Ariel B. Bolledo1 and Beatriz C. Jadina2
1Science Research Assistant, Philippine Higher Education Research Network, Visayas State University (email@example.com)
2Associate Professor, Department of Agronomy and Soil Science, Visayas State University (firstname.lastname@example.org)
Soil accumulation of heavy metals coming from industrial and municipal wastes poses contamination risk to groundwater resources. A leaching experiment was conducted to determine the mobility and retention of cadmium (Cd) and lead (Pb) in soils derived from limestone and to relate the properties of such soils to the mobility and retention of cadmium (Cd) and lead (Pb). A 2 x 5 factorial leaching experiment consisting of two heavy metals, cadmium (Cd) and lead (Pb), and five different Cd and Pb concentrations (0, 50, 150, 250, 350 mg l–) was conducted. Solutions containing Cd(NO3)2·4H20 and Pb(NO3)2 were used as sources of Cd and Pb respectively. The leaching experiment was conducted for 60 hours. Results showed that the electrical conductivity (EC) and pH of the leachates were high at the first 12-h of leaching which decreased as the leaching process was continued. The different concentrations of Cd and Pb did not significantly affect the EC and pH of the leachates. Most of the recovered concentrations of Cd and Pb in the leachates from all the treated soil columns were below the detection limit. In terms of mobility, Pb was found to be more mobile than Cd. However, the concentrations recovered for both Cd and Pb were very low (0.0035 – 1.77 mg l–) which implies high sorption of the heavy metals. Hence, mobility of Cd and Pb was not evident in soils derived from limestone. Fractionation analysis of Cd and Pb in soil revealed the dominance of carbonate-bound fractions which supports the observation of heavy metal immobility. High cation exchange capacity and high calcium carbonate content were the soil properties related to mobility of the heavy metals.