Assessing metal contaminants in Antarctic soils using diffusive gradients in thin-films

Metal contaminants in Antarctic soils are typically found around research stations which are concentrated in ice-free coastal areas. The risk of these contaminants to the Antarctic environment is not well understood, given Antarctica's unique organisms and climate. This study assessed the use of diffusive gradients in thin-films (DGT), a passive sampler that measures fluxes of labile metals from soils to porewaters, in Antarctic soils. DGT-labile measurements were compared to three chemical extractants of increasing strength including high-purity water, dilute acid (1 M HCl), and concentrated acids (3:1 v/v HNO₃:HCl), to understand differences in contaminant geochemistry that may affect environmental risk. One site had high lead concentrations measured with dilute (114 ± 4 mg kg^-1) and concentrated (150 ± 10 mg kg^-1) acids, while DGT-labile concentrations were below the method detection limit (0.5 μg L^-1), indicating that the lead species has low solubility or lability. Another site had low concentrations of zinc measured by dilute (36.2 ± 0.5 mg kg^-1) or concentrated (76 ± 6 mg kg^-1) acid extracts, but had high DGT-labile concentrations (350 ± 80 μg L^-1). This reflects an active source of zinc supplied from soil to pore water over time. Copper was found to be acid extractable, water-soluble, and DGT-labile, with DGT-labile concentrations of up to 12 μg L^-1. Despite the soil and metal-specific geochemical differences, any of the extracts could be used with statistical clustering techniques to identify differences in sites with elevated metal concentrations. This study shows that the DGT-method can identify contaminated sites comparably to chemical extracts but provides environmentally relevant measurements of metal contaminant lability in Antarctic soils.