## 3 Results and Discussion
### Metals
and were identified in points in sites 5, 6, 7, 8, 9, 12, 20 located along the Danube, and sites 26 and 29, in the coastal area of the Black Sea. Manganese, the 7 th element with toxic potential monitored in our study, is known for its presence in relatively large quantities throughout the lower Danube [49]. The values obtained following the analysis carried out by us in the 24 sampling points along the Danube are in the range of 196 \(\mathrm{\SIUnitSymbolMicro}\)/L in site 18 (Ceatal Sf. Gheorghe) and 320 \(\mathrm{\SIUnitSymbolMicro}\)/L in site 1 (Ostrov ferry), values comparable to those reported by ICPDR in 2007 (max 228 \(\mathrm{\SIUnitSymbolMicro}\)/L) [49]. From the ecological status point of view, 72% of surface waters are framed in moderate ecological class and 28% in poor ecological class. Similar concentrations were also identified in the Black Sea coastal area, with an increasing trend in the south, near the border with Bulgaria. For nickel, the lowest value of 12.6 \(\mathrm{\SIUnitSymbolMicro}\)/L was recorded in site 32 (Vama veche) and the highest value of 47.7 \(\mathrm{\SIUnitSymbolMicro}\)/L in site 14 (Reni downstream). According with the Romanian legislation in force [47], 31.25% of surface waters had good ecological status (quality standard of 25 \(\mathrm{\SIUnitSymbolMicro}\)/L) and 67.75% had moderate ecological status (quality standard of 50 \(\mathrm{\SIUnitSymbolMicro}\)/L). It was observed that the entire coastal area presented values at least 50% lower compared to the lower Danube sector. Most likely, the high concentrations that were identified at the Danube level are attributed to the riverside industrial capacities, which might have major influences on the concentrations of heavy metals, including nickel or chromium and cadmium which correlated very well with the areas neighboring industrial activities. The values of lead concentrations classify the surface waters in 71.87% of sites of the MONITOX network in good ecological status, whose quality standard is 10 \(\mathrm{\SIUnitSymbolMicro}\)/L (71.87% sites), and 28.13% of sites in moderate ecological status, with a quality standard of 25 \(\mathrm{\SIUnitSymbolMicro}\)/L. Along the Black Sea coast, all the sampling sites had good ecological status. The minimum value of 5.2 \(\mathrm{\SIUnitSymbolMicro}\)/L was obtained in site 29 (Constanta) and the maximum of 12.4 \(\mathrm{\SIUnitSymbolMicro}\)/L in site 3 (Fetesti). Compared with the results reported by ICPDR for JDS3 in 2013 [30], the levels of heavy metals recorded in the Danube water (sites 1-24) in this work (3.0-5.9 \(\mathrm{\SIUnitSymbolMicro}\)/L As; 0.51-1.32 \(\mathrm{\SIUnitSymbolMicro}\)/L Cd; 26.0-61.2 \(\mathrm{\SIUnitSymbolMicro}\)/L Cr; 10.2-28.6 \(\mathrm{\SIUnitSymbolMicro}\)/L Cu; 19.7-47.67 \(\mathrm{\SIUnitSymbolMicro}\)/L Ni; 6.0-15.5 \(\mathrm{\SIUnitSymbolMicro}\)/L Pb; 44-73 \(\mathrm{\SIUnitSymbolMicro}\)/L Zn; 0.02-0.06 \(\mathrm{\SIUnitSymbolMicro}\)/L Hg) are higher than JDS3 values obtained for the entire river length (1.09-2.46 \(\mathrm{\SIUnitSymbolMicro}\)/L As; <0.01-0.145 \(\mathrm{\SIUnitSymbolMicro}\)/L Cd; 0.29-6.73 \(\mathrm{\SIUnitSymbolMicro}\)/L Cr; 1.06-9.93 \(\mathrm{\SIUnitSymbolMicro}\)/L Cu; 0.78-24.63 \(\mathrm{\SIUnitSymbolMicro}\)/L Ni; 0.2-8.08 \(\mathrm{\SIUnitSymbolMicro}\)/L Pb; 1.13-12.95 \(\mathrm{\SIUnitSymbolMicro}\)/L Zn; <0.002-0.007 \(\mathrm{\SIUnitSymbolMicro}\)/L Hg). For selected metals, our results are similar to the maximum values obtained for Danube tributaries (5.33 \(\mathrm{\SIUnitSymbolMicro}\)/L As; 1.05 \(\mathrm{\SIUnitSymbolMicro}\)/L Cd; 67.13 \(\mathrm{\SIUnitSymbolMicro}\)/L Zn) [30], suggesting the fact that the effluents may add an important input of pollutants into the Danube River.