Hydrogeochemical Assessment of Metals Contamination in an Urban Drainage System: A Case Study of Osogbo Township, SW-Nigeria

Abstract

With increasing urban population, attention had been focused on environmental degradation of urban drainage system with respect to trace/heavy metal contaminations. Such concerns underlie the ever-increasing impacts of urbanization and industrial activities on urban watershed in the developing regions of the world, especially in areas with inadequate land-use plan and poor waste disposal and management practices. Hence, this study highlights the hydrogeochemical assessment of surface water and bottom-sediment samples from an urban drainage system in Osogbo Township, SW-Nigeria with respect to trace metals contaminations.The results show that the surface water samples have generally low TDS with average value of 362mg/l, while the average dissolved concentrations of the trace metals (Cu, Pb, Zn, Ni, As and Cr) vary from 0.01 to 0.5mg/l. Cu, Cr and As exhibit concentrations similar to the local background concentrations (LBC) in the pristine stream water with low single metal contamination factor (CF ≈ 1). Pb, Zn and Ni are 5 folds enriched with contamination factor (CF) of >5 indicating moderate to high contamination. For the sediment phase, the adsorbed concentrations of the trace metals (Cu, Pb, Zn, Ni, As, Cr and Co) vary between 0.1 to 3.1mg/kg. These represent about 1 to 3% of the respective total metal concentrations with average values of 18.2-533.4mg/kg. Also low anthropogenic factor, AF (0.002 to 0.08) and mostly negative values (-5 to -15) of Mueller's geo-accumulation index (Igeo) for adsorbed metal contents in the sediments suggest dominant geogenic controls.However, the total metals concentrations in the sediment phase have high estimated AF of 1.1 to 9.3 and positive values of the estimated Igeo (0.9-2.0) and metal contamination index (MCI) of 2.5-8.3. All these suggest a medium to high level enrichment (of 2 to 10 factor) for most of the metals with respect to the local background concentration (LBC) in the basement bedrock units (with the exception of Cr and Ni). This is consistent with the preferential metal enrichment in the sediment phase as indicated by the estimated partitioning/distribution coefficient, K d of >1 exhibited by the total metal concentrations in the stream sediment. Nonetheless, the correlated high peaks of electrical conductivity of the stream water samples and adsorbed concentrations of some trace metals within the urban stretches are indications of point source inputs of untreated sewage into the drainage system.

Hydro-geochemical and Geophysical Study of Groundwater in the Suburb of Osogbo, South Western Nigeria

“…The TDS measurements vary from 61.5 to 308.25 with average values of 172.31 while the conductivity measurements vary from 82.00 μs/cm to 459.00 μs/cm with average value of 249.95 μs/cm ( Table 1). The results obtained from these analyses are in conformity with the works of Tijani et al [12,13] …”

Evaluation of heavy metal content in Qaroun Lake, El-Fayoum, Egypt. Part I: Bottom sediments

“…The geo-accumulation index (Igeo) is a common criterion used for quantifying the intensity of heavy metal contamination in terrestrial, aquatic and marine environments (Gaur, Sanjay, Pandey, Gopal, & Misra, 2005;Ozkan & Buyukisik, 2012;Tijani & Onodera, 2009). This index is a single metal approach to evaluate the sediment contamination with heavy metals.…”

Ecological vulnerability assessment of trace metals in topsoil around a newly established metal scrap factory in southwestern Nigeria: geochemical, geospatial and exposure risk analyses

“…The climatic condition of the region is classified as humid tropical climate and controlled by the Tropical Maritime and Tropical Continental air masses. The climate is characterized by a dry season, which starts from November to early March, and a rainy season between late March and early November (Tijani and Onodera 2009). This region experiences annual precipitation of 1335 mm (NIMET 2014).…”

“…Geologically, the region is essentially homogeneous; it lies within the Pre-Cambrian Basement Complex of southwestern Nigeria, and belongs to the Pan-African mobile belt east of West African Craton. The dominant basement rocks in the region are schists and migmatites, associated with quartzite ridges forming the characteristic undulating terrain (Tijani and Onodera 2009). The soil of the area is classified as Iwo Association (Smyth and Montgomery 1962; Tijani and Onodera 2009), derived from coarse-grained granitic rocks and gneisses; according to FAO classification (FAO 1990), it is ferric acrisol.…”