Document Type : Research Paper
Abstract
Decades of crude oil exploration and exploitation in the Niger Delta region of Nigeria have left agricultural soils heavily laden with hydrocarbons, posing serious ecological and public health risks. Before any bioremediation strategy can be designed, the contaminated soil itself needs to be properly characterised. In this study, the physicochemical, microbiological, and contaminant-loading properties of a composite soil assembled from five historically crude oil-impacted sites in Delta and Rivers States, with contamination histories ranging from 4 to over 40 years, were examined. The results show that the composite soil was strongly acidic (pH 4.89 ± 0.05), with low electrical conductivity (162.88 μS/cm), low moisture content (2.25%), and a total organic carbon content of 3.33%. Benzo(a)pyrene and anthracene were the dominant polycyclic aromatic hydrocarbons (PAHs) detected, at mean concentrations of 20.36 mg/kg and 1.43 mg/kg, respectively. Both PAHs were found to be above the maximum permissible limits set by the Canadian Council of Ministers of the Environment (CCME). Heavy metal analysis by inductively coupled plasma-optical emission spectrometry (ICP-OES) revealed particularly high lead concentrations, reaching 456.67 mg/kg, nearly three times the 164 mg/kg limit set by Nigeria's National Environmental Standards and Regulations Enforcement Agency (NESREA). Four indigenous bacterial strains capable of utilising anthracene and benzo(a)pyrene as sole carbon sources were isolated and identified by 16S rRNA gene sequencing: Lysinibacillus fusiformis, a member of the Bacillus cereus group (B. paramycoides/tropicus/cereus), a member of the Bacillus subtilis group (B. aerophilus/aerius/stratosphericus), and Streptomyces albidoflavus. Together, these findings give a detailed picture of contamination at these sites and establish a baseline for future bioremediation efforts, particularly the development of locally derived biosurfactants.
