Evaluation of Heavy Element Levels in Leachate, Soil and Groundwater in the Lagos Landfill Areas of Nigeria

Landfills imbued with heavy elements are major threats to the environment. To assess anthropogenic enrichment, soil, leachate and groundwater samples were collected from active landfills in Lagos and analysed for some heavy elements. The geology of the sampled areas is essentially that of the Oligocene to Pleistocene Coastal Plain Sands except for those of Epe and Badagry which are Recent Deposits. The groundwater showed a range of values (in mg/l) of: Zn, 0-0.08; Fe, 0.009-1.104; Ni, 0.007-0.039; Cd, 0.013-0.062; Hg, 0.00008-0.00384; Pb, 0.004-0.63; Cr, 0.017-0.075; Mn, 0.01-0.043; As, 0-0.053. From the results, some of the boreholes in Olusosun, Soluos, and the hand-dug well water in Ewu-Epe are unfit for drinking. In soils, concentrations were highest at the top and lowest at base of sampling. Generally, the concentrations of most of the elements decreased with increased distance and/or depth from the landfill soils. These suggest that the landfills contribute significantly to the level of these elements in these environments and imply significant attenuation with depth possibly due to adsorption and/or precipitation. The elevated levels of cadmium and arsenic do not support their use as compost for food cultivation. Also, the presence of arsenic above prescribed limits in the Epe leachate is a major concern because the lithology is sandy, and has a reported depth of about 3 m to the unconfined aquifer that adjoins the Epe Lagoon.