Index model equation analysis: A case study of the risk and source of inorganic contaminants in roadside uncontaminated soil of the Egi oil producing area, Niger Delta

This study examined the sources, health risk and pollution status of selected inorganic contaminants such as iron (Fe), nickel (Ni), cadmium (Cd), cobalt (Co), arsenic (As), manganese (Mn), lead (Pb), copper (Cu), zinc (Zn), and chromium (Cr) in representative roadside uncontaminated soil (n = 72) from the Egi crude oil mining areas (Oboburu, Obagi, and Ogbogu), Niger Delta, Nigeria, using a combination of multiple models (Principle component analysis (PCA), correlation analysis, geo-accumulation index (Igeo), contamination factor (CF), enrichment factor (EF), pollution load index (PLI), cancer risk (CR), hazard quotient (HQ), and metal daily intake (MDIm)). A random sampling method was applied in the sampling and analysis using inductively coupled plasma mass spectroscopy. The result revealed that the mean (mg/kg) for Oboburu, was the highest for Fe (89.95 ± 28.83) and Mn (26.12 ± 7.642), whereas Obagi, had less Fe (28.90 ± 7.601) and Mn (16.80 ± 5.021), and Ogbogu, Fe (44.67 ± 28.15) and Pb (19.38 ± 8.731) was the second highest heavy metal. The order of contamination was F > Mn > Zn > Pb > Cu > Cr > Ni > Cd > Co. The Igeo and CF had cadmium as a metal of concern. The contamination level was low from the PLI estimation. The EF revealed anthropogenic sources for all the metals except for Ni, which was biogenic. The correlations at p < 0.05 and p < 0.01 showed much positive significance amongst the metals. Variations of the cumulative percentages, loading percentages, and eigenvalues from the regression plot gave a coefficients of determination (r²) of 0.9936, 0.9995, and 0.9994, respectively. The PCA indicated that Cd and Ni were of anthropogenic origin; Mn, Fe, and Co were biogenic or natural, and Zn and Pb were of mixed origins. The CR assessment indicated a possible cancer risk due to Cr, Cd, and Ni, and the rest of elements have no carcinogenic risk. These findings suggest there should be regular monitoring, source control, and integrated environmental management of the study area.