Field determination of labile Cu and Pb in contaminated soils by using diffusive gradients in thin film technique

Field determination of labile heavy metal(loid)s (HM) is essential for environmental risk assessment. The diffusive gradients in thin film (DGT) technique, though promising for quantifying labile HMs, remains largely limited to laboratory settings for unsaturated soils. This study optimized DGT parameters based on the CDGT-W index (HM accumulation normalized to soil weight in the device cavity) to develop a field method for measuring copper (Cu) and lead (Pb) in soils. Results showed that CDGT-W was minimally affected by pre-equilibration time, variably influenced by soil particle size depending on the HM-soil system, and increased with environmental temperature. Consequently, a 15-min pre-equilibration time without soil sieving was recommended, with ambient temperature recorded in situ. The method was validated using contaminated soils from mining areas, comparing field-measured CDGT-W with laboratory DGT measurements and CaCl2 extraction. Field-measured values positively correlated with both laboratory CDGT-W and CaCl2-extractable concentrations. These findings demonstrate that the refined DGT approach enables effective field assessment of labile Cu and Pb in unsaturated polluted soils, potentially broadening DGT applications in soil environmental monitoring.