Surface water infiltration and sediment degradation shaping dissolved organic matter in groundwater related to chronic kidney disease of unknown etiology

Chronic kidney disease of unknown cause (CKDu) poses a serious threat to the life safety of people in many countries. Dissolved organic matter (DOM) in groundwater has been proposed to be a potential pathogenic factor of CKDu, but its sources are still controversial. Herein, the combination of excitation-emission matrix spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry was used to reveal the shaping of groundwater DOM predominantly by water-soluble sedimentary organic matter (WSOM) and surface water DOM. Compared to sediments from non-CKDu areas, WSOM in CKDu-endemic areas exhibited lower degrees of humification and aromaticity, but higher bioavailability, indicating a weaker degree of biodegradation. CKDu groundwater contained more exogenous DOM, which mainly originated from the infiltration recharge of surface water DOM, but non-CKDu groundwater was more enriched in biogenic DOM, which mostly stemmed from the biodegradation of WSOM in aquifer sediments. During groundwater recharge, aromatic compounds and unsaturated compounds in surface water were directly migrated into groundwater, especially in CKDu groundwater. Peptides, aliphatic, and unsaturated compounds with low oxygen in aquifer sediments were mostly transformed into biogenic groundwater DOM by in-situ biodegradation, especially in non-CKDu groundwater. This study highlights the shaping of the features of groundwater DOM related to CKDu by recharge of surface water OM.