Contamination Indices and Heavy Metal Concentrations in Soils in Okpoko and Environs, Southeastern Nigeria

Author(s): Nwankwoala HO, Ememu AJ

This study is carried out to assess the soil and ground water quality in Okpoko and Environs in Anambra State. Fifteen soil and groundwater samples were collected and analyzed for physico-chemical, heavy metals and hydrocarbon content. Soils were sampled at 15cm and 30 cm depth. Heavy metals in soil and groundwater were analyzed using Atomic Absorption Spectrometer. Grain size analysis shows that top-soils (0-15 cm) and sub-soils (15-30 cm) in the area are predominantly sands (>70%), and soil classification scheme based on SAR (<13), pH (<8.5) and EC (>4 μS/cm) shows that the soils are saline. Apart from Ni, all the other metals show concentrations that decrease with depth. Total Petroleum Hydrocarbons (TPH) ranges from 109.43 to 2112.64 mg/kg and 105.57 to 1747.82 mg/kg in topsoil and sub-soils in the area. The average TPH content is 654.01 ± 582.12 and 568.27 ± 502.11 mg/kg in topsoil and sub-soils respectively, and 54.43 and 16.63 mg/kg at control site. The TOC content is higher in the vicinity of the fuel filling and service station than at the control site which is an indication of anthropogenic influences. The TPH content generally decreases with depth and is lower at the control than at the vicinity of the fuel filling and service station. Apart from Fe and Mn, all other metal concentration exceeds those of the control. The metal concentrations were within DPR regulatory limits for safe agricultural soils. Assessment of anthropogenic influences on the soil quality in the area with the control site as baseline was accomplished using soil quality models including: Contamination Index (CI), Pollution Load Index (PLI), Modified Contamination Degree (mCD), Geo-accumulation Index (Igeo), and Nemerov Integrated Pollution Index (NIPI) which shows that the soils are heavily polluted from the activities at the fuel filling and service stations in the area. Regular soil and groundwater assessment is recommende

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