Occurrence, Origin and Risk Assessment of Trace Metals Measured in Petroleum Tank-farm Impacted Soils

Abstract

ABSTRACT The objective of this study was to determine the occurrence, origin, and risk of Cadmium (Cd), lead (Pb), chromium (Cr), nickel (Ni), copper (Cu), manganese (Mn), zinc (Zn), and iron (Fe) in soil profiles from petroleum tank-farms in Western Delta, Nigeria. The soil samples were digested with aqua-regia, and the concentrations of the metals were determined using an atomic absorption spectrophotometry. The mean concentrations of metals varied for all sites and depths and ranged from 1.86 ± 1.73 mg kg−1 (Cd) to 3535 ± 1802 mg kg−1 (Fe). The mean concentrations of Cd, Pb, and Cu exceeded the Dutch and DPR-EGASPIN target limits in 80%, 5%, and 45% of the samples, respectively. Concerning soil depths, the metals showed irregular occurrence and exhibited concentration load in the order of subsoil > bottom soil > topsoil. The results also showed that the metals had the highest concentrations at site SS1, SS2, SS4, SS6, SS8, SS9, SS10, and SS11. The linear regression between TOC and metals indicates a weak correlation. The ANOVA shows that there is a significant variation for the total concentrations of the metals concerning soil depths. The PCA, enrichment factors and the geo-accumulation index suggest that the trace metals originated from the anthropogenic and geologic means. The average contamination factor and the ecological risk factor followed the order: Cd > Pb > Cu > Zn > Mn > Cr > Ni, and Cd > Pb > Cu > Ni > Zn > Cr > Mn, respectively. The non-carcinogenic risk shows no adverse non-carcinogenic health effects for human exposure to metals. The total cancer risk values are within acceptable safety limits. The results of the heavy metals from this study suggest that soils from the petroleum tank farms require sustainable remediation measures.