Study of the Suitability of NIR Spectroscopy for Monitoring the Contamination of Soils with Oil Products

Abstract

The suitability of near-infrared (NIR) spectroscopy for monitoring the contamination of soils with oil products has been studied with a view to expanding the application range of NIR analyzers used in the agrochemical laboratories of Russia. Experiments have been performed on arable soils of various types and varieties differing in texture and the contents of humus and nutrients sampled from different regions of European Russia and artificially contaminated with commercial oil products (gasoline, kerosene, diesel fuel, and motor oil). Laboratory-scale scanning diffusion-reflectance NIR analyzers have been used. It has been shown that the differences in soil types, soil moisture, and humus content, which are reflected in the NIR spectra, affect the results of the NIR analysis of soils. Their effect can be reduced using samples in the entire range of the affecting parameters for the calibration set of NIR analyzers. Using separate calibrations for two soil groups (organomineral and mineral soils) gives better results than the same calibration for all soil types. The effect of particle size distribution can be reduced by unifying the sample preparation procedure used to calibrate the instrument and analyze unknown samples and using spectral derivation. The level at which the soil is supplied with the main nutrients (P, K, Ca, and Mg) has no effect on the results of analysis. The content of a selected oil product in the soil can be determined in the presence of other oil products, if the calibration set of the NIR analyzer includes all expected oil products. The NIR analyzer calibrated for a single oil product will determine the content of all the oil products in the soil. The relatively high determination limit of about 0.2 % and the calibration on a large number of native soil samples have to be taken into consideration. The obtained results showed that NIR spectroscopy is a promising technique for monitoring the contamination of soils with oil products. When the NIR methods are introduced into further laboratories in Russia, based on our results, standardized procedures for sampling, calibration, and analysis can be developed.