Soil contaminated with chromium by tannery sludge and identified by vis-NIR-mid spectroscopy techniques

Soil contamination is an ever-growing concern and demands efficient methods for diagnosis of areas under suspected contamination. Spectroscopy reflectance vis-NIR has been shown to be a reliable and environmentally friendly method for the rapid detection and monitoring of soil properties. Despite the use of vis-NIR it is necessary to test the effectiveness of other wavelengths (mid-IR 4000–400 cm−1). We aim with this study to (1) evaluate the contamination of Cr applied by tannery sludge and CrCl3·6H2O in tropical soils through sequential extraction procedures and spectroscopy techniques; (2) identify parameters of soil spectral variation (vis-NIR-mid) associated with Cr and explore their viability in the evaluation of contaminated soils; and (3) investigate the feasibility of using soil spectral data and chemometrics methods to predict Cr in soils. Results indicate that metal adsorption to soil constituents caused expressive changes in soil spectral curves, showing differentiation between highly contaminated soils and those that are relatively contaminant-free. Cr content can be predicted by spectroscopy reflectance in vis-NIR-mid data. The mid-IR models of Cr outperformed vis-NIR. Organic matter played a more important role in determining soil spectral signatures than the mineralogical characteristics of soils, especially in those with high organic carbon content.