INFLUENCE OF BENTONITE, DOLOMITE, NATURAL ZEOLITE AND MANURE ON HEAVY METAL IMMOBILIZATION IN A CONTAMINATED SOIL

Abstract

Using organic or inorganic amendments to immobilize the heavy metals in soils is a cost-effective remediation technique for contaminated soils. The aim of study was to assess the efficiency of 4 amendments to immobilize cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) in soil and reduce their phyto availabilty. An experimental field was set-up in Copșa Mica area and four amendments were applied: Na-bentonite, dolomite, natural zeolite and manure. Following the application of the amendments, a mix of perennial grasses and straw cereals, belonging to the family of Gramineae, were sown. The efficiency of in situ immobilization of heavy metals was assessed using DTPA extraction of metals and plant uptake. All treatments produced significant increases of pH values in soil. The mean soil pH of the control plots was 5.18. Comparing the effects of treatments on soil reaction, the best results were observed after applications of bentonite or dolomite. The highest mean value of pH was measured in plots treated with Na-bentonite (pH 7.16). The bioavailability of metals is related to soil pH. Therefore the effects of treatments on pH are reflected on metals bioavailability assessed by DTPA-extractable metal fractions. All amendments caused a reduction of heavy metal (Cu, Cd, Pb or Zn) mobility compared to the control but the magnitude of effects depends on metal and amendment. For copper and zinc, addition of Na-bentonite reduces statistically significant the mobile forms in soil from 13.6 mg•kg-1 Cu (control) to 9.4 mg•kg-1 Cu and from 327 mg•kg-1 Zn (control) to 143 mg•kg-1 Zn. By using the natural zeolite the values of heavy metal contents in mobile forms in soil decreased significantly comparing with control. The results demonstrate the high potential of studied amendments for immobilization of heavy metals in contaminated agricultural soils.