CuO nanoparticles in irrigation wastewater have no detrimental effect on rice growth but may pose human health risks.

The possibility of metal-based nanoparticles (NPs) being released into agricultural soils via sewage systems has raised widespread concern about their negative effects on crop plants, soils, and potential risks to human health via the food chain. The objectives of this study were to (i) determine the effect of CuO NPs in irrigation water on plant growth and Cu accumulation in a rice-soil system using continuous sub-irrigation with treated wastewater (CSI), and (ii) assess the Cu exposure and potential health risk associated with rice consumption. CuO NPs were examined in treated municipal wastewater (TWW) at environmentally acceptable concentrations (0, 0.02, 0.2, and 2.0 mg Cu L), allowing for effluent discharge and/or crop irrigation reuse. Low CuO NP concentrations in TWW had no adverse effect on plant growth, yield, or grain quality. Cu accumulation significantly increased in various parts of rice plants and paddy soils at 2.0 mg Cu L. CuO NPs had no discernible effect on rice plants when compared to CuSO at 0.2 mg Cu L. The estimated daily intake of Cu derived from inadvertent consumption of Cu-contaminated rice (by CuO NPs in TWW) for young children aged 0-6 years exceeded the oral reference dose for toxicity. Overall, we found no acute toxicity of CuO NPs in TWW to rice plants, but significant Cu accumulation in grains. This implies that there is a high risk of human health problems associated with rice that was intensively irrigated with TWW containing CuO NPs.