Development of Visible/Near-Infrared Hyperspectral Imaging for the Prediction of Total Arsenic Concentration in Soil

Soil total arsenic (TAs) contamination caused by human activities-such as mining, smelting, and agriculture-is a problem of global concern. Visible/near-infrared (VNIR), X-ray fluorescence spectroscopy (XRF), and laser-induced breakdown spectroscopy (LIBS) do not need too much sample preparation and utilization of chemicals to evaluate total arsenic (TAs) concentration in soil. VNIR with hyperspectral imaging has the potential to predict TAs concentration in soil. In this study, 59 soil samples were collected from the Daye City mining area of China, and hyperspectral imaging of the soil samples was undertaken using a visible/near-infrared hyperspectral imaging system (wavelength range 470-900 nm). Spectral preprocessing included standard normal variate (SNV) transformation, multivariate scatter correction (MSC), first derivative (FD) preprocessing, and second derivative (SD) preprocessing. Characteristic bands were then identified based on Spearman's rank correlation coefficients. Four regression models were used for the modeling prediction: partial least squares regression (PLSR) (R-2 = 0.71, RMSE = 0.48), support vector machine regression (SVMR) (R-2 = 0.78, RMSE = 0.42), random forest (RF) (R-2 = 0.78, RMSE = 0.42), and extremely randomized trees regression (ETR) (R-2 = 0.81, RMSE = 0.38). The prediction results were compared with the results of atomic fluorescence spectrometry methods. In the prediction results of the models, the accuracy of ETR using FD preprocessing was the highest. The results confirmed that hyperspectral imaging combined with Spearman's rank correlation with machine learning models can be used to estimate soil TAs content.