Assessment of Trace and Major Elements Contamination in Waste Soils: Leaching Potential from Active and Closed Landfills in Lagos, Nigeria

Abstract

Lagos with a population of about 21 million people is the commercial capital of Nigeria. About nine million metric tonnes of wastes were deposited into various landfill sites in Lagos in 2014. Many existing and abandoned landfills pose serious detrimental health impacts to the environment. This study evaluates the trace and major elements (Zn, Pb, Ni, Cd, Cu, Mn, Fe, Ca, K and Na) composition of waste soils from five landfills (three closed and two active landfills) in Lagos and the leaching potential of these elements from waste soils with a view to assessing the potential contamination of the groundwater resources near the landfill sites. The US EPA Toxicity Characteristics Leaching Procedure (TCLP) was employed as the leaching test method. The concentrations of trace and major elements in waste soils were determined. TCLP extracts were also analyzed for the selected trace and major elements. The concentrations of Zn in all the landfill sites (closed and active) exceeded the LASEPA regulatory limit for soil. Worthy of note was the high concentration of Pb in waste soils from Abule-Egba (closed landfill). The concentrations of the analyzed metals in TCLP extracts were found to be lower than the allowable concentrations (especially Cd, Pb and Ni) based on the TCLP standard. With the exception of Zn and Ni in Abule–Egba landfill where a leaching rate of about 24% was observed the leaching rate of trace metals were higher in active landfill sites than the closed landfills. Considering the high leaching rate of Zn and Ni in Abule-Egba landfill and the considerable leaching potential of other trace metals, it is recommended that Abule-Egba landfill, despite its current closure to waste disposal activities, should be more closely monitored in order to prevent possible contamination of groundwater resources around the landfill.

Keywords: Landfill, Solid waste, waste soil, leaching potential, trace and major elements, Lagos