IMPACT OF CRUDE OIL REMEDIATION ON SOIL FERTILITY IN KHANA LOCAL GOVERNMENT AREA, RIVERS STATE, NIGERIA 0 0

Abstract

Crude oil contamination degrades soil physicochemical, microbial, and structural properties, yet the effectiveness of remediation exercises carried out in response to oil spillage in Ogoniland, Rivers State, has rarely been evaluated against unimpacted control soils using a common analytical framework. This study evaluated the physicochemical, heavy metal, and microbial properties of crude oil-remediated soils in Kwawa and Kpean communities, Khana Local Government Area, Rivers State, Nigeria, in comparison with adjoining unimpacted soils that served as controls, to ascertain the impact of the remediation exercise on soil fertility. Sixteen composite soil samples were collected from eight sampling stations, three remediated stations and one control station in each community, at two depths (0-15 cm and 15-30 cm), and analysed for physicochemical parameters, heavy metals, polycyclic aromatic hydrocarbons (PAHs), total petroleum hydrocarbons (TPH), and microbial counts following American Public Health Association (APHA) standard methods. Data were analysed using descriptive statistics and one-way analysis of variance (ANOVA) at the .05 significance level, and results were benchmarked against Department of Petroleum Resources (DPR, 2002) and FAO/WHO (2011) limits. Soil pH was acidic (4.99-5.83) and mostly within permissible limits, electrical conductivity (37.62-84.47 microS/cm) remained well below regulatory limits, and cadmium, zinc, and lead concentrations at all stations remained below their respective DPR and FAO/WHO limits, while iron concentrations exceeded the FAO/WHO limit of 200 mg/kg at a minority of stations, including the most contaminated remediated station (381.402 mg/kg). Total PAH and TPH levels were below DPR intervention values at all stations, and total heterotrophic bacteria counts were consistently higher at remediated stations than at controls, indicating active microbial recovery. ANOVA showed statistically significant differences between stations for most parameters (p < .05), except organic carbon, organic matter, and one exchangeable cation at each depth. The study concludes that the remediation exercise has been largely effective in restoring soil quality in the affected communities and recommends that the quality of remediation work be sustained and further improved, with continued monitoring of iron levels at the more contaminated stations.