Diffusive gradients in thin films technique coupled to X-ray fluorescence spectrometry for the determination of bioavailable arsenic concentrations in soil

Abstract

Many of the procedures for assessing the bioavailability of contaminant including arsenic (As) in soil are time-consuming, thus there is need to develop more effective methods. In this regard, a direct analysis of the binding resin in the diffusive gradient in thin film (DGT) by using wavelength dispersive X-ray fluorescence spectrometry (WDXRF) was tested in determining bioavailable As concentrations in soil. The binding resin obtained from the DGT was dried at room temperature in a desiccator with silica gel for 2 h, and directly analyzed by the WDXRF. The mass of As loaded in the DGT binding resin was plotted against the X-ray intensity obtained from the WDXRF analysis to a draw calibration curve, which showed good linearity (R-2 = 0.997) with a limit of quantification of 0.2 mu g. A correction factor (CF) for compensating the spectral interference between As-K alpha and Pb-L alpha was determined by considering the slope between the X-ray intensity measured at a Bragg angle of 48.781 degrees for As-K alpha and the Pb mass on the DGT binding resin. The use of the derived CF value (0.113) is reasonable to obtain As concentrations with a high accuracy. The relation between phytotoxicity of As to barley Hordeum vulgare and bioavailable As concentrations in soils, which were determined by means of the combined use of DGT and WDXRF, was observed. The study supports that the DGT-WDXRF can be a promising tool to predict soil phytotoxicity for As-contaminated soil risk management.