Cellulose nanocrystals for green remediation of contaminated soil with multiple heavy metals

In soil contamination management, simultaneous remediation of soil contaminated with multiple heavy metals (MHM-contaminated soil) continues to present a substantial scientific challenge. This study utilized cellulose nanocrystals (CNC) as an environmentally friendly washing agent to remediate soil contaminated with cadmium (Cd), lead (Pb), copper (Cu), and zinc (Zn). We investigated how CNC affects heavy metals removal under various conditions through soil washing experiments and its impact on soil health (including heavy metal distribution and ecological risk, soil phytotoxicity, soil microbial abundance and diversity) and the metals removal mechanism determined via Fourier transform infrared and 2D correlation spectroscopy (FTIR-2D COS). The results showed that CNC's pH significantly influenced the removal of heavy metals. CNC treatment reduced mobile Cd fractions by > 20.7%, lowered ecological risk from moderate (RI = 153.9) to low (< 150), maintained seed germination rates (comparable to controls) with 1.57 cm longer roots, and enhanced microbial richness (Chao1/ACE) while preserving diversity (Shannon/Simpson). FTIR-2D COS results showed that functional groups (-COOH and O-H) of CNC play a critical role in metals removal through electrostatic adsorption, displacement, and complexation reaction. This study suggested that CNC holds considerable potential for green-remediating MHM-contaminated soil.