Magnet-assisted nanoscale zerovalent iron soil washing in chlorpyrifos-contaminated soil remediation: Proof of concept

Abstract

Chlorpyrifos (CPF)––a widely used organophosphate pesticide––is banned in many countries due to its persistence in the environment and high toxicity. Residue levels often vastly exceed safety thresholds, posing significant risks to human health and ecosystems. This persistent contamination challenges farmers, especially those transitioning to organic practices. Here, we propose magnet-assisted soil washing with nanoscale zerovalent iron (nZVI) for the rapid remediation of CPF-contaminated soil. Soil mixed with water and nZVI facilitates CPF adsorption and degradation, with the CPF-sorbed nZVI being magnetically separated. We tested various nZVI conditions (inactivated [IZ] and activated [AZ], with and without hydrogen peroxide [H2O2]) against controls, including untreated soil and conventionally washed soil. The control experiments showed that conventional washing without nZVI removed 50.54 ± 3.48 % of the CPF via volatilization, leaving CPF residues in the soil (25.44 ± 2.12 %) that were above the maximum contamination level (MCL). Inactivated nZVI increased the removal by 24.38 ± 0.78 % via CPF sorption, but the MCL was still exceeded. However, AZ or nZVI with H2O2 achieved complete CPF removal (>99.95 %) within 180 min, reducing its concentration to below the MCL (<0.03 mg/kg). Thus, CPF sorption followed by either reductive dechlorination or oxidative degradation proved effective. Additionally, nZVI demonstrated reusability for three rounds while mitigating CPF toxicity, improving seed germination and plant growth. This method offers a promising solution for rapid soil decontamination, supporting the transition to organic farming.