Evaluating heavy metal contamination from leachate percolation for sustainable remediation strategies

Abstract

Leachate is an extremely contaminated liquid generated as rainwater permeates through the open dumps and contains significantly high concentrations of heavy metals, organic pollutants and hazardous compounds. This study focused on assessing the concentration of heavy metals in leachate and their potential to contaminate soil near the Lohsar dumpsite in Rawalpindi. The leachate samples were collected from inside the dumpsite and the soil samples were collected at varying distances (25, 50, 75, 100 and 125 m) from the dumpsite, and a control was selected 1 km away. The samples were also collected vertically at depths of 0.2, 0.4, 0.6, 0.8 and 1 m from each of the sampling points. The leachate analysis from Lohsar dumpsite revealed elevated levels of organic and inorganic constituents surpassing acceptable limits. Except for Zinc (Zn) (2.26 mg l^-1), Chromium (Cr) (0.52 mg l^-1), and Nickel (Ni) (0.83 mg l^-1), the concentrations of other heavy metals including Cadmium (Cd) (0.43 mg l^-1), Copper (Cu) (1.73 mg l^-1), Lead (Pb) (1.38 mg l^-1) and Iron (Fe) (69.1 mg l^-1), exceeded the appreciable limits as prescribed by Pakistan National Environmental Quality Standard (NEQS) for municipal and industrial effluent discharge. Soil analysis indicated silty clay to silty clay loam composition, with pH, Electrical conductivity (EC), and organic contents decreasing with distance from the dumpsite, while bulk density increased. Concentrations of heavy metals, including Fe (18,330–54,320 mg Kg^-1), Pb (69.4–909 mg Kg^-1.), Cu (93.8–447.4 mg Kg^-1), Ni (31–248.9 mg Kg^-1), Cr (61–436.6 mg Kg^-1), Zn (171–1283.2 mg Kg^-1), and Cd (0.2–45.1 mg Kg^-1), exceeded the World Health Organization (WHO) appreciable limits for agricultural soils, with higher levels near the dumpsite. The geoaccumulation index (I_geo) suggested moderate contamination, while contamination factor (CF) indicated high levels for Cd and Pb. Pollution load index (PLI) depicted severe pollution, affirming anthropogenic contamination and a significant contribution from leachate. Pearson correlation analysis corroborated leachate-associated contamination. Mitigating measures are recommended, including efficient waste disposal and landfill practices, leachate treatment, continuous monitoring and adherence to pollution control standards.