Copper oxide nanoparticles mitigate cadmium–arsenic phytotoxicity to rice plants (O. sativa) and protect Daphnia magna via soil–water partitioning

Abstract

Serving as a staple food for over half of the world population, rice plants tend to accumulate higher levels of cadmium (Cd) and arsenic (As) than other cereal crops. Copper oxide nanoparticles (nCuO), known for their stability and adsorption capacity, show potential for remediating soils contaminated with Cd and As. This study investigated the regulatory effects of nCuO on rice (O. sativa) seedling growth under combined Cd–As stress and the potential detoxification efficacy of nCuO for Cd and As via soil–water partitioning in two distinct soil environments, i.e., acidic organic-rich red soils and neutral high cation-exchange-capacity (CEC) brown soils. Results demonstrated that nCuO at 10–100 mg L⁻¹ alleviated oxidative stress caused by Cd–As and promoted seedling growth. In particular, nCuO reduced Cd–As accumulation in rice seedlings grown in the brown soil by inhibiting the expression of related genes OsNRAMP5 and OsLsi1. However, in the red soil, greater mobility of Cd–As resulted in their higher root accumulation and stronger antioxidant responses in rice seedlings, requiring higher doses of nCuO to achieve effective remediation. Furthermore, nCuO reduced the toxicity of simulated drainage water to Daphnia magna, showing its efficacy in mitigating ecological risks associated with Cd–As partitioning from contaminated soils to aquatic ecosystems. This alleviation was more effective in the brown soil. These findings provide insights into the mechanisms by which nCuO mitigates Cd–As co-stress in rice, and nCuO behaviors in contrasting soil environments for remediating contaminated paddy fields and the adjacent water environments.