Labile fraction of metals in water bodies with different humic substances content and component composition of dissolved organic matter

ABSTRACT This study summarises long-term research on the labile fraction of metals (Al, Fe, Cu, Mn, Zn, Pb, Cr, Cd) in surface waters of Ukraine differing in humic substances content and dissolved organic matter composition. The investigations covered the reservoirs of the Dnieper cascade, the Dnipro–Bug and Dniester estuaries, rivers of Polissia, central and southwestern Ukraine, as well as small lakes and urban streams. The selected metals are environmentally relevant due to their toxicity and role in aquatic systems. The proportion of the labile fraction of Al, Fe, Cu, Mn, Zn, and Pb increased with decreasing humic substance concentrations and was highest in waters of the southwestern region and urban areas. Seasonal variability was most pronounced in summer and autumn, reflecting changes in dissolved organic matter composition. In highly anthropogenically impacted waters, elevated labile metal fractions showed limited seasonal variation. Higher labile Fe and Mn concentrations were observed in bottom waters under oxygen-deficient conditions. The applicability of anodic stripping voltammetry and chemiluminescent analysis is discussed, as these sensitive techniques allow direct determination of labile fraction of metals. The results provide a scientific basis for assessing surface water quality under current and future environmental and climatic pressures.