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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.

Taking into consideration that fish are valuable bioindicators for assessing pollution with potentially toxic elements (PTEs) such as heavy metals from aquatic environments, this study aimed to assess bioaccumulation factors in relation to water (BAF) and sediment (BASF) for the following potential toxic elements: Cd, Pb, Hg, Cu, Cr, Ni and Zn from 6 different fish species (Alburnus alburnus, Carassius gibelio, Scardinius erythrophthalmus, Ameiurus nebulosus, Perca fluviatilis, Lepomis gibbosus). Fish species have been captured from the waters of the Arges River (Hotarele village area) and the Colentina River (particularly from Mogosoaia, Herastrau and Panteliom lakes), from crowded areas located in the southern part of Romania. The results of the analysis indicated BAF values > 1 for the most fish species captured from the Colentina River. BASF values > 1 were obtained for BASFPb (Carassius gibelio - Arges River), BASFNi (Scardinius erythrophthalmus - Herastaru L. and Perca fluviatillis - Pantelimon L.), BASFCr (Perca fluviatillis - Pantelimon L.) and BASFZn (Alburnus alburnus and Scardinius erythrophthalmus - Mogosoaia L. and Carassius gibelio - Pantelimon L.). The obtained results can be used to describe the transfer of these elements from water and sediments to the fish tissue.

One of the main concerns of the developing world is the mitigation of pollution of environmental components together with the recovery and reuse of valuable substances from waste resulting during diverse anthropic activities. Wastewater generated by agro-zootechnic activities is a source of nutrients (nitrogen and phosphorus compounds) and traditionally it is reused for crops irrigation. However adverse effects on the environment may be caused should a proper treatment not be performed, considering the spread of additives/drugs altering the natural metabolism in modern livestock industries and subsequently their presence in waste. In this context, research was conducted on laboratory scale setups of some advanced treatment processes for wastewater resulting from cattle farms. UV disinfection and oxidation using ozone were investigated in order to emphasize the antimicrobial effect and their contribution to the improvement of water quality. The permissible irrigation water quality which varied based on the crop type was the decisive factor in adjusting the experimental setup and effluent quality. The results have revealed the inactivation of bacteriological indicators up to 99% and even 100% in the case of faecal coliforms and faecal streptococci. Moreover, ozonation allows also the removal of organic matter, with an efficiency of over 80%. This research offers solutions suitable for areas where the water demand exceeds availability and in the regions affected by drought.

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