Environmental Implications of Heavy Metals in Spent Oil - Contaminated Soil of Kaduna Northern Guinea Savanna Ecozone of Nigeria

Abstract

Pollution of the city/urban soil by contaminants arising from spent oil and other sources is considered a serious problem. Lead (Pb) has long been known as a potential hazard to health, especially in cities where users of spent oil, especially mechanics, indiscriminately dump the oil in the farmlands, which releases high quantities of lead into the soil and environment. Consequently, this study assessed heavy metals in soil samples polluted with spent oil in the Kaduna Northern Guinea Savanna ecozone of Nigeria. Soil samples were collected from six (6) different farmlands (Mando, Rigachuku, Panteka, Sabo-Birnin, Buruku, and Jaji) where spent engine oil was frequently dumped by mechanics near auto mechanic workshops and where mechanic activities had been carried out for a period of 5 – 7 years using a subjective sampling method. Topsoil only was collected from each site; these soil samples were thoroughly mixed and labeled as polluted samples (PS). Topsoil samples were equally collected from six (6) other farms located within the same sites where no auto mechanic workshops had been sited before, nor had any mechanic activities been carried out. These samples were bulked and also labelled as an unpolluted sample (US). Soil heavy metal analysis was carried out using an Atomic Absorption Spectrophotometer (Model Buck 210 VGP) following Association of Official Analytical Chemists (AOAC) procedures. The results show increases in Cd (100%), Pb (71.94%), Sn (65.91%), Cr (63.83%), Hg (58.14%), and Ni (63.93%), while silver (Ag) remains undetected in both PS and US. In conclusion, the soil absorbs and accrues heavy metals above the allowable limits of the WHO/FAO/EEA permissible limit standard, respectively. In view of these negative effects, the general public, especially the mechanics, should be enlightened about the dangers involved in indiscriminate dumping of spent oil on farmlands, from a health and environmental point of view, with convincing reasons, while it needs to be controlled.