Diagnostic Screening of Urban Soil Contaminants Using Diffuse Reflectance Spectroscopy

Abstract

There is increasing demand for cheap and rapid screening tests for soil contaminants in environmental consultancies. Diffuse infrared reflectance spectroscopy in the visible–near-infrared (vis–NIR) and mid-infrared (MIR) has the potential to meet this demand. The aims of this chapter are to develop diagnostic screening tests for heavy metals and polycyclic aromatic hydrocarbons (PAHs) in soil using vis–NIR and MIR diffuse reflectance spectroscopy. Cadmium, copper, lead, and zinc were analysed, as were total PAHs and benzo[a]pyrene. An ordinal logistic regression technique was used for predictions in the screening tests and to determine false-positive and false-negative rates. Zinc had the best prediction accuracy (89%) and copper predictions were consistently above 75%. Cadmium and lead were the least well predicted of the heavy metals (67 and 70%, respectively), and PAH predictions averaged 78.9%. MIR analysis (average prediction accuracy of 79.9%) was only slightly more accurate than vis–NIR analysis (average prediction accuracy of 77.1%), but the latter may currently be used in situ, thereby reducing cost and time of analysis and providing diagnosis in real time. Diffuse reflectance spectroscopy in the vis–NIR can substantially decrease both the time and the cost associated with screening for soil contaminants.