In situ high-resolution mapping of Cr(VI) in soil using an NFR-functionalized diffusive gradients in thin-films technique
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Updated: Oct 30, 2026
Two-Dimensional Visualization and Quantification of Labile, Inorganic Plant Nutrients and Contaminants in Soil
Published on: September 1, 2020
Zhaodong Liu1, Paul N Williams2, Danxing Yang3
1State Key Laboratory of Water Pollution Control and Green Resource Recycling, School of Environment, Nanjing University, Nanjing, 210023, China; State Key Laboratory of Nutrient Use and Management, Key Laboratory of Agro-Environment of Huang-Huai-Hai Plain, Ministry of Agriculture and Rural Affairs, Institute of Agricultural Resources and Environment, Shandong Academy of Agricultural Sciences, Jinan, 250100, China.
Background:
Chromium (Cr) speciation governs its environmental behavior, toxicity, and biogeochemical cycling in soils, especially within the highly dynamic rhizosphere where steep redox gradients prevail. Accurate assessment of Cr(VI) bioavailability and its microscale distribution is essential for risk evaluation and remediation of contaminated sites. However, conventional sampling and laboratory methods often perturb Cr speciation, and few low-disturbance analytical techniques are available for reliable in situ speciation data at relevant spatial resolutions. This leaves a critical gap in our ability to characterize Cr(VI) dynamics in complex soil microenvironments.
Results:
We developed and systematically validated a novel diffusive gradients in thin-films (DGT) technique using an optimized N-methyl-d-glucamine functionalized resin (NFR) for selective Cr(VI) detection. NFR binding gels fabricated with two distinct particle sizes exhibited strong adsorption affinity and rapid uptake kinetics, sequestering >96% of Cr(VI) within 24 h while displaying negligible Cr(III) accumulation. Performance matched theoretical predictions across pH 3.50-9.52 and ionic strengths of 0.1-100 mmol L-1 NaNO3. Blank values were below 0.028 μg L-1 and method detection limits under 0.017 μg L-1 for a 1-day deployment. Coupling the 500NFR binding gel with a planar optode enabled simultaneous high-resolution two-dimensional imaging of Cr(VI) and O2 in the rice rhizosphere, revealing localized Cr(VI) depletion zones within 2.5 mm of the root axis and excellent spatial uniformity (RSD <10%).
Significance And Novelty:
This work establishes the 500NFR-DGT as a robust and selective platform for high-resolution in situ mapping of Cr(VI), overcoming heterogeneity limitations of conventional DGT binding gels. The integration of NFR with a planar optode enables simultaneous imaging of Cr(VI) and O2, providing a powerful tool to elucidate redox-driven Cr dynamics in the rhizosphere and inform remediation strategies for contaminated soils.
