環境および分析毒性学

Geochemical Study of Soils, Road Dust and Stream Sediments around Ijebu-Ode, Southwestern, Nigeria

Abstract

Olatunji Akinade S and Olisa O

The study was aimed at an assessment of the heavy metal distribution in soils, road dust and stream sediments of the city of Ijebu-Ode in order to evaluate the effects of increased urbanization on the quality of the environmental media89 samples comprising 30 topsoil, 54 road dust and 5 stream sediments samples were collected. The samples were air-dried, disaggregated and sieved for the fine fractions (< 75 μm). Portion of the samples were soaked in deionized water for forty-eight hours in the laboratory and the resulting solution was measured for Electrical Conductivity (EC), pH and Total Dissolved Solids (TDS) using standard digital probes. 0.5 g of the fine fractions of each sample was subsequently digested using hoy aqua-regia and analyzed for elemental concentration using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The sieve analysis showed that the soils in the area are silty-sands in nature. The measured pH ranges from (6.1 to 7.6); (6.1-7.6) and (7.0-7.2) for Soil, road dust and stream sediments respectively. The EC ranges from (1-131 μS/cm); (6-27 μS/cm) and (24-387 μS/cm) in soil, stream sediments and in road dust while the TDS ranges from (0.4-89 mg/l); (3-16 mg/l) and (13-248 mg/l) in soils, stream sediments and in road dust. The elemental analysis revealed the following trends for selected metals in soils, sediments and road dusts respectively Cu (9.0-23.0, 12.0-1170 and 7.0-37.0); Pb (11.0-1056, 14.0-679.0 and 16.0-127.0); Zn (15.0-348.0, 86.0-730.0 and 36.0-412.0); Ni (6.0-12, 5.0-21.0 and 4.0-15.0); V(35.0-121.0, 34.0-113.0 and 29.0-135.0), Cr (25.0-94.0, 34.0-213.0 and 36.0-177.0) and As (2.0-11.0, 2.0-22.0 and Below detection limit, bdl-19.0). Further geochemical evaluation of the metals using metal ratio, geo-accumulation index revealed significant concentration of Cu, Pb, Zn, Ni, As and Cr in the environmental media from within the city Centre and along major roads in the city. Extreme metal loads associated with areas of huge vehicular activities, waste dumps and zones with agricultural activities.