Soil contamination with total petroleum hydrocarbons (TPH) as a result of crude oil exploration and exploitation activities is currently a major environmental challenge. This study proposed diffuse reflectance spectroscopy as a viable technique for rapid assessment of hydrocarbon contamination on oil spill sites in the Niger Delta, Nigeria. Spectroscopy approach was carried out in the laboratory for the prediction of TPH concentrations (mg kg -1 ) in genuine petroleum contaminated soils (fresh wet), as compared with analytically measured TPH concentrations. Very strong positive correlation (r = 0.9686) was achieved between analytically and spectroscopically-predicted TPH (mg kg -1 ). Actual and predicted absorbance (ABS act and ABS pred , respectively) values were determined and appear not to be consistent. However, very strong positive correlation appears when each of parameter was plotted against measured TPH concentration. Diffuse reflectance spectroscopy methodology was found to be as good as the labour-intensive and expensive traditional laboratory analysis of soil PHCs and could be an alternative for laboratory methods and as a viable field-screening tool to enhance risk decision making on-site.

This study assessed the potential of using visible-near infrared diffuse reflectance spectroscopy to determine the effect of tillage (ploughing) on oil-contaminated sites. Crude oil contaminated samples were collected from the Ikarama, Bayelsa State, Niger Delta, Nigeria. 62 and 20 samples were collected from untilled and tilled (ploughed) sites, respectively. All samples were analysed in the laboratory with an Analytical Spectral Device spectrometer with a spectral range of 350 to 2500 nm. Principal component analysis was performed on the soil spectral data using chemometric. Sequential ultrasonic solvent extraction was also carried out followed by gas chromatography coupled to mass spectrometry analysis to validate the visible-near infrared diffuse reflectance spectroscopy sensitivity and ability to detect change due to hydrocarbons profile changes. 27% and 15% concentrations of polycyclic aromatic hydrocarbons were present in the untilled and tilled sites, respectively. Gas Chromatography-Mass Spectrometry analysis also showed that PAHs and allkanes concentrations in the untilled site ranged from 0.05 to 48.493 mg/kg and 0.07 to 528.147mg/kg, respectively. For the tilled (ploughed) site, the concentrations for polycyclic aromatic hydrocarbons and alkanes quantified by Gas Chromatography-Mass Spectrometry ranged from 0.04 to 0.742 mg/kg and 0.06 to 159.280mg/kg, respectively. In addition, non-metric Multidimensional scaling was carried out using Primer version 6 to investigate the statistical significance of the hydrocarbon profiles and concentrations of the samples. To minimise the extent of overlap of the samples, the 82 samples collected were reduced to 49 samples (43 untilled and 6 tilled). Results show that visiblenear infrared diffuse reflectance spectroscopy may be a valuable tool for grouping hydrocarbon contaminated soils into hydrocarbon content and concentrations.

Crude oil contaminated sites delineation by soil quality index (SQI) is presented. This study used SQI proposed by the Canadian Council of Ministers of the Environment (CCME) to delineate three genuinely petroleum-contaminated sites in the Niger Delta, Nigeria to prioritise sites to inform risk decision making and/or remediation. In assessing the potential impact on human health risks at the contaminated sites, soil screening levels (SL) and gas chromatography-mass spectrometry (GC-MS) reference concentrations of total petroleum hydrocarbon (TPH) fractions with higher exposure potential (nC 10 -nC 16 , nC 16 -nC 35 , nC 35 -nC 40 ), and risk indicator compound (benzo[a]pyrene) were used in calculating the SQI scores. The sites were assessed by scoring them on a scale spanning from 0 to 100, where 0 indicates a very high level of human health risks and 100 indicates no action is required. The following results were obtained: (a) Site 1, SQI=36.9. This indicates high priority for remediation; (b) Site 2, SQI=49.1, which implies there is high priority for remediation and (c) Site 3 (SQI=45), which means site 3 requires high priority for remedial action. Thus, SQI method can be used to prioritse crude oil contaminated sites to enhance risk classification and decision-making and provide further insight to the contaminated land sector.