The assessment of surface water quality of the Danube River and Black Sea was performed taking into account the amounts determined for heavy metals (As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, Zn), nutrients (compounds of N and P, chlorophyll a), emerging contaminants (CECs) (pharmaceutics and endocrine disruptors—19 quantified compounds, out of 30 targeted chemicals), heterotrophic bacteria and total coliforms, in thirty-two locations from the lower Danube sector (starting with km 375 up to the river mouths), the Danube Delta Biosphere Reserve (three Danube branches—Chilia, Sulina, and Sf. Gheorghe) and the Romanian coastal area of the Black Sea. The heavy metals levels were found in the following ranges: 3.0–6.5 μg/L As; 0.51–1.32 μg/L Cd; 21.6–61.2 μg/L Cr; 10.2–28.6 μg/L Cu; 196–351 μg/L Mn; 12.3–47.67 μg/L Ni; 5.2–15.5 μg/L Pb; 44–74 μg/L Zn; 0.01–0.08 μg/L Hg. The nutrient concentrations vary in the intervals: 0.04–0.45 mg/L N-NH₄; 0.01–0.06 mg/L N-NO₂; 0.07–1.9 mg/L N-NO₃; 1.0–3.2 mg/L N total; 0.01–0.05 mg/L P-PO₄; 0.02–0.27 mg/L P total, and 0.8–17.3 μg/L chlorophyll a. The concentrations of CECs from various classes (sulfamethoxazole, trimethoprim, ciprofloxacin, flumequine, amoxicillin, cefuroxime, dicloxacillin, carbamazepine, pravastatin, erythromycin, piroxicam, ketoprofen, diclofenac, naproxen, enilconazole (imazalil), clotrimazole, drospirenone, 17α-ethinylestradiol, and bisphenol A) were compared with values reported for European rivers and the Danube River water in various river sectors. The highest detection frequencies were registered for bisphenol A (100%), sulfamethoxazole (96%), carbamazepine and diclofenac (87%), trimethoprim (78%), pravastatin (46%), and imazalil (34%). Bisphenol A exhibited the largest concentrations (342 ng/L), followed by diclofenac (132 ng/L), carbamazepine (38 ng/L), and sulfamethoxazole (36 ng/L). For most of the contaminants, Black Sea coastal water showed lower concentrations than the Danube water and good ecological status for surface water. Correlations between CECs and total coliforms suggest insufficient treated wastewater effluents as a common contamination source and possible use of CECs as indirect fecal pollution indicator in aquatic systems. This is the first study carried out in the connected system Danube River–Danube Delta–Black Sea for a large palette of toxicants classes and microbial pollutants, which will serve as a baseline for future monitoring of water quality in the region.

The Chilia branch is the north branch of the Danube River at the Romania-Ukraine border in the Danube Delta; it is a complex system with economic and ecological values. The surface water quality is a major concern and monitoring programs have been developed at the national and international level. The objective of this study was to evaluate the water quality of the Chilia branch in different sampling points from the mouth to the discharge in the Black Sea. The assessment of water quality was done at the individual level taking into account the nutrient concentrations and the standard limits for good ecological status and at integrative levels, using CCME WQI. The longitudinal distribution of Chilia branch water quality was done using GIS method. A total of 106 water samples were collected between 2013 and 2019 from five sampling points. At the individual level, the Chilia branch has a good ecological status except for its levels of total nitrogen, due to the organic nitrogen contribution in 2015. In 90% of nutrient concentrations, low values predominate and high values are considered extreme; only in 10% do high values predominate and low values are considered extreme concentrations. In equal percentages, 50% of the nutrient concentrations have a high degree of heterogeneity and the other 50% of concentration values are very close to the average values, with a high degree of homogeneity. CCME WQI method indicated that 39.93% of surface waters from the Chilia branch had an excellent quality, 45.45% a good quality, and only 14.62% a fair quality.

The assessment of surface water quality of Danube river and Black Sea was performed taking into account the amounts of 9 heavy metals (As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, Zn), nutrients (6 N and P compounds, chlorophyll a), emerging contaminants (pharmaceutics and endocrine disruptors) and heterotrophic bacteria and total coliforms (fecal indicator bacteria) in thirty-two locations from the lower Danube sector (starting with km 375 up to the river mouths), the Danube Delta Biosphere Reserve (three Danube branches – Chilia, Sulina and Sf. Gheorghe) and the Romanian coastal area of the Black Sea. The results for heavy metals, nutrients and bacteria were compared with norms set up in the national legislation for good ecological status for surface water. The concentrations of pharmaceutics and endocrine disruptors from various classes (19 quantified compounds, out of 30 investigated chemicals) were compared with values reported for Danube River water in other studies performed in various river sectors. Correlations between contaminant levels and physicochemical parameters of water samples were studied. This is the first study carried out in the connected system Danube River–Danube Delta–Black Sea for a large palette of toxicants classes and microbial pollutants .

Pesticides play an important role in boosting agricultural production by controlling pests. Pesticides can be algicides, antimicrobials, disinfectants, herbicides, insecticides, molluscicides, pheromones, rodenticides (raticides), and biopesticides. Despite regulations, pesticide pollution remains a threat to human health, food security, and the environment. Pesticides can harm the environment, affecting water quality and biodiversity, and can be toxic to non-target species. This study aimed to assess the impact of pesticide residues on the surface waters of the Danube River through concentrations determined in the period 1995–2023 in the Danube River Basin. In the present study, scientific techniques were used to collect scientific evidence, consulting academic literature databases such as Google Scholar, Science Direct, MDPI, etc. The study also looked at the quantities of pesticides used in the countries of the Danube River Basin compared to agricultural production during 2014–2022. Five compounds from the pesticide class were selected from the literature. This selection was based on the frequency of determination in surface waters from the Danube River Basin. Pesticides have a negative effect on both the aquatic ecosystem and humans, directly affecting the proper functioning of the body. Continuous monitoring of pesticide residues is essential for determining the quality of the Danube water, as well as for biodiversity.