Effect of natural soil nanocolloids on the fate and toxicity of cadmium to rice (Oryza sativa L.) roots

Toxic heavy metals are common contaminants and will most likely interact with ubiquitous natural nanocolloids (Ncs) in the soil environment. However, the effect of soil Ncs on the fate and health risk of cadmium (Cd) have not been well addressed. Here, the interaction between Ncs and Cd is investigated using two-dimensional correlation spectroscopy (2DCOS) combined with synchronous fluorescence and Fourier transform infrared spectroscopy. Our results reveal that Cd binding to the soil Ncs surface is mainly driven through strong hydrophilic effects and π - π interactions, which contribute to a high adsorption capacity (366-612 mg/g) and strong affinity (KL = 4.3-9.7 L/mg) of Cd to soil Ncs. Interestingly, soil Ncs and Cd coexposure can significantly mediate the phytotoxicity (e.g., uptake, root growth, and oxidative stress) of Cd to rice (Oryza sativa L.) roots after 7 days of exposure. At the molecular level, metabolomic analysis reveals that the downregulated metabolic pathways (e.g., isoquinoline alkaloid and aminoacyl-tRNA biosynthesis, glycine, serine and threonine metabolism) may contribute to the above adverse phytotoxicity. This study provides new insight into the effect of natural Ncs on the fate and health risks of toxic heavy metals in soil environments.