Mitigating combined internalized toxicity of nanoplastics and cadmium in rice through metabolic and biochemical regulations under supply of biochar biofilters derived from Mikania Micrantha

Abstract Nanoplastics and cadmium are common pollutants in agricultural systems, posing significant risks to rice. This study explored the effectiveness of biochar biofilters derived from invasive plant Mikania micrantha in mitigating the combined toxicity of polystyrene nanoplastics and cadmium on rice. The combined toxic effects of cadmium and polystyrene nanoplastics were more severe than their individual impacts. Polystyrene nanoplastics under cadmium stress adversely affected rice growth, reducing biomass by 16.46%, whereas the invasive plant Mikania micrantha biochar biofilters significantly improved biomass by 84.60% and 52.59% when applied alone or together with polystyrene nanoplastics under cadmium stress, respectively. Additionally, total chlorophyll content improved by 82.09% in the MBC treatment and by 36.66% in the MBC + PS NPs treatment compared to sole cadmium stress conditions. The invasive plant Mikania micrantha biochar biofilters alleviated these stress effects by reducing the cadmium translocation to roots and shoots, restoring chlorophyll and carotenoid levels, proteins, carbohydrates, preserving cellular structures, and enhancing oxidative defence through gene modulation. Scanning electron microscopy revealed the polystyrene nanoplastics internalization in root cells, but biochar biofilters acted as a physical barrier, limiting their translocation. Furthermore, the invasive plant Mikania micrantha biochar biofilters improved rice performance under dual stress by regulating metabolic pathways, nutrients cycle, TCA cycles and nitrogen transport. In contrast, polystyrene nanoplastics disrupted ATP-binding transporters and hormone signalling, increasing cadmium absorption and intensifying toxicity, thereby impairing growth, root development, and photosynthesis. These findings underscore the potential of invasive plant Mikania micrantha biochar biofilters in mitigating the environmental impacts of cadmium and nanoplastics in agricultural systems. Graphical Abstract