Rapid estimation of heavy metals in crude oil contaminated soils by X-ray fluorescence (XRF) spectroscopy

Abstract

Crude oil exploration and exploitation activities in the Niger Delta, Nigeria have caused the contamination of numerous land sites. A total of 45 sub-surface soil samples were collected from three genuinely crude-oil spill sites and their heavy metal concentrations were measured using X-Ray fluorescence spectroscopy. The range of measured heavy metal concentrations (mg/kg) in the three study sites are as follows: chromium (Cr) 54-75, copper (Cu) 5.4-16.6, iron (Fe) 14841-23404, lead (Pb) 13.5-21.4, manganese (Mn) 158-555, zinc (Zn) 32.6-47.2 in Site 1; Cr (35-66), Cu (5-16.1), Fe (10166-20967), Pb (12-17.8), Mn (209-440), Zn (17.6-33.6) in Site 2; and in Site 3: Cr (32-115), Cu (6.5-20.8), Fe (7538-22800), Pb (12-135), Mn (98-338), Zn (19.9-177). The trend of heavy metals contamination in the three sites are as follows: Fe > Mn > Cr > Zn > Pb > Cu. Their mean concentrations were relatively higher than background concentrations of heavy metals in soils previously reported in same region. Using the contamination factor (CF), the intensity of heavy metal (Mn, Cr, Zn, Pb, and Cu) contamination in soils from the three oil spill sites were evaluated and compared. The index showed Cr > Mn across the three sites, which was highest in site 1 and least in site 2. The trend of CF varies for the other metals. The high values of CF for Mn and Cr show that Mn and Cr have extreme level of contamination while Cu, Pb, and Zn lie within the range of moderate level contamination. Furthermore, statistical analyses shows significant (p < 0.05) correlation between the concentrations of the metals, which indicates the link between the metals. Thus, crude-oil spill may be the common denominator for the heavy metal pollution in the study locations. Based on the contamination indicator parameter, the soils of the studied sites are threatened by contamination of Cr and Mn.