Remediation of Lead-Contaminated Soil by Using Saponin Derived from Sapindus Mukorossi

Lead (Pb) contamination in soils is a major global concern for both humans and the environment. Saponin, a plant-based based and environment-friendly surfactant was used for remediation of Pb-spiked garden soil to test its effectiveness and suitability for Pb removal. A Box-Behnken design was designed to optimise the washing conditions using the following variables: soil type (100% topsoil; 50% topsoil/50% sand; 20% topsoil/ 80% sand); pH of the washing solution (2; 3.5; 5); and saponin concentration (1%; 3%; 5%). The results showed that optimum removal efficiency of 58.69% was achieved with saponin, while distilled water removed 3.92% Pb in a single wash. Saponin was found to be statistically more effective than distilled water (P< 0.05); an optimum pH of 3.5 significantly increased Pb removal efficiency (P<0.05). The washing process was found to cause slight surface erosion and weathering of the soil grains.