Urea increased nickel and copper accumulation in the leaves of Egeria densa (Planch.) Casp and Ceratophyllum demersum L. during short-term exposure

In the present study, two fresh water plant species Egeria densa (Planch.) Casp. and Ceratophyllum demersum L. were subjected to separate and combined action of urea (2 mM) and metals (Ni and Cu, 10 mu M) to investigate the phytoremediation potential of these two submerged macrophytes during short-term experiments (48 h). Both submerged macrophytes demonstrated high accumulative potential for Ni and Cu (average bioconcentration factors were 2505 for Ni and 3778 for Cu). The urea (2 mM) was not significantly toxic for studied plant species. Futhermore, urea worked as an additional source of nitrogen and stimulated some metabolic processes such as the synthesis of photosynthetic pigments, soluble proteins, non-enzymatic antioxidants, and activated some enzymes. Adding urea to the metals increased their accumulation in both macrophytes (on average by 35% for Ni and 15% for Cu). Combined action of urea and Ni did not have a significant effect on antioxidant response, but caused a sharp increase of urease activity (4 folds on an average) in both plants. The copper exerted a stronger toxic effect on both studied macrophytes compared to nickel. Adding urea to copper in some cases diminished the toxic action of this metal. Study concludes that the responses of E. dense and C. demerswn to urea and metal action (separate and combined) were depended on the type of pollutant and the activity of antioxidant defence system. Therefore, the studied aquatic macrophytes found to be potential phytoremediators of water bodies, the addition of an organic nitrogen source in the form of urea in environmentally relevant concentration will increase the efficiency of phytoextraction of metals.