Abstract
The in situ determination of metals in plants used for phytoremediation is still a challenge that must be overcome to control the plant stress over time due to metals uptake as well as to quantify the concentration of these metals in the biomass for further potential applications. In this exploratory study, we acquired hyperspectral images in the visible/near infrared regions of dried and ground stems and roots of Jatropha curcas L. to which different amounts of copper (Cu) were added. The spectral information was extracted from the images to build classification models based on the concentration of Cu. Optimum wavelengths were selected from the peaks and valleys showed in the loadings plots resulting from principal component analysis, thus reducing the number of spectral variables. Linear discriminant analysis was subsequently performed using these optimum wavelengths. It was possible to differentiate samples without addition of copper from samples with low (0.5–1% wt.) and high (5% wt.) amounts of copper (83.93% accuracy, >0.70 sensitivity and specificity). This technique could be used after enhancing prediction models with a higher amount of samples and after determining the potential interference of other compounds present in plants.
Highlights
Mining and mineral processing results in soils containing all sorts of waste materials
The smoothed spectra and the pre-treated with Standard Normal Variate (SNV) and Multiplicative Scatter Correction (MSC) were very similar (Figure 1a,b,e, respectively), showing peaks around 1214, 1728, 1918 and 2100 nm, which correspond to stretching vibrations of C-H in the first and second overtone, a stretching vibration of C=O in the second overtone of amides and a combination of O-H deformation and C-O stretching vibration, associated to starch, respectively
The pre-treatments that better succeeded in separating samples according to their groups were the first derivative, a combination of SNV + first derivative and the (Figure 3a–c, respectively)
Summary
Mining and mineral processing results in soils containing all sorts of waste materials These mining operations are one of the main anthropogenic sources of heavy metals in soils [1]. The high concentration of heavy metals in mining soils leads to unbalanced textural class, absence or low presence of soil structure, anomalous chemical properties, decrease in the content of essential nutrients, disruption of biogeochemical cycles, difficulty in rooting, low water retention and presence of toxic compounds [2]. These heavy metals represent serious problems for the development of vegetation cover. In addition to the beneficial effects on the soil, the biomass obtained after phytoremediation (stems, leaves and even roots) can be used as a potential source of energy or for the production of catalytic biochars [3]
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