ROLE OF HUMIC SUBSTANCES IN THE COMPLEXATION AND DETOXIFICATION OF HEAVY METALS: CASE STUDY OF THE DNIEPER RESERVOIRS

摘要

Results of long-term investigations of the heavy metal content and speciation in the Dnieper water bodies (Ukraine) are presented. The particular importance was given to the study of dissolved organic matter (DOM) composition, to binding affinity of metals such as Fe, Mn, Cu, Zn, Pb, Cr, and Cd for DOM, and to molecular weight distribution and chemical nature of metal-DOM complexes. The chemiluminescence and anodic stripping voltammetry in combination with membrane filtration, gel permeation chromatography, and ion-exchange chromatography were used for this purpose. It is shown that complexation with natural organic ligands plays the major role in the fate of HM in fresh water systems. The prevailing fraction of dissolved metals is found to present as complexes with humic substances, mainly, with fulvic acids. For the evaluation of the stability of aquatic ecosystems to the toxic action of HM, the potential complexing ability of DOM was investigated. The results on copper toxicity are presented obtained in long-term experiments with distilled and tap waters as well as with the natural water from the Kanev reservoir containing additives of copper ions and humic acids (HA). The toxic effect of free Cu~(2+) ions is determined using biotests with Daphnia magna. It was established that a decrease in integral water toxicity correlated with a reduction in free Cu~(2+) concentration in water medium. Hence, Cu~(2+) ions present in aquatic media in the form of non-toxic complexes with organic ligands. The maximal decrease in toxicity was observed in natural water where the complexation occurred with participation of both DOM and added HA.