Metallic elements copper (Cu), zinc (Zn), nickel (Ni) and manganese (Mn) are some of the most commonly found in water and sediment samples collected from the Danube - Danube Delta. These elements are important as essential micronutrients, being normally present at low concentrations in biological organisms, but in high concentrations they become toxic with immediate and delayed effects. The role of this metals is still controversial, that�s why bioconcentration potential is so important. In this non-clinical study, we tested in vitro effect of heavy metals on carp, Cyprinus carpio, reproducing in vivo presence of Cu, Zn, Ni and Mn in the Romanian�s surface water. The toxicity tests were performed according to OECD 203 by detecting the average (50%) lethal concentration - LC50 on aquatic organisms (freshwater fish) at 96h. The results pointed out that, copper value for LC 50 at 96h was estimated as 3.4 mg/L (concentrations tested in the range of 0.1 - 4.75 mg/L). Zinc value for LC 50 at 96h was estimated as 20.8 mg/L (concentrations tested in the range of 0.028 � 29.6 mg/L). Nickel value for LC 50 at 96h was estimated as 40.1 mg/L (concentrations tested in the range of 0.008 - 84.5 mg/L). For manganese the mortality effects has recorded at LC 50 at 96h at estimated value higher than 53 mg/L (concentrations tested in the range of 0.04 - 53.9 mg/L). The accuracy of the testing metals concentration was insured by the screening of the dilution water, as well as food and control fish, acclimated in laboratory conditions.
