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The water quality assessment of Arges River and its tributary Dambovita River is presented in this paper as second part of an extended study on the evaluation of some freshwater resources quality located in Bucharest and surrounding areas [1]. This case study was carried out mainly for the water in the confluence area of Arges and Dambovita rivers, where a water and sediment sampling campaign was organized in June 2018. 21 quality parameters were determined for water samples and for the sediment samples the heavy metals content was evaluated. The results of the water samples analysis allowed the framing in quality classes, and for sediment samples the values obtained were compared with the chemical quality standards for sediments, according to the current national regulations. Following the assessment, it was established that the freshwaters in both Arge� River and Dambovita River, downstream the confluence with the Dambovita River are loaded with different pollutants, such as organic substances and nutrients leading to a lower water quality classification.

Chemically modified electrodes (CMEs) based on polymeric films of E-5-((5-isopropyl-3,8-dimethylazulen-1-yl) diazenyl)-1H-tetrazole (L) deposited on the surface of the glassy carbon electrode have been used for the recognition of heavy metal (Me) ions. The electrochemical study of L was done by three methods: differential pulse voltammetry (DPV), cyclic voltammetry (CV), and rotating disk electrode voltammetry (RDE). The CV, DPV, and RDE studies for L were performed at different concentrations in 0.1 M tetrabutylammonium perchlorate solutions in acetonitrile. The polymeric films were formed by successive cycling or by controlled potential electrolysis (CPE). The film formation was proven by recording the CV curves of the CMEs in ferrocene solution. The CMEs prepared at different charges or potentials were used for detection of heavy metal ions. Synthetic samples of heavy metal ions (Cd(II), Pb(II), Cu(II), Hg(II)) of concentrations between 10−8 and 10−4 M were analyzed. The most intense signal was obtained for Pb(II) ion (detection limit of about 10−8 M). Pb(II) ion can be detected by these CMEs in waters at such concentrations. The ability of the ligand L to form complexes with Pb(II) and Hg(II) ions was also tested by UV-Vis spectrometry. The obtained results showed the formation of Me(II)L2 complexes.

River ecosystems are exposed to various stressors, surface sediments as a constitutive part thereof are an essential feature for the evaluation of aquatic ecosystems status. This paper aims to assess the surface sediment quality in the lower section of the Danube River, in terms of hazardous substances content (As, Cd, Cr, Cu, Pb, Hg, Zn, Ni, PAH and PCB). For this purpose, 10 monitoring sites have been assigned for a period of September 2011-August 2017, where construction works were carried out with the purpose of improving the navigation conditions, which also involved sediment dredging. A total approximately of 1200 surface sediment samples have been collected from the Danube River (km 375-km 175), from the left and right banks, monthly during the construction period (2011-2015) and quarterly in the post-construction period (2015-2017). This study gives a description and more detailed evaluation of the integrated assessment of hazardous substances which was carried out in the surface sediments from the Lower Danube River using statistical analysis. The surface sediment quality evaluation was based on comparison of the obtained values with the chemical quality standards set out in the Romanian legislation (M.O. 161/2006). For a more in-depth assessment of the relationship between hazardous substances and for the identification of potential anthropogenic and natural sources, Principal Component Analysis (PCA) and Cluster Analysis (CA) have been used.

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The development of a new voltammetric method for the determination of Pb2+ ions in water samples using glassy carbon electrodes modified with 2,6-bis((E)-2-(thiophen-2-yl)vinyl)-4-(4,6,8-trimethylazulen-1-yl)pyrylium perchlorate is here presented. The analytical parameters for differential pulse voltammetry (DPV) were established and the method was applied for Pb2+ ions determination in acetate buffer solution at pH 5.5. For the developed DPV method the linearity of calibration curve was set up between 20.71mg L-1 - 103.6 mg L-1 with a good correlation coefficient R2=0.9988, the intermediate precision was calculated for three lead concentrations:20, 60,100mg L-1.The obtained detection and quantification limits were 3.1 mg L-1, respectively 10.4 mg L-1. An uncertainty budget was developed and the value of expanded uncertainty was assessed. The optimized method was used to analyze Pb2+ ions from of water samples and good correlation with standard method was obtained.

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