Monitoring and flux determination of trace metals in rivers of the Seversky Donets basin (Ukraine) using DGT passive samplers

This paper reports the results of the in situ application of diffusive gradients in thin-films (DGT) passive samplers for trace metals (Cd, Co, Cr, Cu, Ni, Pb and Zn) monitoring in transboundary Udy and Lopan rivers of the Seversky Donets watershed in the Kharkiv region,Ukraine, which has a long history of industrial development. The research discusses potential sources of DGT-measured labile metals in water and seasonal variations. Also, our results demonstrate the performance of using DGT to identify and to measure labile metal concentrations in contrasted climate conditions (cold snowy winter and hot summer) and appropriateness of such a tool for continuous water monitoring with the presence of an ice cover. Results show that DGT-measured concentrations of most of trace metals were much higher downstream of the wastewater treatment plants discharges than upstream; thus wastewater treatment plants seem not able to reduce or to remove the trace metals contaminations and become major sources of studied pollutants in the studied rivers. The calculation of the average metal fluxes to base on the DGT-measured concentrations confirmed that urban wastewater discharges significantly contribute to the metal fluxes into the Udy and the Lopan rivers during both low-flow and high-flow periods. Compared to the wastewaters inputs in the rivers, the transboundary effect is limited, but should also be taken into account as the origin of some metals is from sources located on the adjacent Russian territory.