Soil characterization and differential patterns of heavy metal accumulation in woody plants grown in coal gangue wastelands in Shaanxi, China

Sustainable soil management under drought stress through biochar application: Immobilizing arsenic, ameliorating soil quality, and augmenting plant growth

Rise in climate change-induced drought occurrences have amplified pollution of metal(loid)s, deteriorated soil quality, and deterred growth of crops. Rice straw-derived biochars (RSB) and cow manure-enriched biochars (CEB) were used in the investigation (at doses of 0%, 2.5%, 5%, and 7.5%) to ameliorate the negative impacts of drought, improve soil fertility, minimize arsenic pollution, replace agro-chemical application, and maximize crop yields. Even in soils exposed to severe droughts, 3 months of RSB and CEB amendment (at 7.5% dose) revealed decreased bulk density (13.7% and 8.9%), and increased cation exchange capacity (6.0% and 6.3%), anion exchange capacity (56.3% and 28.0%), porosity (12.3% and 7.9%), water holding capacity (37.5% and 12.5%), soil respiration (17.8% and 21.8%), and nutrient contents (especially N and P). Additionally, RSB and CEB decreased mobile (30.3% and 35.7%), bio-available (54.7% and 45.3%), and leachable (55.0% and 56.5%) fractions of arsenic. Further, pot experiments with Bengal gram and coriander plants showed enhanced growth (62-188% biomass and 90-277% length) and reduced arsenic accumulation (49-54%) in above ground parts of the plants. Therefore, biochar application was found to improve physico-chemical properties of soil, minimize arsenic contamination, and augment crop growth even in drought-stressed soils. The investigation suggests utilisation of cow manure for eco-friendly fabrication of nutrient-rich CEB, which could eventually promote sustainable agriculture and circular economy. With the increasing need for sustainable agricultural practices, the use of biochar could provide a long-term solution to enhance soil quality, mitigate the effects of climate change, and ensure food security for future generations. Future research should focus on optimizing biochar application across various soil types and climatic conditions, as well as assessing its long-term effectiveness.

Evaluation of the effects of dust pollution on specific plant species near and around the marble mining site in Rajasthan, India

Airborne particles (dust pollution) pose a significant threat to both human and plant populations. Plant leaves act as crucial biofilters, capturing significant amounts of air pollution; this characteristic offers a valuable tool to measure local pollution levels and assess individual plant species' ability to intercept and mitigate harmful dust particles. The present study was carried out to asses the effect of responses of various plant species to dust pollution near and around the marble mining site comprising residential site, highway area, and Central University of Rajasthan as control. The anticipated pollution index, air pollution tolerance index (APTI), dust absorption capacity, metal accumulation index (MAI), and biochemical factors were used to evaluate plant responses. Azadirachta indica A. Juss. demonstrated the highest (29.0) and Vachellia nilotica L. showed lowest (5.6) APTI, respectively. A. indica showed maximum MAI values in comparison to other plant species situated at residential site. Additionally, monitoring of particulate matter (PM10) observed to highest at highway, followed by mining, residential, and control sites. Overall A. indica representing highest APTI and effective dust capturing capacity at all sites could serve as potential pollution sinks. V. nilotica, with its very low APTI, can be marked as biomonitoring tool for detecting dust pollution.

Vegetation restoration effects on soil carbon and nutrient concentrations and enzymatic activities in post-mining lands are mediated by mine type, climate, and former soil properties

Vegetation restoration is a widely used, effective, and sustainable method to improve soil quality in post-mining lands. Here we aimed to assess global patterns and driving factors of potential vegetation restoration effects on soil carbon, nutrients, and enzymatic activities. We synthesized 4838 paired observations extracted from 175 publications to evaluate the effects that vegetation restoration might have on the concentrations of soil carbon, nitrogen, and phosphorus, as well as enzymatic activities. We found that (1) vegetation restoration had consistent positive effects on the concentrations of soil organic carbon, total nitrogen, available nitrogen, ammonia, nitrate, total phosphorus, and available phosphorus on average by 85.4, 70.3, 75.7, 54.6, 58.6, 34.7, and 60.4 %, respectively. Restoration also increased the activities of catalase, alkaline phosphatase, sucrase, and urease by 63.3, 104.8, 125.5, and 124.6 %, respectively; (2) restoration effects did not vary among different vegetation types (i.e., grass, tree, shrub and their combinations) or leaf type (broadleaved, coniferous, and mixed), but were affected by mine type; and (3) latitude, climate, vegetation species richness, restoration year, and initial soil properties are important moderator variables, but their effects varied among different soil variables. Our global scale study shows how vegetation restoration can improve soil quality in post-mining lands by increasing soil carbon, nutrients, and enzymatic activities. This information is crucial to better understand the role of vegetation cover in promoting the ecological restoration of degraded mining lands.

Miscanthus sinensis contributes to the survival of Pinus densiflora seedlings at a mining site via providing a possible functional endophyte and maintaining symbiotic relationship between P. densiflora and endophytes from high soil temperature stress

At a sedimentary site in an old mine site, Miscanthus sinensis formed patches, where Pinus densiflora seedlings could grow better compared with those outside the patches, indicating that M. sinensis would improve P. densiflora seedling establishment. The purpose of this study was to understand the mechanisms by which M. sinensis facilitates the survival of P. densiflora seedlings by considering the soil properties, heavy metal tolerance, and root endophytes in P. densiflora seedlings at the sedimentary site. The sedimentary site, which is a bare ground, contained high concentrations of Fe, indicating that plants should be exposed to Fe and high soil temperature stresses. Measurement of soil temperature revealed that M. sinensis suppressed sharp increases and alternation of soil temperature, resulting in reducing high soil temperature stress in P. densiflora seedlings. To adapt to the Fe stress environment, P. densiflora outside and inside the patches produced Fe detoxicants, including catechin, condensed tannin, and malic acid. Ceratobasidium bicorne and Aquapteridospora sp. were commonly isolated from P. densiflora seedlings outside and inside the patches as root endophytes, which might enhance Fe tolerance in the seedlings. Aquapteridospora sp., which is considered as a dark-septate endophyte (DSE), was also isolated from the roots of M. sinensis, suggesting that M. sinensis might play a source of a root endophyte to P. densiflora seedlings. Ceratobasidium bicorne could be classified into root endophytes showing symbiosis and weak pathogenicity to host plants. Therefore, high soil temperature stress would weaken P. densiflora seedlings, causing root endophytic C. bicorne to appear pathogenic. We suggested that P. densiflora could adapt to the Fe stress environment via producing Fe detoxicants, and M. sinensis would facilitate the establishment of P. densiflora seedlings in the sedimentary site by providing a DSE, Aquapteridospora sp., and maintaining symbiosis of C. bicorne from high soil temperature stress.

Application potential of Vaccinium ashei R. for cadmium migration retention in the mining area soil

Despite numerous reports on phytoremediation of heavy metals contaminated soil, there are few reports on plant retention of heavy metals in the mining area slope. This study was the first of its kind to explore the cadmium (Cd) retention capacity of the blueberry (Vaccinium ashei Reade). Firstly, we investigated the stress response of blueberry to different soil Cd concentrations (1, 5, 10, 15, 20 mg/kg) to assess its potential for phytoremediation by pot experiments. The results showed that the blueberry biomass exposed to 10 and 15 mg/kg Cd was significantly increased compared with the control (1 mg/kg Cd); the blueberry crown increased by 0.40% and 0.34% in 10 and 15 mg/kg Cd-contaminated soil, respectively, compared with control; the blueberry heigh did not even change significantly in each treatment group; the total chlorophyll content, peroxidase and catalase activity of blueberry were enhanced in 5-20 mg/kg Cd treatments. Furthermore, the Cd contents of blueberry in the root, stem and leaf increased significantly as the Cd concentration of soil increased. We found that more Cd accumulated in blueberry root: the bioaccumulation concentration factor was root > stem > leaf for all groups; the residual-Cd (Cd speciation) in soil increased by 3.83%-411.11% in blueberry-planted versus unplanted groups; blueberry improved the Cd-contaminated soil micro-ecological environment including soil organic matter, available K and P, as well as microbial communities. Then, to investigate the effect of blueberry cultivation on Cd migration, we developed a bioretention model and revealed that soil Cd transport along the model slope was significantly weakened by blueberry cultivation, especially at the bottom of the model. In a word, this research suggests a promising method for the phytoremediation of Cd-contaminated soil and the reduction of Cd migration in mining areas.

Tracing and quantifying the source of heavy metals in agricultural soils in a coal gangue stacking area: Insights from isotope fingerprints and receptor models

Historic coal gangue stacking probably brings heavy metals (HMs) into the surrounding agricultural soil, posing potential harm to human and environmental health. For better controlling and preventing agricultural soil HMs pollution, the screening of priority pollutants and identification of their pollution pathways are urgent in coal gangue stacking areas. Thus, this study selected a coal gangue stacking area in Chongqing, China as the research object and conducted the pollution evaluation, spatial distribution and source apportionment of the HMs (Cd, Cr, Ni, Cu, Zn, As, Pb and Hg) in surrounding agricultural soil. Results showed that the soil was moderately to heavily contaminated by Cd with average concentrations of 1.23 mg/kg, which were 4.1 times higher than the Environmental Quality Standards for Soils of China. Cd was considered as the soil precedent-controlled pollutant in this study area and subsequent soil δ^114/110Cd values indicated that Cd in surface soils primarily originated from the leachate of coal gangue stacking, which contributed about 89.9 % and 85.47 % to the total soil Cd according to the absolute principal component scores-multiple linear regression model (APCS-MLR) and positive matrix factorization model (PMF), respectively. In addition, other HMs mainly resulted from the leachate of coal gangue, natural and agricultural mixed pollution as well as traffic pollution. Therefore, this study provided basic information for pollution control of the HMs in agricultural soil in the coal gangue stacking area.

Sex-specific competition differently regulates the response of the rhizosphere fungal community of Hippophae rhamnoides-A dioecious plant, under Mn stress

In this study, we investigated the soil physicochemical parameters and responses of rhizospheric fungal communities of Hippophae rhamnoides to Mn stress under different sexual competition patterns. The results showed that competition significantly affects soil physicochemical properties, enzyme activity, and rhizosphere-associated fungal community structures. Under Mn stress, soils with intersexual competition had higher levels of N supply than those with the intrasexual competition. Moreover, fungal communities under intersexual interaction were more positive to Mn stress than intrasexual interaction. Under intrasexual competition, female plants had higher total phosphorus content, neutral phosphatase activity, and relative abundance of symbiotic fungi in soils to obtain phosphorus nutrients to alleviate Mn stress. In contrast, male plants had relatively stable fungal communities in soils. In the intersexual competition, rhizosphere fungal diversity and relative abundance of saprophytic fungi in male plants were significantly higher than in female plants under Mn stress. In addition, female plants showed greater plasticity in the response of rhizosphere microorganisms to their neighbors of different sexes. The microbial composition in soils of female plants varied more than male plants between intrasexual and intersexual competition. These results indicated that sex-specific competition and neighbor effects regulate the microbial community structure and function of dioecious plants under heavy metal stress, which might affect nutrient cycling and phytoremediation potential in heavy metal-contaminated soils.

Lead Responses and Tolerance Mechanisms of Koelreuteria paniculata: A Newly Potential Plant for Sustainable Phytoremediation of Pb-Contaminated Soil

Phytoremediation could be an alternative strategy for lead (Pb) contamination. K. paniculata has been reported as a newly potential plant for sustainable phytoremediation of Pb-contaminated soil. Physiological indexes, enrichment accumulation characteristics, Pb subcellular distribution and microstructure of K. paniculata were carefully studied at different levels of Pb stress (0-1200 mg/L). The results showed that plant growth increased up to 123.8% and 112.7%, relative to the control group when Pb stress was 200 mg/L and 400 mg/L, respectively. However, the average height and biomass of K. paniculata decrease when the Pb stress continues to increase. In all treatment groups, the accumulation of Pb in plant organs showed a trend of root > stem > leaf, and Pb accumulation reached 81.31%~86.69% in the root. Chlorophyll content and chlorophyll a/b showed a rising trend and then fell with increasing Pb stress. Catalase (CAT) and peroxidase (POD) activity showed a positive trend followed by a negative decline, while superoxide dismutase (SOD) activity significantly increased with increasing levels of Pb exposure stress. Transmission electron microscopy (TEM) showed that Pb accumulates in the inactive metabolic regions (cell walls and vesicles) in roots and stems, which may be the main mechanism for plants to reduce Pb biotoxicity. Fourier transform infrared spectroscopy (FTIR) showed that Pb stress increased the content of intracellular -OH and -COOH functional groups. Through organic acids, polysaccharides, proteins and other compounds bound to Pb, the adaptation and tolerance of K. paniculata to Pb were enhanced. K. paniculata showed good phytoremediation potential and has broad application prospects for heavy metal-contaminated soil.

Bacterial community structure and diversity in the rhizospheric soil of Robinia pseudoacacia and Juniperus sabina planted in iron tailings matrix

Iron tailings matrix is deficient in nutrients, and phytoremediation is one of the effective methods to improve tailings nutrients. The response of phytoremediation to tailings microorganisms remains to be studied. The present study analyzed rhizospheric soil of two kinds of plants bacterial diversity and community structure and their relationship with soil environmental factors. The results indicate that the rhizospheric soil bacteria species of Robinia pseudoacacia and Juniperus sabina were not significantly different from that of bare tailings, but rhizospheric soil bacterial community compositions and abundance were significantly different from that of bare tailings. Canonical correlation analysis (CCA) showed that soil alkali-hydrolyzable nitrogen (AN), soil total nitrogen (TN), and soil organic matter (SOM) were the main environmental factors affecting bacterial community diversity. Spearman's correlation analysis showed that AN, TN, and SOM were significantly positively correlated with the relative abundance of Gemmatimonadetes and Nitrospirae, and were significantly negatively correlated with that of Firmicutes, Fusobacteria, and Bacteroidetes. FAPROTAX function prediction showed that the functional microbial communities of rhizospheric soil of the two plants were significantly different from those of bare tailings. Overall, the findings support an increase of microbial diversity, SOM, and nitrogen in rhizospheric soil of revegetated tailings compared to bare tailings. These results provide theoretical support for the development and application of phytoremediation in abandoned mines.

Impact of old environmental burden in the Spiš region (Slovakia) on soil and home-grown vegetable contamination, and health effects of heavy metals

Due to several centuries of ongoing mining activities, Middle Spiš (Slovakia) is one of the areas with a damaged environment. The contents of Fe, Mn, Zn, Cu, Ni, Pb, Cd, and Hg were determined in the soils and home-grown vegetables (potatoes, carrots, tomatoes). Except for Pb, the contents of heavy metals in the soils of some plots were higher than the limit values. Based on the values of Contamination factor (C_f), Degree of contamination (C_deg), Geo-accumulation index (I_geo), and Pollution load index (PLI), very high Fe, Cd, and Hg contamination (C_f ≥ 6), very high soil contamination (C_deg ≥ 20), extremely heavy Fe and Hg contamination (I_geo > 5), resp. moderately pollution to non-pollution (1 < PLI ≤ 2) was found in all plots. In vegetable samples, the maximum levels were exceeded for Cu, Pb, Hg (potato), Pb (carrot, tomato), and Hg (carrot, plot E). Bioaccumulation factor values BAF > 1 were for Cu (carrots, potatoes). Estimated daily intake values for all heavy metals were lower than their tolerable daily intake. Chronic daily intake of heavy metals ranged 2.495E−06 (Hg)—0.1416 (Fe) mg/kg/day. Based on Hazard index values, potato consumption poses a risk (0.8068–1.3057). The results showed that the monitoring of soils and cultivated production is necessary for the investigated area.

Intervention factors associated with environmental stressors resulting from cross-provincial transfers by coal resource-based enterprises

The environmental stressors associated with the cross-provincial transfer of coal resource-based enterprises (CREs) have become a critical concern for the green, sustainable, and high-quality development of resource-rich areas in central and western regions. This study referred to socioeconomic statistics and carried out an interview survey, literature review, and systematic analysis to clarify the mechanism underlying environmental stressors arising from the cross-provincial transfer of CREs. The intervention factors associated with such environmental stressors were identified, and the study conducted an empirical analysis of relevant data related to the coal-resources industry in three central and western provinces in China for the period 1997-2016. Research findings: (1) The intensity ranking of the influencing factors associated with environmental stressors caused by cross-provincial transfers of CREs has certain rules. The 'level of the enterprise's investment in environmental protection' is the weakest, the 'enterprise's development mode level' is slightly stronger, the 'enterprise scale' is stronger, and 'environmental regulation' is the strongest. (2) Stricter endogenous and exogenous policy regulations for environmental governance in rich coal resource-based regions are associated with weaker negative externalities in respect of resource development and the intensity of stressors. (3) Larger CREs are associated with a better green mining capacity, environmental repair cost advantages, social constraints, self-discipline, and thus, a weaker stress effect. (4) CREs that adopt more superior modes of development that focus on the utilization of the 'three wastes' are associated with a weaker stress effect. (5) The higher the level of investment by CREs in environmental protection technology, facilities, and equipment, the weaker the stress effect. The conclusions of the study can provide a theoretical basis to assist the Chinese government to develop relevant regulations to control inter-provincial transfers by CREs and to thereby diminish environmental stressor effects.

Coal gangue modified bioretention system for runoff pollutants removal and the biological characteristics

In this study, coal gangue (CG) was applied as media in bioretention system to remove runoff pollutant. CG modified bioretention systems show good removal efficiency towards runoff pollutant due to the high adsorption capacity of CG. The removal of total phosphorus (TP), total nitrogen (TN), ammonia (NH₄⁺-N) and chemical oxygen demand (COD) by CG modified bioretention systems was influenced by diverse rainfall conditions including rainfall concentration, recurrence period and drying period, and their removal rate ranged 94-99%, 30-70%, 83-97% and 33-86%, respectively. The effluent concentration of Zn, Pb and Cu was as low as 3.14-10.99 μg/L, 0.66-2.56 μg/L and 0.60-3.15 μg/L, respectively. In addition, CG could promote the plant heavy metal uptake and thus decrease their accumulation in soil to a certain extent. Meanwhile, Malondialdehyde (MDA) content and peroxidases (POD) activities of plants in CG modified bioretention were lower than that in tradition bioretention, indicating that CG could help plants recovery and lessened the oxidative stress for the negative impact of high heavy metals accumulation. CG-based media alleviated the inhibitory effect of rainwater runoff pollutant accumulation (especially heavy metals) on microbial diversity and the enhancement of the dominant bacteria (such as Proteobacteria and Bacteroidota) could conduce the nutrients removal in the bioretention systems. In overall, this study demonstrated that the CG modified bioretention systems show an excellent removal performance combine with biological effects.

Release characteristics of elemental mercury during low calorific value coal combustion

The dynamic release characteristics of Hg⁰ during low calorific value coal combustion were investigated in a combining laboratory-scale furnace coupled with atomic fluorescence spectroscopy. The results show that the sulfur has an inhibitory effect on the homogeneous oxidation of Hg⁰ in flue gas. The instant intensity of Hg⁰ release increases with increasing temperature while the amount of Hg⁰ release gradually decreases with increasing temperature. Compared with that under air, the instant intensity of Hg⁰ release under O₂/CO₂ atmosphere increases to some extent with a lower decreasing rate of Hg⁰ release peak. The release ratio of elemental mercury (Hg) from Yuwu (YW) and Qinxin (QX) coal increases while that from Yonghao (YH) coal decreases under O₂/CO₂ atmosphere. In the range of 800-1100°C, the release rate of Hg reaches more than 96% under the residence time of 50 s.

Evaluation of phytoremediation capability of French marigold (Tagetes patula) and African marigold (Tagetes erecta) under heavy metals contaminated soils

The pot experiment was conducted to explore the phytoremediation potential of two different marigold species grown in heavy metals contaminated red, black, alluvial, recent river clay, sewage irrigated, sewage sludge, and garden soil. Different soil types were treated uniformly with lead (20 mg Pb kg^-1 soil), cadmium (5 mg Cd kg^-1 soil), chromium (30 mg Cr kg^-1 soil) and nickel (10 mg Ni kg^-1 soil). Completely randomized design (CRD) was used with three replications. African marigold (Tagetes erecta) recorded ∼89.4% more dry matter yield over French marigold (Tagetes patula) when grown under metals treated soils. Both the marigold species were highly effective for removing Cd and Ni from contaminated soils (TF >1) however, Ni (TF ∼14.9) was more efficiently accumulated by T. patula and Cd (TF ∼12.1) by T. erecta. Higher biomass yield in T. erecta resulted higher accumulation of heavy metals (except Cr) compared to T. patula. Assessment of contamination factor (CF) and geo-accumulation index (I_geo) of heavy metals indicates that post-harvest soils had moderate to high degree of contamination by different metals, Cr being the highest. It may be concluded that T. erecta was more efficient in extracting heavy metals from different heavy metals contaminated soils.Novelty statement Contamination of land with heavy metals poses severe environmental threats. Physical and chemical remediation techniques are generally used for remediating metals contaminated sites. These methods are cost-intensive and therefore, commercially non-viable, besides being disruptive in nature and causing deterioration of soil. Alternatively, bio-remediation techniques are cost-effective and environment friendly. Among the various phytoremediation techniques, hyperaccumulator plants are most commonly used for the remediation of the contaminated sites. It has been found that different species of the same plant (marigold) differ in their ability to accumulate metals under various contaminated soils having different properties. Thus, this experiment provided an unique opportunity to investigate the effect of various soil properties on metal accumulation efficacy of marigold under metal-spiked soils. Marigold plants can grow rapidly by developing a robust root system which helps them to survive under contaminated soil environment. Thus, marigold being ornamental plant could be used to decontaminate polluted sites while providing ornamental value and may serve as a source of commercially valuable products extracting metals from biomass by way of incineration. However, meager information is available about the usage of various marigold species for phytoremediation of heavy metals under different metal-polluted soils. In the current experiment, we intend to evaluate the potential use of two different marigold species (Tagetes patula and Tagetes erecta) in remediating heavy metals under nine soils of different nature spiked with metals and assessing heavy metals pollution load indexes in these polluted soils.

Performance evaluation of crop residue and kitchen waste-derived biochar for eco-efficient removal of arsenic from soils of the Indo-Gangetic plain: A step towards sustainable pollution management

Biochar was produced from wheat straw (Triticum aestivum), rice straw (Oryza sativa), and kitchen waste at varying pyrolysis temperatures (300°C-700 °C). The biochars were screened depending on their production and physicochemical properties for the adsorptive removal of arsenic (As). The morphological analysis by Field emission scanning electron microscope revealed a porous biochar surface. Spectroscopic characterization of biochars indicated the co-existence of minerals, carboxyl, carbonyl, amide, and hydroxyl groups, which implies the suitability of biochar to immobilize metal (loid)s from soils. Changes in peaks were observed in Fourier-transform infrared and X-ray diffraction images after As sorption indicating the involvement of chemisorption. The thermogravimetric analysis and a low H/C value derived from the CHNS analyzer confirmed the high stability of biochar. The BET analysis was used to estimate the surface areas of wheat straw (15.8 m² g^-1), rice straw (12.5 m² g^-1), and kitchen waste (2.57 m² g^-1) -derived biochars. Batch sorption studies were performed to optimize experimental parameters for maximum removal of As. Maximum removal of As was observed for wheat straw-derived biochar (pyrolyzed at 500 °C) at 8 mg L^-1 initial concentration (IC), 7.5 % dose, 25 °C temperature, and 60 min contact time (83.7 ± 0.06 %); in rice straw-derived biochar (pyrolyzed at 500 °C) at 8 mg L^-1 IC, 7.5 % dose, 25 °C temperature, 90 min contact time (83.6 ± 0.37 %); and in kitchen waste-derived biochar (pyrolyzed at 500 °C) at 8 mg L^-1 IC, 5 % dose, 25 °C temperature, 60 min contact time (76.7 ± 0.16 %). The sorption model parameters suggested the possibility of chemisorption, physisorption, diffusion, and ion exchange for the removal of As. Therefore, it could be recommended to farmers that instead of disposing or burning straws and waste openly, they could adopt the process of charring to generate livelihood security and mitigation of geogenic contaminants from the soil/water dynamic systems.

Heavy Metals Presence in the Soil and Their Content in Selected Varieties of Chili Peppers in Slovakia

Capsicum chili peppers are popular vegetables in Slovakia. They provide a supply of health-promoting substances, but contaminated vegetables can pose a serious health risk to the people who consume them. Therefore, the aim of this study was to determine the content of heavy metals (Mn, Zn, Cr, Cu, Ni, Cd, Pb and Hg) in the soil as well as in selected varieties of the genus Capsicum grown in southern Slovakia. The results were compared with the limit values given by the Law no. 220/2004 (valid in the SR) as well as threshold values proposed by the European Commission (EC) (2006). The gained result showed that the total content of Cd (1.64 mg/kg) as well as the available mobile forms of Cd (0.12 mg/kg) and Pb (0.26 mg/kg) was exceeded on the soil on which Capsicum cultivars were grown. The limit values of other monitored heavy metals (Mn, Zn, Cr, Cu, Ni, and Hg) were not exceeded. The studied species of the genus Capsicum did not accumulate monitored heavy metals. It can be stated that consumption of chili peppers does not pose any risk for human health.

Hygienic quality of soil in the Gemer region (Slovakia) and the impact of risk elements contamination on cultivated agricultural products

The Gemer region (Slovakia) belongs to areas with a high concentration of risk elements. The contents of Cu, Ni, Pb, Cd, Hg and Mn were determined in soils and cultivated agricultural production from lands in three cadastres of the Gemer region (Henckovce (48.713845, 20.426189) and Nižná Slaná (48.717373, 20.4208423), cultivated crop—spring triticale; Gemerská Poloma (48.704523, 20.487645), cultivated crop—maize). Bioavailable forms of Pb (0.306–0.532 mg/kg) and Cd (0.104–0.154 mg/kg), pseudototal forms of Cd (3.07–3.98 mg/kg) and Hg (0.484–2.18 mg/kg) represented the highest risk in soils. The highest contents of Pb (Cd, Hg) were in maize from Gemerská Poloma: 0.898 (0.081, 0.399) mg/kg DM. Soils were classified based on several indicators of soil contamination. The highest values of indicators are: Contamination factor (C_f 29.1—Hg), Degree of contamination (C_deg 51.5), Potential ecological risk factor (E_r 1163—Hg), Potential ecological risk index (RI 1,520), Pollution load index (PLI 4.76), Geo-accumulation index (I_geo 5.60—Hg). All indicators concerned the lands of Henckovce and Gemerská Poloma, RI also concerned the land of Nižná Slaná. Bioaccumulation factor (BAF) was calculated to assess the plant's ability to absorb the risk element. For both crops and all risk elements, BAF values were < 1. Obtained results indicate heavy metal contamination of soils, therefore monitoring of soils in investigated area is necessary.

Spatial Heterogeneity of Vegetation Response to Mining Activities in Resource Regions of Northwestern China

Aggregated mining development has direct and indirect impacts on vegetation changes. This impact shows spatial differences due to the complex influence of multiple mines, which is a common issue in resource regions. To estimate the spatial heterogeneity of vegetation response to mining activities, we coupled vegetation changes and mining development through a geographically weighted regression (GWR) model for three cumulative periods between 1999 and 2018 in integrated resource regions of northwestern China. Vegetation changes were monitored by Sen’s slope and the Mann–Kendall test according to a total of 72 Landsat images. Spatial distribution of mining development was quantified, due to four land-use maps in 2000, 2005, 2010, and 2017. The results showed that 80% of vegetation in the study area experienced different degrees of degradation, more serious in the overlapping areas of multiple mines and mining areas. The scope of influence for single mines on vegetation shrunk by about 48%, and the mean coefficients increased by 20%, closer to mining areas. The scope of influence for multiple mines on vegetation gradually expanded to 86% from the outer edge to the inner overlapping areas of mining areas, where the mean coefficients increased by 92%. The correlation between elevation and vegetation changes varied according to the average elevation of the total mining areas. Ultimately, the available ecological remediation should be systematically considered for local conditions and mining consequences.

Mushroom residue modification enhances phytoremediation potential of Paulownia fortunei to lead-zinc slag

Phytoremediation is an effective strategy for the remediation of lead-zinc slag, while the response of plant on lead and zinc was less concerned. In this study, mushroom residue was adding in lead-zinc slag to enhance the phytoremediation potential of P. fortunei, the effects of three treatments (lead-zinc slag, red soil, lead-zinc slag + 10% (m/m) mushroom residue) on the growth, physiology and microstructure of P. fortunei were determined. The results showed that the addition of mushroom residue increased the biomass, plant height and chlorophyll concentration of P. fortunei, indicating that the addition of mushroom residue can facilitate the growth of P. fortunei. Moreover, the proportions of oxalate-Pb forms and phosphate-Zn were dominant in leaves and stems of P. fortunei. With the addition of mushroom residue, Pb and Zn were transformed to the extraction state with weak migration activity, which can reduce the damage level of Pb and Zn to P. fortunei. The results from scanning transmission electron microscopy (STEM) showed that, the mushroom residue amendment could maintain the integrity of the cell structural of P. fortunei. The results from fourier transform infrared spectrometer (FTIR) analysis showed that the mushroom residue amendment could increase the contents of proteins and polysaccharides in P. fortunei, which can combine with the metals. Clearly, the mushroom residue amendment could promote the growth ability of P. fortunei in lead and zinc slag and strengthen the phytoremediation potential.

Excess sulfur and Fe elements drive changes in soil and vegetation at abandoned coal gangues, Guizhou China

Coal gangue piles accumulate outside mines and can persist for years, negatively impacting the regional environment. To determine the main cause of soil pollution at coal gangues, several coal gangues in Guizhou Province, China that had undergone natural recovery via native plants for 8 years were investigated in summer 2019. Three plots (2 m × 2 m) from the coal gangue area were selected for the treatment (GP). Control plots that were 100 m away from GP were also investigated in contrast (CK-near). In addition, plots from forest, farmland and lake land that were far from GP and largely undisturbed were also investigated as more extreme contrasts (CK-far). A series of soil indicators that can be affected by coal-gangue, such as heavy metals (Mn, Cr, Cd, Ni, Zn, Cu, Pb), As, pH, cation exchange capacity (CEC), sulfur (S) and iron (Fe), were tested for in the plots. Plant species, coverage and height were also analyzed to uncover biodiversity and dominant species information. The results suggested that coal gangue significantly influences soil S, pH and plant species after 8 years of natural recovery. The CK-far plots contained relatively low soil sulfur content, normal pH (close to 7) and abundant plant biodiversity. Generally, pH related positively with both the Patrick (R = 0.79, n = 22, p < 0.001) and Shannon indices (R = 0.67, n = 22, p < 0.001); the soil S related negatively with both the Patrick (R = 0.85, n = 22, p < 0.001) and Shannon indices (R = − 0.79, n = 22, p < 0.001). S content was highest (S = 1.0%) in GP plots, was lower in CK-near plots (S = 0.3%) and was the lowest of all in the plots distant from the coal mine (S = 0.1%, CK-far). S content was negatively correlated with pH. Soil pH decreased significantly, from 7.0 in CK-far, to 5.9 in CK-near, to 4.2 in GP. Soil Fe was 3.4 times higher in GP and CK-near than in CK-far. The excess sulfur and Fe elements and the acidified soil drove changes in soil and vegetation in the coal gangue areas. After 8 years of natural recovery, only a few plants, like Miscanthus floridulus, were able to live near the coal gangue in the area where the soil was still acidic and high in S and Fe.

Air pollution tolerance, metal accumulation and dust capturing capacity of common tropical trees in commercial and industrial sites

Total nine tree species of common tropical trees were assessed for their air pollution tolerance, dust capturing capacity and possibility to act as metal bio-monitors in commercial, industrial and control sites. Two seasons sampling was done respectively in monsoon and post-monsoon, to study their seasonal variations. According to Air Pollution Tolerance Index (APTI) values Mangifera indica, Azadirachta indica and Ficus religiosa were the most tolerant species while Ficus bengalensis and Alstonia scholaris were intermediately tolerant towards air pollution. Single factor ANOVA of biochemical parameters between the sampling sites, revealed that APTI of plants did not vary significantly in both the seasons. Site-wise variation was significant both at commercial and industrial sites. The same trend of result was also found in Anticipated Performance Index (API) which also includes other social benefits. So, these species can be recommended for the green belt development in urban commercial and industrial areas. Ficus bengalensis, Ficus religiosa and Mangifera indica were also having the best dust capturing capacity as Scanning Electron Microscope image revealed that they have rough and large surface area of leaf with short petiole and large canopy structure. According to the Geoaccumulation index (Igeo) and Enrichment Factor (EF) of soil in the sampling sites were found to be contaminated with copper and cadmium. Psidium guajava, Mangifera indica, Alstonia scholaris and Ficus religiosa were found to be good phytoextractors of copper. They did not accumulate cadmium. So, these plants can be recommended as copper bioindicators. However, the metals accumulation efficiencies were high for Mangifera indica and Ficus religiosa.

Distribution and health risk assessment of potentially toxic elements in soils around coal industrial areas: A global meta-analysis

Coal production and utilization are recognized as two principal sources of potentially toxic elements in the environment. Here the published literature (2008-2018) was searched to collect data on As, Ni, Cd, Cu, Cr, Hg, Pb and Zn concentrations in soils near different types of coal industrial areas such as coal mines, thermal power plants, coal chemical plants, coal mining cities and coal waster piles. The contamination levels of soils and associated health risks were assessed using global reference materials and multiple contamination indices. The results revealed that average concentrations of potentially toxic elements varied widely, yet most of them exceeded global averages in background soils and upper continental crust concentrations. Spatial distribution analysis suggested the concentrations of potentially toxic elements varied according to coalification and combustion conditions. Higher concentrations were found in Southeast Asia, South Europe, and North Africa compared with other regions. Assessment of the geoaccumulation index revealed that contamination levels of Cd and Hg were higher than those of other elements. In particular, Ni, Cd, Zn, and Hg were most likely to accumulate in soils near coal mining areas, while Cd and Hg tended to accumulate near coal chemical plants. Regarding non-carcinogenic risks, oral ingestion was the major pathway of exposure to potentially toxic elements in coal industry-associated soils, followed by dermal contact and inhalation. Tolerable non-carcinogenic risk of potentially toxic elements and relatively high carcinogenic risks of As were observed. Children were most vulnerable to non-carcinogenic risks, while the carcinogenic risks estimated for adult and children populations were similar. Accordingly, As should be designated as top candidates for priority control to protect human health in the vicinity of coal industry-associated areas. This study provides timely information for developing control and management strategies to reduce soil contamination by potentially toxic elements in different types of coal industrial areas.

Evaluation of the phytoremediation potential of dominant plant species growing in a chromium salt-producing factory wasteland, China

The metal contents of the soil and plant tissues in a large chromium salt-producing factory wasteland were determined to assess the properties of soil contamination and to identify plant species accumulating a range of heavy metals. Total metal contents in the factory soils presented a high heterogeneity, and the principal contaminants were Cd and Cr. All plant species examined were metal-tolerant, but to different extents. Especially, the maximum accumulation of Cd (15.61 mg kg^-1) and Cr (925.07 mg kg^-1) was found in Melia azedarach L. Subsequently, the Cd and Cr bioaccumulation and diverse physiological properties of M. azedarach seedlings exposed to different concentrations of Cd(II), Cr(VI), or Cd(II) + Cr(VI) in nutrient solutions were further investigated. All treated seedlings were able to survive under heavy metal stress, and the accumulation of both metals in plant tissues increased with elevation of metal exposure strength. M. azedarach showed a BCF greater than 147.56 for Cd and 36.76 for Cr. Meanwhile, the TF was lower than 0.25 for Cd and 0.32 for Cr. The highest bioaccumulation in root tissues was 2708.03 mg kg^-1 Cd and 824.65 mg kg^-1 Cr for seedlings cultured with 20 mg L^-1 Cd(II) or 20 mg L^-1 Cr(VI). Cd and Cr increased each other's uptake in seedlings although a reduced accumulation in roots occurred when exposed to the highest concentration of Cd(II) + Cr(VI) treatment (20 mg L^-1). At either level of concentration, the degree of plant growth inhibition and oxidative damage caused by heavy metals was Cd(II) + Cr(VI) > Cr(VI) > Cd(II). Superoxide dismutase and peroxidase exhibited positive and effective responses to low-Cd(II) or Cr(VI) concentration stress, but their activities decreased with increasing metal exposure strength. The behavior of the non-enzymatic antioxidants (GSH, soluble protein, and proline) in plant involved in the detoxification of ROS induced by metal exposure was correlated well with higher Cd and Cr accumulations. Here, the potentiality of M. azedarach with the capacity to accumulate and stabilize Cd/Cr in metal-contaminated soil by phytoremediation process has been explored.

The potential of elm trees (Ulmus glabra Huds.) for the phytostabilisation of potentially toxic elements in the riparian zone of the Sava River

The use of trees to immobilise potentially toxic elements (PTEs) is a low-cost and effective method of soil remediation. Thus, the objective of this study was to assess the content of total and bioavailable As, Cd, Cr, Cu, Ni, Pb and Zn in soil samples, as well as their levels in the roots and leaves of elm (Ulmus glabra Huds.) in order to evaluate its potential for the phytostabilisation of PTEs in the riparian zone of the Sava River. Analysis of soils showed that the availability of PTEs ranged from low to medium, while the pollution load index (PLI) and potential ecological risk index (RI) showed that the examined soil fell into the category of uncontaminated to moderately contaminated, as well as into the category of low risk of PTEs contamination. However, the levels of Cr, Cu and Ni in soils were above the critical range for plants. The content of As and Cr measured in roots and leaves was in the toxic range for plants, while the content of Cd and Ni was elevated but not in the toxic range. Bioaccumulation (BCF) and translocation (TF) factors indicated that U. glabra is suitable for the phytostabilisation of As, Cu, Cr, Ni and Pb. Additionally, this species displayed the ability to transport most of the acquired Cu and Zn to the leaves. Correlation analysis showed that PTE content in U. glabra roots was significantly positively correlated to their respective levels in soil (total and DTPA-extractable), except for Cu, indicating that PTE levels in soil strongly influence those in plants. This research into a successful phytoremediating species provides new possibilities when selecting PTE-tolerant native trees in riparian zones of large regional rivers such as the Sava.

Assessment of the content, occurrence, and leachability of arsenic, lead, and thallium in wastes from coal cleaning processes

The aim of the study was to evaluate the content, occurrence, and leachability of arsenic (As), lead (Pb), and thallium (Tl) in wastes from coal cleaning processes with respect to the safe management of this waste. The study focused on wastes resulting from the wet gravitation and flotation processes employed for the purposes of coking coal cleaning in four coal mines situated in the Upper Silesian Coal Basin (Poland). The scope of the study included (i) determination of the content of these elements in the investigated wastes using atomic absorption spectrometry, (ii) evaluation of their mode of occurrence using electron microprobe analysis, and (iii) preliminary assessment of their leachability in deionized water. The content of the analyzed elements in the examined samples of coal waste was twice as high as the average content of these elements in the Earth's crust. The contents of As and Pb, however, did not exceed their permissible contents in inert waste in accordance with Polish legal regulations based on EU directives. The limit on the content of Tl is not specified by these regulations, but its amount in the examined samples was similar to that occurring in the soils. Moreover, leaching tests have shown that these elements are hardly eluted from the analyzed material. Their content in the water leachates was generally lower than the detection limit of the analytical method, complying with the standards for good and very good water quality. Low leachability of these elements most probably results from their mode of occurrence in the investigated wastes. The chemical analysis using an electron microprobe and the analysis of the correlation between these elements, e.g., total and pyritic sulfur, have shown that Pb, As, and Tl are mainly found in sulfide minerals which are characterized by negligible solubility. In conclusion, the investigated hard coal processing waste does not constitute a threat to the environment and can be commercially used or safely neutralized, e.g., by landfilling.

Response to cadmium and phytostabilization potential of Platycladus orientalis in contaminated soil

The tolerance characteristics and phytostabilization potential of Platycladus orientalis grown in soil contaminated by cadmium (Cd) were studied using a greenhouse experiment. The results showed that the ornamental plant P. orientalis had high tolerance for Cd in contaminated soil at 24.6 mg·kg^-1 and its physiological activities were slightly affected after 203 days (d) of cultivation. Moreover, Cd in soil at 9.6 mg·kg^-1 was beneficial for P. orientalis growth, and the total biomass after 203 d cultivation was significantly (p < 0.05) increased by 35.03%, while the contents of chlorophyl a, chlorophyl b and carotenoid in leaves also increased by 20.84%, 44.06% and 28.25% compared to the control, respectively. Meanwhile, the Cd content in the tissues of P. orientalis was increased with both plant growth and the Cd content in the soil. The uptake of Cd in P. orientalis roots was greater than in shoots, with the Cd content in roots reaching 41.45 mg·kg^-1. P. orientalis, an ornamental plant, that accumulates Cd predominantly in its roots, can be suggested as a promising plant for phytostabilization in Cd-contaminated soil.

Municipal sewage sludge compost promotes Mangifera persiciforma tree growth with no risk of heavy metal contamination of soil

Application of sewage sludge compost (SSC) as a fertilizer on landscaping provides a potential way for the effective disposal of sludge. However, the response of landscape trees to SSC application and the impacts of heavy metals from SSC on soil are poorly understood. We conducted a pot experiment to investigate the effects of SSC addition on Mangifera persiciforma growth and quantified its uptake of heavy metals from SSC by setting five treatments with mass ratios of SSC to lateritic soil as 0%:100% (CK), 15%:85% (S15), 30%:70% (S30), 60%:40% (S60), and 100%:0% (S100). As expected, the fertility and heavy metal concentrations (Cu, Zn, Pb and Cd) in substrate significantly increased with SSC addition. The best performance in terms of plant height, ground diameter, biomass and N, P, K uptake were found in S30, implying a reasonable amount of SSC could benefit the growth of M. persiciforma. The concentrations of Cu, Pb and Cd in S30 were insignificantly different from CK after harvest, indicating that M. persiciforma reduced the risk of heavy metal contamination of soil arising from SSC application. This study suggests that a reasonable rate of SSC addition can enhance M. persiciforma growth without causing the contamination of landscaping soil by heavy metals.

Phytoextraction of potentially toxic elements by six tree species growing on hazardous mining sludge

The aim of the study was to compare the phytoextraction abilities of six tree species (Acer platanoides L., Acer pseudoplatanus L., Betula pendula Roth, Quercus robur L., Tilia cordata Miller, Ulmus laevis Pall.), cultivated on mining sludge contaminated with arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), thallium (Tl), and zinc (Zn). All six tree species were able to survive on such an unpromising substrate. However, A. platanoides and T. cordata seedlings grown on the polluted substrate showed significantly lower biomass than control plants (55.5 and 45.6%, respectively). As, Cd, Cu, Pb, and Tl predominantly accumulated in the roots of all the analyzed tree species with the following highest contents: 1616, 268, 2432, 547, and 856 mg kg^-1, respectively. Zn was predominantly localized in shoots with the highest content of 5801 and 5732 mg kg^-1 for U. laevis and A. platanoides, respectively. A. platanoides was the most effective in Zn phytoextaction, with a bioconcentration factor (BCF) of 8.99 and a translocation factor (TF) of 1.5. Furthermore, with the exception of A. pseudoplatanus, the analyzed tree species showed a BCF > 1 for Tl, with the highest value for A. platanoides (1.41). However, the TF for this metal was lower than 1 in all the analyzed tree species. A. platanoides showed the highest BCF and a low TF and could, therefore, be a promising species for Tl phytostabilization. In the case of the other analyzed tree species, their potential for effective phytoextraction was markedly lower. Further studies on the use of A. platanoides in phytoremediation would be worth conducting.