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Heavy metal pollution in farmland soil threatens soil environmental quality. It is an important task to quickly grasp the status of heavy metal pollution in farmland soil in a region. Hyperspectral remote sensing technology has been widely used in soil heavy metal concentration monitoring. How to improve the accuracy and reliability of its estimation model is a hot topic. This study analyzed 440 soil samples from Sihe Town and the surrounding agricultural areas in Yushu City, Jilin Province. Considering the differences between different types of soils, a local regression model of heavy metal concentrations (As and Cu) was established based on projection pursuit (PP) and light gradient boosting machine (LightGBM) algorithms. Based on the estimations, a spatial distribution map of soil heavy metals in the region was drawn. The findings of this study showed that considering the differences between different soils to construct a local regression estimation model of soil heavy metal concentration improved the estimation accuracy. Specifically, the relative percent difference (RPD) of As and Cu element estimations in black soil increased the most, by 0.30 and 0.26, respectively. The regional spatial distribution map of heavy metal concentration derived from local regression showed high spatial variability. The number of characteristic bands screened by the PP method accounted for 10–13% of the total spectral bands, effectively reducing the model complexity. Compared with the traditional machine model, the LightGBM model showed better estimation ability, and the highest determination coefficients (R2) of different soil validation sets reached 0.73 (As) and 0.75 (Cu), respectively. In this study, the constructed PP–LightGBM estimation model takes into account the differences in soil types, which effectively improves the accuracy and reliability of hyperspectral image estimation of soil heavy metal concentration and provides a reference for drawing large-scale spatial distributions of heavy metals from hyperspectral images and mastering soil environmental quality. [ABSTRACT FROM AUTHOR]

Purpose. The problem of heavy metal Cd pollution in the soil is still very serious. The widely used treatment measure is in situ passivation chemical remediation technology. Some studies have shown that the single application of phosphate or silicate can control soil cadmium pollution, but few studies have been conducted on the effect of the thermal activation temperature of nano phosphate and silicate-combined application on the transformation of Cd form in the soil. Materials and methods. Cadmium-contaminated soil was indoor-simulated, after which the 2.0% soil-weight dose of potassium dihydrogen phosphate was mixed with thermal activation nano serpentine or nano zeolite (potassium dihydrogen phosphate: thermal activation nano serpentine or nano zeolite = 1:2) at different temperatures (0, 350, 550, 700, 850 °C) and compared with the simulated cadmium-contaminated soil without adding a mixture of phosphate and silicate; cadmium content in soil was determined by Tessier five-step continuous extraction method after incubating for 0, 7, 14, 28, and 56 d in jars in the constant-temperature box. Results and discussion. Thermal activation temperature of nano phosphate and silicate could reduce the amount of exchangeable Cd content in the soil to a different degree; the content of Cd in carbonate-bound form, Fe–Mn–oxide-bound form, organically-bound form, and residual form increased. The order of effect of nanoscale potassium dihydrogen phosphate and serpentine or zeolite thermal activation temperature on remediation of Cd contaminated soil is nPS700-2.0 > nPS550-2.0 > nPS850-2.0 > nPS350-2.0 > nPS0-2.0, nPF700-2.0 > nPF550-2.0 > nPF850-2.0 > nPF350-2.0 > nPF0-2.0 (n, P, S, and F represent nanometer, KH2PO4, serpentine, and zeolite, respectively; 0, 350, 550, 700, and 850 represent different activation temperatures T); 700 °C treatments performed better than other thermal activation temperature treatments, and nPS700-2.0 was better than nPF700-2.0. Conclusion. Thermal activation temperature of nano phosphate and silicate-combined application can stabilize heavy metal Cd to some extent and promote the transition of Cd from a bioavailable state to a biounavailable state. The results showed that the combined application of thermal activation temperature of nano phosphate and silicate has a certain potential to control soil cadmium pollution. [ABSTRACT FROM AUTHOR]

Soil pollution by heavy metals as a result of mining activities is increasingly taking place. Once accumulated in soil, the heavy metals can then be dispersed, with serious effects on the environment and human health. It is therefore necessary to minimize, or even remove, all heavy metals from polluted areas, and one of the environmentally friendly and sustainable methods to do so is phytoremediation. A greenhouse pots experiment was conducted to evaluate the phytoremediation capacity of Silphium perfoliatum L. plants, in the vegetative growth stages, on a soil polluted with Cu, Zn, Cr and Pb, taken from a former mining area compared to an unpolluted soil (Us). The initial heavy metal content of polluted soil (Ps) was 208.3 mg kg−1 Cu; 312.5 mg kg−1 Zn; 186.5 mg kg−1 Cr and 195.2 mg kg−1 Pb. This shows that for Cu and Pb, soil concentrations exceed the intervention threshold, and for Zn and Cr, they are above the alert threshold. The removal efficiency, bioaccumulation factor, translocation factor, metal uptake and contamination factor index of Cu, Zn, Cr and Pb by S. perfoliatum L. were quantified to determine the bioremediation success. The data show that plants grown in Ps accumulated a significantly higher amount of Cu by 189% and Zn by 37.95% compared to Us. The Cr and Pb content of the plants recorded a progressive and significant increase from one developmental stage to another, being more intense between three and five leaves. [ABSTRACT FROM AUTHOR]

Civilization development has contributed to environmental pollution. In recent years, the number of vehicles has increased significantly; according to the Central Statistical Office, the number of passenger cars in Poland in 2000 was nearly 10 million, while in 2020 it was slightly more than 25 million. The study aimed to determine the content and spatial distribution of trace elements (Fe, Mn, Cd, Pb, Cr, Ni, Zn and Cu) in the roadside topsoil along the trunk road Białystok–Budzisko on different types of land use (urban, rural, agricultural and forestal areas). Forty-five soil samples were collected from a 160 km road section, at intervals of approximately 4 km. Metal contents were analyzed by atomic absorption spectrometry. The concentrations of metals in roadside soils occurred in the following order: Fe > Mn > Zn > Cr > Cu > Pb > Ni > Cd. The average contents of Cd, Zn, Cu, and Pb were higher than the geochemical background values of the Polish soils. Moreover, the values of the Igeo showed for Cd moderate to strong, while for Zn, Cu and Pb, moderate soil contamination. The study indicates that significant metal-binding factors in the studied roadside soils are Fe and Mn oxides. The crucial source of metals is road transport, depending on its intensity, which means amount, type, and speed of vehicles. Moreover, based on the analysis of the course of the factor values and their dynamics, it was observed that the areas where typical activities connected with the population take place (urban and agricultural areas) are additional sources of heavy metals. The results of this paper are relevant to the prevention and control of heavy metal pollution in roadside soils. The study can contribute to reducing the concentration of toxic elements in ecosystems due to vehicle emissions with appropriate land-use policies. [ABSTRACT FROM AUTHOR]