Enhancing soil ecological security through phytomanagement of tailings in erosion-prone areas

Lead source apportionment and climatic impacts in rural environmental justice mining communities

After a sequence of natural disasters in Gila County, Arizona, USA environmental justice (EJ), mining areas, community members raised concerns about metal(loid)s exposure and origin. To address these concerns, non-residential sediments (0-2 cm, 2-15 cm, and 15-30 cm), household soil (0-2 cm), and indoor and outdoor dust samples were analyzed for metal(loid)s concentration and Pb isotopes via inductively coupled plasma mass spectrometry. To identify the potential sources of Pb, 37 studies were considered, and 21 different Pb isotopic ratios were documented and compared. Spearman's correlation and principal component analysis were used to investigate the co-occurrence of metal(loid)s associated with Pb. The results demonstrated a clear association (p < 0.05) between Pb and mining activity in households and non-residential locations as well as a co-occurrence with As, Cd, Cu, Mo, Sb, and Zn at 0-2 cm and in non-residential with As, Cd, and Zn at 2-15 cm and 15-30 cm. The outdoor household dust was impacted by a mixture of Pb sources and was associated with metal(loid)s coming from mining, wildfire, lead based-paint and landfill, whereas indoor Pb dust was associated mainly with metal(loid)s coming from geogenic sources. Further, 66% of town/city sediment samples across depth and 53.8% of outdoor dust samples were aligned with mining fingerprint and 30.1% of outdoor dust and 25% of household soil samples were aligned with the wildfire Pb isotopic ratio/fingerprint. The Positive Matrix Factorization model illustrates flood's ability to remobilize metal(loid)s from neighboring mine sites to the households' locations. Currently there is no established Pb isotopic ratio composition for wildfires in Arizona; this study lays the foundation for understanding the complex relationship between the myriads of lead sources in our environment, wildfires, and flooding.

Phytostabilization potential and microbial response to the reclamation of native Cynodon dactylon in spoil heaps from a multiple-metal mining site in Southwest China

Phytocapping offers a sustainable approach for managing exposed tailings by mitigating pollutant spread and enhancing phytoremediation. This study investigates the potential of Bermudagrass (Cynodon dactylon) as a pioneering plant for rehabilitating tailings from an open-pit lead-zinc mine in Southwest China. Our findings demonstrate that Bermudagrass significantly improved soil quality and multifunctionality compared to adjacent bare tailings. Soil improvements included increases in organic matter (107%), total and available nitrogen (50% and 110%, respectively), available phosphorus (170%), and soil enzyme activities, including β-glucosidase (170%), sucrase (1729%), alkaline phosphatase (3722%), and acid phosphatase (168%). The reclamation process also promoted microbial community succession, altering community composition, improving microbial diversity, and enhancing bacterial biomass from (0.89 ± 0.54) × 1015 to (9.06 ± 3.25) × 1015 copies/g in rhizosphere soils. Greenhouse experiments further confirmed Bermudagrass's resilience to cadmium (Cd), with both mining and non-mining ecotypes thriving in tailing soils and Cd2+ hydroponic solutions (up to 44.5 μM) without evident phytotoxicity. Bermudagrass roots exhibited exceptional Cd accumulation (bioconcentration factor: 181-1006) while minimizing Cd translocation to shoots (translocation factor: <0.13). Inoculation with Funneliformis mosseae, a restored root-mutually symbiotic fungus, further mitigated Cd-induced phytotoxicity and enhanced plant growth. These findings highlight Bermudagrass as a promising pioneer species for phytostabilization in severely contaminated mining environments, with its rhizosphere microbiome playing a critical role in facilitating ecosystem restoration. Sustainable plant establishment in mine waste rock requires concurrent development of belowground fertility and healthy rhizospheric soil. Ultimately, successful revegetation depends on integrated above and belowground development to achieve long-term ecological restoration.

Arsenic and Heavy Metals in Soils and Plants near Sulfide Mines: Implications for Phytoremediation and Phytomanagement

The accumulation of heavy metals (i.e., As, Cu, Ni, Pb, and Zn) in soils and native plant species near copper, nickel, and pyrite mines in Vietnam was assessed. The highest soil As, Cu, Ni, Pb, and Zn concentrations recorded in mine soils were 42.3, 1570, 9870, 128, and 462 mg/kg, and those in agricultural soils were 11.4, 453, 94.9, 34.4, and 147 mg/kg, respectively. Pollution index (PI) values indicated heavy pollution (PI = 3.99-13.0) for mine soils, and unpolluted to severely polluted (PI = 0.65-2.84) for agricultural soils. Soil enrichment factors had a wide range, from minimal to extreme enrichment of heavy metals (EF = 0.03-91.4). Arsenic minerals may be the main source of high As concentrations in sulfide mines. The As, Cu, Ni, Pb, and Zn concentrations of 20 native plant species near three mines were in the ranges of 0.05-1150, 3.17-123, 0.47-291, 0.08-6.34, and 6.87-168 mg/kg (dry weight, DW), respectively. Based on the recorded hyperaccumulation levels (1150 mg/kg, DW), bioaccumulation factors (BAF = 2.4-90.0), biomass, and rapid growth, Pteris vittata L. is considered a promising plant for phytoextraction of As in soils. Bidens pilosa L. has potential for phytostabilization of sulfide-bearing soils, given its low concentrations of heavy metals in plant shoots, BAF values of <1, high biomass, and wide distribution. Integrated phytoremediation and phytomanagement are applicable to metal-contaminated soils. Phytomining, energy crops, and vegetation cover should be investigated for the phytomanagement of metal-contaminated soils in mining areas.

The impact of abandoned iron ore on the endophytic bacterial communities and functions in the root systems of three major crops in the local area

Introduction

Global mining activities have significant impacts on ecosystems, but most studies have focused only on the relationship between soil physicochemical properties and microbial diversity in soils. The present study provides an insight into the effects of mining activities on soil physico-chemical properties and endophytic bacterial community composition in the rhizosphere of three different crops.

Methods

Musa basjoo Siebold L., Amygdalus persica L., and Triticum aestivum L. were collected from the inter-root soils and plant roots to determine the soil physicochemical properties and endophytic bacterial communities in the root system.

Results

The results showed that mining resulted in soil acidification, altered trace element content and increased organic carbon. There was an increase in the Ascomycota and Actinobacteria phylum of crop root bacteria. Interestingly, the chao1 and shannon indices of the root endophytes of the mining crop were significantly elevated compared to the contro (p < 0.05). Among them, Musa basjoo Siebold showed the highest level of community richness in the mining environment. The mining environment resulted in functional enrichment of histidine kinases and oxidoreductases in the bacterial community. The total potassium (TK) content in the soil, as well as the Fe and Pb content, were positively correlated with the α-diversity index and Streptomyces. Zn and Ti content were significantly negatively correlated with the α-diversity index.

Discussion

This study provides data support for exploring the mechanisms of plant response to the mining environment and developing ecological restoration strategies for mining areas.

Machine learning models with innovative outlier detection techniques for predicting heavy metal contamination in soils

Machine learning (ML) models for accurately predicting heavy metals with inconsistent outputs have improved owing to dataset outliers, which influence model reliability and accuracy. A comprehensive technique that combines machine learning and advanced statistical methods was applied to assess data outlier's effects on ML models. Ten ML models with three outlier detection methods predicted Cr, Ni, Cd, and Pb in Narayanganj soils. XGBoost with density-based spatial clustering of applications with noise (DBSCAN) improved model efficacy (R2). The R2 of Cr, Ni, Cd, and Pb was considerably enhanced by 11.11 %, 6.33 %, 14.47 %, and 5.68 %, respectively, indicating that outliers affected the model's HM prediction. Soil factors affected Cr (80 %), Ni (72.61 %), Cd (53.35 %), and Pb (63.47 %) concentrations based on feature importance. Contamination factor prediction showed considerable contamination for Cr, Ni, and Cd. LISA revealed Cd (55.4 %), Cr (49.3 %), and Pb (47.3 %) as the significant pollutant (p < 0.05). Moran's I index values for Cr, Ni, Cd, and Pb were 0.65, 0.58, 0.60, and 0.66, respectively, indicating strong positive spatial autocorrelation and clusters with similar contamination. Finally, this work successfully assessed the influence of data outliers on the ML model for soil HM contamination prediction, identifying crucial regions that require rapid conservation measures.

Bacterial consortium amendment effectively reduces Pb/Cd bioavailability in soil and their accumulation in wheat

Microbial remediation can maintain the sustainability of farmlands contaminated with heavy metals (HMs). However, the effects of bacterial consortium on crop growth and potential risks under HM stress, as well as its mechanisms, are still unclear compared with a single microorganism. Here, we investigated the effect of a bacterial consortium consisting of some HMs-resistant bacteria, including Bacillus cereus, Bacillus thuringiensis, and Herbaspirillum huttiense, on plant growth promotion and inhibition of Pb/Cd accumulation within different contaminated soil-wheat systems through pot experiments. The results showed that microbial inoculation alleviated HMs-induced growth inhibition by activating antioxidant enzymes and inhibiting lipid peroxidation, and enhanced plant growth in the bacterial consortium. Compared to a single strain (Bacillus cereus, Bacillus thuringiensis, or Herbaspirillum huttiense), the bacterial consortium was more conducive to improving root development and reducing the content of available HMs in soil (4.5-10.3%) and its transfer to shoot (4.3-8.4%). Moreover, bacterial consortium significantly increased soil enzyme activities and available nutrients, resulting in nearly twice that of a single strain on the effect of soil quality and plant growth. Correlation analysis and least square path analysis showed that the bacterial consortium could significantly reduce the HMs-enrichment/transport from soil to shoot than a single strain by regulating soil available HMs and biochemical properties, as well as the parameters for plant growth. This study emphasizes that bacterial consortium promotes the growth of the crop wheat and reduces the risk of HMs entering human food chain, further providing an effective strategy for the safe production of food crops in contaminated soils.

Biochar Organic Fertilizer Combined with Indigenous Microorganisms Enhances the Growth of Landscape Grass Cultivated in a Substrate Mixed with Iron Tailings and Mining Topsoil

Iron tailings from the mining process occupy vast land areas and pose a significant ecological risk. In order to reuse iron tailings resources and carry out in situ ecological restoration of a mine, in this study, a medium of mixed iron tailings and mining topsoil (m:m = 3:1) was used to plant landscape grasses, including Lolium perenne L. (L. perenne), Pennisetum alopecuroides (L.) Spreng. (P. alopecuroides), Melilotus officinalis (L.) Lam. (M. officinalis), and Medicago sativa L. (M. sativa). Biochar and chicken manure were used as biochar organic fertilizers and indigenous microorganisms were isolated from the rhizosphere soil of tested grasses. They were applied to enhance landscape grass growth by regulating rhizosphere microbial communities and nutrient conditions. The results showed that the biochar organic fertilizers significantly promoted the growth of the four landscape grasses, notably P. alopecuroides, increasing plant height, root length, root weight, and leaf fresh weight by 169%, 60%, 211%, and 388%, respectively. Additionally, L. perenne exhibited the greatest height increase (10%) following the application of bacterial solutions. Moreover, indigenous bacterial solutions enhanced chlorophyll content and phenylalanine ammonia-lyase (PAL) activity, with P. alopecuroides showing the highest chlorophyll increase of 58% and M. sativa exhibiting a 30.58% rise in PAL activity. The biochar organic fertilizer also significantly elevated soluble protein content in P. alopecuroides and M. sativa by 195% and 152%, respectively. It also effectively enhanced peroxidase (POD) activity in Poaceae grasses by 120% to 160%. After adding indigenous microorganisms, the rhizosphere soil of the landscape grass showed the highest Shannon-Wiener diversity index, reaching 3.561. The rhizosphere soil of M. officinalis had the highest microbial richness, with a value of 39. Additionally, the addition of indigenous microorganisms increased the nitrogen, phosphorus, and potassium content of the four plants by 8-19%, 6-14%, and 8-18%, respectively. This study offers a new approach for managing mining waste and ecological restoration in mining areas.

Diversified Vegetation Cover Alleviates Microbial Resource Limitations within Soil Aggregates in Tailings

Resource demand by soil microorganisms critically influences microbial metabolism and then influences ecosystem resilience and multifunctionality. The ecological remediation of abandoned tailings is a topic of broad interest, yet our understanding of microbial metabolic status in restored soils, particularly at the aggregate scale, remains limited. This study investigated microbial resources within soil aggregates from revegetated tailings and applied a vector model of ecoenzymatic stoichiometry to examine how different vegetation patterns (grassland, forest, or bare land control) impact microbial resource limitation. Five-year vegetation restoration significantly elevated carbon (C) and nitrogen (N) concentrations and their stoichiometric ratios in soil aggregates (approximately 2-fold), although these increases were not translated to in the microbial biomass and its stoichiometry. The activities of C- and phosphorus (P)-acquiring extracellular enzymes in these aggregates increased substantially postvegetation, with the most pronounced escalation in macroaggregates (>0.25 mm). The vector model results indicated soil microbial metabolism was colimited by C and P, most acutely in microaggregates (<0.25 mm). This colimitation was exacerbated by monotypic vegetation cover but mitigated under diversified vegetation cover. Soil nutrient stoichiometric ratios in vegetation restoration controlled microbial resource limitation, overshadowing the impact of heavy metals. Our findings underscore that optimizing resource allocation within soil aggregates through strategic revegetation can enhance microbial metabolism in tailings, which advocates for the implementation of diverse vegetation covers as a viable strategy to improve the ecological development of degraded landscapes.

Accelerated export and transportation of heavy metals in watersheds under high geological backgrounds

The geological background level of metals plays a major role in mineral distribution and watershed diffuse heavy metal (HM) pollution. In this study, field research and a distributed hydrological model were used to analyze the distribution, sources, and pollution risk of watershed HMs in sediments with high geological HM backgrounds. Study showed that the mineral distribution and landcover promoted the transport differences of watershed HMs from upstream to the estuary. And the main sources of Co, Ni, and V in the estuarine sediments were natural sources. Sources of Pb and Zn were dominated by anthropogenic sources, accounting for 76% and 64% of their respective totals. The overall ecological risk of anthropogenically sourced HMs was dominated by Pb (46.6%), while the contributions of Co and Ni were also relatively high, accounting for 35.70% and 33.40%. Moreover, redundancy analysis showed that HM variations in the sediments were most sensitive to soil erosion and mineralizing rock distribution. The spatial patterns of watershed HMs from natural sources were significantly influenced by P loading, precipitation, and forest distribution. This combination of experiments and model improves the understanding of watershed HM variation and provides a new perspective for formulating effective watershed HM management strategies.

Effects of naturally aged microplastics on the distribution and bioavailability of arsenic in soil aggregates and its accumulation in lettuce

Naturally aged microplastics (NAMPs) and arsenic (As) have been reported to coexist in and threaten potentially to soil-plant ecosystem. The research explored the combined toxic effects of NAMPs and As to lettuce (Lactuca sativa L.) growth, and the distribution, accumulation and bioavailability of As in soil aggregates. The As contaminated soil with low, medium and high concentrations (L-As, M-As, H-As) were treated with or without NAMPs, and a total of six treatments. The results displayed that, in comparison to separate treatments of L-As and M-As, the presence of NAMPs increased the total biomass of lettuce grown at these two As concentrations by 68.9 % and 55.4 %, respectively. Simultaneous exposure of NAMPs and L-As or M-As led to a decrease in As content in shoot (0.45-2.17 mg kg-1) and root (5.68-14.66 mg kg-1) of lettuce, indicating an antagonistic effect between them. In contrast, co-exposure to H-As and NAMPs showed synergistic toxicity, and the leaf chlorophyll and nutritional quality of lettuce were also reduced. NAMPs altered the ratio of different soil aggregate fractions and the distribution of bioavailable As within them, which influenced the absorption of As by lettuce. In conclusion, these direct observations assist us in enhancing the comprehend of the As migration and enrichment characteristics in soil-plant system under the influence of NAMPs.