Sorption Behavior of Lead (Pb) onto Agricultural Soils of Khyber Pakhtunkhwa, ‎Pakistan: Potentials for Leaching

Lead (Pb) contamination in soil and subsequent transport in groundwater poses severe threats to the food safety and human health. In current study, the effects of soil organic matter on sorption behavior of Pb onto six agricultural soils were investigated by batch sorption experiments and microscopic characterization. Results indicated that Pb sorption onto agricultural soils was dominated by the soil organic matter content and soil texture. The decrease of organic matter content reduced the sorption capacity of Pb onto agricultural soils. Based on soil texture, the Pb sorption was highest in clay soil and lowest in silt type of soil. The overall Pb sorption was in the order of clay > clay loam > silty clay loam ≈ loam > silt loam > silt. The sorption isotherms of measured aqueous and soil phase Pb concentrations were fit well with the linear sorption model. The organic carbon normalized partition coefficients (Log KOC) ranged from 2.90 to 2.99. Linear partition coefficient (Kd) values were positively correlated with the soil properties, such as clay (R2 =0.90), OC (R2 =0.94) and pH (R2 = 0.45); however, weak correlation was found between Kd and soil sand contents (R2 = 0.12). The leachability model showed potential risk of Pb leaching from silt soil with lowest organic matter content. The findings are of significant importance for understanding potential threats of Pb to the soil ecosystem, groundwater, plants, and humans.