Pollution Levels and Chemical Remediation of Metal-Contaminated Surface Dust Using Soil Washing Techniques

Metal contamination in industrial and urban surface dust (SD) poses significant risks to both human health and ecological systems. Hence, it is essential to identify and quantify the sources of pollution to support improved surface dust and soil management strategies. In this study, 22 surface dust samples were collected from the Bhiwadi Industrial Cluster (BIC) to evaluate total metal concentration, their pollution levels and remediation of metal form surface dust through soil washing technique by using various soil organic and inorganic agents. In the soil washing technique, the removal of metals was studied by using organic acids (OA) like acetic acid (AA), citric acid (CA), malonic acid (MA), sodium citrate (SC) salt, ethylenediaminetetraacetic acid (EDTA) and combining organic acids (AA+CA+MA) assisted with the ultrasonic process. For investigating removal efficiency, OA and SC salt were employed at 0.2 M concentrations, whereas EDTA and a combination of OAs were used at 0.1 M concentrations. Results showed that the average concentrations of Cd, Cr, Cu, Fe, Mn, Ni, Pb, V, and Zn in surface dust samples were 44.4, 172, 40, 3.6, 11, 10, 29, 2, and 17.7 times higher than their respective background values in the Upper Continental Crust (UCC). SD samples showed none to very strong contamination (Contamination Factor: CF >> 6) and the Pollution Load Index (PLI) exceeded unity, indicating a deterioration of soil quality. Geo-accumulation index in SD samples was in extremely high contaminated category for Cd, Cr, Cu, Mn, Ni, Pb and Zn and in the moderate category for Fe and V. The soil washing results suggested that a significant amount of metal can be removed from contaminated soils through washing techniques. The average metal removal percentage ranged from 0.01 to 8% (V = 0.01% and Cd = 8%) in AA, 0.4 to 17.2% (Fe = 0.4% and Cd = 17.2%) in CA, 0.02 to 11.7% (Cr = 0.02% and Pb = 11.7%) in EDTA, 0.8 to 18.1% (Fe = 0.8% and Cd = 18.1%) in EDTA, 0.02 to 1.1% (Cr = 0.02% and Cu = 1.1%) in SC and 1.7 to 24.15% (Cr = 1.7% and Cd = 24.1%) in the combination of OAs. Combining washing agents can markedly increase the removal efficiency as compared to single OA and EDTA, except for Pb. Metals can be removed efficiently by increasing the washing agent concentration, contact time and ultrasonic assistance. Therefore, soil washing might be an effective technique for metal remediation in surface dust/soils before disposing in open areas.