Groundwater contamination is a growing global challenge, but predicting how pollutants behave underground remains difficult. A new review suggests that an often overlooked property of sediments, their ability to donate and accept electrons, could provide scientists and engineers with a powerful way to understand contaminant transformation and design more efficient groundwater remediation strategies.
Writing in Environmental and Biogeochemical Processes, researchers review the emerging role of electron exchange capacity, or EEC, as a quantitative measure of the chemical reactivity of aquifer sediments. The concept describes how many electrons sediments can donate or accept through naturally occurring minerals and organic matter.
"Aquifer sediments are not chemically uniform, and this hidden chemical heterogeneity can strongly influence whether contaminants persist, transform, or respond to remediation treatments," said corresponding author Chenglong Yu of Chengdu University of Technology. "Electron exchange capacity gives us a quantitative framework for describing that reactivity rather than relying only on the total amount of iron, organic matter, or other sediment components."
Aquifers contain minerals, natural organic matter and sulfur-containing compounds that can participate in electron-transfer reactions. Iron-bearing minerals and natural organic matter are particularly important contributors. These reactions can determine whether contaminants are reduced, oxidized, immobilized or released into groundwater.
The review distinguishes between electron-donating capacity, or EDC, and electron-accepting capacity, or EAC. Together, they provide information about the direction, extent and potential rate of redox reactions occurring underground.
The researchers summarize advances in both chemical-probe and mediated electrochemical methods for measuring EEC. Newer approaches have improved sensitivity, shortened analysis times and expanded measurements to more heterogeneous sediment samples. Some recently developed systems may also make on-site EEC measurements increasingly practical.
The implications extend well beyond laboratory characterization. Sediment EEC can influence anaerobic microbial respiration, mineral dissolution, direct reduction of contaminants and the formation of reactive oxygen species. For example, electron-donating components of sediments can directly reduce contaminants such as hexavalent chromium, while oxygen entering reduced sediments can trigger the formation of highly reactive species capable of degrading organic pollutants.
EEC may also help improve engineered remediation. In situ chemical oxidation commonly involves injecting oxidants such as persulfate or hydrogen peroxide into contaminated aquifers. However, sediment components can consume these chemicals before they reach their intended targets. The review highlights evidence that persulfate consumption can be quantitatively related to sediment EDC, suggesting that EEC measurements could help estimate oxidant demand and optimize treatment doses.
The same concept could support bioremediation, where microorganisms transform contaminants through electron-transfer processes. Changes in sediment EEC have been associated with microbial dechlorination and transformations of redox-sensitive contaminants such as arsenic, making EEC a potentially practical indicator of remediation performance.
"Ultimately, EEC could help shift groundwater remediation from empirical, high-consumption approaches toward strategies that are more predictable, efficient and sustainable," said corresponding author Shengyan Pu.
The authors identify several priorities for future research, including portable EEC measurement technologies, better identification of environmentally relevant electron-transfer processes, and incorporation of EEC into reactive transport models. Such models could potentially predict contaminant and remediation-agent movement without having to explicitly represent every individual chemical reaction occurring in a complex aquifer.
The study provides a framework for treating sediment electron exchange capacity as a practical bridge between aquifer geochemistry, contaminant fate and sustainable groundwater remediation.
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Journal reference: Yu C, Fan L, Zhang P, Cui Y, Pu S. 2026. Electron exchange capacities of sediments as chemical controls on natural attenuation and engineered remediation of contaminated aquifers. Environmental and Biogeochemical Processes 2: e018 doi: 10.48130/ebp-0026-0013
https://www.maxapress.com/article/doi/10.48130/ebp-0026-0013
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About the Journal:
Environmental and Biogeochemical Processes (e-ISSN 3070-1708) is a multidisciplinary platform for communicating advances in fundamental and applied research on the interactions and processes involving the cycling of elements and compounds between the biological, geological, and chemical components of the environment.
