Investigating the Roles of Dissolved Organic Matter on Arsenic Mobilization and Speciation in Environmental Water

Arsenic (As) contamination of environmental water has attracted much attention in recent years, due to its high mobility and various species. In this work, water samples collected from Chenjiang, Liuyang, and Xiangjiang River, the most heavily As-contaminated rivers in China, were investigated using size exclusion chromatography (SEC), combined with inductively coupled plasma mass spectrometry (ICP-MS), as well as three-dimensional excitation-emission matrix (3DEEM) fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC). By EEM-PARAFAC modeling, all EEM peaks could be decomposed into a five-component model including: one fulvic acid-like component, one tryptophan-like component, and three humic-like components. Using SEC-ICP-MS, arsenite, arsenate, arsenobetaine, and DOM-bound As were eluted and detected according to different molecular weights, and the co-elution of Fe-56 and DOM-bound As under the same elution condition indicated the complexation between DOM and As through Fe ions. Furthermore, obvious quenching effects of fluorescent DOM components in the presence of As(III) were observed, suggesting that strong complexation or adsorption occurred between As(III) and different DOM components. Among five DOM components identified by PARAFAC, the humic-like components played a key role in forming complexes with As(III), thus leading to the changes of As species in natural water. The results exhibited considerable implications for the role of DOM components on the mobilization and speciation of As, which could be applied to the As removal in natural water and act as an indicator to evaluate the capacity of As complexation or adsorption in the environment.