Immobilization Potential of Cow Manure for Heavy Metal Remediation from Refuse Dump Soil

Abstract

Aims: The present study investigated the effect of cow manure amendment on fractionation and availability of some heavy metals (Cd, Cu, Cr, Mn, Pb and Zn) in refuse dump soil. Study Design: A greenhouse study experiment was conducted to determine the uptake of the metals by Ricinus communis in dump soil treated with 0%, 5%, 10% and 20% cow manure. Place and Duration of Study: The study was carried out at the Department of Pure and Industrial Chemistry, Nnamdi Azikiwe University Awka, Anambra State, Nigeria, between May and October 2018. Methodology: Experimental pots were filled with 2.0kg refuse dump soil in a green house and treated with 5%, 10% and 20% of Cow manure in three replicates per treatment. The seeds of Ricinus communis were planted in each pot and analysed after 12 weeks of planting for heavy metals using AAS. Sequential extraction was carried out on the treated soil after the harvest with each extract further analysed for heavy metals using AAS. Results: Application of cow manure significantly (p ˂ 0.05) affected the redistribution and the mobility of the heavy metals in the dump soil; as the concentration of the amendment increased, heavy metals in the mobile fractions reduced. 20% amendment had the best immobilization effect as the mobility factor decreased with increasing manure amendment. The mobility factors at 20% amendment were 18.34%, 15.82%, 5.23%, 15.86%, 25.56% and 12.81% for Cd, Cr, Cu, Mn, Pb and Zn respectively with the general trend of metal forms given as: residual > bound to organic > bound to Fe-Mn oxide > bound to carbonate > exchangeable. Conclusion: Cow manure amendment of the dump soil decreased the availability of heavy metals for plant uptake; and the metal uptake generally decreased as percentage amendment increased. Cow manure is therefore a good immobilizing agent for remediation of Cd, Cr, Cu, Mn, Pb and Zn in polluted soils.