Rice cultivation and safety concerns from irrigation with ZnO nanoparticle-contaminated treated municipal wastewater

ABSTRACT The proliferation of metal-based nanoparticles in treated municipal wastewater (TWW) has raised environmental and health concerns. This study examined the health risks and effects of ZnO nanoparticles (NPs) in TWW on rice growth, yield, and nutrition. Continuous fertigation was used to irrigate rice plants with TWW containing 0, 2, and 5 mg L−1 of either ZnO NPs or ZnSO4. Results indicated that TWW with higher ZnO NP concentrations significantly reduced plant height and root mass but increased shoot biomass and rice yield. ZnO NPs or ZnSO4 exposure increased Zn accumulation in rice roots, shoots, and grains while reducing Cd levels by 30%. However, elevated Zn levels also increased toxic metal accumulation, such as As and Mo. The estimated daily intake values for As, Zn, and Mo increased by over 100, 29–47, and 14–18%, respectively, raising cumulative health risks from trace element exposure, with hazard index (HI) values exceeding the safe threshold (HI > 1). Despite no acute toxicity in rice plants, the continuous use of ZnO NP-contaminated TWW presents significant long-term environmental and health risks. This highlights the urgent need for stringent monitoring and management of TWW quality to safeguard the sustainability of agricultural wastewater reuse.