Assessment of using bentonite, dolomite, natural zeolite and manure for the immobilization of heavy metals in a contaminated soil: The Copsa Mica case study (Romania)

The aim of study was to assess the effectiveness of organic and inorganic amendments to immobilize cadmium (Cd), lead (Pb) and zinc (Zn) in soil and reduce their availability in a contaminated soil. We present the results of a field experiment organised in the Copp Mica area in which different types of amendments were applied: Na-bentonite, dolomite, natural zeolite and manure. The effectiveness of applied amendments was assessed using single extraction of metals from soil (using DTPA-CaCl2-TEA at pH 7.3 or NH4NO3) and metal accumulation in plants. All treatments produced significant increases of soil pH, but the best results were observed after applications of dolomite and Na-bentonite. After two years from applications all amendments decreased the metal (Cd, Pb or Zn) availability compared to the control, but the magnitude of effects depends on each metal and amendment. The addition of dolomite and Na-bentonite reduced significantly the concentrations of Pb and Zn in plants, but this reduction is not enough to produce healthy food or fodder. The application of manure led to a significant increasing of biomass yield comparing with control, even if the extractability of metals in manure treated plots was moderate. The results demonstrate the high potential of Na-bentonite and dolomite to reduce the availability and possible toxicity of heavy metals in contaminated soils but more attention should be paid to the transitory liming effect and metal remobilizing over time.