ASSESSMENT OF TOXIC METAL CONTAMINATION OF METAL SCRAP DUMPSITE SOIL IN AKURE SOUTH LOCAL GOVERNMENT AREA, ONDO STATE

Abstract

Soil contaminated with toxic metals can result to very serious environmental hazard. As a result of this problem, the study was carried out to investigate the concentration of heavy metals (Fe, Zn, Pb, Cu and Cd) and physicochemical properties (pH, Total Organic Carbon and Electrical Conductivity) in Araromi and Gbogi metal scrap dumpsites soil of Akure South Local Government area, Ondo State. A total of 79 soil samples were taken for laboratory analysis, the soil samples were collected at various depths at the dumpsite, and at distances away from the scrap dumpsites, in order to ascertain the concentration and mobility of toxic metals on the dumpsites and surrounding soil. Heavy metals in the waste soils samples were sequentially quantified using atomic absorption spectrophotometry (AAS). Physicochemical properties (pH, total organic carbon and electrical conductivity) of the soils were also determined under standard procedures. Iron, Lead, Cadmium and Copper with concentration of 611.7mg/kg, 200.8mg/kg, 4.9mg/kg and 103mg/kg respectively, all exceeded National Environmental Standards and Regulation Enforcement Agency (NESREA) acceptable limit and index of 2007, except Zinc (229.2mg/kg). For Gbogi soil, none of the heavy metals was above the limit as Iron, Lead, Cadmium, Copper and Zinc showed Concentration of 209mg/kg, 9.2mg/kg, 3.6mg/kg, 0.1mg/kg and 39.7mg/kg respectively. For physicochemical properties of Araromi soil analysed, pH ranged from 4.3-6.6, Total Organic Carbon was between 1.0-4.1(%), Electrical Conductivity varied from 0.4-4.5(μs/cm) while Gbogi soil showed pH range of 7.0-8.8, Total Organic Carbon was between 2.1-6.1(%) and Electrical Conductivity ranged from 1.1-4.4(μs/cm). Besides, concentration of these heavy metals and physicochemical properties of the soils decreased with increasing vertical depth at the dumpsite and horizontal distances away from the dumpsites. The order was Fe>Zn>Pb>Cu>Cd for Araromi metal scrap dumpsite and Fe>Cu>Pb>Zn>Cd for Gbogi. Furthermore, the use of Araromi and Gbogi scrap metal dumpsites should be discontinued and the Mitigating the infiltration of metal leachate of scrap metal yards into soil and putting into consideration geology of the locality, prevalent climatic condition, type of waste generated and nature of settlement, a well designed sanitary landfill should be encouraged. Legislative measures should also be considered in regulation of waste management.