The Integrated Water Resources Management regulations aim to ensure a good status of surface water quality and its sustainable use. Water quality monitoring of various water users supports the identification of pollution sources and their environmental impacts. The priority pollutants generated by wastewater discharges from municipal, industrial wastewater treatment plants or agricultural areas are of great interest due to their eco-toxicological effects and bio-accumulative properties. The aim of this study was to monitor the priority organic and inorganic pollutants from the Siret River basin, in Romania, with the purpose of assessing the surface water quality status and evaluating it by the Water Quality Index (WAWQI) method. The monitoring of inorganic priority pollutants (e.g., As, Cd, Hg, Ni, Pb) and organic priority pollutants (e.g., Naphthalene, Anthracene, Phenanthrene, Fluoranthene, Benzo(a)anthracene, Benzo(b)fluoranthene, Benzo(k)fluoranthene, Benzo(a)pyrene, Benzo(ghi)perylene, Indeno(1,2,3-cd)pyrene, α, β, and γ-Hexachlorocyclohexane, and Di-2-ethyl-hexyl-phthalate) was conducted within the Siret River basin, during the period 2015–2020. With this purpose, 21 sampling points (18 river sections and 3 lakes) were considered to assess the water quality. The results of this study proved that the water quality within the Siret River basin is generally classified in the 2nd or 3rd class. The spatial distribution of the water quality index values, using ARCGIS, also highlighted the fact that the water quality is mostly unsuitable for drinking water supplies, being influenced by the quality of its main tributaries, as well as by the effluent of wastewater treatment plants.

As water management is still a problem of international concern, scientists and practitioners are collaborating to develop new tools and methods to improve and help in the decision-making process. When addressing the priority pollutant monitoring and impact assessment, the ecotoxicity effects, carcinogenic and non-carcinogenic, should be considered together with the exposure factor and health hazards. The main goals of this study were to assess the ecological and health hazards and to apply integrated impact and risk assessment based on the ecotoxicity and exposure factors of each priority pollutant present in the aquatic ecosystem. This study used as a database the measured concentrations of 5 inorganic and 14 organic priority pollutants from the Siret river basin from NE Romania, from 18 river sections monitored in the period 2015–2020. The USEtox methodology and a new integrated index for environmental impact and risk assessment were developed and applied to evaluate the ecological and health hazards and environmental impacts and risks within the river basin. The total impact scores for heavy metals ranged from 2 × 103 to 2.25 × 109, and those for organic pollutants ranged from 2.72 × 10−1 to 2.95 × 106. The environmental risk in the case of inorganic priority pollutants ranged between 5.56 and 3136.35, and that in the case of organic pollutants was between 4.69 and 4059.17. The results revealed that there is a major to catastrophic environmental impact in almost all monitored river sections (10 out of 18), and the overall risk exposure was found to be at a significant to a major level. This study proved the harmful effects that the priority pollutants may have, even in very small concentrations, on non-target organisms and suggests that greater control over the pollution sources and mitigation of environmental impacts and risks should be applied.