Evaluation and Application of the Diffusive Gradients in Thin Films Technique Using a Mixed-Binding Gel Layer for Measuring Inorganic Arsenic and Metals in Mining Impacted Water and Soil

Trang Huynh, Hao Zhang, Barry Noller

The diffusive gradients in thin films (DGT) equipped with a Chelex or ferrihydrite binding gel has been designed to enable the measurement of either labile metal species or inorganic arsenic, respectively. In the mine impacted environment, metals and metalloids commonly coexist in a variety of species. This study, for the first time reports the performance of the DGT with a mixed-binding layer (MBL), consisting of Chelex and ferrihydrite for measurements of both metals and arsenic in a single assay. The MBL that consists of a combination of Chelex and ferrihydrite at a ratio of 1:2 has the greatest binding capacity for arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn). The elemental concentrations measured by using MBL-DGT (C(DGT)) were comparable (92-104%) with the original test solution concentrations (C(SOL)). The measurement of As by using MBL-DGT was consistent across a wide pH range (3-8) and ionic strength (0.001-0.1 M). At high pH (9), As measurement was slightly affected (∼80%). The measurements of Cd, Pb, and Zn were affected at low pH (<3) and high pH (9). Measurements of Cd, Cu, and Pb were affected at low ionic strength (0.001 M). At high ionic strength (0.1 M), measurements of Cd; Cu and Pb were slightly affected. The capacity of MBL-DGT for quantitative measurement in a multielements solution is effectively limited to 15 μg for As and 70 μg for metals per MBL-DGT device. Good correlations (p < 0.01) between MBL-DGT measurements and ferrihydrite or Chelex DGT were obtained for As, Cd, Cu, Pb, and Zn in water and soil with exception for Cd and Cu (p < 0.05) when deployed in soil.