Rapid prediction of total petroleum hydrocarbons in soil using a hand-held mid-infrared field instrument

•We present a novel field technique for the rapid prediction of TPH.•Accurate predictions of TPH were obtained.•Technique tested across different soil types and TPH concentrations.•Technique suitable for commercial use and number of applications.•Results pave the way for using hand-held mid-infrared instruments in the field.

This manuscript reports on the performance of a hand-held diffuse reflectance (mid)-infrared Fourier transform (DRIFT) spectrometer for the prediction of total petroleum hydrocarbons (TPH) in three different diesel-contaminated soils. These soils include: a carbonate dominated clay, a kaolinite dominated clay and a loam from Padova Italy, north Western Australia and southern Nigeria, respectively. Soils were analysed for TPH concentration using a standard laboratory methods and scanned in DRIFT mode with the hand-held spectrometer to determine TPH calibration models. Successful partial least square regression (PLSR) predictions, with coefficient of determination (R2) ~0.99 and root mean square error (RMSE) <200 mg/kg, were obtained for the low range TPH concentrations of 0 to ~3,000 mg/kg. These predictions were carried out using a set of independent samples for each soil type. Prediction models were also tested for the full concentration range (0–60,000 mg/kg) for each soil type model with R2 and RMSE values of ~0.99 and <1,255 mg/kg, respectively. Furthermore, a number of intermediate concentration range models were also generated for each soil type with similar R2 values of ~0.99 and RMSE values <800 mg/kg. This study shows the capability of using a portable mid-infrared (MIR) DRIFT spectrometer for predicting TPH in a variety of soil types and the potential for being a rapid in-field screening method for TPH concentration levels at common regulatory thresholds.A novel hand-held mid-infrared instrument can accurately detect TPH across different soil types and concentrations, which paves the way for a variety of applications in the field.

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