Chemical Speciation and Potential Mobility of Heavy Metals in Organic Matter Amended Soil

Organic matter (OM) degradation from amendments used in the remediation of metal-contaminated soils leads to modifications in soil chemical properties immediately after addition, which can also affect the soil metal distribution. Therefore, the speciation and potential mobility of heavy metals e.g., lead (Pb) and cadmium (Cd) were evaluated in three soils amended with OM. Soils, both spiked (with lead nitrate and cadmium nitrate solution) and unspiked, were treated with OM at a rate of 5 tons/ha in a moist condition. The samples were in incubation for 30 days in 30% moist condition. A chemical fractionation procedure was applied to determine the distribution of Pb and Cd in soils. The potential mobility of metals was also determined. Metals transformed from mobile to immobile fractions in both spiked and unspiked soils (not treated with organic matter), but OM increased the mobile fraction of Pb in unspiked soil and decreased it in spiked soil. In contrast, the mobile fraction of Cd decreased in soils (not treated with OM), but the OM increased the mobile fractions in spiked and unspiked soils. The mobile fraction (as a percentage of total) of Cd was higher than the mobile fraction of Pb indicating the greater mobility of Cd compared to Pb. However, the three soils showed a more or less similar pattern in transforming Pb and Cd in soils since their characteristics were almost the same.