Heavy Metal Distribution and Assessment of Ecological Risk in Surface Waters and Sediment within the Flow stations in Kolo Creek, Nigeria

Abstract

The environmental quality report of Kolo creek is constantly been influenced by daily human activities as well as oil and gas activities in the region. In view of this, the ecological risk of heavy metals released into the environment was evaluated. Samples of water and sediment were randomly collected from seven spatially varying locations A to G across the stretch of water course. Locations A and G represent 500 metres up and downstream of crude oil flow station at Imiringi community respectively, while Points B to F reflect samples around the midstream locations where oil activities are most concentrated. Each field location was sampled in triplicate to ensure data repeatability. Samples were collected in the dry season month of November 2017. The heavy metal loading status of Kolo creek surface water and sediments were determined using the atomic absorption spectrophotometer – GBC Avanta PM A6600 model. Surface water metals ranged from <0.001 to 0.007 mg/l, <0.001 to 0.023 mg/l and 0.807 to 3.450 mg/l for lead (Pb), nickel (Ni) and iron (Fe) respectively, while cadmium (Cd) was reportedly below measurable detection limit. Apart from iron, with concentrations exceeding DPR limit of 1.0 mg/l at locations B, C, F and G, all other metals were within regulatory limit. Sediment metal concentrations ranged from 0.120 to 0.480 mg/kg, 1.180 to 7.303 mg/kg, 3.150 to 8.803 mg/kg and 1,619.55 to 4,183.60 mg/kg for Cd, Pb, Ni and Fe respectively. All sediment metals were reportedly within DPR limit of 0.8, 85 and 35 mg/kg for Cd, Pb and Ni respectively. Heavy metal pollution indices such as degree of contamination (CD), pollution load index (PLI) and index of geoaccumulation (IGEO) were used to further evaluate the potential risk of residual metals. Test metals were qualified as tending from non-contamination to moderate/considerable contamination. Sample locations of potential cadmium and lead hazard were identified as locations A and B, for water and sediment respectively. Consequently, the results of positive contamination factor and negative geoaccumulation index in surface waters and sediment is proof that lead and cadmium micropollutants are from anthropogenic sources. Keywords: Kolo creek, index of geoaccumulation (IGEO), degree of contamination (CD), pollution load index (PLI), Department of Petroleum Resources (DPR).