Simultaneous measurement of labile As (III) and As (V) in soils combining DGT and HPLC-ICP-MS

The speciation of arsenic (As) determines its biogeochemistry and ecotoxicity in soils. However, the approach to in situ monitor labile As (III) and As (V) in soils still requires more exploration. In this study, we developed a method for simultaneously obtaining in-situ data on labile As (III) and As (V) in soils using diffusive gradients in thin films (DGT) and high performance liquid chromatography-inductively coupled plasma mass spectrometry. The Fe₂O₃∙xH₂O DGT sampler exhibited rapid and simultaneous accumulation of As (III) and As (V) in solutions within 90 min. The high efficiency of simultaneous elution of As (III) (~84 %) and As (V) (~97 %) was achieved using 0.8 % H₃PO₄ as eluent at 90 °C for 80 min. The method detection limits for As (III) and As (V) were 0.01 and 0.005 μg/L, respectively. This method was applied to reveal the labile As (III) and As (V) in soils in the water level fluctuation zones of the Three Gorges Reservoir, which is the largest reservoir in China. The concentrations of As (III) and As (V) measured by DGT varied with different sampling sites, ranging from 0.01 μg/L to 1.20 μg/L and from 0.01 μg/L to 0.26 μg/L, respectively. The labile As (III) exhibited the higher resupply rate from soil solid phase to soil solution than labile As (V). This study helps to achieve simultaneous in-situ quantification of labile As (III) and As (V) in soils, and will improve the understanding of As mobilization and ecotoxicity in soils.