Association between arsenic and different-sized dissolved organic matter in the groundwater of black-foot disease area, Taiwan.
The formation of an arsenic (As)-dissolved organic matter (DOM) complex is important in driving the release of arsenic in groundwater. This study collected groundwater samples from a 20 m deep well throughout 2014 and separated each into three subsamples by ultrafiltration: high molecular weight-DOM (HDOM, 0.45 μm-10 kDa), medium molecular weight-DOM (MDOM, 10-1 kDa), and low molecular weight-DOM (LDOM, <1 kDa) solutions. The fractional DOM was measured with a three-dimensional excitation-emission matrix (EEM) via fluorescence spectroscopy. A fluorescence quenching method was used to calculate the apparent stability constant (Ks) between arsenic and the fractional DOM. Based on the EEM records, three fluorescence indicators were further calculated to characterize the DOM sources, including the fluorescence index (FI), the biological index (BI), and the humification index (HI). The experimental results indicated that arsenic in the groundwater was mainly partitioned into the MDOM and LDOM fractions. All fractional DOMs contained humic acid-like substances and were considered as microbial sources. LDOM had the highest humification degree and aromaticity, followed by MDOM and HDOM. The As and DOM association could be formed by a Fe-bridge, which was demonstrated by the Ks values and fourier transform infrared (FTIR) spectra of the DOM. The formation of AsFe-DOM complex was only significant in the MDOM and LDOM.
Department of Environmental Science and Engineering, National Pingtung University of Science and Technology, Pingtung 92101, Taiwan.
Ting-Chien
TC
Chen
Department of Agricultural Chemistry, National Taiwan University, Taipei 10617, Taiwan. Electronic address: zyhseu@ntu.edu.tw.
Zeng-Yei
ZY
Hseu
Department of Earth Sciences, National Cheng Kung University, Tainan 70101, Taiwan.
Jiin-Shuh
JS
Jean
Department of Earth Sciences, National Cheng Kung University, Tainan 70101, Taiwan.
Mon-Lin
ML
Chou
D001151:Arsenic / Q000032:analysis / Q000737:chemistry* / Q000633:toxicity; D005453:Fluorescence; D005534:Foot Diseases / Q000139:chemically induced* / Q000453:epidemiology; D060587:Groundwater / Q000737:chemistry*; D006801:Humans; D006812:Humic Substances / Q000032:analysis / Q000633:toxicity*; D009930:Organic Chemicals / Q000032:analysis / Q000737:chemistry* / Q000633:toxicity; D013050:Spectrometry, Fluorescence; D013624:Taiwan / Q000453:epidemiology; D014462:Ultrafiltration; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry* / Q000633:toxicity
D006812:Humic Substances; D009930:Organic Chemicals; D014874:Water Pollutants, Chemical; D001151:Arsenic
Arsenic; Black-foot disease; Dissolved organic matter; Fluorescence; Groundwater