TRACE ELEMENTS IN THE GROUNDWATER OF THE NEMYRIV DEPOSIT (UKRAINE)

Abstract

The data obtained and published to date by experts in various fields indicate that there are no absolutely harmful or absolutely beneficial trace elements, the only question is their concentration and form in natural waters (including groundwater). The forms of occurrence in natural waters are particularly important for elements that may have different degrees of oxidation (e.g., arsenic, manganese) or a high ability to form complexes with water anions (e.g., nickel). In addition, the possible positive and negative effects of biological exposure to drinking water that meets the quality criteria but has slightly elevated levels of trace elements (the so-called “chronic” effect) are currently being actively discussed. The aim of this study is to determine the speciation of biologically active trace elements in the waters of the Nemyriv drinking water deposit in the Southern Bug River basin by geochemical modelling. The modelling was performed using the PHREEQC software. Trace elements found in water in concentrations measured by analytical methods are considered in this paper. The data on the content of 7 elements (As, Mn, Sr, Ni, P, Si and F) in the water of 6 wells in the Skifska area (3 wells in the ravine and 3 wells along the Ustia River) were analysed. The concentrations of Sr, Ni, P and F in the water of the wells considered in the Nemyriv drinking water deposit do not exceed the MPC. The concentration of As exceeds the MPC. Mn concentrations in the wells located in the ravine do not exceed the MPC, but significant excesses are observed in the wells located along the Ustia River. Based on the mineral composition of the rocks, the results of geochemical modelling, and the different supply mechanisms of the wells located in the ravine and along the river, it can be concluded that the manganese is of anthropogenic origin. None of the water in the Skifska area under consideration meet the water quality requirements in terms of the total specific content of pollutants of the first and second hazard classes. The main reason for this discrepancy is the increased concentration of arsenic in the water. However, this is in the relatively safe form of As(V). Phosphorus and arsenic concentrations are largely determined by co-precipitation with iron minerals. Fluorine behaves like a classical halogen in the well water of the Skifska area and is in oxidation state-1, and the main source of fluorine is biotite and fluorite. Strontium and manganese in the well waters of the Skifska area of the Nemyriv deposit are in oxidation degree +2, mainly in the form of Me2+ cations. The manganese occurrence in such a oxidation degree indicates its potential bioavailability, so it is necessary to carry out additional analytical studies to determine the concentrations of Mn and organic compounds, perform repeated geochemical modelling, assess the hazard of these waters to humans and develop additional water treatment measures.