Unraveling the impact of iron oxides-organic matter complexes on iodine mobilization in alluvial-lacustrine aquifers from central Yangtze River Basin.

Sci Total Environ

State Environmental Protection Key Laboratory of Source Apportionment and Control of Aquatic Pollution, Hubei Key Laboratory of Yangtze River Basin Environmental Aquatic Science & School of Environmental Studies, China University of Geosciences, Wuhan 430078, PR China; State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430078, PR China.

Published: March 2022

The biodegradation of organic matter triggers the reductive dissolution of iron oxides with the transformation among iodine species has been mostly accepted as the key iodine mobilization process in groundwater system. However, molecular characteristics of natural organic matter (NOM) and their interaction with iron oxides on geogenic iodine enrichment remain unclear. We used Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to characterize the molecular composition of both dissolved organic matter (DOM) in groundwater and water-soluble organic matter (WSOM) in aquifer sediments being depth-matched with groundwater from monitoring wells in typical iodine-affected aquifers within the central Yangtze River Basin. The results show that WSOM in high-iodine sediments contains more high molecular weight (HMW) organic compounds with higher aromaticity and nominal oxidation state of carbon (NOSC), including polycyclic aromatics, polyphenols and highly unsaturated compounds. These compounds are mostly positively associated with amorphous iron oxides (Fe) in aquifer sediments. The association between iodine and WSOM is highly consistent with that between amorphous Fe and WSOM, but is contrary to that between crystalline iron oxides (Fe) and WSOM. DOM in groundwater with higher iodine concentration contains more aliphatic compounds and less polyphenols. The complexation of HMW organic compounds of WSOM to iodine-bearing amorphous Fe plays an important role in iodine mobilization, which could inhibit the amorphous Fe transformation to crystalline Fe. These observations indicate the biodegradation of HMW organic matter (polycyclic aromatics, polyphenols and highly unsaturated compounds) in WSOM fueling the reductive dissolution of amorphous Fe predominantly promotes the release of iodine from aquifer sediments into groundwater. This research provides new insights into the mobilization mechanisms of iodine in alluvial-lacustrine groundwater system controlled by the Fe-OM complexation at the molecular level.

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Source
http://dx.doi.org/10.1016/j.scitotenv.2021.151930DOI Listing

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