Machine learning (ML) reveals the key factors influencing the removal of chlorinated hydrocarbons (CAHs) by nanoscale zero-valent iron (nZVI)

Chlorinated hydrocarbons contaminate soil and groundwater and pose significant health and ecological risks. Nanoscale zero-valent iron is widely used for in situ remediation, but its reactivity can decline because of oxidation, surface passivation, and particle aggregation. This review first delineates chlorinated hydrocarbon removal mechanisms by nanoscale zero-valent iron, including adsorption, reduction, oxidation, and co-precipitation. We then summarize how pH, dissolved oxygen, coexisting ions, temperature, reaction time, and initial contaminant concentration shape removal outcomes. To quantify multivariable effects, we compiled 5,923 experimental datapoints from 90 publications and applied machine learning models with interpretable feature attribution. Reaction time and specific surface area were the strongest synergistic drivers, and their effects leveled off after approximately 4 days and at around 120 m 2 /g, respectively. The analysis also identified a high-efficiency window within 0.25 day, an economical dosage near 0.2 g/L, and a concentration sensitivity threshold around 25 mg/L. Bicarbonate below 500 mg/L inhibited chlorinated hydrocarbon removal, whereas copper ions promoted reactivity. These quantitative insights can guide the design of modified nanoscale zero-valent iron and hybrid technologies for robust remediation in complex water matrices. • Machine learning identifies reaction time and specific surface area as key factors • The reaction occurs within 0.25 days and stabilizes after about 4 days at 120 m²/g. • The economical dosage is ~0.2 g/L with a concentration sensitivity ~25 mg/L. • Bicarbonate ＜500 mg/L inhibits the process, whereas copper ions enhance reactivity.