Metal Pollution In Soil Research Articles

Distribution, Risk Assessment, and Source Apportionment of Heavy Metal Pollution in Cultivated Soil of a Typical Mining Area in Southwest China.

The present study investigates heavy metal pollution and its sources in cultivated soils in Bijie City, Guizhou Province, China. The ground accumulation index method was used to evaluate the associated risks, while correlation, principal component, and positive matrix factor model analyses were used to identify sources. The results show that the overall contamination levels, except for Cd, were not serious. Agricultural materials, industrial activities, transportation, coal combustion and atmospheric deposition, parent rock, and irrigation accounted for 19.66%, 14.11%, 14.54%, 16.33%, 20.70%, and 14.67% of the total accumulation of metals, respectively. Copper, Ni, Zn, and Cr came mainly from parent rocks; Pb was mainly from traffic emissions; Hg was mainly from coal deposition; As was mainly from irrigation; and Cd was mainly from industrial activities. The main sources of soil metals were irrigation, agricultural activities, and coal deposition in the east and industrial activities and soil-forming parent rocks in the west. Environ Toxicol Chem 2023;00:1-13. © 2023 SETAC.

Analysis and Evaluation of Heavy Metal Pollution in Kosasthalaiyar River near Ennore Creek Using Geo Statistical Approach

<p>The increasing industrialization and urbanization in recent times has led to a significant increase in heavy metal pollution in soil and sediment. The present study aims to evaluate the heavy metal contamination (HmC) in surface sediments collected from the Kosasthalaiyar River located between latitudes 13°12′03″N and 13°16′34″N and longitudes 80°18′6″E and 80°19′56″E. Ten sampling locations were selected in the study area and samples of surface sediments were collected and analyzed for 16 geochemical and heavy metal parameters, including Silver (Ag), Aluminium (Al), Calcium (Ca), Cadmium (Cd), Chloride, Cobalt (Co), Total Chromium (Cr), Copper (Cu), Mercury (Hg), Manganese (Mn), Molybdenum (Mo), Nickel (Ni), Lead (Pb), Silica (Si), Titanium (Ti), and Zinc (Zn). The study aims to determine the potential environmental hazards of heavy metals in the sediment through calculation of the potential environmental hazard index (RI). Assess the impact of human activities on HmC in the surface sediments using four pollution indices: the Geo-accumulation index (Igeo), the Contaminant factor (CF), the degree of contamination (DC), the potential contamination index (PCI), and the pollution load index (PLI) and Conduct a human health risk assessment (HHRA) of heavy metals in the sediment. The study results will provide insight into the contamination levels and help inform measures for controlling pollution and promoting sustainability in the area.</p>

Source Apportionment and Model Applicability of Heavy Metal Pollution in Farmland Soil Based on Three Receptor Models.

The identification of the source of heavy metal pollution and its quantification are the prerequisite of soil pollution control. The APCS-MLR, UNMIX and PMF models were employed to apportion pollution sources of Cu, Zn, Pb, Cd, Cr and Ni of the farmland soil in the vicinity of an abandoned iron and steel plant. The sources, contribution rates and applicability of the models were evaluated. The potential ecological risk index revealed greatest ecological risk from Cd. The results of source apportionment illustrated that the APCS-MLR and UNMIX models could verify each other for accurate allocation of pollution sources. The industrial sources were the main sources of pollution (32.41~38.42%), followed by agricultural sources (29.35~31.65%) and traffic emission sources (21.03~21.51%); and the smallest proportion was from natural sources of pollution (11.2~14.42%). The PMF model was easily affected by outliers and its fitting degree was not ideal, leading to be unable to get more accurate results of source analysis. The combination of multiple models could effectively improve the accuracy of pollution source analysis of soil heavy metals. These results provide some scientific basis for further remediation of heavy metal pollution in farmland soil.

The I1NF-YC6 transcription factor of Iris lactea var. chinensis (Fisch.) activates the llCDT1 gene and enhances tolerance to cadmium stress in Arabidopsis thaliana

Heavy metal pollution of soil has become a serious global concern in recent years. In particular, cadmium (Cd) contamination is a ubiquitous environmental problem among heavy metals. Iris lactea var. chinensis is a perennial herb with significant ecological and industrial value. It is known for its good cadmium tolerance and cadmium enrichment capabilities; thus, it is considered an important plant for the restoration of cadmium-contaminated soil. Previous studies have shown that the cysteine-rich gene, IlCDT1 isolated from I. lactea conferred tolerance to Cd stress in yeast and Arabidopsis thaliana. However, the molecular mechanism of its regulation is poorly understood to date. In the current study, we screened and identified the transcription factor IlNF-YC6 that regulates IlCDT1 using yeast one-hybrid assay (Y1H). Overexpression of IlNF-YC6 conferred a significant tolerance to Cd stress in A. thaliana. Furthermore, the detection of physiological markers and transcriptome analysis revealed that IlNF-YC6 might increase plant tolerance to Cd stress primarily by improving plant detoxification ability and antioxidant capacity. Overall, our study would provide a genetic resource for candidate gene selection that might enhance plant tolerance to Cd contamination in soil or groundwater and subsequently lowering Cd absorption in the future.

Cadmium-absorptive Bacillus vietnamensis 151–6 reduces the grain cadmium accumulation in rice (Oryza sativa L.): Potential for cadmium bioremediation

Microbial bioremediation of heavy metal-polluted soil is a promising technique for reducing heavy metal accumulation in crops. In a previous study, we isolated Bacillus vietnamensis strain 151–6 with a high cadmium (Cd) accumulation ability and low Cd resistance. However, the key gene responsible for the Cd absorption and bioremediation potential of this strain remains unclear. In this study, genes related to Cd absorption in B. vietnamensis 151–6 were overexpressed. A thiol-disulfide oxidoreductase gene (orf4108) and a cytochrome C biogenesis protein gene (orf4109) were found to play major roles in Cd absorption. In addition, the plant growth-promoting (PGP) traits of the strain were detected, which enabled phosphorus and potassium solubilization and indole-3-acetic acid (IAA) production. Bacillus vietnamensis 151–6 was used for the bioremediation of Cd-polluted paddy soil, and its effects on growth and Cd accumulation in rice were explored. The strain increased the panicle number (114.82%) and decreased the Cd content in rice rachises (23.87%) and grains (52.05%) under Cd stress, compared with non-inoculated rice in pot experiments. For field trials, compared with the non-inoculated control, the Cd content of grains inoculated with B. vietnamensis 151–6 was effectively decreased in two cultivars (low Cd-accumulating cultivar: 24.77%; high Cd-accumulating cultivar: 48.85%) of late rice. Bacillus vietnamensis 151–6 encoded key genes that confer the ability to bind Cd and reduce Cd stress in rice. Thus, B. vietnamensis 151–6 exhibits great application potential for Cd bioremediation.

Glomus mosseae improved the adaptability of alfalfa (Medicago sativa L.) to the coexistence of cadmium-polluted soils and elevated air temperature.

The coexistence of heavy metal-polluted soils and global warming poses serious threats to plants. Many studies indicate that arbuscular mycorrhizal fungi (AMF) can enhance the resistance of plants to adverse environments such as heavy metals and high temperature. However, few studies are carried out to explore the regulation of AMF on the adaptability of plants to the coexistence of heavy metals and elevated temperature (ET). Here, we investigated the regulation of Glomus mosseae on the adaptability of alfalfa (Medicago sativa L.) to the coexistence of cadmium (Cd)-polluted soils and ET. G. mosseae significantly enhanced total chlorophyll and carbon (C) content in the shoots by 15.6% and 3.0%, respectively, and Cd, nitrogen (N), and phosphorus (P) uptake by the roots by 63.3%, 28.9%, and 85.2%, respectively, under Cd + ET. G. mosseae significantly increased ascorbate peroxidase activity, peroxidase (POD) gene expression, and soluble proteins content in the shoots by 13.4%, 130.3%, and 33.8%, respectively, and significantly decreased ascorbic acid (AsA), phytochelatins (PCs), and malondialdehyde (MDA) contents by 7.4%, 23.2%, and 6.5%, respectively, under ET + Cd. Additionally, G. mosseae colonization led to significant increases in POD (13.0%) and catalase (46.5%) activities, Cu/Zn-superoxide dismutase gene expression (33.5%), and MDA (6.6%), glutathione (22.2%), AsA (10.3%), cysteine (101.0%), PCs (13.8%), soluble sugars (17.5%), and proteins (43.4%) contents in the roots and carotenoids (23.2%) under ET + Cd. Cadmium, C, N, G. mosseae colonization rate, and chlorophyll significantly influenced shoots defenses and Cd, C, N, P, G. mosseae colonization rate, and sulfur significantly affected root defenses. In conclusion, G. mosseae obviously improved the defense capacity of alfalfa under ET + Cd. The results could improve our understanding of the regulation of AMF on the adaptability of plants to the coexistence of heavy metals and global warming and phytoremediation of heavy metal-polluted sites under global warming scenarios.

Accumulation Characteristics and Influencing Factors of Heavy Metals in Cultivated Land Surface Soil in Lanzhou

In this study, As, Cd, Cr, Hg, and Pb in the surface soil of cropland in Lanzhou were studied, and the combination of descriptive statistics, single-factor accumulation index, comprehensive accumulation index, geostatistical method, and a geographically weighted regression model (GWR) was used to investigate their accumulation status, spatial distribution, and influencing factors, in order to provide scientific basis for the precise control of heavy metal accumulation risk in the study area. The results showed that:①the single-factor accumulation index showed that the accumulation of Hg and Cd in the study area was the largest, followed by that of Pb and As, and that of Cr was the smallest; the comprehensive accumulation index showed that the accumulation rate of heavy metals was as high as 98.11%, of which 54.81% was mild accumulation and 43.30% was moderate and above accumulation. However, there was no heavy metal pollution in the surface soil of cultivated land in Lanzhou. ② Spatial autocorrelation analysis showed that there was no heavy metal pollution in the surface soil of Lanzhou, but there was accumulation in a few areas. The spatial autocorrelation analysis showed that the spatial autocorrelation of the Cr, Hg, and Pb single-factor accumulation indices was moderate, indicating that they were influenced by both random and structural factors; the spatial autocorrelation of the other two heavy metals was weak, indicating that they were mainly influenced by random factors, among which human factors were more influential. The Hg single-factor accumulation index was high in the middle and low in the fourth; the integrated accumulation index increased from northwest to southeast and decreased from the middle to both sides. ③ Geographically weighted regression (GWR) analysis showed that altitude, slope length, distance from rivers, soil organic matter (SOM) content, precipitation, air temperature, and surface temperature all showed positive driving effects, whereas the rest of the factors showed negative driving effects and significant spatial heterogeneity and instability (P<0.05). The magnitudes of the factor effects were in the order of soil characteristics>topographic characteristics>climate characteristics>location characteristics>socioeconomic characteristics>vegetation characteristics, with the largest contribution of SOM content, followed by that of altitude and air temperature, and the smallest of normalized difference vegetation index (NDVI) values. Compared with the other feature factors, the location feature factors had stronger spatial heterogeneity.

Spatial Distribution Characteristics and Assessment of Heavy Metal Pollution in Cultivated Soil of Agricultural Small Watershed in Typical Mining Area in South China

In order to clarify the spatial distribution characteristics and the present situation of heavy metal pollution in cultivated soil of a typical mining basin in southern China, the contents of Cd, As, Mn, Cu, Zn, and Pb in cultivated soil in the selected small watershed were determined, and the spatial distribution characteristics of heavy metals were analyzed using the spatial interpolation method. Further, the ecological risk was evaluated using the geo-accumulation index and potential ecological risk coefficient (PERC). The results showed that the average contents of Pb, Zn, Cu, As, and Cd in the topsoil (0-20 cm) in the small watershed were approximately 11.9, 3.8, 8.2, 4.7, and 14.2 times that of the background value in Hunan soil, respectively. Compared with the soil risk screening value of agricultural land, the over-standard rates of Pb, Zn, Cu, As, and Cd were approximately 24%, 56%, 75%, 44%, and 48%, respectively. Zn and Mn showed medium variation, whereas Pb, As, Cu, and Cd showed strong variation, which indicated that there was an obvious enrichment of heavy metals in the small watershed. The spatial analysis results showed that there was an obvious consistent characteristic of six heavy metals in the topsoil, that is, there was enrichment in the mining activity area and its downstream and the township streets in the west of the small watershed. Additionally, there were high value points of some heavy metals on both sides of the main river, indicating that the main pollution sources in the study area were mining and metallurgy activities and sewage irrigation. The results of the geo-accumulation index and potential ecological risk index showed that there was compound pollution of heavy metals, in which the degree of Cd pollution was the highest, and the soil of both sides of the river could pose the strongest potential ecological risk.

Arbuscular Mycorrhizal Fungi Promote the Degradation of the Fore-Rotating Crop (Brassica napus L.) Straw, Improve the Growth of and Reduce the Cadmium and Lead Content in the Subsequent Maize

Arbuscular mycorrhizal fungi (AMF) are widely present in heavy metal-polluted soils, but their effects on straw degradation and plant growth of rotated crops are poorly understood. In this study, a pot experiment was used to simulate the return of fore-rotating crop (Brassica napus L.) straw to farmland with a subsequent planting of maize in a lead–zinc mining area on the Yunnan Plateau, Southwest China, which included four treatments: control (CK), addition of rape straw (SR), inoculation of AMF (AMF), and both AMF inoculation and straw addition (AMF + SR). The effects of AMF on the degradation and nutrient release of the fore-rotating rape straw and the growth, mineral nutrition and the cadmium (Cd) and lead (Pb) contents of the subsequent maize were investigated. Compared with the CK treatment, AMF significantly promoted the degradation of rape straw and the release of mineral nutrients (nitrogen, phosphorus and potassium) as well as the Cd and Pb, increased the content of available nutrients in soil, and improved the mineral nutrient contents in the maize. AMF + SR significantly increased the maize height and biomass by 32–35% and decreased the available Cd and Pb contents in soil and the Cd and Pb contents in the maize by 20–30% and 18–25%, respectively. Moreover, the available Cd and Pb contents in the soil presented significant positive correlations with their contents in the maize but negative correlations with the height and biomass of the maize. Thus, AMF played an important regulatory role in the nutrient cycling and heavy metal accumulation of the crop rotation.

Effect of Pb Stress on Ionome Variations and Biomass in Rhus chinensis Mill

This study examined changes in the ionome of Rhus chinensis in response to Pb stress so as to understand Pb phytotoxicity-related processes and provide theoretical support for improving the efficiency of this plant in remediating heavy metal-polluted soils. Rhus chinensis seedlings were cultured in pots with soil. The concentrations of 12 elements in the roots, stems, and leaves of the seedlings under treatments of 0, 500, and 1000 mg·kg−1 Pb(NO3)2 were determined. Principal component analysis (PCA), correlation analysis, and partial least squares path modeling (PLS-PM) were used to analyze the contributions of the affected elements in the ionomes of different organs of the seedlings under Pb stress. PCA showed that 74% of the total ionome variation was caused by the difference in organ types. N, Mg, K, Cu, Ca, and Zn were the important elements contributing to the variation of the ionome. Pb disturbed the ionome of different organs at varying levels, and the order of the interference levels between the organs was: stem &gt; root &gt; leaf. Correlation analysis showed that biomass had a significant positive correlation with N and K and a significant negative correlation with Pb, Mn, and the C:N ratio. Stem biomass had a significant positive correlation with Ca, Cu, and the N:P ratio. Root biomass had a significant negative correlation with the C:P ratio. PLS-PM analysis indicated that Pb stress had a major, direct, and inhibitory effect on biomass. The variation of ionomic profiles caused by Pb stress was mainly caused by the difference in organ types; the variation of the ionomic profiles of each organ was mainly caused by Pb stress. The elements that caused the variation of ionomic profiles varied with organ types, and the plant biomass was directly affected by a strong Pb poisoning effect and indirectly affected by a weak ionomic profile variation effect.

Foliar application of silicon, selenium, and zinc nanoparticles can modulate lead and cadmium toxicity in sage (Salvia officinalis L.) plants by optimizing growth and biochemical status

Different techniques have been used to alleviate metal toxicity in medicinal plants; accordingly, nanoparticles (NPs) have a noticeable interest in modulating oxidative stresses. Therefore, this work aimed to compare the impacts of silicon (Si), selenium (Se), and zinc (Zn) NPs on the growth, physiological status, and essential oil (EO) of sage(Salvia officinalis L.)treated with foliar application of Si, Se, and Zn NPs upon lead (Pb) and cadmium (Cd) stresses. The results showed that Se, Si, and Zn NPs decreased Pb accumulation by 35, 43, and 40%, and Cd concentration by 29, 39, and 36% in sage leaves. Shoot plant weight showed a noticeable reduction upon Cd (41%) and Pb (35%) stress; however, NPs, particularly Si and Zn improved plant weight under metal toxicity. Metal toxicity diminished relative water content (RWC) and chlorophyll, whereas NPs significantly enhanced these variables. The noticeable raises in malondialdehyde (MDA) and electrolyte leakage (EL) were observed in plants exposed to metal toxicity; however, they were alleviated with foliar application of NPs. The EO content and EO yield of sage plants decreased by the heavy metals but increased by the NPs. Accordingly, Se, Si, and Zn NPS elevated EO yield by 36, 37, and 43%, respectively, compared with non-NPs. The primary EO constituents were 1,8-cineole (9.42-13.41%), α-thujone (27.40-38.73%), β-thujone (10.11-12.94%), and camphor (11.31-16.45%). This study suggests that NPs, particularly Si and Zn, boosted plant growth by modulating Pb and Cd toxicity, which could be advantageous for cultivating this plant in areas with heavy metal-polluted soils.

Evaluation of soil heavy metals pollution and the phytoremediation potential of copper-nickel mine tailings ponds.

Heavy metal pollution in soils caused by mining has led to major environmental problems around the globe and seriously threatens the ecological environment. The assessment of heavy metal pollution and the local phytoremediation potential of contaminated sites is an important prerequisite for phytoremediation. Therefore, the purpose of this study was to understand the characteristics of heavy metal pollution around a copper-nickel mine tailings pond and screen local plant species that could be potentially suitable for phytoremediation. The results showed that Cd, Cu, Ni, and Cr in the soil around the tailings pond were at the heavy pollution level, Mn and Pb pollution was moderate, and Zn and As pollution was light; The positive matrix factorization (PMF) model results showed that the contributions made by industrial pollution to Cu and Ni were 62.5% and 66.5%, respectively, atmospheric sedimentation and agricultural pollution contributions to Cr and Cd were 44.6% and 42.8%, respectively, the traffic pollution contribution to Pb was 41.2%, and the contributions made by natural pollution sources to Mn, Zn, and As were 54.5%, 47.9%, and 40.0% respectively. The maximum accumulation values for Cu, Ni, Cr, Cd, and As in 10 plants were 53.77, 102.67, 91.10, 1.16 and 7.23 mg/kg, respectively, which exceeded the normal content of heavy metals in plants. Ammophila breviligulata Fernald had the highest comprehensive extraction coefficient (CEI) and comprehensive stability coefficient (CSI) at 0.81 and 0.83, respectively. These results indicate that the heavy metal pollution in the soil around the copper nickel mine tailings pond investigated in this study is serious and may affect the normal growth of plants. Ammophila breviligulata Fernald has a strong comprehensive remediation capacity and can be used as a remediation plant species for multiple metal compound pollution sites.

Pollution and health risk assessment of mine tailings contaminated soils in India from toxic elements with statistical approaches

The rapid mining activities of mica mines in Giridih district, India, have led to toxic metal pollution of agricultural soil. This is a key concern for environmental risk and human health. 63 top soil samples were collected at a distance of 10 m (Zone 1), 50 m (Zone 2), and 100 m (Zone 3) from near 21 mica mines with agriculture fields. The mean concentration of total and bio-available toxic elements (TEs - Cr, Ni, Pb, Cu, Zn, and Cd) was higher in zone 1 across three zones. The Positive matrix factorization model (PMF) and Pearson Correlation analysis were used to identify waste mica soils with TEs. Based on PMF results, Ni, Cr, Cd, and Pb were the most promising pollutants and carried higher environmental risks than the other TEs. Using the self-organizing map (SOM), zone 1 was identified as a high-potential source of TEs. Soil quality indexes for TEs risk zone 1 were found to be higher across three zones. Based on the health risk index (HI), children are more adversely affected than adults. Monte Carlo simulations (MCS) model and sensitivity analysis of total carcinogenic risk (TCR), children were more affected by Cr and Ni than adults through ingestion exposure pathways. Finally, a geostatistical tool was developed to predict the spatial distribution patterns of TEs contributed by mica mines. In a probabilistic assessment of all populations, non-carcinogenic risks appeared to be negligible. The fact that there is a TCR can't be ignored, and children are more likely to develop it than adults. Mica mines with TEs contamination were found to be the most significant anthropogenic contributor to health risks based on source-oriented risk assessment.

Biochar: An effective measure to strengthen phosphorus solubilizing microorganisms for remediation of heavy metal pollution in soil.

OPINION article Front. Bioeng. Biotechnol., 02 March 2023Sec. Bioprocess Engineering Volume 11 - 2023 | https://doi.org/10.3389/fbioe.2023.1127166

Immobilization of Heavy Metals in Contaminated Soil using Calcium Phosphate Amendment and Phosphate-solubilizing Fungi (Penicillium sp) in Benin City, Edo state, Nigeria

Soil is a limited resource that is continually contaminated by the presence of heavy metals as a result of human activities. This study used a combination of calcium phosphate amendment and phosphate-solubilizing fungi to immobilize heavy metals in polluted soil. Bovine bones were collected at an Abattoir Market in Aduwawa, Benin City, Nigeria with coordinates 6°22’6.24” N and 5°41’0.24” E and calcined to extract calcium-phosphate (hydroxyapatite), serial dilution and plating on Pikovskaya medium were utilized to obtain fungi extract from fertile soil. Prior to remediation, heavy metal analysis of polluted soil indicated high value of metal concentrations zinc 120.60mg/kg, chromium 22.67 mg/kg, cadmium 11.23 mg/kg, lead 18.43 mg/kg, iron 187.27 mg/kg and nickel 10.62 mg/kg above the World Health Organization permissible limit. There was a decrease in zinc and iron contents after the first week of treatment. The second week demonstrated a significant decrease in all metal concentrations; 27.53% for Zn, Cr 39.83%, Cd 46.13%, Pb 7.60%, Fe 46.26% and Ni 15.07% – indicating the treatment’s effectiveness.

Heavy Metal Pollution and Risk Assessment of Vegetables and Soil in Jinhua City of China

To understand the heavy metal (Cd, Cr and Pb) pollution situation and exposure risk of the vegetables and soil in Jinhua City, soil–vegetable samples collected from three districts of Jinhua City were analyzed in detail, and the risks of heavy metal concentration in vegetable and soil were evaluated using the single pollution index, Nemerow pollution index, Hakanson potential ecological index and a health risk assessment. The results indicate that: (1) The soil in Jinhua City is mainly polluted by Cd, and the BCF of heavy metals in vegetables was leafy vegetables &gt; rootstalk vegetables &gt; solanaceous vegetables. (2) Heavy metals had slight pollution in the surrounding environment, and the ecological risk of soil heavy metals in the sampling area was generally at a low risk level. (3) Children are more likely to suffer from non-carcinogenic risks; Cr is the main source of this risk (HQCr = 0.74). More than 90% of vegetables in the sampling had cancer risk, adults are more likely to suffer from carcinogenic risks, and Cd is the main source of potential cancer risk (TCR = 4.34 × 10−4). Therefore, in our study area, Cd is the main factor of soil pollution that can cause potential cancer risk through vegetable enrichment, and Cr is the main factor causing the non-carcinogenic risk of leafy vegetables.

Effects of different heavy metal pollution levels on microbial community structure and risk assessment in Zn-Pb mining soils.

Heavy metal contamination in soils seriously threatens human health and aggravates the global pollution burden. In this study, we investigated the risk of heavy metal contamination in soils at a Zn-Pb mineral processing plant in Longnan, China, and the effects of different heavy metal contamination levels on diverse microbial communities. Statistical analysis showed that, except for Ni, the average content of all detected metals (Zn, Pb, As, Cu, Cd, Hg) in the soil was higher than the background value of soil in the study area, which was most seriously contaminated with Pb and As. Comparison of functional divisions showed that heavy metal soil contamination was most serious in the raw material stacking area and the production area. Interpolation analysis showed that areas closer to the wastewater discharge area had higher contents of each heavy metal and were more seriously polluted. From the point of pollution index, the risk of heavy metal soil pollution in the study area was very high (RI = 2845.24, i.e., > 600), with Cd and Hg being the most serious pollutants compared with other heavy metals. Microbial community abundance, diversity, and structure differed at different levels of heavy metal contamination. The community diversity of bacteria decreased with increasing heavy metal concentrations, while no significant change in fungi was observed. Evidence from variation redundancy analysis (RDA) and the Spearman correlation analysis showed that the leading factors affecting microbial community composition were Cu, Cd, Hg, and pH. Actinobacteria and Gemmatimonadetes at the uncontaminated level (CL) were significantly and negatively correlated with the concentrations of Cu, Zn, Cd, and Pb. Proteobacteria and Chloroflexi at the severely contaminated level (SL) were significantly correlated with pH and Hg. However, heavy metal contamination had less effect on most of the dominant fungi. In conclusion, microbial communities such as Proteobacteria, Actinobacteria, Chloroflexi, and Ascomycota showed greater tolerance to heavy metals. These results could be used as important references for the remediation of heavy metal-contaminated soils.

Physiological regulation of salicylic acid on Helianthus tubeuosus upon copper stress and root FTIR analysis

Phytoremediation plays an important role in the treatment of heavy metal pollution in soil. In order to elucidate the mechanism of salicylic acid (SA) on copper absorption, seedlings from Xuzhou (with strong Cu-tolerance) and Weifang Helianthus tuberosus cultivars (with weak Cu-tolerance) were selected for pot culture experiments. 1 mmol/L SA was sprayed upon 300 mg/kg soil copper stress, and the photosynthesis, leaf antioxidant system, several essential mineral nutrients and the changes of root upon copper stress were analyzed to explore the mechanism of copper resistance. The results showed that Pn, Tr, Gs and Ci upon copper stress decreased significantly compared to the control group. Meanwhile, chlorophyll a, chlorophyll b and carotenoid decreased with significant increase in initial fluorescence (F0), maximum photochemical quantum yield of PSⅡ (Fv/Fm), electron transfer rate (ETR) and photochemical quenching coefficient (qP) content all decreased. The ascorbic acid (AsA) content was decreased, the glutathione (GSH) value was increased, the superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activity in the leaves were decreased, and the peroxidase (POD) activity was significantly increased. SA increased the Cu content in the ground and root system, and weakened the nutrient uptake capacity of K, Ca, Mg, and Zn in the root stem and leaves. Spray of exogenous SA can maintain the opening of leaf stomata, improve the adverse effect of copper on photosynthetic pigment and PSⅡ reaction center. Mediating the SOD and APX activity started the AsA-GSH cycle process, effectively regulated the antioxidant enzyme system in chrysanthemum taro, significantly reduced the copper content of all parts of the plant, and improved the ion exchange capacity in the body. External SA increased the content of the negative electric group on the root by changing the proportion of components in the root, promoted the absorption of mineral nutrient elements and the accumulation of osmoregulatory substances, strengthened the fixation effect of the root on metal copper, and avoided its massive accumulation in the H. tuberosus body, so as to alleviate the inhibitory effect of copper on plant growth. The study revealed the physiological regulation of SA upon copper stress, and provided a theoretical basis for planting H. tuberosus to repair soil copper pollution.

Modeling Analysis of Heavy Metal Evaluation in Complex Geological Soil Based on Nemerow Index Method

To accurately understand soil environmental quality and improve the problem of the traditional method, which is that it has a single evaluation factor and cannot reflect the overall condition of the soil, a complex geological soil heavy metal evaluation modeling method based on the Nemerow index method is proposed. Index evaluation methods, ArcGIS technology, and a human health risk assessment were carried out to obtain the spatial distribution of heavy metals in the soil and the current status of pollution accumulation. The comprehensive pollution index (CPI) method, geo-accumulation index (GAI) method, and potential ecological hazard (PEH) index were adopted to analyze the pollution degree of soil heavy metals. On this basis, the Nemerow index method was used to establish a complex geological soil heavy metal evaluation model, and the standard Nemerow index was calculated to complete the evaluation of heavy metal pollution in complex geological soils. The research results showed that this method could make the evaluation factors obtain reasonable scores and obtain more reasonable soil evaluation results.

Arbuscular mycorrhizal fungi facilitate Astragalus adsurgens growth and stress tolerance in cadmium and lead contaminated saline soil by regulating rhizosphere bacterial community

Soil worldwide has been severely damaged by various stresses, particularly heavy metal pollution in natural saline soils. The rhizosphere microbial community and arbuscular mycorrhizal fungi (AMF) can effectively facilitate the phytoremediation of contaminated soil. However, the effects of heavy metals and AMF on plant growth and rhizosphere bacterial community in natural saline soils remain uncertain. Here, pot experiments (orthogonal experiments) were designed to investigate the effects of cadmium (Cd) and lead (Pb) on the rhizosphere bacterial community of Astragalus adsurgens with or without AMF, and the microbial regulation mechanism of AMF in promoting phytoremediation of Cd and Pb contaminated saline soil. The results showed that heavy metals inhibited plant growth with and without AMF, however, AMF significantly increased shoot biomass by 536 %–970 % and root biomass by 272 %–382 %. Heavy metals reduced the richness and diversity of the rhizosphere bacterial community without AMF, however, no significant reduction was observed with AMF. In all four treatments, AMF significantly enhanced the richness and diversity of the rhizosphere bacterial community. Linear discriminant analysis effect size revealed that heavy metals significantly enriched heavy metal-tolerant rhizosphere bacteria with and without AMF. AMF significantly enriched more beneficial rhizosphere bacteria (mainly Rhodobacter, Archangium, and Longimicrobium) that tolerated heavy metals and promoted plant growth. Network analysis showed that heavy metals weakened bacterial interactions without AMF, but did not influence it with AMF. AMF strengthened the interaction and enhanced negative correlation ratio between bacteria, suggesting less stress and a stable and healthy environment. Finally, the structural equation model confirmed that AMF could improve the phytoremediation efficiency by regulating the rhizosphere bacterial community. This study enables us to understand the influence of heavy metals and AMF on plants and rhizosphere bacterial community, providing a theoretical basis for further improving the phytoremediation of heavy metal-contaminated saline soils.