The role of organic and inorganic fractions of cow manure and biosolids on lead sorption

Organic and inorganic fractions of residuals can immobilize heavy metals in soil. The objective of this study was to investigate the role of organic carbon, easily reducible iron (Fe) and manganese (Mn), and free Fe oxides fractions of cow manure and biosolids (sewage sludge) on lead (Pb) sorption. In addition, Pb sorption capacity of a soil as affected by application of organic amendments was investigated. Sub-samples of organic amendments were separately treated for removal of organic carbon, easily reducible Fe and Mn, and free Fe oxides fractions. Organic carbon removal decreased the affinity of manure and biosolids for Pb sorption by 44.4% and 25.1% respectively. Removal of easily reducible Fe and Mn significantly decreased Pb sorption on the manure and biosolids by 28.1% and 19.8% respectively. Removing free Fe oxides from the manure decreased the Pb sorption by 12.5%, while increased the Pb sorption capacity of biosolids by 18%. Lead sorption was also separately measured for a soil treated with cow manure or biosolids at a rate of 10% w/w and compared to the control untreated soil. Application of 10% cow manure and biosolids to the soil significantly increased Pb sorption by 23.1 and 12.2% respectively. The results indicated that inorganic fraction of organic amendments plays an important role in Pb sorption, although the Pb sorption is not limited to the inorganic fraction.