Evaluation of heavy metals status and microbiological properties of some oil exposed soils in Obama Flow Station in Bayelsa State, Nigeria

Abstract

Crude oil exploration has been associated with disruptions in soil chemical and microbial balance in oil-producing regions, raising environmental concerns. This study assessed heavy metal contamination and microbiological properties of soils from the Obama Flow Station, Bayelsa State, Nigeria, during the wet and dry seasons of 2022. Soil samples were collected from surface (0–15 cm) and subsurface (15–30 cm) depths across thirteen oil-exposed sites and one control site and analyzed for selected heavy metals and microbial populations. Chromium, cadmium, lead, and nickel were below detection limits (<0.001 mg kg⁻¹) in all samples. Iron was the most abundant metal, with higher concentrations recorded in subsurface soils (705.20 mg kg⁻¹) compared with surface soils (473.04 mg kg⁻¹), with seasonal variation between wet and dry periods. Zinc concentrations remained low, ranging from 0.19 to 0.22 mg kg⁻¹ across depths and seasons. Total heterotrophic bacterial counts were generally higher in surface soils during the wet season (1.80×10⁵–2.90×10⁵ cfu g⁻¹), while fungal counts ranged from 1.40×10⁴ to 2.86×10⁴ cfu g⁻¹. Overall microbial populations were higher in surface soils during the wet season, reflecting seasonal influences. Comparable microbial values in control soils suggest limited alteration of microbial communities due to oil exposure. Overall, the soils showed no significant heavy metal contamination, though continued monitoring is recommended to prevent future accumulation.