Disentangling the Fe species-dependent electron donating capacity and abiotic reduction capacity towards nitrobenzene of the sediment cores

Abstract

Iron is a redox-sensitive element and plays a critical role in governing the abiotic natural reduction of organic contaminants in aquifers. However, proper quantification and prediction of contaminant attenuation processes mediated by Fe species remain inadequately characterized, particularly under field conditions. Herein, 43 aquifer sediment cores were collected from four locations at two sites, and nitrobenzene (NB) was used as a representative organic contaminant to evaluate the Fe species–dependent reduction capacity. A systematic investigation was conducted to establish the relationships among Fe species distribution, electron donating capacity (EDC), and abiotic reduction capacity toward NB of sediments. Results revealed a strong positive correlation between carbonate-bound iron (Fe_carb) concentration (0.06–3.11 mg·g^-1) and sediment EDC (R² = 0.89, p < 0.05, n = 10) when silicate-bonded iron (Fe_Si) content was low (<4.0 mg·g^-1). For the reduction of NB, due to thermodynamic constraints imposed on certain electron donors, the correlation between EDC and NB reduction rate was weak. However, Fe_carb content exhibited a strong quantitative linear correlation with the reduction rate of NB (R² = 0.89; p < 0.05; n = 19). The derived quantitative relationship indicates a dose-dependent increase in the NB reduction rate of 0.12 d⁻¹ for every 1 mg·g^-1 increase in Fe_carb content. The 95 % prediction interval can be used to effectively predict the NB reduction kinetics of sediments. These findings provide a new perspective for predicting the abiotic natural reduction capacity of sediments and groundwater organic contaminant remediation.