Comparative assessment of ethanol leaf extracts of chromolaena odorata, azadirachta indica and persea americana for heavy metal remediation in landfill leachate

Abstract

Landfill leachate constitutes a major environmental challenge because it contains elevated concentrations of heavy metals capable of contaminating surface water, groundwater, and surrounding ecosystems. The present study evaluated the effectiveness of ethanol leaf extracts of Persea americana, Chromolaena odorata, and Azadirachta indica, applied individually and in different combinations, for the removal of heavy metals from landfill leachate. Fresh leaves of the three plant species were collected, air-dried, pulverized, and extracted with ethanol using standard extraction procedures. The extracts were applied to landfill leachate at concentrations of 1, 2, and 3 mg/mL as single, binary, and ternary treatments. Heavy metal concentrations before and after treatment were determined using Atomic Absorption Spectrophotometry (AAS), and the data were analyzed using analysis of variance (ANOVA) at a 95% confidence level. The results shows significant (p < 0.05) reductions in the concentrations of iron (Fe), manganese (Mn), copper (Cu), cobalt (Co), zinc (Zn), lead (Pb), silver (Ag), and nickel (Ni) following treatment with the plant extracts. The heavy metal removal efficiency generally increased with extract concentration and was consistently higher in binary and ternary extract combinations than in single-plant treatments. Among all treatments, the combined extract of P. americana + C. odorata + A. indica at 3 mg/L exhibited the highest remediation efficiency, producing the lowest residual concentrations for most of the metals investigated. Copper and zinc concentrations were reduced to levels below the World Health Organization (WHO) drinking water guidelines, while manganese and lead approached acceptable limits in several combined treatments. Iron concentrations were substantially reduced to values approaching aesthetic guideline limits. However, nickel concentrations remained above the WHO permissible limit in all treatments despite marked reductions, indicating that additional polishing treatment would be required before potable use. This study demonstrates that ethanol leaf extracts of Persea americana, Chromolaena odorata, and Azadirachta indica, particularly when applied in combination, possess environmentally friendly, and sustainable properties for heavy metal remediation of landfill leachate.