The microbial mechanisms by which long-term heavy metal contamination affects soil organic carbon levels

Globally, reducing carbon emissions and mitigating soil heavy metal pollution pose pressing challenges. We evaluated the effects of lead (Pb) and cadmium (Cd) contamination in the field over 20 years. The five treatment groups featured Pb concentrations of 40 and 250 mg/kg, Cd concentrations of 10 and 60 mg/kg, and a combination of Pb and Cd (60 and 20 mg/kg, respectively); we also included a pollution-free control group. After 20 years, soil pH decreased notably in all treatments, particularly by 1.02 in Cd10-treated soil. In addition to the increase of SOC in Cd10 and unchanged in Pb40 treatment, the SOC was reduced by 9.62%-12.98% under the other treatments. The α diversities of bacteria and fungi were significantly changed by Cd10 pollution (both p < 0.05) and the microbial community structure changed significantly. However, there were no significant changes in bacterial and fungal communities under other treatments. Cd10 pollution reduced the numbers of Ascomycota and Basidiomycota fungi, and enhanced SOC accumulation. Compared to the control, long-term heavy Cd, Pb, and Pb-Cd composite pollution caused SOC loss by increasing Basidiomycota which promoting carbon degradation, and decreasing Proteobacteria which promoting carbon fixation via the Krebs cycle. Our findings demonstrate that heavy metal pollution mediates Carbon-cycling microorganisms and genes, impacting SOC storage.

Development of a novel and fast XRF instrument for large area heavy metal detection integrated with UAV

The disadvantages of the current chemical and instrumental analysis methods for soil heavy metal pollution are that they have a high detection cost, long cycle times, and may cause secondary pollution. The aims of this study were to improve the rapid detection of soil heavy metal pollution over large areas. This study combined aircraft technology, embedded development, computer software, electronic information, and other technical methods to create a novel solution to the problem, i.e., an integrated unmanned aerial vehicle (UAV) based soil heavy metal pollution rapid detection system (UAV-SHMPRDS) was built. The key technologies required for a rapid detection system were developed, including the development of a hardware system based on a UAV and an X-ray fluorescence spectrum (XRF) analyzer, the design and implementation of a control system software system, and the implementation of a data inversion processing algorithm. Finally, a prototype UAV-SHMPRDS was constructed. Testing showed that the system improved regionalized soil heavy metal pollution detection efficiency. This study provides new solutions for the current problems encountered in the actual rapid detection of soil heavy metal pollution.

Promotion effect of graphene on phytoremediation of Cd-contaminated soil

Echinacea purpurea (L.) Moench was selected as a remediation plant in this study, and different concentrations of graphene oxide (GO) were added to Cd-contaminated soil. Through pot experiments, the effect of E. purpurea on Cd-contaminated soil was determined at 60 days, 120 days, and 150 days. A preliminary study on the remediation mechanism of GO was explored through changes in the forms of Cd in the rhizosphere soil, soil pH, and soil functional groups. Results showed that the optimal concentration of GO was 0.4 g/kg, and under the condition, the accumulation of Cd in the roots of E. purpurea was as high as 113.69 ± 23.86 mg/kg, and the maximum EF reached 5.87 ± 1.34. Compared with those of the control group, accumulated Cd concentration and EF in the roots increased by 60.34% and 2.32, respectively. Correlation analysis showed that the absorption and accumulation of Cd was negatively correlated with the exchangeable Cd content at 120 days, and the exchangeable Cd was negatively correlated with the relative content of functional groups in the soil with 0.4 g/kg GO (E2). The artificial application of GO to the soil can be used as an effective way to improve the effect of E. purpurea in the remediation of Cd soil pollution, and it has great application potential in the stabilization of plants and vegetations and restoration of high-concentration Cd-contaminated soil.

Hyperspectral monitor of soil chromium contaminant based on deep learning network model in the Eastern Junggar coalfield

In China, over 10% of cultivated land is polluted by heavy metals, which can affect crop growth, food safety and human health. Therefore, how to effectively and quickly detect soil heavy metal pollution has become a critical issue. This study provides a novel data preprocessing method that can extract vital information from soil hyperspectra and uses different classification algorithms to detect levels of heavy metal contamination in soil. In this experiment, 160 soil samples from the Eastern Junggar Coalfield in Xinjiang were employed for verification, including 143 noncontaminated samples and 17 contaminated soil samples. Because the concentration of chromium in the soil exists in trace amounts, combined with the fact that spectral characteristics are easily influenced by other types of impurity in the soil, the evaluation of chromium concentrations in the soil through hyperspectral analysis is not satisfactory. To avoid this phenomenon, the pretreatment method of this experiment includes a combination of second derivative and data enhancement (DA) approaches. Then, support vector machine (SVM), k-nearest neighbour (KNN) and deep neural network (DNN) algorithms are used to create the discriminant models. The accuracies of the DA-SVM, DA-KNN and DA-DNN models were 95.61%, 95.62% and 96.25%, respectively. The results of this experiment demonstrate that soil hyperspectral technology combined with deep learning can be used to instantly monitor soil chromium pollution levels on a large scale. This research can be used for the management of polluted areas and agricultural insurance applications.

Factors influencing heavy metal availability and risk assessment of soils at typical metal mines in Eastern China

China exemplifies the serious and widespread soil heavy metal pollution generated by mining activities. A total of 420 soil samples from 58 metal mines was collected across Eastern China. Total and available heavy metal concentrations, soil physico-chemical properties and geological indices were determined and collected. Risk assessments were applied, and a successive multivariate statistical analysis was carried out to provide insights into the heavy metal contamination characteristics and environmental drivers of heavy metal availability. The results suggested that although the degrees of pollution varied between different mine types, in general they had similar contamination characteristics in different regions. The major pollutants for total concentrations were found to be Cd and As in south and northeast China. The availability of Zn and Cd is relatively higher in south China. Soil physico-chemical properties had major effect on metal availability where soil pH was the most important factor. On a continental scale, soil pH and EC were influenced by the local climate patterns which could further impact on heavy metal availability. Enlightened by this study, future remediation strategies should be focused on steadily increasing soil pH, and building adaptable and sustainable ecological system to maintain low metal availabilities in mine site soils.

A review of soil heavy metal pollution from industrial and agricultural regions in China: Pollution and risk assessment

Soil heavy metal pollution has been becoming serious and widespread in China. To date, there are few studies assessing the nationwide soil heavy metal pollution induced by industrial and agricultural activities in China. This review obtained heavy metal concentrations in soils of 402 industrial sites and 1041 agricultural sites in China throughout the document retrieval. Based on the database, this review assessed soil heavy metal concentration and estimated the ecological and health risks on a national scale. The results revealed that heavy metal pollution and associated risks posed by cadmium (Cd), lead (Pb) and arsenic (As) are more serious. Besides, heavy metal pollution and associated risks in industrial regions are severer than those in agricultural regions, meanwhile, those in southeast China are severer than those in northwest China. It is worth noting that children are more likely to be affected by heavy metal pollution than adults. Based on the assessment results, Cd, Pb and As are determined as the priority control heavy metals; mining areas are the priority control areas compared to other areas in industrial regions; food crop plantations are the priority control areas in agricultural regions; and children are determined as the priority protection population group. This paper provides a comprehensive ecological and health risk assessment on the heavy metals in soils in Chinese industrial and agricultural regions and thus provides insights for the policymakers regarding exposure reduction and management.

A review of soil heavy metal pollution from mines in China: pollution and health risk assessment

Heavy metal pollution has pervaded many parts of the world, especially developing countries such as China. This review summarizes available data in the literature (2005-2012) on heavy metal polluted soils originating from mining areas in China. Based on these obtained data, this paper then evaluates the soil pollution levels of these collected mines and quantifies the risks these pollutants pose to human health. To assess these potential threat levels, the geoaccumulation index was applied, along with the US Environmental Protection Agency (USEPA) recommended method for health risk assessment. The results demonstrate not only the severity of heavy metal pollution from the examined mines, but also the high carcinogenic and non-carcinogenic risks that soil heavy metal pollution poses to the public, especially to children and those living in the vicinity of heavily polluted mining areas. In order to provide key management targets for relevant government agencies, based on the results of the pollution and health risk assessments, Cd, Pb, Cu, Zn, Hg, As, and Ni are selected as the priority control heavy metals; tungsten, manganese, lead-zinc, and antimony mines are selected as the priority control mine categories; and southern provinces and Liaoning province are selected as the priority control provinces. This review, therefore, provides a comprehensive assessment of soil heavy metal pollution derived from mines in China, while identifying policy recommendations for pollution mitigation and environmental management of these mines.