State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences (Beijing), Beijing 100083, PR China.
School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 100083, PR China.
Environ Sci Technol. 2020 Jun 16;54(12):7280-7290. doi: 10.1021/acs.est.0c00737. Epub 2020 May 29.
Molecular characteristics of natural organic matter (NOM) and their potential connections to arsenic enrichment processes remain poorly understood. Here, we examine dissolved organic matter (DOM) in groundwater and water-soluble organic matter (WSOM) in aquifer sediments being depth-matched with groundwater samples from a typical arid-semiarid basin (Hetao Basin, China) hosting high arsenic groundwater. We used Fourier transform ion cyclotron resonance mass spectrometry to determine molecular characteristics of DOM and WSOM and evaluate potential roles of biodegradable compounds in microbially mediated arsenic mobility at the molecular level. High-arsenic groundwater DOM was generally enriched in recalcitrant molecules (including lignins and aromatic structures). Although potential contribution of recalcitrant compounds to arsenic enrichment cannot be ruled out, preferential degradation of the labile molecules coupled with reduction of Fe(III) (oxyhydr)oxides seemed to dominate arsenic mobilization. Both the number and the intensity of biodegradable compounds (including aliphatic/proteins and carbohydrates) were higher in WSOM than those in DOM in depth-matched high-arsenic groundwater (arsenic >0.67 μmol/L or 50 μg/L). Groundwater arsenic concentration generally increased with the increase in the number and the intensity of unique biodegradable compounds (especially N-containing compounds) in WSOM at matched depths. Anoxic incubations of sediments and deionized water show that more arsenic and Fe(II) were released from aquifer sediments with greater numbers and intensities of consumed biodegradable compounds in WSOM (especially N-containing compounds), with a higher proportion of microbially derived compounds produced. These observations indicate that the biodegradation of aliphatic/proteins and carbohydrates (especially CHON formulas) in WSOM fueling the reductive dissolution of Fe(III) (oxyhydr)oxides predominantly promotes arsenic release from aquifer solids. Our unique data present a better understanding of arsenic mobilization shaped by microbial degradation of labile organic compounds in anoxic aquifers at the molecular level.
天然有机物（NOM）的分子特征及其与砷富集过程的潜在联系仍知之甚少。在这里，我们研究了典型干旱半干旱盆地（河套盆地，中国）地下水中的溶解有机物（DOM）和含水层沉积物中的水溶性有机物（WSOM），这些水样与高砷地下水的地下水样本深度匹配。我们使用傅里叶变换离子回旋共振质谱法来确定 DOM 和 WSOM 的分子特征，并评估在分子水平上微生物介导的砷迁移中可生物降解化合物的潜在作用。高砷地下水中的 DOM 通常富含难降解的分子（包括木质素和芳香结构）。尽管难降解化合物对砷富集的潜在贡献不能排除，但易降解分子的优先降解以及 Fe(III)（氧氢）氧化物的还原似乎主导了砷的迁移。在深度匹配的高砷地下水中，WSOM 中可生物降解化合物（包括脂肪族/蛋白质和碳水化合物）的数量和强度均高于 DOM（砷>0.67 μmol/L 或 50 μg/L）。在匹配深度下，WSOM 中可生物降解化合物（特别是含氮化合物）的数量和强度与地下水砷浓度呈正相关。缺氧条件下沉积物和去离子水的孵育表明，在 WSOM 中，可生物降解化合物的数量和强度越大（特别是含氮化合物），从含水层沉积物中释放的砷和 Fe(II)就越多，产生的微生物衍生化合物的比例也越高。这些观察结果表明，WSOM 中脂肪族/蛋白质和碳水化合物（特别是 CHON 公式）的生物降解为 Fe(III)（氧氢）氧化物的还原溶解提供了动力，主要促进了砷从含水层固体中的释放。我们的独特数据从分子水平上更好地理解了在缺氧含水层中微生物降解易降解有机化合物对砷迁移的影响。
