An assessment of trace metal pollution indicators in soils around oil well clusters

Abstract

Due to the metallic ion constituents of crude oil, environmental levels of toxic metals are often exacerbated when oil is spilt. Biseni community plays host to numerous oil production companies in Bayelsa state, Nigeria. However, the tendency for this clan to be flooded, particularly owing to its lowland features has continued to negatively impact on the environment. Sometimes, floods are accompanied by spilt residual oil that encroach living areas, thus leading to the contamination of open water bodies, underground water resources, and fish and crop farms. This study surveyed the impact of oil seepages from oil well clusters on the overall soil quality by applying trace metal pollution indicators. Trace metals were analyzed by atomic absorption spectrometry, and concentration ranged from 5893.0-6263.8 mg/kg, 0.03–11.52 mg/kg, 3.15–6.46 mg/kg, 4.46–58.64 mg/kg, 13.61–29.83 mg/kg, 0.23–0.73 mg/kg, 8.32–20.69 mg/kg, and 4.24–9.31 mg/kg for iron, copper, nickel, lead, zinc, cadmium, chromium and cobalt respectively. Concentrations were within target limits stipulated by the Department of Petroleum Resources, Dutch standard limit and World Health Organization. Zinc and chromium showed the strongest correlation (r = 0.92, p < 0.05) in the study area, whilst one-way ANOVA revealed equality (p > 0.05) among the different sampling points. This is evidence that the field area is affected by similar contamination source. Whereas, the micro-pollutant metals depicted significant variability (p < 0.05), probably due to the outlier concentration of iron. Overall, lead was the most contaminating metal, while location BNS2 (0.3m) was the most considerably contaminated area. Enrichment factor revealed the anthropogenic origination of lead. Index of geo-accumulation of lead ranged from moderate to heavy contamination, with lead recording very high contamination factor, and the degree of contamination depicting considerable risk, especially at the top soil. Pollution load index showed most contamination (moderately polluted) at BNS2. Quantification of contamination showed relative contamination for most locations, whereas potential ecological risk index mostly depicted low risk, apart from the exhibition of moderate risk of lead and cadmium at BNS2. Conversely, sum of pollution indices and risk index revealed low contamination and low risk respectively.