Determination of As species distribution and variation with time in extracted groundwater samples by on-site species separation method

It is challenging to dependably keep the native distribution of arsenic (As) species before sample analysis in the laboratory. The on-site separation method can avoid sample contamination and species change in the process of sample collection and transportation from field to laboratory. In this study, As species distribution and variation of the extracted groundwater was first analyzed by an on-site species separation method in Jianghan Plain, China. Our study illustrated that: 1) high-As groundwater generally existed under mildly reducing conditions (Eh < 200 mV), weak alkaline conditions (pH < 7.2), elevated concentrations of dissolved Fe(II) and S(-II), and high proportions of As (III); 2) As species in the groundwater changed dramatically at room temperature in 36 hours post extraction (HPE). Fe-sulfide and Fe oxides minerals, which adsorbed As (V), were the main reasons influencing the As species concentration; 3) Acidification and strong complexing agents cannot preserve As species effectively. The average proportion of As (III) in the wells, where groundwater samples from the depth of 25 m exceed 10 μg L-1 As, can be reduced by 61% and 63% after HCl and EDTA were added, respectively. Accurate assessment of concentrations and distribution variation of As species in groundwater can guide the removal of As and the safe use of water resources, especially in drought areas relying on drinking well water.