Abstract
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 visible-near infrared diffuse reflectance spectroscopy may be a valuable tool for grouping hydrocarbon contaminated soils into hydrocarbon content and concentrations.
Highlights
There are millions of hydrocarbon contaminated soils globally, and upon the pressure on land for food production, increasing pace of urbanization and the associated risk there is emergent need for rapid identification and remediation of these contaminated sites [1,2,3]
The present paper evaluates the potential of vis-NIR diffuse reflectance spectroscopy (DRS) (350-2500 nm) to differentiate two set of samples collected on an oil contaminated site in the Niger Delta region where tillage was applied on one area of the site
This study has provided new window opportunity for grouping hydrocarbon contaminated soils into hydrocarbon content and concentrations by vis-NIR spectroscopy
Summary
There are millions of hydrocarbon contaminated soils globally, and upon the pressure on land for food production, increasing pace of urbanization and the associated risk there is emergent need for rapid identification and remediation of these contaminated sites [1,2,3]. The authors used SUSE-GC as a validating tool and they achieved a coefficient of determination (R2 of 0.77-0.89), residual prediction deviation (RPD of 1.86-3.12), and root-mean-square error (RMSE of 1.16-1.95 mg/kg) for the partial least square (PLS) regression calibration model They recommended that the method may be promising for quick evaluation of the spatial variability of polycyclic aromatic hydrocarbons (PAHs) in petroleum-released soils, and assist site risk assessment. With PLS regression and boosted regression tree (BRT) calibration models, the authors obtained R2 of 0.64 and RPD of 1.70 as best TPH from the field-moist scans, since the air-dried scans yielded 0.57 and 1.25 for R2 and RPD, respectively They concluded that within the visible and near infrared range, there is the possibility of vis-NIR DRS as proximal soil sensing tool for petroleum hydrocarbons. Soil samples were analysed using SUE-GC to characterise the hydrocarbon profiles and concentrations in the oil-contaminated soil samples and validate the visNIR DRS sensitivity and ability to detect change due to hydrocarbons profile changes
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