TiO₂ (BT) was used at 10, 100, and 1000 mg L⁻¹ to amend hydroponic rice seedling systems co-contaminated with arsenic (1 mg L⁻¹) and lead (2 or 10 mg L⁻¹) for mechanistic understanding of contaminant interactions. A simultaneous decrease of arsenic and lead bioaccumulation in rice plants and their retention in the root iron plaque were achieved by significant metal sorption to 1000 mg L⁻¹ NAT and NRT. The arsenic uptake mitigation by NRT (82–93%) was much higher than that by NAT (46–65%), while their lead uptake inhibition was comparable (47–89% for NRT vs. 37–78% for NAT). When the lead/arsenic exposure ratio increased, 100 mg L⁻¹ nano-TiO₂ and BT at all doses also significantly reduced the root metal content, attributable to their enhanced sorption on TiO₂ and iron plaque. TiO₂ amendment posed no risk to the plant and completely alleviated oxidative stress from exposure thus restoring it to healthy control levels. Our findings highlight the potential application of 1000 mg L⁻¹ nano-TiO₂, particularly with a rutile structure, for combined arsenic and lead reduction in rice, effectively enhancing both food safety and human health.