The Danube is a source of water for the household and industrial needs of Ukrainian population, industry and agriculture. The Danube waters are used for drinking centralized water supply in the cities of Kiliya and Vilkovo, as well as fisheries in the region. Therefore, it was important to carry out the “Environmental Risk Assessment for Drinking and Fisheries Use (on the example of the Danube River –the city Vilkovo)”. The purpose of the study was to evaluate the effectiveness of the application of the environmental risk criterion R on the basis of hydrochemical observations to verify the safety of drinking and fishery use. Analysis of environmental problems of the lower Danube River - Vilkovo; assessment of the environmental situation; calculation of water quality risk indicators according to the methodology of the Institute of Market Problems and Economic and Environmental Research of the NAS of Ukraine; establishing a link between water quality and risk is the finding of the research. It is established that the environmental situation is “critical” due to suspended substances, phenols, manganese and HCC for drinking water supply and “strained” through chromium, manganese, HCC, copper for fishery use. An assessment of the water quality by the modified Water Pollution Index (IWM) showed that the water is “moderately polluted” and “contaminated”. For both types of water use, normalized aggregated pollution indices were calculated taking into account the likelihood of a risk event occurring and R risk indicators were determined by year. It is established that there is a close linear relationship between WSS and R. It is shown that environmental risk estimates, based on the probability of exceeding concentrations of pollutants above the MPC, reflect well the ecological status of the water.

The analysis of current scientific work on the use of statistical methods in hydrochemical research has shown that this approach is sufficiently substantial, both in Ukraine and abroad. The purpose of this work is to determine the main statistical parameters and to research the possibility of applying theoretical laws of distribution to the time series of water mineralization.This research presents the results of the application of standard statistical methods of hydrometeorological information processing for data on water mineralization at 28 gauges of the Dnipro basin (within Ukraine) for the period from 1990 to 2015. The dynamics of the obtained statistical parameters (long-term annual average, coefficients of variation, asymmetry and autocorrelation) within the Dnipro basin in Ukraine has been analyzed. The average annual values of mineralization vary substantially within the studied part of the Dnipro basin - in the northern part the maximum value of the annual average mineralization is 447 mg/l, as it moves to the south, the mineralization increases and in the sub-basin of the Middle Dnipro it reaches a maximum of 971 mg/l; the highest values are observed in the south (sub-basin of the Lower Dnipro), where they can reach extremely high values for particular small rivers (the Solon River - Novopavlivka village, 3356 mg / l). The long-term variability of mineralization in the rivers of the studied area is insignificant, and the autocorrelation coefficients of the mineralization series are quite high, in most cases they are significant and tend to decrease from the sub-basin of the Prypyat’ river in the north to the sub-basin of the Lower Dnipro river in the south. Within the framework of the presented research, the possibility of using theoretical distribution curves known in hydrology to describe the series of river mineralization, using the example of the Dnipro basin, has also been analyzed. Using Pearson’s fitting criterion, the Pearson type III distributions and the three-parameter distributions by S.M.Krytsky and M.F.Menkel have been verified on their correspondence with the empirical series of mineralization. As a result, it was found that in 85% of cases the Pearson type III distribution can be used, and the three-parameter by S.M.Krytsky and M.F.Menkel can be used in 60% of cases.

Виконана оцінка придатності вод р. Кучурган та Кучурганського водосховища за комплексом гідрохімічних показників за методикою Гідрохімічного Інституту (м. Київ, Україна) для потреб рибного господарства. Досліджена динаміка якості води у часі та просторі. За розрахунками комбінаторного індексу забрудненості за 2003-2018 роки на досліджуваних водних об'єктах води ІІІ-IV класу-«брудні» та «дуже брудні». На даному етапі можна зробити висновок, що вода р. Кучурган та Кучурганського водосховища є непридатною для рибогосподарського використання Ключові слова: комплекс гідрохімічних показників, комбінаторний індекс забрудненості, оцінка якості води