Seasonal Variations and Correlation of Heavy Metal Concentrations in Oil-Polluted Soils of the Niger Delta, Nigeria

This study investigated the concentrations and interrelationships of selected heavy metals—iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), cadmium (Cd), chromium (Cr), lead (Pb), and nickel (Ni) in soils collected from three oil-impacted communities (Ayamasa, Ibelebiri, Ikarama) and a control site (Okumbiri) in the three senatorial districts of Bayelsa State, Niger Delta region of Nigeria. Composite oil samples were collected along four line transects measuring 10 by 50 m with allowance of 20 m at two depths (0–15 cm and 15–30 cm) during dry and wet seasons and analyzed using an atomic absorption spectrophotometer following standard digestion protocols. ANOVA in SPSS was used to compare mean values for soil data, and Duncan’s multiple range test was used to differentiate the generated mean values. Results revealed significantly elevated heavy metal concentrations in the oil-impacted sites compared to the control, particularly in surface soils. Across all sites and seasons, Fe ranged from 212.26 to 1,248.96 mg/kg, Mn from 29.16 to 250.18 mg/kg, Cu from 0.18 to 7.05 mg/kg, Zn from 1.53 to 105.03 mg/kg, Cd from 0.32 to 8.43 mg/kg, Cr from 0.44 to 14.02 mg/kg, Pb from 1.55 to 28.06 mg/kg, and Ni from 1.23 to 15.20 mg/kg. The dry season generally exhibited higher concentrations, indicating reduced leaching compared to the wet season. Correlation analyses showed strong positive associations among most metals, particularly in the dry season, suggesting common anthropogenic sources likely linked to oil exploration and related activities. These findings highlight the environmental risks posed by oil pollution in the region and the need for proactive soil remediation and regulatory monitoring.