Less is more: A new strategy combining nanomaterials and PGPB to promote plant growth and phytoremediation in contaminated soil

Novel combination strategies of nanomaterials (NMs) and plant growth-promoting bacteria (PGPB) may facilitate soil remediation and plant growth. However, the efficiency of the NM-PGPB combination and interactions among NMs, PGPB, and plants are still largely unknown. We used multiwalled carbon nanotubes (MWCNTs) and zero-valent iron (nZVI) combined with Bacillus sp. PGP5 to enhance the phytoremediation efficiency of Solanum nigrum on heavy metal (HM)-contaminated soil. The NM-PGPB combination showed the best promoting effect on plant growth, which also had synergistic effects on the bioaccumulation of HMs in S. nigrum. The MWCNT-PGP5 combination increased the Cd, Pb, and Zn removal efficiency of S. nigrum by 62.03%, 69.44%, and 61.31%, respectively. The underlining causes of improved plant growth and phytoremediation by NMs-PGPB combination were further elucidated. NM application promoted PGPB survival in soil. Compared with each single application, the combined application minimized disturbance to plant transcription levels and rhizosphere microbial community, resulting in the best performance on soil remediation and plant growth. The NM-PGPB-induced changes in the microbial community and root gene expression were necessary for plant growth promotion. This work reveals the "less is more" advantage of the NM-PGPB combination in soil remediation, providing a new strategy for soil management.

Exploring the primary magnetic parameters affecting chemical fractions of heavy metal(loid)s in lake sediment through an interpretable workflow

The magnetic properties of lake sediments account for close relationships with heavy metal(loid)s (HMs), but little is known about their relationships with chemical fractions (CFs) of HMs. Establishing an effective workflow to predict HMs risk among various machine learning (ML) methods in conjunction with magnetic measurement remains challenging. This study evaluated the simulation efficiency of nine ML methods in predicting the risk assessment code (RAC) and ratio of the secondary and primary phases (RSP) of HMs with magnetic parameters in sediment cores of a shallow lake. The sediment cores were collected and sliced, and the total amount and CFs of HMs, as well as magnetic parameters, were determined. Support vector machine (SVM) outperformed other models, as evidenced by coefficient of determination (R2) > 0.8. Interpretable machine learning (IML) methods were employed to identify key indicators of RAC and RSP among the magnetic parameters. Values of χARM, HIRM, χARM/χ, and χARM/SIRM of sediments ranging in 220-500 × 10-8 m3/kg, 30-40 × 10-5Am2/kg, 15-25, and 0.5-1, respectively, indicated the potential ecological risks of Cd, Hg, and Sb. This study offers new perspectives on the risk assessment of HMs in lake sediments by combining magnetic measurement with IML workflow.

Long-term and combined heavy-metal contamination forms a unique microbiome and resistome: A case study in a Yellow River tributary sediments

Microorganisms have developed mechanisms to adapt to environmental stress, but how microbial communities adapt to long-term and combined heavy-metal contamination under natural environmental conditions remains unclear. Specifically, this study analyzed the characteristics of heavy metal composition, microbial community, and heavy metal resistance genes (MRGs) in sediments along Mang River, a tributary of the Yellow River, which has been heavily polluted by industrial production for more than 40 years. The results showed that the concentrations of Cr, Zn, Pb, Cu and As in most sediments were higher than the ambient background values. Bringing the heavy metals speciation and concentration into the risk evaluation method, two-thirds of the sediment samples were at or above the moderate risk level, and the ecological risk of combined heavy metals in the sediments decreased along the river stream. The high ecological risk of heavy metals affected the microbial community structure, metabolic pathways and MRG distribution. The formation of a HM-resistant microbiome possibly occurred through the spread of insertion sequences (ISs) carrying multiple MRGs, the types of ISs carrying MRGs outnumber those of plasmids, and the quantity of MRGs on ISs is also higher than that on plasmids. These findings could improve our understanding of the adaptation mechanism of microbial communities to long-term combined heavy metal contamination.

Influence of bioaugmented fungi on tolerance, growth and phytoremediation ability of Prosopis juliflora Sw. DC in heavy metal-polluted landfill soil

The research aimed to determine the influence of endophytic fungi on tolerance, growth and phytoremediation ability of Prosopis juliflora in heavy metal-polluted landfill soil. A consortium of 13 fungal isolates as well as Prosopis juliflora Sw. DC was used to decontaminate heavy metal-polluted landfill soil. Enhanced plant growth (biomass and root and shoot lengths) and production of carotenoids, chlorophyll and amino acids L-phenylalanine and L-leucine that are known to enhance growth were found in the treated P. juliflora. Better accumulations of heavy metals were observed in fungi-treated P. juliflora over the untreated one. An upregulated activity of peroxidase, catalase and ascorbate peroxidase was recorded in fungi-treated P. juliflora. Additionally, other metabolites, such as glutathione, 3,5,7,2',5'-pentahydroxyflavone, 5,2'-dihydroxyflavone and 5,7,2',3'-tetrahydroxyflavone, and small peptides, which include Lys Gln Ile, Ser Arg Ala, Asp Arg Gly, Arg Ser Ser, His His Arg, Arg Thr Glu, Thr Arg Asp and Ser Pro Arg, were also detected. These provide defence supports to P. juliflora against toxic metals. Inoculating the plant with the fungi improved its growth, metal accumulation as well as tolerance against heavy metal toxicity. Such a combination can be used as an effective strategy for the bioremediation of metal-polluted soil.

Impacts of gas flaring on soil physicochemical and microbial properties: A case study on kailashtila gas field

Gas flaring, a common practice in many countries, has been associated with environmental and health concerns. A recent study in Bangladesh's largest gas field, Kailashtilla, assessed the influence of gas flaring on soil quality in the surrounding areas. Physical, chemical, and microbiological characteristics were assessed on soil samples collected from three union zones. Considerable influences have been found on soil quality, with several physical and chemical characteristics failing to meet the standards for healthy plant growth. Heavy metal contamination in the earth's soil was identified, specifically cadmium and lead, having a risk index indicating a moderate risk to the ecosystem in the future. Gas flaring also impacted the amount of bacteria in the soil, with the highest number being found farthest from the flaring zone. The soil was only marginally contaminated and potential health risks found. AAS and digestion methods were used to estimate the content of heavy metal contamination in the soil. To depict the geographically distributed abundance of heavy metals in the study area, the Kriging spatial interpolation procedure was utilized, and PCA and CA were used to assess the condition of soil. Findings indicate that particular gas flaring may have a deleterious influence on soil bacteria, which could have further consequences for the ecosystem. The study is likely to contribute to our understanding of the current state of soil's surrounding gas fields and serve as a platform for future research in this area emphasizing the necessity for sustainable energy methods and the importance of limiting environmental repercussions.

How plants respond to heavy metal contamination: a narrative review of proteomic studies and phytoremediation applications

MAIN CONCLUSION

Heavy metal pollution caused by human activities is a serious threat to the environment and human health. Plants have evolved sophisticated defence systems to deal with heavy metal stress, with proteins and enzymes serving as critical intercepting agents for heavy metal toxicity reduction. Proteomics continues to be effective in identifying markers associated with stress response and metabolic processes. This review explores the complex interactions between heavy metal pollution and plant physiology, with an emphasis on proteomic and biotechnological perspectives. Over the last century, accelerated industrialization, agriculture activities, energy production, and urbanization have established a constant need for natural resources, resulting in environmental degradation. The widespread buildup of heavy metals in ecosystems as a result of human activity is especially concerning. Although some heavy metals are required by organisms in trace amounts, high concentrations pose serious risks to the ecosystem and human health. As immobile organisms, plants are directly exposed to heavy metal contamination, prompting the development of robust defence mechanisms. Proteomics has been used to understand how plants react to heavy metal stress. The development of proteomic techniques offers promising opportunities to improve plant tolerance to toxicity from heavy metals. Additionally, there is substantial scope for phytoremediation, a sustainable method that uses plants to extract, sequester, or eliminate contaminants in the context of changes in protein expression and total protein behaviour. Changes in proteins and enzymatic activities have been highlighted to illuminate the complex effects of heavy metal pollution on plant metabolism, and how proteomic research has revealed the plant's ability to mitigate heavy metal toxicity by intercepting vital nutrients, organic substances, and/or microorganisms.

Revolutionizing soil heavy metal remediation: Cutting-edge innovations in plant disposal technology

Soil contamination with heavy metals has emerged as a global environmental threat, compromising agricultural productivity, ecosystem integrity, and human health. Conventional remediation techniques often fall short due to high costs, operational complexities, and environmental drawbacks. Plant-based disposal technologies, including biochar, phytometallurgy, and phrolysis, have emerged as promising solutions in this regard. Grounded in a novel experimental framework, biochar is studied for its dual role as soil amendment and metal adsorbent, while phytometallurgy is explored for its potential in resource recovery and economic benefits derived from harvested metal-rich plant biomass. Pyrolysis, in turn, is assessed for transforming contaminated biomass into value-added products, thereby minimizing waste. These plant disposal technologies create a circular model of remediation and resource utilization that holds the potential for application in large-scale soil recovery projects, development of environmentally friendly agro-industries, and advancement in sustainable waste management practices. This review mainly discussed cutting-edge plant disposal technologies-biochar application, phytometallurgy, and pyrolysis-as revolutionary approaches to soil heavy metal remediation. The efficacy, cost-effectiveness, and environmental impact of these innovative technologies are especially evaluated in comparison with traditional methods. The success of these applications could signal a paradigm shift in how we approach both environmental remediation and resource recovery, with profound implications for sustainable development and circular economy strategies.

Nanoparticles synergy: Enhancing wheat (Triticum aestivum L.) cadmium tolerance with iron oxide and selenium

Nanotechnology is capturing great interest worldwide due to their stirring applications in various fields and also individual application of iron oxide nanoparticle (FeO - NPs) and selenium nanoparticles (Se - NPs) have been studied in many literatures. However, the combined application of FeO and Se - NPs is a novel approach and studied in only few studies. For this purpose, a pot experiment was conducted to examine various growth and biochemical parameters in wheat (Triticum aestivum L.) under the toxic concentration of cadmium (Cd) i.e., 50 mg kg-1 which were primed with combined application of two levels of FeO and Se - NPs i.e., 15 and 30 mg L-1 respectively. The results showed that the Cd toxicity in the soil showed a significantly (P < 0.05) declined in the growth, gas exchange attributes, sugars, AsA-GSH cycle, cellular fractionation, proline metabolism in T. aestivum. However, Cd toxicity significantly (P < 0.05) increased oxidative stress biomarkers, enzymatic and non-enzymatic antioxidants including their gene expression in T. aestivum. Although, the application of FeO and Se - NPs showed a significant (P < 0.05) increase in the plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds and their gene expression and also decreased the oxidative stress, and Cd uptake. In addition, individual or combined application of FeO and Se - NPs enhanced the cellular fractionation and decreases the proline metabolism and AsA - GSH cycle in T. aestivum. These results open new insights for sustainable agriculture practices and hold immense promise in addressing the pressing challenges of heavy metal contamination in agricultural soils.

Interaction of titanium dioxide nanoparticles with PVC-microplastics and chromium counteracts oxidative injuries in Trachyspermum ammi L. by modulating antioxidants and gene expression

The emergence of polyvinyl chloride (PVC) microplastics (MPs) as pollutants in agricultural soils is increasingly alarming, presenting significant toxic threats to soil ecosystems. Ajwain (Trachyspermum ammi L.), a plant of significant medicinal and culinary value, is increasingly subjected to environmental stressors that threaten its growth and productivity. This situation is particularly acute given the well-documented toxicity of chromium (Cr), which has been shown to adversely affect plant biomass and escalate risks to the productivity of such economically and therapeutically important species. The present study was conducted to investigate the individual effects of different levels of PVC-MPs (0, 2, and 4 mg L-1) and Cr (0, 150, and 300 mg kg-1) on various aspects of plant growth. Specifically, we examined growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress responses, antioxidant compound activity (both enzymatic and nonenzymatic), gene expression, sugar content, nutritional status, organic acid exudation, and Cr accumulation in different parts of Ajwain (Trachyspermum ammi L.) seedlings, which were also exposed to varying levels of titanium dioxide (TiO2) nanoparticles (NPs) (0, 25, and 50 µg mL-1). Results from the present study showed that the increasing levels of Cr and PVC-MPs in soils significantly decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes, sugars, and nutritional contents from the roots and shoots of the plants. Conversely, increasing levels of Cr and PVC-MPs in the soil increased oxidative stress indicators in term of malondialdehyde, hydrogen peroxide, and electrolyte leakage, and also increased organic acid exudation pattern in the roots of T. ammi seedlings. Interestingly, the application of TiO2-NPs counteracted the toxicity of Cr and PVC-MPs in T. ammi seedlings, leading to greater growth and biomass. This protective effect is facilitated by the NPs' ability to sequester reactive oxygen species, thereby reducing oxidative stress and lowering Cr concentrations in both the roots and shoots of the plants. Our research findings indicated that the application of TiO2-NPs has been shown to enhance the resilience of T. ammi seedlings to Cr and PVC-MPs toxicity, leading to not only improved biomass but also a healthier physiological state of the plants. This was demonstrated by a more balanced exudation of organic acids, which is a critical response mechanism to metal stress.

Unlocking the phytoremediation potential of organic acids: A study on alleviating lead toxicity in canola (Brassica napus L.)

Soil contamination with toxic heavy metals [such as lead (Pb)] is becoming a serious global problem due to the rapid development of the social economy. Organic chelating agents such as maleic acid (MA) and tartaric acid (TA) are more efficient, environmentally friendly, and biodegradable compared to inorganic chelating agents and they enhance the solubility, absorption, and stability of metals. To investigate this, we conducted a hydroponic experiment to assess the impact of MA (0.25 mM) and TA (1 mM) on enhancing the phytoremediation of Pb under its toxic concentration of 100 μM, using the oil seed crop canola (Brassica napus L.). Results from the present study showed that the Pb toxicity significantly (P < 0.05) decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes and nutritional contents from the roots and shoots of the plants. In contrast, toxic concentration of Pb significantly (P < 0.05) increased oxidative stress indicators in term of malondialdehyde, hydrogen peroxide, and electrolyte leakage, increased enzymatic and non-enzymatic antixoidants and their specific gene expression and also increased organic acid exudation patter in the roots of B. napus. In addition, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that Pb toxicity significantly affected double membranous organelles while Fourier-transform infrared (FTIR) spectroscopy showed an nveiled distinct peak variations in Pb-treated plants, when compared to control. Additionally, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that Pb toxicity significantly affected double-membrane organelles, while Fourier-transform infrared (FTIR) spectroscopy unveiled distinct peak variations in Pb-treated plants compared to the control. The negative impact of Pb toxicity can overcome the application of MA and TA, which ultimately increased plant growth and biomass by capturing the reactive oxygen species, and decreased oxidative stress in B. napus. With the application of MA and TA, the values of the bioaccumulation factor (BAF) and translocation factor (TF) exceeded 1, indicating that the use of MA and TA enhances the phytoremediation potential of B. napus under Pb stress conditions. This finding could be beneficial for field environment studies, especially when explored through in-depth genetic and molecular analysis.

Environmental risk assessment related to using resource recovery-based bio-composite materials in the aquatic environment with new laboratory leaching test data

The concept of circular economy, aiming at increasing the sustainability of products and services in the water and other sectors, is gaining momentum worldwide. Driven by this concept, novel bio-composite materials produced by recovering resources from different parts of the water cycle are now manufactured in The Netherlands. The new materials are used for different products such as canal bank protection elements, as an alternative to similar elements made of hardwood. As much as these new materials are appealing from the sustainability point of view, they may leach toxic substances into the aquatic environment given some of their ingredients, e.g., cellulose recovered from wastewater treatment. Therefore, a methodology for the assessment of related environmental risks is needed and it does not exist currently. This paper addresses this knowledge gap by presenting a framework for this. The framework is based on European environmental risk assessment guidelines, and it includes four key steps: (i) hazard identification, (ii) dose-response modelling, (iii) exposure assessment and (iv) risk characterisation (i.e. assessment). As part of the first step, laboratory leaching tests were carried out to evaluate the potential release of specific chemical substances such as heavy metals and resin compounds into the aquatic environment. Laboratory test results were then used as input data to evaluate the risk of potential leaching from canal bank protection elements into surface water. A deterministic model was used first to identify the chemicals exceeding the guideline threshold. Subsequently, a stochastic model was applied to evaluate the environmental risks across a range of leachate concentrations and water velocities in the canal, thereby simulating a broader spectrum of possible situations. The risk analyses were conducted for four alternative bio-composite materials made of different ingredients, two different flow conditions (stagnant water and advective flow) in two types of canals (wide ditch and primary watercourse) and for two different water levels based on season conditions (summer and winter conditions). The results obtained from leaching tests identified Cu, Mn, Zn, styrene and furfuryl alcohol as potentially troublesome chemicals. In the case of stagnant water, the absence of a flow rate increases the residence time of the chemicals in the surface water, resulting in a higher PEC/PNEC (i.e. risk) value. However, under stagnant case conditions, environmental risks for all chemicals considered turned out to be below the safety threshold. In the advective case, the existence of a flow rate, even at low velocities simulating the conditions of 'almost no flow,' contributes to increased dilution, resulting in lower PEC/PNEC ratio values. The results presented here, even though representing real-case scenarios, are only indicative as these are based on laboratory leaching tests and a number of assumptions made. Additional field tests involving collecting and analysing water and sediment samples from the canal where the canal bank protection elements are located, over a prolonged period, are required to come up with more conclusive findings.

Contamination and health risk assessment of heavy metals in soil surrounding an electroplating factory in JiaXing, China

A total of 30 samples from the downwind direction of a certain electroplating company in Jiaxing were collected in layers to analyze their heavy metal content. The soil risk assessment was conducted from the perspective of ecological and human health risks using the ground accumulation index method and human health risk assessment method. The results showed that in all samples, cadmium and arsenic far exceeded the soil background values, with an average exceeding multiple of 14.31 and 64.42, respectively, and a exceeding rate of 100%. After evaluation by the ground accumulation index, among these six heavy metals, arsenic and cadmium belong to extremely serious pollution levels. The human health risk assessment of electroplating plants found that in the exposure risk assessment, the ingestion value was much greater than the harm caused by breathing and skin, and the maximum exposure damage value of arsenic to children and adults was 4.17 × 10-3, among the carcinogenic risks, the risk brought by consumption is much greater than the respiratory and skin carcinogenic risk index, with the highest value score of 3.37 for cadmium, arsenic, and zinc carcinogenic risks 3.37 × 10-6, 2.42 × 10-3, 1.10 × 10-4.

Environmental surveillance in Jinan city of East China (2014-2022) reveals improved air quality but remained health risks attributable to PM2.5-bound metal contaminants

PM2.5-bound metal contaminants are associated with multiple chronic diseases in human. At global level, the contamination status has not been well controlled yet. Here we report findings from a long-term air pollution surveillance in Jinan city of Shandong, China. During 2014-2022, the dynamics and trends of PM2.5-bound heavy metal contaminants were monitored in an industrial area and a downtown area. The surveillance targets included: antimony (Sb), aluminum (Al), arsenic (As), beryllium (Be), cadmium (Cd), chromium (Cr), mercury (Hg), lead (Pb), manganese (Mn), nickel (Ni), selenium (Se). The human exposure and health risks were calculated and we found that the health risks of most contaminants showed peak values in autumn and winter. But Al, Mn, Hg and Be were found to result in highest health risk in spring or summer in the downtown area. In the industrial area we identified 100% alarming health index >1 (ranged from 1.12 to 3.35) in autumn and winter. In winter the total non-carcinogenic HI was all above 1 (peak value 2.21). Mn and As together posed >85% non-carcinogenic risk. As and Cd were ranked as major drivers of carcinogenic risks (5.84 × 10-6 and 2.78 × 10-6). Pd and Cd both showed non-negligible environmental levels but risk assessment model for their air-exposure associated non-carcinogenic risks are not yet available. This study updates air pollution data and status for air pollution status in China. This study provides valuable 9 year long-term reference to experimental and field studies in the related fields.

Geochemical properties, heavy metals and soil microbial community during revegetation process in a production Pb-Zn tailings

Lead-zinc (Pb-Zn) tailings pose a significant environmental threat from heavy metals (HMs) contamination. Revegetation is considered as a green path for HM remediation. However, the interplay between HM transport processes and soil microbial community in Pb-Zn tailings (especially those in production) remain unclear. This study investigated the spatial distribution of HMs as well as the crucial roles of the soil microbial community (i.e., structure, richness, and diversity) during a three-year revegetation of production Pb-Zn tailings in northern Guangdong province, China. Prolonged tailings stockpiling exacerbated Pb contamination, elevating concentrations (from 10.11 to 11.53 g/kg) in long-term weathering. However, revegetation effectively alleviated Pb, reducing its concentrations of 9.81 g/kg. Through 16 S rRNA gene amplicon sequencing, the dominant genera shifted from Weissella (44%) to Thiobacillus (17%) and then to Pseudomonas (comprising 44% of the sequences) during the revegetation process. The structural equation model suggested that Pseudomonas, with its potential to transform bioavailable Pb into a more stable form, emerged as a potential Pb remediator. This study provides essential evidence of HMs contamination and microbial community dynamics during Pb-Zn tailings revegetation, contributing to the development of sustainable microbial technologies for tailings management.

A review on sea cucumber (Bengali: Somuddro Sosha) as a bioindicator of heavy metal contamination and toxicity

This review paper exhibits the underexplored realm of heavy metal contamination and associated risks in sea cucumbers (SCs), which hold significant importance in traditional Asian marine diets and are globally harvested for the Asian market. The assessment focuses on heavy metals (HMs) presence in various SC species, revealing a global trend in HMs concentrations across anatomical parts: Fe > Zn > As > Cu > Hg > Pb > Mn > Cr > Ni > Cd. Specific species, such as Eupentacta fraudatrix, Holothuria mammata, Holothuria polii, Holothuria tubulosa, and Holothuria atra, exhibit heightened arsenic levels, while Stichopus herrmanni raises concerns with mercury levels, notably reaching 3.75 mg/kg in some instances, posing potential risks, particularly for children. The study sheds light on anthropogenic activities such as cultivation, fishing, and shipping, releasing HMs into marine ecosystems and thereby threatening ocean and coastal environments due to the accumulation and toxicity of these elements. In response to these findings, the paper suggests SCs as promising bioindicator species for assessing metal pollution in marine environments. It underscores the adverse effects of human actions on sediment composition and advocates for ongoing monitoring efforts both at sea and along coastlines.

Combining Cd and Pb isotope analyses for heavy metal source apportionment in facility agricultural soils around typical urban and industrial areas

Facility agriculture enhances food production capabilities. However, concerns persist regarding heavy metal accumulation resulting from extensive operation of this type of farming. This study integrated the total content, five fractions, and isotope composition of Cd and Pb in intensively farmed soils in regions characterized by industrialization (Shaoguan, SG) and urbanization (Guangzhou, GZ), to assess the sources and mechanisms causing metals accumulation. We found significantly more severe Cd/Pb accumulation and potential mobility in SG than GZ. Cd displayed higher accumulation levels and potential mobility than Pb. The distinct isotopic signals in SG (-0.54 to 0.47‰ for δ114/110Cd and 1.1755 to 1.1867 for 206Pb/207Pb) and GZ (-0.86 to 0.12‰ for δ114/110Cd and 1.1914 to 1.2012 for 206Pb/207Pb) indicated significant differences in Cd/Pb sources. The Bayesian model revealed that industrial activities and related transportation accounted for over 40% and approximately 30%, respectively, of the average contributions of Cd/Pb in SG. While urban-related (26.6%) and agricultural-related (26.3%) activities primarily contributed to Cd in GZ. The integration of δ114/110Cd and 208Pb/206Pb has further enhanced the regional contrast in sources. The present study established a comprehensive tracing system for Cd-Pb, providing crucial insights into the accumulation and distribution of these metals in facility agricultural soils.

Tartaric acid coupled with gibberellin improves remediation efficiency and ensures safe production of crops: A new strategy for phytoremediation

Phytoremediation is the direct use of living green plants and it is an effective, inexpensive, non-invasive, and environmentally friendly technique used to transfer or stabilize all the toxic metals and environmental pollutants in polluted soil or ground water. To study the effect of tartaric acid, gibberellin, and tartaric acid coupled with gibberellin on rape-kenaf or rape-sweet sorghum rotation, a field experiment was carried out on a farmland combined polluted with Cd and Pb in eastern Hunan Province, China. The results showed that these two rotation systems coupled with superposition measure has potential to enhance yield and biomass of rape (Brassica napus L.), kenaf (Hibiscus cannabinus) and sweet sorghum (Sorghum dochna (F.) Snowden), as well as to increase Cd and Pb uptake of the three crops, thus accelerating phytoextraction. The Cd and Pb annual removal by rape-kenaf rotation in one year under different treatments were 269-438 and 112-149 g·hm-2, respectively. And the Cd and Pb annual removal by rape-sweet sorghum rotation in one year under different treatments were 68.0-111 and 43.8-92.3 g·hm-2, respectively. Under the two rotation systems, these integrated management measures can remove Cd and Pb up to 438 g·hm-2·year-1 and 149 g·hm-2·year-1, respectively. The Cd and Pb content in rape seeds or sweet sorghum stems and leaves were lower than the food or forage standard, indicating that we can use this rotation system for both remediation and safety production. Furthermore, the two rotation systems also generated considerable economic value. These results showed that the combination of phytoremediation and agricultural production is a feasible technical mode in the field of Cd and Pb co-contamination, and also provides useful information for further study of the interaction mechanism between rotation crops and enhancement measures. In subsequent experiments we can set concentration gradients for tartaric acid and gibberellin, and we can also select other crops for rotation, with a view to finding the optimal auxiliary measure and crop rotation modern.

Inversion of heavy metal copper content in soil-wheat systems using hyperspectral techniques and enrichment characteristics

The growing problem of heavy metal contamination in soil will seriously threaten the China's grain safety. The development of hyperspectral remote sensing technology provides the possibility to achieve rapid and non-destructive monitoring of soil heavy metal content. In this study, we used hyperspectral techniques and enrichment characteristics to explore the potential of wheat leaf spectral inversion for heavy metal copper (Cu) content in the soil-wheat system. First, we conducted potting experiments to plant wheat on soil contaminated with varying concentrations of the heavy metal Cu. Then, we analyzed the migration characteristics, correlation characteristics and enrichment characteristics of Cu in the soil-wheat system under different soil heavy metal Cu concentration treatments. Next, we analyzed the spectral and correlation features of wheat leaves, and explored the potential of wheat leaf spectra for the inversion of Cu content in full-band and eigen-band modeling. Finally, using the estimated Cu content of wheat leaves from the best inversion model, we further conducted inversions to obtain the Cu content and precision of the grain, stem, root, total soil, and soil-available states based on the enrichment characteristics. The results showed that: (1) The accumulation pattern was root > grain > leaf > stem when the soil Cu concentration was <200 mg kg-1, and root > leaf > stem > grain when the soil Cu concentration was >200 mg kg-1. (2) The correlation coefficients between the different analyzed elements of the soil-wheat system were high, and all of them reached a highly significant level (P < 0.01). This supports the use of wheat leaves to estimate the Cu contents of soil and different parts of wheat. (3) The best inversion accuracies were obtained by modeling second derivative (SD) spectra that were pre-processed by screening the characteristic bands. The modeled R2cv, RMSEcv,R2ev and RMSEev were 0.94, 2.72 mg kg-1, 0.91 and 3.64 mg kg-1, respectively. This indicates an excellent ability to estimate Cu content in wheat leaves. (4) Using the hyperspectral estimation of Cu content in wheat leaves and the grouped inversion of enrichment characteristics, the inversion accuracy was lower only for grains, and the R2cv and R2ev for stems and roots exceeded 0.90, those for total soil exceeded 0.85, and those for the soil available state exceeded 0.70. Therefore, it is possible to use the spectra of wheat leaves in combination with the inversion of enrichment characteristics to estimate the soil-wheat Cu content. This study provides guarantee and support for the detection of grain safety.

Combined exposure of PVC-microplastic and mercury chloride (HgCl2) in sorghum (Pennisetum glaucum L.) when its seeds are primed titanium dioxide nanoparticles (TiO2-NPs)

The present work studied the impact of different levels of PVC-microplastics (PVC-MPs), namely 0 (no PVC-MPs), 2, and 4 mg L-1, along with mercury (Hg) levels of 0 (no Hg), 10, and 25 mg kg-1 in the soil, while concurrently applying titanium dioxide-nanoparticles (TiO2-NPs) at 0 (no TiO2-NPs), 50, and 100 µg mL-1 to sorghum (Pennisetum glaucum L.) plants. This study aimed to examine plant growth and biomass, photosynthetic pigments and gas exchange characteristics, oxidative stress indicators, and the response of various antioxidants (enzymatic and non-enzymatic) and their specific gene expression, proline metabolism, the AsA-GSH cycle, and cellular fractionation in the plants. The research outcomes indicated that elevated levels of PVC-MPs and Hg stress in the soil notably reduced plant growth and biomass, photosynthetic pigments, and gas exchange attributes. However, PVC-MPs and Hg stress also induced oxidative stress in the roots and shoots of the plants by increasing malondialdehyde (MDA), hydrogen peroxide (H2O2), and electrolyte leakage (EL) which also induced increased compounds of various enzymatic and non-enzymatic antioxidants and also the gene expression and sugar content. Furthermore, a significant increase in proline metabolism, the AsA-GSH cycle, and the pigmentation of cellular components was observed. Although, the application of TiO2-NPs showed a significant increase in plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds, and their gene expression and also decreased oxidative stress. In addition, the application of TiO2-NPs enhanced cellular fractionation and decreased the proline metabolism and AsA-GSH cycle in P. glaucum plants. These results open new insights for sustainable agriculture practices and hold immense promise in addressing the pressing challenges of heavy metal contamination in agricultural soils.

Biochar derived from tobacco waste significantly reduces the accumulations of cadmium and copper in edible parts of two vegetables: an in-situ field study

Biochar, as a soil amendment, can be applied to remediate heavy metal (HM) contaminated farmland. However, there is little research on the effect of tobacco biochar (TB) derived from tobacco waste on HM controlling in edible parts of vegetables. In this study, the impact of two TB levels on the plant growth, copper (Cu) and cadmium (Cd) accumulation in the edible parts of lettuce and chrysanthemum, and on Cu and Cd bioavailability of rhizosphere soil was investigated through in-situ field experiments. The results showed that TB has rich oxygen containing functional groups, high porosity, high nitrogen adsorption capacity. The addition of 5 t ha-1 and 10 t ha-1 TB significantly increased the shoot biomass of chrysanthemum, but had no effect on the growth of lettuce. Two levels of TB significantly increased the pH value, but decreased the available Cu and Cd concentrations of rhizosphere soil, thereby reducing the Cu and Cd accumulations in the edible parts of lettuce and chrysanthemum. The findings provided effective evidences that TB derived from tobacco waste is an efficient strategy for controlling Cu and Cd accumulation in the edible parts of vegetables to ensure agri-product safety production in HM-polluted farmland.

Source-specific probabilistic contamination risk and health risk assessment of soil heavy metals in a typical ancient mining area

Heavy metal pollution (HMP) from mining operations severely threatens soil ecosystems and human health. Identifying the sources of soil heavy metals (HMs) and assessing source-specific risks are critical for developing effective risk mitigation strategies. In this study, a combination of methodologies including PMF, Monte Carlo analysis, soil pollution risk index, and a human health risk assessment model were utilized to investigate soil HM risks in a typical ancient mining area in Daye City, China, considering both environmental pollution and human health impacts. Cu emerged as the most significant soil pollution risk, whereas As posing the highest health risk. About 48.44 % of the multi-element integrated soil pollution risk has escalated to the heavy level. Furthermore, around 22.42 % of the non-carcinogenic risk (NCR) and 9.53 % of the carcinogenic risk (CR) exceeded unacceptable thresholds (THI > 1 for NCR and TCR > 1E-4 for CR). The PMF model identified four distinct sources: the smelting industry, traffic emissions, a combination of agricultural and natural factors, and mining activities. The mixed agricultural and natural source significantly impacted health risks, contributing 42.17 % to NCR and 53.88 % to CR, followed by the mining source, contributing 31.67 % to NCR and 24.07 % to CR. Interestingly, the mining source contributed the highest soil pollution risk at 42.45 %, while the mixed agricultural and natural source exhibited the lowest at 16.33 %. Furthermore, the study explored source-specific risk components by evaluating the contributions of different sources to specific elements. The mining source was identified as the focus for soil HMP control, followed by the mixed agricultural and natural source. Overall, this study provided an in-depth analysis of soil heavy metal risks in mining areas from the source apportionment perspective, which broadened the research framework of soil heavy metal source analysis and risk assessment, potentially providing scientific guidance for managing regional soil HMP.

Toxic metals in cyanobacterial mat of Big Lachman Lake, James Ross Island, Antarctica

The northern part of James Ross Island is the largest deglaciated area in the Antarctic Peninsula region with a unique ecosystem created during the Late Glacial. This research aims to evaluate the degree of contamination of the locality with toxic metals (As, Hg, Cd, and Pb) through bioindicators in the aquatic environment-colonies of cyanobacteria and algae. For this purpose, bottom lake sediments of Big Lachman Lake were studied for contents of Fe, As, Hg, Cd, Pb, Cr, Co, Ni, Cu, and Zn, as well as samples of cyanobacterial mat, in which Fe, As, Hg, Cd, and Pb were determined. Metal contents were determined by means of inductively coupled plasma optical emission spectrometry and atomic absorption spectrometry. The contents of metals in sediments did not differ from the usual values in the area of the Antarctic Peninsula. The bioaccumulation of metals in cyanobacterial mat was evaluated by calculating enrichment factors (the calculation to Fe as a reference element). According to this method, moderate pollution of Big Lachman Lake was confirmed for Hg and Cd.

Foliar application of iron-lysine to boost growth attributes, photosynthetic pigments and biochemical defense system in canola (Brassica napus L.) under cadmium stress

In the current industrial scenario, cadmium (Cd) as a metal is of great importance but poses a major threat to the ecosystem. However, the role of micronutrient - amino chelates such as iron - lysine (Fe - lys) in reducing Cr toxicity in crop plants was recently introduced. In the current experiment, the exogenous applications of Fe - lys i.e., 0 and10 mg L - 1, were examined, using an in vivo approach that involved plant growth and biomass, photosynthetic pigments, oxidative stress indicators and antioxidant response, sugar and osmolytes under the soil contaminated with varying levels of Cd i.e., 0, 50 and 100 µM using two different varieties of canola i.e., Sarbaz and Pea - 09. Results revealed that the increasing levels of Cd in the soil decreased plant growth and growth-related attributes and photosynthetic apparatus and also the soluble protein and soluble sugar. In contrast, the addition of different levels of Cd in the soil significantly increased the contents of malondialdehyde (MDA) and hydrogen peroxide (H2O2), which induced oxidative damage in both varieties of canola i.e., Sarbaz and Pea - 09. However, canola plants increased the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and non-enzymatic compounds such as phenolic, flavonoid, proline, and anthocyanin, which scavenge the over-production of reactive oxygen species (ROS). Cd toxicity can be overcome by the supplementation of Fe - lys, which significantly increased plant growth and biomass, improved photosynthetic machinery and sugar contents, and increased the activities of different antioxidative enzymes, even in the plants grown under different levels of Cd in the soil. Research findings, therefore, suggested that the Fe - lys application can ameliorate Cd toxicity in canola and result in improved plant growth and composition under metal stress.

Impacts of climate change and coastal salinization on the environmental risk of heavy metal contamination along the odisha coast, India

Climate change-mediated rise in sea level and storm surges, along with indiscriminate exploitation of groundwater along populous coastal regions have led to seawater intrusion. Studies on groundwater salinization and heavy metal contamination trends are limited. Present study investigated the heavy metal contamination, associated risks and provided initial information on the impacts of groundwater salinization on heavy metals along the coastal plains of Odisha, India. Total 50 groundwater samples (25 each in post- and pre-monsoon) were collected and analysed. Concentrations of Fe (44%), Mn (44%), As (4%) and Al (4%) in post-monsoon and Fe (32%), Mn (32%), As (4%), B (8%) and Ni (16%) in pre-monsoon exceeded Bureau of Indian Standards (BIS) drinking water limits. High concentrations of heavy metals (Fe, Sr, Mn, B, Ba, Li, Ni and Co) and high EC (>3000 μS/cm) indicated that the groundwater-seawater mixing process has enhanced the leaching and ion exchange of metallic ions in central part of the study area. Multivariate statistical analysis suggested leaching process, seawater intrusion and agricultural practices as the main heavy metal sources in the groundwater. 4% of samples in post- and 16% in pre-monsoon represented high heavy metal pollution index (HPI). Pollution indices indicated the central and south-central regions are highly polluted due to saline water intrusion and high agricultural activities. Ecological risks in the groundwater systems found low (ERI <110) in both seasons. Children population found more susceptible to health risks than adults. Hazard index (HI > 1) has shown significant non-carcinogenic risks where Fe, Mn, As, B, Li and Co are the potential contributors. Incremental lifetime cancer risk (ILCR >1.0E-03) has suggested high carcinogenic risks, where As and Ni are the major contributors. The study concluded that groundwater salinization could increase the heavy metal content and associated risks. This would help policymakers to take appropriate measures for sustainable coastal groundwater management.

A critical review on the migration and transformation processes of heavy metal contamination in lead-zinc tailings of China

The health risks of lead-zinc (Pb-Zn) tailings from heavy metal (HMs) contamination have been gaining increasing public concern. The dispersal of HMs from tailings poses a substantial threat to ecosystems. Therefore, studying the mechanisms of migration and transformation of HMs in Pb-Zn tailings has significant ecological and environmental significance. Initially, this study encapsulated the distribution and contamination status of Pb-Zn tailings in China. Subsequently, we comprehensively scrutinized the mechanisms governing the migration and transformation of HMs in the Pb-Zn tailings from a geochemical perspective. This examination reveals the intricate interplay between various biotic and abiotic constituents, including environmental factors (EFs), characteristic minerals, organic flotation reagents (OFRs), and microorganisms within Pb-Zn tailings interact through a series of physical, chemical, and biological processes, leading to the formation of complexes, chelates, and aggregates involving HMs and OFRs. These interactions ultimately influence the migration and transformation of HMs. Finally, we provide an overview of contaminant migration prediction and ecological remediation in Pb-Zn tailings. In this systematic review, we identify several forthcoming research imperatives and methodologies. Specifically, understanding the dynamic mechanisms underlying the migration and transformation of HMs is challenging. These challenges encompass an exploration of the weathering processes of characteristic minerals and their interactions with HMs, the complex interplay between HMs and OFRs in Pb-Zn tailings, the effects of microbial community succession during the storage and remediation of Pb-Zn tailings, and the importance of utilizing process-based models in predicting the fate of HMs, and the potential for microbial remediation of tailings.

Cd contamination determined assembly processes and network stability of AM fungal communities in an urban green space ecosystem

The effects of cadmium (Cd) contamination on the assembly mechanism and co-occurrence patterns of arbuscular mycorrhizal (AM) fungal communities remain unclear, especially in urban green spaces. This study sequenced AM fungal communities in greenbelt soils in Zhengzhou (China). The effects of Cd contamination on the AM fungal diversity, community assembly processes, and co-occurrence patterns were explored. We found that (1) an increase in Cd contamination changed the community composition, which resulted in a significant improvement in the diversity of specialists of AM fungi and a significant decrease in the diversity of generalists. (2) Deterministic processes dominated the community assembly of specialists and stochastic processes dominated the community assembly of generalists. (3) Specialists played a more important role than generalists in maintaining the stability of AM fungal networks under Cd contamination. Overall, Cd contamination affected the ecological processes of AM fungi in urban green space ecosystems. However, the effects on the assembly processes and network stability of different AM fungi taxa (specialists and generalists) differed significantly. The present study provides deeper insight into the effect of Cd contamination on the ecological processes of AMF and is helpful in further exploring the ecological risk of Cd contamination in urban green spaces.

Distribution, contamination assessment, and sources of heavy metals in surface sediments from the south of the North Yellow Sea, China

This paper reports the contents of six heavy metals and particle sizes in the surface sediments of 120 sampling stations in the southern North Yellow Sea to reveal heavy metal distribution characteristics, contamination assessment, and sources. Cu and Cr enrichments were mainly found in coastal areas with high mud content (silt and clay). However, Zn, Cd, Pb, and Hg were enriched in Weihai Bay and Dongpu Bay, which have denser populations, estuaries, and shipyards. The geoaccumulation index and principal component analysis showed that Cu and Cr contamination was low, and the sources were mainly natural processes. In addition, Zn and Cd pollution in the nearshore area was moderate, and its provenance was natural processes and human activity. However, most areas exhibited Pb and Hg contamination due to waterborne traffic and industries, including shipbuilding and gold mining.

Microplastic characteristics and microplastic-heavy metal synergistic contamination in agricultural soil under different cultivation modes in Chengdu, China

Microplastics have significant implications for global ecosystems. The microplastic distribution, types, sources, and quantified microplastic-heavy metal synergistic pollution in agricultural soil in Chengdu, China were analyzed. The microplastics were detected in all soil samples collected from 103 sites, with concentrations ranging from 1333 to 15067 particle kg-1. The abundance of microplastics in grassland (12,667 ± 3394 particle kg-1) was more than twice higher than that in open field, vegetable field, orchard, and woodland. The main morphological types of microplastics included fibers, films, and granules (all "3-Dimensional" microplastics), with the colors red, blue, and transparent. Granular and fiber microplastics were predominantly in particles < 500 mm, while film microplastics were uniformly distributed at all sizes. The plastic compositions were mainly polypropylene and polyethylene plastics, accounting for 20.73% and 27.90% of the soil microplastic, respectively. Agricultural plastic applications and irrigation water were the sources of soil microplastics. The concentration of Cd, Cr, and Cu in the microplastics was strongly correlated with the corresponding concentration in the soils (p < 0.01), and the microplastic-heavy metal synergistic pollution might deteriorate the soil environment. The results of soil TOC measurements were influenced by microplastics in the soil. The results provide important data for the characteristics of microplastics in the agroecosystem.

Sorption of As, Cd, and Pb by soil amendments: in situ immobilization mechanisms and implementation in contaminated agricultural soils

The contamination of agricultural soils by toxic heavy metals, such as As, Cd, and Pb, is of great concern for crop safety as well as environmental and public health. Various adsorbents for the in situ immobilization of these metals have been widely studied, but researches on the potential and superiority of metal adsorption in agricultural soil amendments are still lacking. This study was conducted to investigate the nature of their sorption processes on soil amendments including slaked lime (SL), phosphogypsum (PG), bone meal (BM), and biochar (BC) using a series of laboratory batch tests. The Langmuir adsorption isotherm was used to predict sorption parameters. The experimental data fitted reasonably well on the Langmuir model with high correlation coefficients (R2 = 0.64-0.99) suggesting that monolayer sorption/complexation/precipitation was the dominant mechanism. Among the amendments, SL achieved the highest maximum adsorption capacity (qmax) for As and Cd at 714.3 and 2000 mg g-1, respectively, while PG had the highest qmax for Pb at 196.08 mg g-1. The results indicate that there is no direct correlation between sorption stability and maximum adsorption capacity. Among the sorbents, BC had the highest sorption stability for As (0.007 L mg-1), Cd (0.121 L mg-1), and Pb (2.273 L mg-1), respectively, albeit the qmax values for these three metals were not high. This indicates that the As, Cd, and Pb sorbed on biochar tended to be more stable than those retained on other amendments. While a large sorption capacity is important, our results provide important insights into the metal sorption stability/energy of adsorbents that will aid in the development of long-term management efficiency strategies to rehabilitate metal-contaminated arable soils.

Impacts of heavy metal exposure on the prostate of murine models: Mechanisms of toxicity

Heavy metals are elements found into the environment mainly due to anthropogenic activities. Naturally occurring and higher released doses cause disorders in the prostate, which depends on appropriate hormonal regulation, and exposure to heavy metals may impair prostate homeostasis. The current work highlighted the main mechanisms of toxicity of different environmental heavy metal contaminants, such as aluminum, arsenic, cadmium, chromium, lead, mercury, and nickel, and their impacts found in the prostate morphophysiology of murine models. The repercussions triggered by heavy metals on the prostate include hormonal imbalance and oxidative damage, leading to morphological alterations, which can vary according to the chemical properties of each element, exposure time and concentration, and age. The information of altered biological pathways and its impacts on the prostate of exposed murines are related to human outcomes being useful in the real context of human exposure.

Cadmium exposure through the food chain reduces the parasitic fitness of Chouioia cunea to Hyphantria cunea pupae: An ecotoxicological risk to pest control

The toxicity of heavy metals on various trophic levels along the food chain has been extensively investigated, but no studies have focused on parasitic natural enemy insects. Herein, we constructed a food chain consisting of soil-Fraxinus mandshurica seedlings-Hyphantria cunea pupae-Chouioia cunea to analyze the effects of Cd exposure through food chain on the fitness of parasitic natural enemy insects and its corresponding mechanism. The results showed that the transfer of Cd between F. mandshurica leaves and H. cunea pupae and between H. cunea pupae and C. cunea was a bio-minimization effect. After parasitizing Cd-accumulated pupa, the number of offspring larvae, and the number, individual size (body weight, body length, abdomen length) and life span of offspring adults decreased significantly, while the duration of embryo development extended significantly. The contents of malondialdehyde and H₂O₂ in Cd-exposed offspring wasps increased significantly, accompanied by a significantly decrease in antioxidant capacity. The cellular immunity parameters significantly decreased in Cd-accumulated pupae, including the number of hemocytes, melanization activity and the expression level of cellular immunity genes (e.g. Hemolin-1 and PPO1). The humoral immunity disorder was found in the Cd-accumulated pupae, as evidenced by that the expression level of immune recognition gene (PGRP-SA), signal transduction genes (IMD, Dorsal, and Tube), as well as all antimicrobial peptide genes (e.g. Lysozym and Attacin) decreased significantly. Cd exposure decreased the content of glucose, trehalose, amino acid, and free fatty acid in H. cunea pupae. The expression of Hk2 in glycolysis pathway and the expression of Idh2, Idh3, Cs, and OGDH in TCA cycle pathway were significantly down-regulated in Cd-accumulated pupae. Taken together, exposure to Cd through the food chain causes oxidative damage on the offspring wasps and disrupts energy metabolism of the host insect, ultimately reducing the parasitic fitness of C. cunea to H. cunea pupae.

Environmental risks of organic fertilizer with increased heavy metals (Cu and Zn) to aquatic ecosystems adjacent to farmland in the northern biosphere of Japan

In Abashiri, Hokkaido, northern Japan, composted sewage sludge (CSS) containing a large amount of zinc (Zn) and copper (Cu) is used as fertilizer in agriculture. The local environmental risks of Cu and Zn from such organic fertilizers were studied. The study area, especially the brackish lakes located near the farmlands, is important for inland fisheries. The risks posed by heavy metals to the brackish-water bivalve, Corbicula japonica, was therefore investigated as an example. First, the long-term effect of CSS application in agricultural fields was monitored. Second, using pot cultivation, factors influencing Cu and Zn availability in the presence of organic fertilizers were evaluated under different scenarios of SOM content. In addition, the mobility and availability of Cu and Zn in organic fertilizers were evaluated in a field experiment. In the pot cultivation, both organic and chemical fertilizers increased the availability of Cu and Zn with a decrease in pH, possibly caused by nitrification. However, this decrease in pH was inhibited by higher SOM content, i.e. SOM mitigated the heavy metal risk from organic fertilizer. In the field experiment, potato (Solanum tuberosum L.) was cultivated using CSS and pig manure (PM). As observed in the pot cultivation, the applied chemical and organic fertilizers increased the soil-soluble and 0.1 N HCl-extractable Zn with increased nitrate. Considering the habitat and the LC₅₀ values of C. japonica that were lower than the concentration of Cu and Zn in the soil solution phase, there is no significant risk from heavy metals in the organic fertilizers. However, the K_d values for Zn were significantly lower for CSS or the PM-applied plot in the field experiment soil, indicating a higher Zn desorption rate from organically fertilized soil particles. The potential risk of heavy metals from agricultural lands under changing climate conditions must therefore be monitored carefully.

Copper and lead isotope records from an electroplating activity in sediments and biota from Sepetiba Bay (southeastern Brazil)

An old electroplating plant in Sepetiba Bay discharged metal-enriched wastes into the surrounding mangroves for 30 years (from the 1960s to 1990s), resulting in a hotspot zone of legacy sediments highly concentrated in toxic trace metals. This study applies Cu and Pb isotope systems to investigate the contributions of past punctual sources relative to emerging modern diffuse sources. The electroplating activity imprinted particular isotopic signatures (average δ⁶⁵Cu_SRM-976: 0.4 ‰ and ²⁰⁶Pb/²⁰⁷Pb: 1.14) distinct from the natural baseline and urban fluvial sediments. The isotopic compositions of tidal flat sediments show intermediate isotope compositions reflecting the mixing of Cu and Pb from the hotspot zone and terrigenous materials carried by rivers. Oyster isotope fingerprints match legacy sediments, attesting that anthropogenic Cu and Pb are bioavailable to the biota. These findings confirm the interest in combining two or more metal isotope systems to discriminate between modern and past metal source emissions in coastal environments.

Conditional remediation performance of wheat straw biochar on three typical Cd-contaminated soils

Undoubtedly biochar has excellent remediation performance for Cd-contaminated soil. Nevertheless, the remediation performance may be not invariable considering highly variable soil conditions including soil properties and environmental conditions. This work investigated the fate of Cd in three typical Cd-contaminated soils (acidic, neutral and saline-alkali soils) treated with wheat straw biochar and its driving mechanisms under specific soil conditions through aging and remediation experiment, Cd availability experiment and leaching column experiment. The results indicated that biochar addition facilitated Cd immobilization and reduced the uptake of Cd by green vegetables in acidic, neutral and saline-alkali soils under wetting-drying conditions. In contrast to neutral and saline-alkali soils, the release of exchangeable aluminum from biochar-treated acidic soil under flooding-drying cycles lowered the pH of leachate, thus promoting the leaching of Cd from leaching column, especially at 7 and 14 days, when the leaching of Cd increased by 25.3 and 32.6 times, respectively. This result was further supported by the increase in the exchangeable fraction and total leaching amounts of Cd in the topsoil layer (0-20 cm) of biochar-treated acidic soil of leaching column. Additionally, the leaching of Cd was positively correlated with DOC contents of leachate in biochar-treated neutral and saline-alkali soils. In summary, the remediation performance of biochar for Cd-contaminated soils is conditional, and its remediation effect is better in neutral and saline-alkali soils. Notably, the inherent conditions of soil must be fully considered when applying biochar for Cd remediation, especially in acidic Cd-contaminated paddy soils in South China.

Statistical and spatial analysis for soil heavy metals over the Murray-Darling river basin in Australia

Heavy metals (HMs) are a vital elements for investigating the pollutant level of sediments and water bodies. The Murray-Darling river basin area located in Australia is experiencing severe damage to increased crop productivity, loss of soil fertility, and pollution levels within the vicinity of the river system. This basin is the most effective primary production area in Australia where agricultural productivity is increased the gross domastic product in the entire mainland. In this study, HMs contaminations are examined for eight study sites selected for the Murray-Darling river basin where the inverse Distance Weighting interpolation method is used to identify the distribution of HMs. To pursue this, four different pollution indices namely the Geo-accumulation index (I_geo), Contamination factor (CF), Pollution load index (PLI), single-factor pollution index (SPLI), and the heavy metal pollution index (HPI) are computed. Following this, the Pearson correlation matrix is used to identify the relationships among the two HM parameters. The results indicate that the conductivity and N (%) are relatively high in respect to using I_geo and PLI indexes for study sites 4, 6, and 7 with 2.93, 3.20, and 1.38, respectively. The average HPI is 216.9071 that also indicates higher level pollution in the Murray-Darling river basin and the highest HPI value is noted in sample site 1 (353.5817). The study also shows that the levels of Co, P, Conductivity, Al, and Mn are mostly affected by HMs and that these indices indicate the maximum HM pollution level in the Murray-Darling river basin. Finally, the results show that the high HM contamination level appears to influence human health and local environmental conditions.

Zeolite amendment reduces lead accumulation and improves growth and yield in tomato plants irrigated with sewage water

Although sewage water (SW) is a source of nutrients, it also causes heavy metal accumulation in soil; especially, lead (Pb⁺) contamination of soil is a serious concern in agriculture. Soil contaminants limit the bioavailability of nutrients to plants. So, they affect plant growth and produce quality. Therefore, a pot experiment was conducted to investigate the effect of zeolite soil amendment on the accumulation of Pb⁺ in tomato crop grown with SW irrigation. The pot media of SW-irrigated plants was amended with different concentrations of zeolite, viz., 0.75%, 1.50%, and 2.25%. The results showed that the application of 0.75% zeolite increased leaf area, plant height, fruit number, and plant fresh and dry biomasses by 37%, 17%, 14%, 24%, and 7% compared to freshwater irrigation. Moreover, the lowest zeolite dose also led to higher chlorophyll content (68.02 SPAD) compared to SW-irrigated plants (55.13 SPAD). Similarly physiological traits, such as A, gs, and E, were higher (17.68 µmol m^-2 s^-1, gs 0.28 mmol m^-2 s^-1, and 7.88 mmol m^-2 s^-1, respectively) in 0.75% zeolite-treated plants than in SW-irrigated plants (12.99 µmol m^-2 s ^-1, 0.19 mmol m^-2 s^-1, and 7.00 mmol m^-2 s ^-1, respectively). On the contrary, a reduced level of hydrogen peroxide and malondialdehyde and decreased activity of antioxidant enzymes were observed in low-dose zeolite applied plants. Zeolite reduced Pb⁺ accumulation in tomato plants as compared to SW-irrigated plants, whereby Pb accumulation in the fruits of SW-irrigated plants was 80% more than those of zeolite + SW-treated plants. Conclusively, this study has revealed the improvement in morphological and physiological growth attributes of the SW-irrigated tomato plant in response to zeolite application.

Highly effective biosorption capacity of Cladosporium sp. strain F1 to lead phosphate mineral and perovskite solar cell PbI2

Fungus Cladosporium sp. strain F1 showed highly effective biosorption capacity to lead phosphate mineral and perovskite solar cells lead iodide compared to other fungi Aspergillus niger VKMF-1119 and Mucor ramannianus R-56. Scanning electron microscopy and transmission electron microscopy analyses shows that Cladosporium sp. strain F1, which previously showed high biosorption capacity to uranium phosphate nanorods and nanoplates, can accumulate lead phosphate mineral and lead iodide on the fungal hyphae surface in large amounts under a wide range of pH conditions, while A. niger VKMF-1119 and M. ramannianus R-56 adsorbed small amounts of minerals. After biosorption of lead iodide minerals on Cladosporium sp. strain F1, aqueous dimethyl sulfoxide (50%) at pH 2 (70 °C) released the mineral more than 99%. Based on the fungal surface analyses, hydrophobic properties on the surfaces of Cladosporium sp. strain F1 could affect the higher biosorption capacity of strain F1 to lead phosphate mineral and lead iodide as compared to other tested fungi. Cladosporium sp. strain F1 may be the novel biosorbents to remediate the phosphate rich environment and to recover lead from perovskite solar cells lead iodide.

Citric Acid and Poly-glutamic Acid Promote the Phytoextraction of Cadmium and Lead in Solanum nigrum L. Grown in Compound Cd-Pb Contaminated Soils

Phytoextraction is an efficient strategy for remediating heavy metal-contaminated soil. Chelators can improve the bioavailability of heavy metals and increase phytoextraction efficiency. However, traditional chelators have gradually been replaced due to secondary pollution. In this study, a typical organic acid (citric acid, CA) and a novel biodegradable chelator (poly-glutamic acid, PGA), were investigated using pot experiments to compare the phytoextraction efficiency of Solanum nigrum L. (a Cd (hyper)accumulator) for cadmium (Cd) and lead (Pb) in contaminated soil. The results showed CA and PGA significantly improved plant growth, and total Cd and Pb amounts of S. nigrum, both CA and PGA significantly increased the shoot Cd and Pb concentrations. However, only PGA significantly increased the root Pb concentration. CA and PGA application promoted the bioavailability of Cd and Pb in rhizosphere soils and their translocations from roots to shoots in S. nigrum. Both CA and PGA increased the phytoextraction efficiency of Cd and Pb in S. nigrum plants, and the PGA for Cd and Pb phytoextraction was more effective than CA. Our findings demonstrate that the biodegradable chelator PGA has great potential for enhancing phytoextraction from compound Cd-Pb contaminated soils, suggesting that biodegradable chelator-assisted phytoextraction with (hyper)accumulator is strongly recommended in severely contaminated sites.

Does the presence of heavy metal and catechol contaminants in organic waste challenge the physiological performance of the bioconverter Hermetia illucens?

The increased human activities and the worldwide population growth are constantly increasing the production of solid wastes. Over the years, waste management has thus become a prominent issue for several companies and municipalities, and several engineering techniques have been developed over the years in order to convert wastes into other solid materials or fuels. Yet, several techniques are important contributors to environmental pollution, and biological-based solutions have thus become progressively very popular. In particular, insect-based conversion of organic wastes represent eco-friendly tools, and the growth and development of insect species such as the black soldier fly have been tested and improved for a large diversity of organic wastes. However, organic wastes, including food wastes, may contain several pollutants such as heavy metals and catechol which could affect the bioconversion efficiency by incurring physiological costs that would be undetectable at the organismal level, i.e. have null to little effects on the life cycle of Hermetia illucens. In this context, assessments of antioxidant capacities can provide a rapid and low-cost evaluation of the capability of insects to handle exposure to heavy metals and catechol. Here, we aimed at measuring the physiological responses of the black soldier fly H. illucens grown on food wastes (kitchen, fruit or vegetable wastes) contaminated by cadmium, iron, lead or catechol. Biomarkers of oxidative stress (concentrations of hydrogen peroxide and protein carbonyls), non-enzymatic total antioxidant capacity (ascorbic acid amounts) and activity of enzymatic antioxidants (activities of superoxide dismutase and polyphenoloxidase) were measured from the gut of the larvae. We found no evidence of deleterious impacts of food waste contamination by catechol or heavy metals on H. illucens. In most experimental treatments, the array of physiological endpoints we measured for evaluating the degree of oxidative stress experienced by the larvae remained similar to controls. Possible physiological effects were reported for cadmium and catechol only, which tended to increase the oxidation of proteins and hydrogen peroxide in the larvae. Finally, our results suggested that the nature of the food waste could equally affect the physiological responses of the insect.

PVA-integrated graphene oxide-attapulgite composite membrane for efficient removal of heavy metal contaminants

Graphene oxide (GO) is an excellent membrane-forming material with unique two-dimensional transport channels and excellent adsorption properties for heavy metal contaminants. However, swelling under cross-flow conditions and long-term water immersion leads to poor separation performances. To improve the stability of GO membrane materials, we propose a PVA-integrated graphene oxide/attapulgite membrane (GOAP) with a 3D microstructural arrangement of "brick-mortar-brick." The addition of PVA as mortar reinforces the strength of the structures via induced hydrogen bonding within the 3D water transport network. Furthermore, the Al₂O₃ ceramic substrate pre-treated with (3-aminopropyl) triethoxysilane (APTES) provided high mechanical stability to the composite membrane, extending the membrane's stability beyond a month of immersion without swelling or shedding. The PVA-integrated GO/ATP composite membrane maintained a rejection rate of 99% for Cu²⁺ solution (100 mg/L) in a 26-h continuous with nearly 100% rejection for various metals ions such as Cu²⁺, Ni²⁺, Pb²⁺, and Cd²⁺. The membrane exhibited a water flux of 20.7 L·m^-2·h^-1, which was 15.9-fold high than the pure GO membrane (GOM). The high water flux and heavy metal filtration rate with superior stability proved the practical suitability of the composite film for removing heavy metal ions.

Soil microbial community assembly model in response to heavy metal pollution

Heavy metal pollution affected the stability and function of soil ecosystem. The impact of heavy metals on soil microbial community and the interaction of microbial community has been widely studied, but little was known about the response of community assembly to the heavy metal pollution. In this study, we collected 30 soil samples from non (CON), moderately (CL) and severely (CH) contaminated fields. The prokaryotic community was studied using high-throughput Illumina sequencing of 16s rRNA gene amplicons, and community assembly were quantified using phylogenetic-bin-based null approach (iCAMP). Results showed that diversity and composition of both bacterial and archaeal community changed significantly in response to heavy metal pollution. The microbial community assembly tended to be more deterministic with the increase of heavy metal concentration. Among the assembly processes, the relative importance of homogeneous selection (deterministic process) increased significantly (increased by 16.2%), and the relative importance of drift and dispersal limitation (stochastic process) decreased significantly (decreased by 11.4% and 5.4%, respectively). The determinacy of bacterial and archaeal community assembly also increased with heavy metal stress, but the assembly models were different. The deterministic proportion of microorganisms tolerant to heavy metals, such as Thiobacillus, Euryarchaeota and Crenarchaeota (clustered in bin 32, bin59 and bin60, respectively) increased, while the stochastic proportion of microorganisms sensitive to heavy metals, such as Koribacteraceae (clustered in bin23) increased. Therefore, the heavy metal stress made the prokaryotic community be deterministic, however, the effects on the assembly process of different microbial groups differed obviously.

Mutagens in raw ewe milk in Orava region, northern Slovakia: metals

The aim of this work was to determine the concentrations of selected mutagenic elements (As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Se) in raw ewe milk from undisturbed environment in Orava region, northern Slovakia. There are possible sources of some of the analyzed metals which may be distributed from the metallurgical plants located in the Ostrava region, Czech Republic, and Katowice, Poland. In total, forty milk samples were analyzed in June and August using an inductively coupled plasma optical emission spectrometry. The differences in elements concentrations between the seasonal periods were not significant except of iron (p < 0.0001). The concentrations of most of the metals in ewe milk were low and under the permissible or recommended limits. However, arsenic and selenium concentrations were elevated and could pose a risk of the mutagenic effect, particularly in children. The frequency of element occurrence in June was as follows: Se > Fe > As > Cu > Mn > Ni > Co > Pb > Cr > Cd, and in August: Se > Fe = As > Cu > Mn > Pb > Co > Ni > Cr > Cd. The correlation analysis revealed very strong positive correlation between Cu:Pb (p < 0.05), very strong negative correlation between Fe:Se (p < 0.05). The strong correlations were also found between other elements. The present study showed that milk produced in the relatively undisturbed environment might contain various mutagenic elements. The relationships between the elements might result in the additive or synergistic effects of elements and increase the risk of their mutagenic effects even in low concentrations. Therefore, attention must be paid to the monitoring of metals in the areas where food sources destined especially for child nutrition are produced.

Spatial distribution, pollution assessment, and source identification of heavy metals in the Yellow River

The discharge of pollutants into the Yellow River has been strictly controlled since 2013 due to the severe pollution. Thus, the overall water quality of the Yellow River has been becoming better year by year. However, the contamination status and source identification of heavy metals from the entire Yellow River remains unclear. Our results demonstrated that heavy metal contents in sediments showed little changes over time, whereas significant alleviation was observed in surface water compared to the reported metal concentrations before 2013. No heavy metal contamination was observed in surface water, and the distribution of all heavy metals in surface water fluctuated along the mainstream without a significant spatial difference. Heavy metals in sediments were assessed as low to moderate contamination degree. The majority of heavy metal concentrations were higher in the upstream and midstream than that in the downstream. Besides anthropogenic activities, the natural contribution from soil erosion of the Loess Plateau was also an important source of heavy metals in the Yellow River sediments. Our results highlight that control of anthropogenic activities and soil erosion of the Loess Plateau are necessary measures to reduce heavy metals in the Yellow River.

Ecological-health risks assessment and source apportionment of heavy metals in agricultural soils around a super-sized lead-zinc smelter with a long production history, in China

Smelting activities are considered as the primary cause of heavy metal (HM) accumulation in soils, and the human health around the smelter has been a great concern worldwide. In this study, a total of 242 agricultural soil samples were collected around a large scale Pb/Zn smelter in China, and eight HMs (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn) were analyzed to assess HMs status, ecological -health risks, and identify source. Monte Carlo simulation was utilized to evaluate the probabilistic health risks, and positive matrix factorization (PMF) was employed to identify sources. The results revealed the average contents of five heavy metals (Cd 5.28 mg/kg, Pb 203.36 mg/kg, Hg 0.39 mg/kg, Zn 293.45 mg/kg, Cu 37.14 mg/kg) are higher than their background values in Hunan province. Cd had the highest mean pollution index (PI) of 41.8 and the greatest average ecological risk index (E_r) of 1256.34, indicating that Cd was the primary enriched pollutant and had a higher ecological risk than other HMs. The mean hazard index (HI) through exposure to eight HMs was 2.95E-01 and 9.74E-01 for adults and children, respectively, with 35.94% of HI values for children exceeding the risk threshold of 1. Moreover, the mean total cancer risks (TCR) were 2.75E-05 and 2.37E-04 for adults and children, respectively, with 75.48% of TCR values for children exceeding the guideline value of 1E-04. In addition, the positive matrix factorization results showed smelting activities, natural sources, agricultural activities and atmospheric deposition were the three sources in soils, with the contribution rate of 48.62%, 22.35%, and 29.03%, respectively. The uncertainty analysis of the PMF indicated that the three-factor solution is reliable. This work will provide scientific reference for the comprehensive prevention of soil HM pollution adjacent to the large smelter.

Insight into soilless revegetation of oligotrophic and heavy metal contaminated gold tailing pond by metagenomic analysis

Soilless revegetation is an efficient way for gold tailing remediation, and micro-ecological environments in plant rhizosphere are important for vegetation establishment and pollution removal. In the present study, a field experiment of soilless revegetation has been carried out in a gold tailings pond, and the key genera and functional genes in the plant rhizosphere of gold mine tailings were revealed by metagenomics analysis. Soilless revegetation significantly decreased rhizosphere tailing pH from 8.54 to 7.43-7.87, reduced heavy metal (HM) concentration by 29.81-44.02% and enhanced the nutrient content by 50.30-169.50% averagely. Such improvements were strongly and closely correlated to microbial community and functional gene composition variation. The relative abundance of ecologically beneficial genus such as Actinobacteria (increased 9.7-18.8%) and functional genes involved in carbon, nitrogen and phosphorus cycling such as pyruvate metabolism (relatively increased 8.7-15.0%), assimilatory (increased to 1.44-2.08 times), phosphate ester mineralization (increased to 1.12-1.29 times) and phosphate transportation (increased to 1.28-1.85 times) were significantly increased. Moreover, the relative abundance of most As and Zn resistance genes were reduced, which may relate to the decrease of As and Zn concentration in the rhizosphere tailings. These results revealed the correlation among HM concentrations, microbial composition and functional genes, and provided clear strategies for improving gold mine tailing ecological restoration efficiency.

Increase of P and Cd bioavailability in the rhizosphere by endophytes promoted phytoremediation efficiency of Phytolacca acinosa

The information about the spatial distribution of bioavailable phosphorus (P) and heavy metal (HM) in the rhizosphere could aid in the precise phytoremediation regulation. In this study, a rhizobox system was adapted to study soil-root interactions and used to access the endophyte inoculation variation on bioavailable P and cadmium (Cd) spatial distribution during phytoremediation of Cd contaminated soils. Results showed that endophyte PE31 Bacillus cereus inoculation enhanced Cd uptake of P. acinosa by 52.70% and 46.73% in low and high Cd contaminated soils, increasing the phytoremediation hotspot area from 45.78% and 15.29% to 60.97% and 21.80%, respectively. Available P and Cd significantly diminished because root activities depleted large amounts of bioavailable P and Cd concentrations. However, PE31 increased bioavailable P and Cd concentration in the rhizosphere soil. The bioavailable P enhancement in the rhizosphere was positively correlated to plant growth and Cd accumulation. Overall, endophyte inoculation compensated the diminution of bioavailable P and Cd in the rhizosphere to improve plant biomass and HM absorption, and thus promote phytoremediation efficiency. This study helped to better understand bioavailable P and Cd spatial distribution under endophyte inoculation, which could provide effective management strategies for the precise regulation of phytoremediation.

Heavy metal resistance of marine bacteria on the sediments of the Black Sea

The Black Sea is unfortunately globally established as a highly polluted sea, with contaminants from various sources polluting its marine sediments. This study aimed at analyzing heavy metal resistance levels by heterotrophic bacteria colonizing marine sediments across Black Sea shores within Turkey. Twenty-nine bacterial samples from marine sediments were investigated through exposure to sixteen heavy metal salts using the microdilution method. The minimum inhibitory concentration values for bacterial colonies within such marine sediment samples ranged from <0.97 mM/L to >1000 mM/L. Trough and peak minimum inhibitory concentration values were determined at <0.17 mg/mL and > 331 mg/mL. Peak tolerated and peak toxic heavy metals were identified as iron and cadmium, respectively. Resistance ratios were also obtained in this study. Bacillus wiedmannii was identified as the most resistant bacterial population when exposed to heavy metal salts. This study shows occurrence of heavy metal resistant bacteria within Black Sea sediments.

Metal Contamination of Oman Sea Seaweed and Its Associated Public Health Risks

Oman Sea region is a major gateway for international and local shipping. Metal pollution of aquatic environment is primarily caused by such shipping and industrial activities. Agricultural runoffs are also of concern. Seaweed contamination with heavy metals in this area is therefore a distinct possibility. We examined seaweed of Oman Sea for heavy metal content and potential risk of its consumption to the public. During winter of 2019, water, sediment, and seaweed were collected along twelve stations on the coast of Oman Sea. Triplicates of each sample were analyzed for metal content by atomic absorption spectroscopy. Biomarkers of metals in seaweed (metallothionein and phytochelatin) were also analyzed. A significant positive correlation exists among levels of Zn, Ni, Pb, Cr, Cu, and Fe in water, sediment, and seaweed (P < 0.05). Cadmium correlations were weak. The highest levels of metallothionein and phytochelatin were found in brown and red seaweed (118.6 µg/g wet weight, 16.4 amol/cell; 111.4 µg/g ww, 12.1 amol/cell), respectively. For nickel and lead, human consumption of red, brown, and green seaweed was associated with "some health hazard," with a target hazard quotient of > 1. We conclude that concerns over heavy metal contamination of some parts of Oman Sea are valid, and we invite policy makers to implement measures for protection of public and environment from metal toxic effects in the region.

Source-specific ecological risk assessment and quantitative source apportionment of heavy metals in surface sediments of Pearl River Estuary, China

In this study, surface sediments of the Pearl River Estuary were collected from 29 stations and investigated the spatial distribution, pollution level, quantitative source apportionment, and source-specific ecological risk of 10 heavy metals. The mean concentrations followed the order of Mn > Zn > Cr > Cu > Ni > Pb > As > Co > Cd > Hg. In terms of spatial distribution, it showed that the heavy metals were enriched in the inner Pearl River Estuary with 'extremely high' level of Hg, whereas, Cd and Zn posed 'moderate to high' contamination potential. We apportioned four main sources using positive matrix factorization model, in which natural geogenic and industrial manufacturing sources accounted for 36.84% and 27.11% of the total, respectively. However, the source-specific risk assessment suggested that mixed anthropogenic sources were the main contributors, and ecological risks were strongly affected by anthropogenic imports from the surrounding cities.

Oyster shell amendment reduces cadmium and lead availability and uptake by rice in contaminated paddy soil

Contamination with cadmium (Cd) and lead (Pb) in rice and paddy soil threatens food safety and human health. This study determined the effects of oyster shell amendment (0, 6, and 12 g kg^-1) on the mobility and uptake of Cd and Pb by two rice plants (ZY18, japonica and DL5, indica) in contaminated paddy soil. Oyster shell amendment significantly increased the pH of soil and pore water, and decreased the DTPA-extractable Cd concentration in soil, but not the Cd concentration in pore water. Furthermore, the DTPA-extractable Pb concentration in rhizosphere soil was not significantly influenced by oyster shell addition. Application of oyster shell reduced the Pb concentration in pore water and Pb uptake by both cultivars, but excessive application (12 g kg^-1) resulted in Cd accumulation in tissues for ZY18. Furthermore, oyster shell addition significantly increased the dissolved organic carbon, calcium, and magnesium concentrations in soil pore water, and decreased glutathione and phytochelatin levels in roots, all of which alleviated heavy metal toxicity and improved rice growth. These results demonstrate that amendment with the appropriate amount of oyster shell, combined with rice cultivar type, could simultaneously reduce Cd and Pb accumulation in rice grown in heavy metal-contaminated soil.