Sources and remediation techniques for mercury contaminated soil

Novel coumarin-based ratiometric bifunctional fluorescent probe mimicking a set-reset memorized device

A novel coumarin-based fluorescent sensor CHE, incorporating 2-hydrazinylbenzothiazole and coumarin aldehyde, has been developed that demonstrated a preferential detection of Hg2+ and Ag+ in presence of interferences. Compared to previously prevalent intensity-based fluorescent probes, CHE exhibited a ratiometric fluorescence response to Hg2+ and Ag+, and further accurately differentiated Hg2+ and Ag + using the differential extractive ability of EDTA when interacting with ion-CHE complexes. Sensing mechanism was investigated and elucidated. The chemosensor CHE was successfully applied to detect Hg2+ and Ag+ in six distinct samples with satisfactory results. Additionally, combinatorial logic circuits were constructed utilizing three distinct logic gates (NOT, OR, and INH) based on the sensor's differential output signals in response to Hg2+/Ag+ and other cations. Interestingly, utilizing the reversible and reproducible switching behavior of the EDTA interaction with Hg2+, a conceptual 'Write-Read-Erase-Read' memory function with multi-write capability was proposed, offering a novel perspective for molecular-based memory systems.

Investigating the role of poly-γ-glutamic acid in Pennisetum giganteum phytoextraction of mercury-contaminated soil

Farmland mercury (Hg) pollution poses a significant threat to human health, but there is a lack of highly efficient phytoextraction for its remediation at present. This study investigates the impact of poly-γ-glutamic acid (γ-PGA) on the phytoextraction capabilities of Pennisetum giganteum (P. giganteum) in Hg-contaminated soil. Our research indicates that amending γ-PGA to soil markedly enhances the assimilation of soil Hg by P. giganteum and transformation of Hg within itself, with observed increases in Hg concentrations in roots, stems, and leaves by 1.1, 4.3, and 18.9 times, respectively, compared to the control. This enhancement is attributed to that γ-PGA can facilitate the hydrophilic and bioavailable of soil Hg. Besides, γ-PGA can stimulate the abundance of Hg-resistance bacteria Proteobacteria in the rhizosphere of P. giganteum, thus increasing the mobility and uptake of soil Hg by P. giganteum roots. Moreover, the hydrophilic nature of Hg-γ-PGA complexes supports their transport via the apoplastic pathway, across the epidermis, and through the Casparian strip, eventually leading to immobilization in the mesophyll tissues. This study provides novel insights into the mechanisms of Hg phytoextraction, demonstrating that γ-PGA significantly enhances the effectiveness of P. giganteum in Hg uptake and translocation. The findings suggest a promising approach for the remediation of Hg-contaminated soil, offering a sustainable and efficient strategy for environmental management and health risk mitigation.

Exploring the origins and cleanup of mercury contamination: a comprehensive review

Mercury is a global pollutant that poses significant risks to human health and the environment. Natural sources of mercury include volcanic eruptions, while anthropogenic sources include industrial processes, artisanal and small-scale gold mining, and fossil fuel combustion. Contamination can arise through various pathways, such as atmospheric deposition, water and soil contamination, bioaccumulation, and biomagnification in food chains. Various remediation strategies, including phytoremediation, bioremediation, chemical oxidation/reduction, and adsorption, have been developed to address mercury pollution, including physical, chemical, and biological approaches. The effectiveness of remediation techniques depends on the nature and extent of contamination and site-specific conditions. This review discusses the challenges associated with mercury pollution and remediation, including the need for effective monitoring and management strategies. Overall, this review offers a comprehensive understanding of mercury contamination and the range of remediation techniques available to mitigate its adverse impacts.

Iodide- and electrochemical assisted removal of mercury by Cirsium arvense from gold tailings in the Amansie West District, Ghana

Mercury (Hg) pollution in Ghana through mining has become a serious environmental challenge. This study investigates the potential of Cirsium arvense to photostabilize Hg using electrokinetic current with or without an iodide solution in gold mine tailings heavily contaminated through mining activities in southern Ghana. An initial Hg concentration of 9.60 mg/kg using cold vapor atomic absorption spectrometry (CVAAS) was determined. The biological absorption coefficient, bioconcentration factor, and translocation factor of Hg have been presented. Cirsium arvense therefore had a higher bioconcentration factor (BCF) of 2.6-5.15 mg/kg, and a transfer factor (TF) of 0.24-0.36 indicating a higher efficiency for phytostabilization. Both the rate and time of extractions of Hg from the tailings by Cirsium arvense are efficiently improved in the combined electric current and iodide treatment. Plant and electric current combined treatment and plant and iodide combined treatment had only 60 and 50% phytostabilization rates, respectively. The combined plant, iodide, and electric current treatment has proven to be superior with about >90% Hg removal rate. Therefore, the combined plant, iodide, and electric current treatment resulted in a higher Hg removal efficiency by Cirsium arvense in a shorter period due to higher solubilization rate and electromigration effects on Hg species.

Level of Heavy Metals and Potential Ecological Risks in Irrigated Horticultural Farms in the Vicinity of Lake Ziway, Central Ethiopian Rift Valley Region

Research on heavy metal pollution in horticultural farms located around lakes in the Central Ethiopian Rift Valley Region has focused on measuring the levels of heavy metals and their health implications. However, the ecological risks of horticultural farms contaminated with heavy metals in this region have not been studied. The current study addresses this gap by providing information on the degree of heavy metal contamination and the ecological risk associated with horticultural farms around Lake Ziway, using various pollution indices. An inductively coupled plasma optical emission spectrometer (ICP-OES) was used to measure the concentrations of nine heavy metals (As, Cd, Co, Cu, Cr, Ni, Pb, Hg, and Zn) in a total of 30 composite soil and irrigation water samples, each consisting of a mix of six subsamples. The results indicated that the mean concentrations of Hg, Cd, Pb, and Zn in soils collected from all the sampling sites exceeded the FAO/WHO maximum permissible limit (MPL). The values of both the contamination factor (CF) and contamination degree (Cd) of the heavy metals ranged from 0.04 to 2.66 and 2.81 to 6.14, respectively, indicating a low to medium level of contamination for both indices. The pollution load index (PLI) values of 0.451, 0.449, and 0.157 for sites 2, 1, and 3, respectively, indicate "unpolluted" to "moderately polluted" levels of heavy metal pollution. However, the ecological risk indices (ERIs) at sites 2 and 1 (158.92 and 141, respectively) showed a potentially high ecological risk due to soil pollution. Therefore, close monitoring and early intervention mechanisms must be in place to control pollution in the study area.

Mercury abatement in the environment: Insights from industrial emissions and fates in the environment

Mercury's neurotoxic effects have prompted the development of advanced control and remediation methods to meet stringent measures for industries with high-mercury feedstocks. Industries with significant Hg emissions, including artisanal and small-scale gold mining (ASGM)-789.2 Mg year-1, coal combustion-564.1 Mg year-1, waste combustion-316.1 Mg year-1, cement production-224.5 Mg year-1, and non-ferrous metals smelting-204.1 Mg year-1, use oxidants and adsorbents capture Hg from waste streams. Oxidizing agents such as O3, Cl2, HCl, CaBr2, CaCl2, and NH4Cl oxidize Hg0 to Hg2+ for easier adsorption. To functionalize adsorbents, carbonaceous ones use S, SO2, and Na2S, metal-based adsorbents use dimercaprol, and polymer-based adsorbents are grafted with acrylonitrile and hydroxylamine hydrochloride. Adsorption capacities span 0.2-85.6 mg g-1 for carbonaceous, 0.5-14.8 mg g-1 for metal-based, and 168.1-1216 mg g-1 for polymer-based adsorbents. Assessing Hg contamination in soils and sediments uses bioindicators and stable isotopes. Remediation approaches include heat treatment, chemical stabilization and immobilization, and phytoremediation techniques when contamination exceeds thresholds. Achieving a substantially Hg-free ecosystem remains a formidable challenge, chiefly due to the ASGM industry, policy gaps, and Hg persistence. Nevertheless, improvements in adsorbent technologies hold potential.

Catchment land use effect on mercury concentrations in lake sediments: A high-resolution study of Qinghai Lake

Mercury (Hg) contamination in aquatic environments presents a significant ecological and human health concern. This study explored the relationship between catchment land use and Hg concentrations within Qinghai Lake sediment, the largest lake in China, situated on the Qinghai-Tibet plateau. The study entailed detailed mapping of Hg sediment concentrations and a subsequent environmental risk assessment. Considering the complex nature of the plateau landform and surface vegetation, the study area was delineated at a 100 km radius centered on Qinghai Lake, which was divided into 30 sectors to quantify relationships between land use and the sediment Hg concentration. The results revealed a mean sediment Hg concentration of 29.91 μg/kg, which was elevated above the background level. Kendall's correlation analysis revealed significant but weak associations between sediment Hg concentrations and three land use types: grassland (rangeland and trees) (rs = 0.27, p < 0.05), crops (rs = -0.37, p < 0.05), and bare ground (rs = -0.25, p < 0.1), suggesting that growing areas of grassland correlated with higher Hg levels in the lake sediment, in contrast to bare ground or crops area, which correlated with lower Hg concentrations. Multiple linear regression models also observed weak negative relationships between bare ground and crops with sediment Hg concentration. This research methodology enhances our understanding of the impact of land use on Hg accumulation in lake sediments and underscores the need for integrated watershed management strategies to mitigate Hg pollution in Qinghai Lake.

Antagonistic effect of mercury and excess nitrogen exposure reveals provenance-specific phytoremediation potential of black locust-rhizobia symbiosis

Interaction of different environmental constrains pose severe threats to plants that cannot be predicted from individual stress exposure. In this context, mercury (Hg), as a typical toxic and hazardous heavy metal, has recently attracted particular attention. Nitrogen (N2)-fixing legumes can be used for phytoremediation of Hg accumulation, whereas N availability could greatly affect its N2-fixation efficiency. However, information on the physiological responses to combined Hg exposure and excess N supply of woody legume species is still lacking. Here, we investigated the interactive effects of rhizobia inoculation, Hg exposure (+Hg), and high N (+N) supply, individually and in combination (+N*Hg), on photosynthesis and biochemical traits in Robinia pseudoacacia L. seedlings of two provenances, one from Northeast (DB) and one from Northwest (GS) China. Our results showed antagonistic effects of combined + N*Hg exposure compared to the individual treatments that were provenance-specific. Compared to individual Hg exposure, combined + N*Hg stress significantly increased foliar photosynthesis (+50.6%) of inoculated DB seedlings and resulted in more negative (-137.4%) δ15N abundance in the roots. Furthermore, combined + N*Hg stress showed 47.7% increase in amino acid N content, 39.4% increase in NR activity, and 14.8% decrease in MDA content in roots of inoculated GS seedlings. Inoculation with rhizobia significantly promoted Hg uptake in both provenances, reduced MDA contents of leaves and roots, enhanced photosynthesis and maintained the nutrient balance of Robinia. Among the two Robinia provenances investigated, DB seedlings formed more nodules, had higher biomass and Hg accumulation than GS seedlings. For example, total Hg concentrations in leaves and roots and total biomass of inoculated DB seedlings were 1.3,1.9 and 3.4 times higher than in inoculated GS seedlings under combined + N*Hg stress, respectively. Therefore, the DB provenance is considered to possess a higher potential for phytoremediation of Hg contamination compared to the GS provenance in environments subjected to N deposition.

Efficient and synergistic treatment of selenium (IV)-contaminated wastewater and mercury (II)-contaminated soil by anaerobic granular sludge: Performance and mechanisms

Wastewater containing selenium (Se) and soil contaminated by mercury (Hg) are two environmental problems, but they are rarely considered for synergistic treatment. In this work, anaerobic granular sludge (AnGS) was used to address both of the aforementioned issues simultaneously. The performance and mechanisms of Se(IV) removal from wastewater and Hg(II) immobilization in soil were investigated using various technologies. The results of the reactor operation indicated that the AnGS efficiently removed Se from wastewater, with a removal rate of 99.94 ± 0.05%. The microbial communities in the AnGS could rapidly reduce Se(IV) to Se0 nanoparticles (SeNPs). However, the AnGS lost the ability to reduce Se(IV) once the Se0 content reached the saturation value of 5.68 g Se/L. The excess sludge of Se0-rich AnGS was applied to remediate soil contaminated with Hg(II). The Se0-rich AnGS largely decreased the percentage of soil Hg in the mobile, extractable phase, with up to 99.1 ± 0.3% immobilization. Soil Hg(II) and Hg0 can react with Se (-II) and Se0, respectively, to form HgSe. The formation of inert HgSe was an important pathway for immobilizing Hg. Subsequently, the pot experiments indicated that soil remediation using Se0-rich AnGS significantly decreased the Hg content in pea plants. Especially, the content of Hg decreased from 555 ± 100 to 24 ± 3 μg/kg in roots after remediation. In summary, AnGS is an efficient and cost-effective material for synergistically treating Se-contaminated wastewater and Hg-contaminated soil.

'Remediability Score' as a tool for selecting the most suitable remediation technology for contaminated sites

Land gets contaminated due to different human activities like illegal industrial discharges, mining activities, and spillage of chemicals. The pollutants released through these activities can have prolonged effects on the environment and human health. Therefore, there is a need for immediate remediation of the contaminated site. Different remediation technologies are available for remediating a land contaminated with a particular contaminant. Selection of the most appropriate remediation technology among all those available would help in quick and efficient remediation of the land. There are multiple factors deciding the appropriateness of a technology for a given case. 'Remediability' is a term introduced in the scientific literature recently to describe the ease with which a contaminated land can be remediated and 'Remediability Score (RS)' quantifies remediability in a 0-100 scale. The higher the value of RS, the greater is the difficulty for remediation. The factors influencing remediability were presented before a group of experts in a Delphi process for assigning comparative importance. From the importance score obtained in a Saaty scale of 1 to 9, the weights of factors were calculated using Fuzzy AHP. The overall RS was calculated by taking the weighted impact of the factors after their magnitudes were normalized. RS for the various remediation technologies feasible for a contaminated site, Kuzhikandam, near Kochi, Kerala was calculated. The site was revealed to be contaminated with heavy metals and organic compounds in a field investigation. The most suitable technology for remediating the selected site was found to be vitrification with an RS of 22. The next best technology, stabilization/solidification, had an RS of 25. The study showed that RS can be a reliable matric for selecting the most suitable remediation technology for a contaminated site.

Effective reducing the mobility and health risk of mercury in soil under thiol-modified biochar amendment

Soil mercury contamination poses health risks. However, effective immobilization techniques are lacking with challenges including low efficiency, limited long-term stability, susceptibility to multi-medium interference, and difficulty in controlling health risks. This study confirmed the feasibility of thiol-modified biochar, and elucidated the underlying mechanisms. Within 32 days of treatment, the leachable mercury decreased from 184.7 μg/L to below the hazardous waste threshold (100 μg/L, HJ/T299-2007, China). After 198 days of treatment, the soil achieved a safe ecological state with a mercury immobilization rate of 79.8-98.2% and a 50% reduction in available methylmercury. Thiol-modified biochar facilitated the conversion of active mercury species (exchangeable, carbonate, and oxide) into stable forms (organic and residual) through complexation and precipitation (e.g., HgS). Soil quality improvements were observed, including enhanced cation exchange capacity, available nitrogen, and total organic carbon. Thiol-modified biochar exhibits long-term effectiveness. After one and two years of treatment, the leachable mercury remained within acceptable health risk limit (hazard quotient < 1) for adults and children, respectively. After three years, the leachable mercury met the Level III groundwater quality standard (< 1 μg/L, GB 14848-2017, China). This study demonstrates an effective strategy for long-term diminishing mercury mobility and health risks in soil.

Tailored bacteria tackling with environmental mercury: Inspired by natural mercuric detoxification operons

Mercury (Hg) and its inorganic and organic compounds significantly threaten the ecosystem and human health. However, the natural and anthropogenic Hg environmental inputs exceed 5000 metric tons annually. Hg is usually discharged in elemental or ionic forms, accumulating in surface water and sediments where Hg-methylating microbes-mediated biotransformation occurs. Microbial genetic factors such as the mer operon play a significant role in the complex Hg biogeochemical cycle. Previous reviews summarize the fate of environmental Hg, its biogeochemistry, and the mechanism of bacterial Hg resistance. This review mainly focuses on the mer operon and its components in detecting, absorbing, bioaccumulating, and detoxifying environmental Hg. Four components of the mer operon, including the MerR regulator, divergent mer promoter, and detoxification factors MerA and MerB, are rare bio-parts for assembling synthetic bacteria, which tackle pollutant Hg. Bacteria are designed to integrate synthetic biology, protein engineering, and metabolic engineering. In summary, this review highlights that designed bacteria based on the mer operon can potentially sense and bioremediate pollutant Hg in a green and low-cost manner.

Tuning active sites on biochars for remediation of mercury-contaminated soil: A comprehensive review

Mercury (Hg) contamination is acknowledged as a global issue and has generated concerns globally due to its toxicity and persistence. Tunable surface-active sites (SASs) are one of the key features of efficient BCs for Hg remediation, and detailed documentation of their interactions with metal ions in soil medium is essential to support the applications of functionalized BC for Hg remediation. Although a specific active site exhibits identical behavior during the adsorption process, a systematic documentation of their syntheses and interactions with various metal ions in soil medium is crucial to promote the applications of functionalized biochars in Hg remediation. Hence, we summarized the BC's impact on Hg mobility in soils and discussed the potential mechanisms and role of various SASs of BC for Hg remediation, including oxygen-, nitrogen-, sulfur-, and X (chlorine, bromine, iodine)- functional groups (FGs), surface area, pores and pH. The review also categorized synthesis routes to introduce oxygen, nitrogen, and sulfur to BC surfaces to enhance their Hg adsorptive properties. Last but not the least, the direct mechanisms (e.g., Hg- BC binding) and indirect mechanisms (i.e., BC has a significant impact on the cycling of sulfur and thus the Hg-soil binding) that can be used to explain the adverse effects of BC on plants and microorganisms, as well as other related consequences and risk reduction strategies were highlighted. The future perspective will focus on functional BC for multiple heavy metal remediation and other potential applications; hence, future work should focus on designing intelligent/artificial BC for multiple purposes.

Selenium and zinc alleviate quaternary metal mixture -induced neurotoxicity in rats by inhibiting oxidative damage and modulating the expressions of NF-kB and Nrf2/Hmox-1 pathway

Background

This study evaluated the potential protective effects of Zn and Se in the cerebellum and cerebral cortex, two fundamentally important brain regions, in albino rats that were exposed to heavy metals mixture (Al, Pb, Hg and Mn).

Methods

Animals were divided into five groups of seven animals per group with following patterns of exposure, controls group 1 were orally treated with deionized water for 60 days; group 2 was exposed to heavy metal mixture (HMM) with following concentrations (20 mg·kg^-1 of Pb body weight; 0.40 mg·kg^-1 of Hg; 0.56 mg·kg^-1 of Mn; and 35 mg·kg^-1; of Al), while groups 3,4 and 5 were exposed to HMM and orally co-treated with zinc chloride (ZnCl₂; 0.80 mg/kg), sodium selenite (Na₂SeO₃;1.50 mg/kg) and zinc chloride plus sodium selenite (ZnCl_0.2 + Na₂SeO₃) respectively.

Results

Exposure to HMM depressed cellular antioxidant apparatus, induced generation of lipid peroxidation markers (Malondialdehyde and NO), downregulated expression of transcription factors (Nrf2, and NF-kB) and upregulated Caspase 3 levels. HMM potentiated acetylcholinesterase activity and induced moderate histopathological alterations. Nevertheless, Zn, Se and in particular Zn + Se had recovering effects on all mentioned hazardous effects produced by HMM exposure in the cerebral cortex and cerebellum.

Conclusions

Selenium and zinc exert neuroprotection via Nrf2/NF-kB signaling pathways against quaternary heavy metal mixture-induced impairments in albino Sprague Dawley rats.

Potential role of apple wood biochar in mitigating mercury toxicity in corn (Zea mays L.)

Mercury (Hg) is a very toxic decomposition-resistant metal that can cause plant toxicity through bioaccumulation and oxidative damage. Biochar, derived from organic waste and agricultural garbage, is an on-site modification technique that can improve soil health in heavy metals-polluted regions. The present experiment was designed to explore the role of apple biochar in the management of mercury toxicity in corn (Zea mays cv. 'PL535'). Different levels of biochar derived from apple wood (0%, 2.5%, 5.0%, and 7.5% w/w) along with different Hg concentrations (0, 20, 40, and 60 mg/L) were used in the experiment that was based on a completely randomized design. Based on the results, HgCl2 at all rates reduced root and shoot dry weight and length, tolerance index, chlorophyll a and b content, the Hill reaction, and dissolved proteins and increased shoot and root Hg content (up to 72.57 and 717.56 times, respectively), cell death (up to 58.36%), MDA level (up to 47.82%), H2O2 (up to 66.33%), dissolved sugars, and proline. The results regarding enzymatic and non-enzymatic antioxidants revealed increases in total phenol and flavonoids content (up to 71.27% and 86.71%, respectively), DPPH free radical scavenging percentage, and catalase (CAT) and ascorbate peroxidase (APX) activity (up to 185.93% and 176.87%, respectively), in corn leaves with the increase in the Hg rate applied to the culture medium. The application of biochar to the substrate of the Hg-treated corns reduced Hg bioavailability, thereby reducing Hg accumulation in the roots (up to 76.88%) and shoots (up to 71.79%). It also reduced the adverse effect of Hg on the plants by increasing their shoot and root dry weight, photosynthesizing pigments, Hill reaction, and APX activity and reducing cell death, H2O2 content, and MDA content. The results reflected the capability of apple wood biochar at all rates in reducing Hg bioavailability and increasing Hg fixation in Hg-polluted soils. However, it was most effective at the rate of 7.5%.

Assessing mercury pollution at a primary ore site with both ancient and industrial mining and smelting activities

The Minamata Convention on Mercury has mandated a renewed global effort to tackle Hg pollution. The present study evaluates Hg pollution at a primary Hg production site exploited since the Qin Dynasty (200s BC), with intensive industrial scale production over the past four decades. This single location accounts for over 95% total Hg production in China in recent years. To assess the environmental risk and effectiveness of recently implemented control measures, we collected 90 soil samples, 60 plant tissue samples, 47 sediment samples, and 47 river water samples from the site and its vicinity. A site-specific conceptual site model was established based on the sources, migration transformation pathways of Hg pollutant and its exposure scenarios. The maximum soil Hg concentration reached 10,451 mg kg-1, posing a high health and ecological risk. Vegetable and crop Hg concentrations outside the site reached 0.23 mg kg-1 in rice grains and 4.24 mg kg-1 in green onion. The highest health risk, with a hazard quotient of 130.66, was observed in the Ore Storage Site, which reduced to 17.14 when Hg bioavailability was considered. Risk control measures implemented in recent years included a stormwater collection system and capping of the tailing pond area with clean imported soil. These measures were generally successful; however, Hg in the tailings were found to be contaminating the imported surficial soil due to rainfall saturation and upward migration, suggesting a need for long-term post remedial site monitoring and maintenance. We also found that mining and smelting activities have contaminated a 6 km stretch of a nearby river, with sediment Hg concentrations reaching 2819 mg kg-1, and water column concentrations reaching 193.21 ng L-1. The sediment and water concentrations are highly correlated (R2 = 0.78), suggesting that, with risk control measures in place, a reservoir of Hg in polluted river sediment is now driving pollution in the water column. This work demonstrates that primary Hg mining has caused widespread and serious soil and water pollution. Risk control measures can reduce human health and ecological risks, but robust monitoring and maintenance are required for remediation to be effective in the long-term.

Addressing Uncertainties in Potential Human Dietary Exposure to Mercury in the Watershed of the South River, Virginia, USA

Much has been published about the harmful effects to humans when they are exposed to mercury (Hg) in environmental media including their diet. Numerous health advisories around the world, including for the South River, Virginia, USA, warn against consumption of Hg-contaminated fish species. Fewer studies have focused on other dietary sources of Hg and how to advise humans potentially exposed by this route. In undertaking a human health risk assessment for the former DuPont facility in Waynesboro, Virginia, USA, and the nearby South River and surrounding watershed, the available published information on Hg exposure through dietary consumption of nonfish items proved unsuitable for extrapolation purposes. In response, an evaluation of potential Hg exposure to residents who might consume livestock, poultry, and wildlife raised or collected in the South River watershed was conducted to inform the risk-assessment process. The newly collected data on Hg in these dietary items filled an important data gap, suggesting that there was little concern about limiting dietary consumption for most items. These results were communicated to the public through print and electronic platforms, in the form of "fact sheets." We describe the studies and actions taken to better explain the potential for human exposures to Hg in nonfish dietary items from a portion of the watershed of the South River. Environ Toxicol Chem 2023;42:2237-2252. © 2023 SETAC.

Performance of electrokinetic remediation system for mercury contaminated marine sediment: Roles of electrode spacing and electrode configuration

Understanding mercury (Hg) species existing after electrokinetic remediation (EK) for marine-sediment remediation is limited. Herein, the Hg fraction removal of EK from contaminated marine sediment was investigated appertaining to bipolar electrode settings along with the effects of electrode spacing and configuration considered. Based on the selective sequential Hg extractions (Hg SSE), much of the Hg in the sediment originated from F5 (i.e., HgS) and F4 (i.e., HgO). The F5 fraction removed by EK was about 30 %, while the F4 fraction had a slight increase of about 34 %. When it comes to electrode configuration, a hexagonal pattern has a higher Hg removal performance than that of a rectangular shape. The addition of anodes increases the remediation surface area, thus allowing superior Hg removal. This study indicates that the electrode spacing significantly affects the mercury removal and the remediation time. Determining suitable spacing enhances the electrical potentials in the migration flux.

Magnetic separation for arsenic and metal recovery from polluted sediments within a circular economy

Several metals and metalloids (e.g., As, Cd, Cu, Pb, Zn) are toxic at low concentrations, thus their presence in sediments can raise environmental concern. However, these elements can be of economic interest, and several techniques have been used for their recovery and some of them have been widely applied to mining or to industrial soils, but not to sediments. In this work, wet high-intensity magnetic separation (WHIMS) was applied for As, Cd, Cu, Pb and Zn recovery from polluted sediments. A composite sample of 50 kg was taken in the Avilés estuary (Asturias, North Spain) with element concentrations above the legislation limits. Element distribution was assessed using wet-sieving and ICP-MS analysis, revealing that the 125-500 μm grain-size fraction accounts for the 62 w% of the material and that element concentration in this fraction is lower than in the other grain size fractions. Subsequently, WHIMS was applied at three different voltage intensities for the 125-500 μm and <125 μm fractions, revealing excellent recovery ratios, especially for the coarser material. Furthermore, magnetic property measurements coupled to microscopy analysis revealed that the success of the technique derives from concentrating metal-enriched iron oxides particles (ferro- and para-magnetic material) in a mixture of quartz and other minerals (diamagnetic particles). These results indicate the feasibility of the magnetic separation for metal and metalloid recovery from polluted sediments, and thus offer a double benefit of coastal area restoration and valuable material recovery in the context of a circular economy.

The potential of microorganisms as biomonitoring and bioremediation tools for mercury-contaminated soils

Mercury (Hg) pollution is a global issue due to the high toxicity and wide dispersion of Hg around the world. Whether due to anthropogenic activities or natural processes, Hg emissions are steadily increasing, with very high levels in some regions, directly threatening human and ecosystem health. However, bacteria and fungi have evolved and adapted in response to Hg-induced stress and have developed tolerance mechanisms, notably based on the mer operon system that is involved in Hg uptake and biovolatilization via Hg reduction reactions. Other processes, such as bioaccumulation or extracellular sequestration, are involved in Hg resistance, and the study of contaminated soils has allowed the isolation of a number of microorganisms capable of these mechanisms, with strong potential for the implementation of bioremediation approaches. In addition to playing an important role in determining the fate of Hg in the biogeochemical cycle, these microorganisms can indeed be applied to reduce Hg concentrations or at least stabilize Hg for the remediation of polluted soils. Moreover, thanks to the development of biotechnological tools, bioremediation based on Hg-tolerant microorganisms can be optimized. Finally, these microorganisms are relevant candidates for biomonitoring, for example, through the engineering of biosensors, because the detection of Hg is a major issue in preserving the health of living beings.

Using multi-technology to characterize transboundary Hg pollution in the largest presently active Hg deposit in China

Active Hg mines are primary sources of Hg contamination in the environment of mining districts and surrounding areas. Alleviation of Hg pollution requires knowledge of pollution sources, migration, and transform pathways across various environmental media. Accordingly, the Xunyang Hg-Sb mine, the largest active Hg deposit in China, presently was selected as the study area. GIS, TIMA, EPMA, μ-XRF, TEM-EDS, and Hg stable isotopes were adopted to investigate the spatial distribution, mineralogical characteristics, in situ microanalysis, and pollution sources of Hg in the environment medium at the macro- and micro-levels. The total Hg concentration in samples showed a regional distribution, with higher levels in areas close to the mining operations. The in situ distribution of Hg in soil was mainly associated with the mineralogical phases of quartz, and Hg was also correlated with Sb and S. Hg was also found to be rich mainly in quartz minerals in the sediment and showed different distributions of Sb. Hg hotspots had S abundances and contained no Sb and O. The contributions from the anthropogenic sources to soil Hg were estimated to be 55.35%, among which 45.97% from unroasted Hg ore and 9.38% from tailing. Natural input of soil Hg due to pedogenic processes accounted for 44.65%. Hg in corn grain was mainly derived from the atmosphere. This study will provide a scientific basis for assessing the current environmental quality in this area and minimizing further impacts that affect the nearby environmental medium.

Selenium/sulfur-modified montmorillonite materials mitigate mercury pollution in farmland

Selenium (Se) amendment could reduce mercury (Hg) bioaccumulation in crops, but sometimes it could cause excessive Se accumulation in crops and potential Se exposure risks for humans. In this study, we designed and synthesized selenium and sulfur-modified montmorillonite materials (Se/S-Mont) to effectively reduce mercury levels and avoid excessive Se enrichment in plants. The results of pot experiments (1 g Se/S-Mont/100 g soil) and field microplot trials (0.3 g Se/S-Mont/100 g soil, 8 t/ha) showed that Se/S-Mont amendments significantly reduced the Hg concentrations in water spinach and hybrid Pennisetum by 28-68% and 57%-92% (P < 0.05), respectively, while they did not lead to excessive Se bioaccumulation in the plants. Se/S-Mont was more efficient in mitigating soil Hg pollution than adding raw materials (e.g., NaSeO₃) and their combinations, and they significantly reduced the available Se fraction in the soil and the Se levels in the plants (P < 0.05). The potential mechanisms revealed by X-ray absorption near-edge spectra (XANES) and pot experiments were the adsorption and slow release of Hg, S, and Se by Se/S-Mont, the high affinity between Hg and Se, competition between Se and S, and the formation of stable complexes containing Se-S-Hg. The Se/S-Mont immobilizer was easy to prepare and required the application of small amounts, and the remediation effect was relatively stable and exhibited few negative effects; therefore, the approach showed high environmental and economic potentials.

Cardamine violifolia as a potential Hg hyperaccumulator and the cellular responses

Cardamine violifolia belongs to the Brassicaceae family and is a selenium (Se) hyperaccumulator found in Enshi, China. In this study, C. violifolia was found to accumulate mercury (Hg) in its roots and aboveground parts at concentrations up to 6000 μg/g. In the seedling and mature stages, the bioaccumulation factors (BAFS) of Hg reached 1.8-223, while the translocation factor (TF) for Hg reached 1.5. We observed a significant positive correlation between THg concentrations in plant tissues and those in the soil (r2 = 0.71-0.84). Synchrotron radiation X-ray fluorescence with focused X-ray (μ-SRXRF) showed that Hg was translocated from the roots to shoots through the vascular bundle and was transported through the leaf veins in leaves. Transmission electron microscopy showed that root cells were more tolerant to Hg than leaf cells. These findings provide insights into the mechanisms of Hg hyperaccumulation in C. violifolia. Overall, we demonstrated that C. violifolia is a promising Hg hyperaccumulator that may be used for phytoremediating Hg-contaminated farmlands.

Mechanisms and biological effects of organic amendments on mercury speciation in soil-rice systems: A review

Mercury (Hg) pollution is a well-recognized global environmental and health issue and exhibits distinctive persistence, neurotoxicity, bioaccumulation, and biomagnification effects. As the largest global Hg reservoir, the Hg cumulatively stored in soils has reached as high as 250-1000 Gg. Even more concerning is that global soil-rice systems distributed in many countries have become central to the global Hg cycle because they are both a major food source for more than 3 billion people worldwide and the central bridge linking atmospheric and soil Hg circulation. In this review, we discuss the form distribution, transformation, and bioavailability of Hg in soil-rice systems by focusing on the Hg methylation and demethylation pathways and distribution, uptake, and accumulation in rice plants and the effects of Hg on the community structure and ecological functions of microorganisms in soil-rice systems. In addition, we clarify the mechanisms through which commonly used humus and biochar organic amendments influence Hg and its environmental effects in soil-rice systems. The review also elaborates on the advantages of sulfur-modified biochars and their critical role in controlling Hg migration and bioavailability in soils. Finally, we provide key information about Hg pollution in soil-rice systems, which is of great significance for developing appropriate strategies and mitigation planning to limit Hg bioconcentration in rice crops and achieving key global sustainable development goals, such as the guarantee of food security and the promotion of sustainable agriculture.

Widespread occurrence of quaternary alkylammonium disinfectants in soils of Hesse, Germany

Quaternary alkylammonium compounds (QAACs) are cationic organic compounds with amphiphilic properties that are widely used as surfactants and disinfectants in industry, households and agriculture. Several studies suggest that QAACs co-select for antibiotic resistant microorganisms and thus may contribute to the spread of antibiotic resistance in the environment. Data on QAAC occurrence in soil are scarce and limited to soils that are prone to direct exposure to QAACs. Therefore, we conducted a comprehensive study on the occurrence of QAACs in soils of Hesse, a federal state in Germany, covering an area of 21,115 km². Sixty-five soil samples that comprised different land uses (arable, grassland, forest, vineyard) and area types (rural, agglomeration) were analysed for concentrations of alkyltrimethylammonium (ATMACs, with alkyl chain lengths C8-C16), benzylalkyldimethylammonium (BACs, C8-C18) and dialkyldimethylammonium compounds (DADMACs, C8-C18) via HPLC-MS/MS after ultrasonic-assisted extraction with acidified acetonitrile. QAACs were detected in 97 % of the soil samples irrespective of land use and area type. The most abundant QAAC homologues were DADMACs > BACs > ATMACs. The highest total QAAC concentrations were detected in alluvial soils influenced by the deposition of suspended particles during flood events, with DADMAC-C16 and -C18 as the dominant homologues. The high abundance of long-chain DADMACs suggests that legacy pollution and accumulation govern QAAC concentrations in soils. The presence of QAACs in forest soils points to a potential input via atmospheric deposition. Our work highlights the widespread occurrence of QAACs in soils of Hesse and the need for more research on their entry paths and fate in the soil ecosystem.

Chitosan-Based Polymer Nanocomposites for Environmental Remediation of Mercury Pollution

Mercury is a well-known heavy metal pollutant of global importance, typically found in effluents (lakes, oceans, and sewage) and released into the atmosphere. It is highly toxic to humans, animals and plants. Therefore, the current challenge is to develop efficient materials and techniques that can be used to remediate mercury pollution in water and the atmosphere, even in low concentrations. The paper aims to review the chitosan-based polymer nanocomposite materials that have been used for the environmental remediation of mercury pollution since they possess multifunctional properties, beneficial for the adsorption of various kinds of pollutants from wastewater and the atmosphere. In addition, these chitosan-based polymer nanocomposites are made of non-toxic materials that are environmentally friendly, highly porous, biocompatible, biodegradable, and recyclable; they have a high number of surface active sites, are earth-abundant, have minimal surface defects, and are metal-free. Advances in the modification of the chitosan, mainly with nanomaterials such as multi-walled carbon nanotube and nanoparticles (Ag, TiO₂, S, and ZnO), and its use for mercury uptake by batch adsorption and passive sampler methods are discussed.

The rhizospheric transformation and bioavailability of mercury in pepper plants are influenced by selected Chinese soil types

Understanding and prediction of mercury (Hg) phytoavailability in vegetable-soil systems is essential for controlling food chain contamination and safe vegetable production as Hg-contaminated soils pose a serious threat to human health. In this study, four typical Chinese soils (Heilongjiang, Chongqing, Yunnan, and Jilin) with varied physicochemical properties were spiked with HgCl₂ to grow sweet pepper (Capsicum annuum L.) in a pot experiment under greenhouse condition. The chemical fractionation revealed a significant decrease in exchangeable Hg, while an increase in organically bound Hg in the rhizosphere soil (RS) compared to bulk soil (BS). This observation strongly highlights the vital role of organic matter on the rhizospheric Hg transformation irrespective of contamination levels and soil properties. Stepwise multiple linear regression (SMLR) analysis between Hg concentration in plants, Hg fractions in RS and BS, and soil properties showed that Hg in plant parts was significantly influenced by soil total Hg (THg) (R² = 0.90), soil clay (R² = 0.99), amorphous manganese oxides (amorphous Mn) (R² = 0.97), amorphous iron oxides (amorphous Fe) (R² = 0.70), and available Hg (R² = 0.97) in BS. Nevertheless, in the case of RS, Hg accumulation in plants was affected by soil THg (R² = 0.99), amorphous Mn (R² = 0.97), amorphous Fe oxides (R² = 0.66), soil pH, and organically bound Hg fraction (R² = 0.96). Among all the evaluated soils (n = 04), metal (mercury) concentration in terms of plant uptake was reported highest in the Jilin soil. Based on SMLR analysis, the results suggested that the phytoavailability of Hg was mainly determined by THg and metal oxides regardless of the rhizospheric effect. These findings facilitate the estimation of Hg phytoavailability and ecological risk that may exist from Hg-contaminated areas where pepper is the dominant vegetable.

Source Apportionment of Heavy Metals Based on Multiple Approaches for a Proposed Subway Line in the Southeast Industrial District of Beijing, China

Apportioning the sources of heavy metals (HMs) in soil is of great importance for pollution control. A total of 64 soil samples from 13 sample points at depths of 0-21 m were collected along a proposed subway line in the southeast industrial district of Beijing. The concentrations, distribution characteristics, and sources of eight HMs were investigated. The results showed that the concentrations of Hg, Cd, Cu, Pb, As, and Zn in the topsoil (0-2 m) exceeded the Beijing soil background values. Three sources were identified and their respective contribution rates calculated for each of the HMs using multiple approaches, including correlation analysis (CA), top enrichment factor (TEF), principal component analysis (PCA), and positive matrix factor (PMF) methods. As (63.11%), Cr (61.67%), and Ni (70.80%) mainly originated from natural sources; Hg (97.0%) was dominated by fossil fuel combustion and atmospheric deposition sources; and Zn (72.80%), Pb (69.75%), Cu (65.36%) and Cd (53.08%) were related to traffic sources. Multiple approaches were demonstrated to be effective for HM source apportionment in soil, whilst the results using PMF were clearer and more complete. This work could provide evidence for the selection of reasonable methods to deal with soils excavated during subway construction, avoiding the over-remediation of the soils with heavy metals coming from natural sources.

A comprehensive investigation of zeolite-rich tuff functionalized with 3-mercaptopropionic acid intercalated green rust for the efficient removal of HgII and CrVI in a binary system

In this study, the 3-mercaptopropionic acid (MA) was chosen to achieve the anionic intercalation into the green rust (GR) materials (MA-GR). The zeolite-rich tuff functionalized with the MA-intercalated GR (MA-GR-tuff) was subsequently synthesized and used to remove both Hg^II cations and Cr^VI anions in a binary system. MA-GR-tuff showed the best adsorption capacities to both Hg^II and Cr^VI among the adsorbent materials. The optimal combination of parameters was determined as the molar ratio of Fe^II to Fe^III of 3.5, the molar ratio of OH^- to the total iron of 3.75, the molar ratio of MA to the total iron of 2.5, and the mass ratio of the total iron to the tuff of 1.25. The pseudo-first-order kinetic model was appropriate in describing the kinetic sorption of Cr^VI by MA-GR-tuff. Both the pseudo-first-order kinetic model and Elovich were suitable for explaining Hg^II sorption. The maximum monolayer adsorption capacities of MA-GR-tuff towards Cr^VI and Hg^II were 185.19 mg/g and 72.99 mg/g, respectively. More flocs and plumes were formed in the MA-GR while the intercalation and more pores and crevices of different sizes were found in the MA-GR-tuff. Sulfhydryl complexation and the molecular sieve of tuff obviously both played a role in influencing the adsorption process. This study directly overcomes the drawback brought by the natural tuff to the treatment of a cationic-and-anionic binary system and supplies a new kind of tuff-based adsorbent for the potential use for the remediation of HM-contaminated wastewater.

Remediation of Mercury-Polluted Farmland Soils: A Review

Mercury (Hg) bioaccumulation in Hg-polluted farmlands poses high health risk for humans and wildlife, and remediation work is urgently needed. Here, we first summarize some specific findings related to the environmental process of Hg in Hg-polluted farmlands, and distinguish the main achievements and deficiencies of available remediation strategies in recent studies. Results demonstrate that farmland is a sensitive area with vibrant Hg biogeochemistry. Current remediation methods are relatively hysteretic whether in mechanism understanding or field application, and deficient for large-scale Hg-polluted farmlands in view of safety, efficiency, sustainability, and cost-effectiveness. New perspectives including environment-friendly functional materials, assisted phytoremediation and agronomic regulations are worthy of further study as their key roles in reducing Hg exposure risk and protecting agricultural sustainability.

Bioavailability and health risk of toxic heavy metals (As, Hg, Pb and Cd) in urban soils: A Monte Carlo simulation approach

Toxic heavy metals pollution in urban soil has become a major global issue due to its adverse effects on the environment and human health. In this paper, 26 soil samples were analyzed to assess the speciation, bioavailability and human health risk of Arsenic (As), Mercury (Hg), Lead (Pb) and Cadmium (Cd) in urban soils of a heavy industrial city in NE China by using a Monte Carlo simulation approach. The results showed that As, Hg, Pb and Cd concentrations in the soil all exceed the corresponding background value of study area. Mercury displays the highest value of geo-accumulation index (Igeo), followed by Cd, Pb and As. The pollution load index (PLI) value (>2) indicates a moderate pollution level in the study area. The chemical speciation of HMs mainly exists in residual fraction except Cd. The probabilistic health risk assessment demonstrated that the mean values of Total Carcinogenic Risk (TCR) and Hazard Index (HI) calculated with total concentration are at the unacceptable level, with a higher risk to children than adults. However, the mean values calculated with bioavailable fraction are all within the acceptable level. The mean value of TCR and HI obtained by bioavailable fraction is about 96% and 95% lower than that obtained by total concentration, respectively. Thus, this study suggested that the bioavailable fraction of HMs is a more reliable parameter for health risk assessment, while the total concentration of HMs can overestimate the true risk. The results of this study provide some insight into the speciation, bioavailability and health risks of toxic heavy metals in urban soils in those heavy industrial cities.

Selection of green remediation alternatives for chemical industrial sites: An integrated life cycle assessment and fuzzy synthetic evaluation approach

The concept of green site remediation calls for a model that can consider environmental impacts in the selection of site remediation alternatives. In this study, an integrated life cycle assessment (LCA)-fuzzy synthetic evaluation (FSE) model is developed to help practitioners select the optimal site remediation plan by incorporating life cycle impacts into the comprehensive suitability evaluation. The LCA module quantifies environmental and economic impacts using ReCiPe and Input-Output LCA methods, respectively. The impacts are evaluated along with other suitability considerations, presented in 32 indicators under ten criteria, by practitioners through a questionnaire survey. FSE is used to process the collected subjective judgments and generate a suitability index for informed selection. The integrated model is applied to a case study of an abandoned chemical industrial site contaminated by various organic chemicals and mercury. Four remediation alternatives, designed as the combined uses of ex-situ thermal desorption, in-situ thermal desorption, and in-situ containment, are evaluated. The LCA results show that the alternative with extensive use (treating 93.8 % of the contaminated soil) of in-situ thermal desorption is associated with the highest environmental and economic impacts, followed by the alternative with less extensive use (6.2 %) of in-situ thermal desorption. The FSE results show that the economic, technical, and environmental impact considerations are the top three important criteria. The integrated LCA-FSE results indicate that the alternative with mixed use of ex-situ thermal desorption and in-situ containment could be the optimal plan. Excluding LCA results could alter the suitability ranks of the alternatives.

Inhibition of in situ coating of sediment ceramsite on sediment nutrient release of eutrophic lakes

Based on the main components in the residual soil to meet the characteristics of ceramic grain production raw materials, and combining with the principle of anti-filter layer technology for seepage control of hydraulic buildings, a lead wire cage filled with silt grains made from lake dehydration silt can be obtained. Moreover, the same-position treatment method of bed surface is desilted by this kind of ceramic lead wire cage in a reasonable structural form to improve water environment. In order to investigate the inhibition effect of this method on sediment resuspension, the effect law on water quality and the growth of indigenous microorganisms, 25 experimental groups were constructed to simulate 5 flow patterns of eutrophic lakes in this paper. We can analyze the inhibition effect of ceramic lead wire cage on sediment resuspension by monitoring the change of suspended matter content, monitoring the concentration change of ammonia nitrogen and soluble phosphorus can show the effect of ceramic lead cage on water quality, and monitoring the dissolved oxygen content can indirectly reflect the effect of the growth of indigenous microorganisms to some extent. The results show that in a certain flow mode, the ceramic lead wire cage can effectively inhibit the resuspension of the sediments, prevent the release of nitrogen and phosphorus nutrients in the sediments, and promote the growth of microbial attachment. The research results will maximize the benefits of the utilization of silt resources, and will optimize the in situ repair methods, and have broad application prospects.

Atmospheric Hg Levels in Tree Barks Due to Artisanal Small-Scale Gold Mining Activity in Bunut Seberang Village in Indonesia

Mercury (Hg) is a useful heavy metal; however, it is toxic to both humans and the environment. Tree bark is an excellent bioindicator, which has been proven to be effective in studying the level of atmospheric Hg contamination. This study aimed to determine the distribution of evaporated Hg using the total weight of Hg (THg) in tree barks in Indonesia at the artisanal and small-scale gold mining (ASGM) area of Bunut Seberang Village and Lampung University, respectively. Samples were taken using purposive sampling, based on the criteria of forestry trees at a height level of 1.3 m above ground as wide as 100 cm2. The samples were analyzed by atomic absorption spectrometry and Scanning electron microscopy to determine the levels of THg and to investigate the bark structures. Results showed that the highest THg values were found in a Magnolia champaca sample (56.5 µg), followed by Swietenia mahagoni (45.8 µg) and Swietenia mahagoni (33.5 µg). All species studied showed THg levels in the tree barks at an elevation from 30 to 320 m above sea level. The Hg amounts found in the sampled barks indicated the dispersion of Hg throughout the ASGM area, which signified hazardous atmospheric conditions in the area.

The mechanisms of iron modified montmorillonite in controlling mercury release across mercury-contaminated soil-air interface in greenhouse

Montmorillonite was modified with iron (Fe-MMT) for controlling mercury release across mercury-contaminated soil-air interface in greenhouse. With addition of Fe-MMT, although the root Hg contents in Brassica Pekinensis increased, the edible part (leaf) Hg concentrations decreased significantly, even achieved the Tolerance Limit of Mercury in Foods. The decrease of leaf Hg concentrations was attributed to the lower atmospheric Hg concentrations, which is caused by the lower soil Hg⁰ release fluxes. Besides the Fe-MMT can direct adsorb soil Hg⁰, it can also immobilize ionic Hg and decrease soil Hg reactivity via surface adsorption, chemical complexation, and situ co-precipitation. Then the contents of leachable Hg and the percentages of bioavailable speciation in soil were reduced, resulting in the soil Hg⁰ generation was inhibited and soil Hg⁰ release fluxes declined. Applying Fe-MMT to soil enhanced the diversity indexes of Streptomyces, which could promote the oxidation of soil Hg⁰ to Hg²⁺; subsequently, the soil Hg⁰ release fluxes decreased. After amending with Fe-MMT, the root Hg contents in Brassica Pekinensis increased because both the soil Hg and microorganisms loaded Hg could be adsorbed by iron oxides and retained on the root surface. This work can provide research basis for Fe-MMT application in Hg-contaminated soil in greenhouse.

Environmental and health risks posed to children by artisanal gold mining: A systematic review

There are an estimated 5 million children working in artisanal and small-scale gold mines worldwide; however, the hazards are poorly characterized and often underreported. We systematically reviewed the literature on reports of hazards among children as a consequence of such activities through PubMed database using pre-defined search terms. We identified 113 articles published between 1984 and 2021 from 31 countries. Toxicological hazards were reported in 91 articles, including mercury, lead, and arsenic. Infectious hazards, noted in 18 articles, included malaria, cholera, and hepatitis. Six articles reported occupational hazards, including malnutrition, heat stroke, and reactive airway disease. Three articles reported traumatic hazards, including cave-ins, burns, animal attacks, falls, and weapon-inflected wounds. Those findings likely indicate a profound underreporting of the prevalence and consequences of such hazards among children. More work is needed both to characterize the burdens of those hazards and to address the underlying drivers of child labor in those settings.

Comparison of concentrations of toxic elements in the hair of first-year students of RUDN University from different regions of the world: a cross-sectional study

Due to the development of the metallurgical and energy industries and the operation of incinerators, more and more environmental pollution is occurring. Toxic elements accumulate in the biosphere and affect the state of the population of the regions of large-scale production or the disposal of industrial waste. The main goal of this study was to compare the toxic elements hair composition in people from different regions of the world. The concentrations of toxic and potentially toxic elements (Al, As, Be, Cd, Hg, Pb, Sn) in 198 people, first-year students of People's Friendship University of Russia, who arrived from different regions of the world, were measured with inductively coupled plasma mass spectrometry. Students were divided into 6 groups: from South and East Asia, from Latin America, from Arab countries, Central Asia and Afghanistan, from South and Central Africa, from Iran and Azerbaijan, and from Russia, Ukraine, and Moldova. Medians of the concentrations of elements in the hair in the general group were 5.8 μg/g for Al, 30 ng/g for As, 0.6 ng/g for Be, 9.0 ng/g for Cd, 0.11 μg/g for Hg, 0.24 μg/g for Pb, and 0.11 μg/g for Sn. All these values fall within the normal range. Students from Russia, Moldova, and Ukraine showed a significantly higher Sn content (0.28 μg/g) in their hair than subjects from other regions except for Latin America, p<0,05. Except for As, cases of exceeding their recommended concentrations in the hair were identified. However, the proportion of subjects with deviations in each group was not high - not more than 7%. In all regions, a positive correlation was found between Cd, Pb, and Sn, p<0.05, r>0.5 for all. Cases of exceeding the maximum permissible concentrations of various toxic elements in the hair were detected in people from all regions of the Earth included in the study. And although the overall picture of the content of toxic elements in the hair of students from all regions in our study does not look critical, the results of previous studies, as well as information about the total deterioration of the environmental situation throughout the Earth, necessitate further large-scale environmental studies.

A Hydroponic Study on Effect of Zinc Against Mercury Uptake by Triticale: Kinetic Process and Accumulation

We investigated the ability of triticale uptake of Mercury (Hg), clarified whether triticale root uptake of Hg²⁺ via Zinc (Zn²⁺) transports, using hydroponic experiments. At 25℃, when Hg exposure in solution was lower than 20 μM, Hg concentration in the roots can be better described by a hyperbolic function, which shows a saturable characteristic. Under ice-cold (< 2℃) conditions, a nonsaturable (linear) component was found. Low exposure of Zn²⁺ (0-1 μM) inhibited plant Hg uptake when Hg exposure in the solution ranged from 1 to 10 μM, it showed an antagonistic effect of Zn on plant uptake of Hg. When Hg exposure was 20 μM, it revealed a synergistic effect of Zn on plant uptake of Hg, Hg in the root increased at the Zn (1 μM) exposure in the solution. Our results will deepen the understanding of Hg transfer in the soil-plant system.

The Mercury Content in the Upper Layers of Soils in the Selected Area of the Masovian Landscape Park

Due to the high toxicity of the element itself and its compounds, mercury poses a significant threat to the human natural environment, in particular to the soil and water environment. An additional risk is the possibility of mercury accumulation in various elements of the environment. Soil is one of the most important elements of the natural environment and is the main link in the mercury cycle. The cycle of this element is related to both the natural processes taking place in the environment and human activity. The presence of mercury in the natural environment poses a particularly high risk of its re-accumulation as a result of its re-emission. The aim of the research was to determine the mercury content in the upper layers of soils collected from the area and buffer zone of the Mazowiecki Landscape Park as a potential source of this element’s re-emission to the environment. The paper presents the results of research on mercury content in the upper soil layer from the areas adjacent to the communication routes running through the area of the Mazowiecki Landscape Park and its buffer zone. The mercury content in the analyzed soil samples collected from the area of the Mazowiecki Landscape Park ranged from 0.082 mgHg·kg−1 dm to 0.183 mgHg·kg−1 dm, and in the soils from the cover, these values were slightly higher and ranged from 0.125 mgHg·kg−1 dm up to 0.362 mgHg·kg−1 dm. In order to avoid uncontrolled re-emission and, consequently, possible accumulation of this element in the environment, it is necessary to continue monitoring the level of mercury contamination, among others, in soil.

The microorganism-plant system for remediation of soil exposed to coal mining

Introduction. Coal mining causes a radical transformation of the soil cover. Research is required into modern methods and complementary technologies for monitoring technogenic landscapes and their remediation. Our study aimed to assess soil and rhizosphere microorganisms and their potential uses for the remediation of technogenic soils in Russian coal regions. Study objects and methods. We reviewed scientific articles published over the past five years, as well as those cited in Scopus and Web of Science. Results and discussion. Areas lying in the vicinity of coal mines and coal transportation lines are exposed to heavy metal contamination. We studied the application of soil remediation technologies that use sorbents from environmentally friendly natural materials as immobilizers of toxic elements and compounds. Mycorrhizal symbionts are used for soil decontamination, such as arbuscular mycorrhiza with characteristic morphological structures in root cortex cells and some mycotallia in the form of arbuscules or vesicles. Highly important are Gram-negative proteobacteria (Agrobacterium, Azospirillum, Azotobacter, Burkholderia, Bradyrizobium, Enterobacter, Pseudomonas, Klebsiella, Rizobium), Gram-positive bacteria (Bacillus, Brevibacillus, Paenibacillus), and Grampositive actinomycetes (Rhodococcus, Streptomyces, Arhtrobacter). They produce phytohormones, vitamins, and bioactive substances, stimulating plant growth. Also, they reduce the phytopathogenicity of dangerous diseases and harmfulness of insects. Finally, they increase the soil’s tolerance to salinity, drought, and oxidative stress. Mycorrhizal chains enable the transport and exchange of various substances, including mineral forms of nitrogen, phosphorus, and organic forms of C3 and C4 plants. Microorganisms contribute to the removal of toxic elements by absorbing, precipitating or accumulating them both inside the cells and in the extracellular space. Conclusion. Our review of scientific literature identified the sources of pollution of natural, agrogenic, and technogenic landscapes. We revealed the effects of toxic pollutants on the state and functioning of living systems: plants, animals, and microorganisms. Finally, we gave examples of modern methods used to remediate degraded landscapes and reclaim disturbed lands, including the latest technologies based on the integration of plants and microorganisms.

Mercury in European topsoils: Anthropogenic sources, stocks and fluxes

Mercury (Hg) is one of the most dangerous pollutants worldwide. In the European Union (EU), we recently estimated the Hg distribution in topsoil using 21,591 samples and a series of geo-physical inputs. In this manuscript, we investigate the impact of mining activities, chrol-alkali industries and other diffuse pollution sources as primary anthropogenic sources of Hg hotspots in the EU. Based on Hg measured soil samples, we modelled the Hg pool in EU topsoils, which totals about 44.8 Gg, with an average density of 103 g ha-1. As a following step, we coupled the estimated Hg stocks in topsoil with the pan-European assessment of soil loss due to water erosion and sediment distribution. In the European Union and UK, we estimated that about 43 Mg Hg yr-1 are displaced by water erosion and c. a. 6 Mg Hg yr-1 are transferred with sediments to river basins and eventually released to coastal Oceans. The Mediterranean Sea receives almost half (2.94 Mg yr-1) of the Hg fluxes to coastal oceans and it records the highest quantity of Hg sediments. This is the result of elevated soil Hg concentration and high erosion rates in the catchments draining into the Mediterranean Sea. This work contributes to new knowledge in support of the policy development in the EU on the Zero Pollution Action Plan and the Sustainable Development Goal (SDGs) 3.9 and 14.1, which both have as an objective to reduce soil pollution by 2030.

A holistic approach to soil contamination and sustainable phytoremediation with energy crops in the Aegean Region of Turkey

The objective of this current review article is to evaluate the current knowledge of the contaminated soil in the study area based on reports and the results of previous experimental studies in the literature and to discuss the feasibility of phytoremediation with biofuel production using energy crops. The results indicated that the soil contamination was related mainly to the thermal power plant and mining activities in Kütahya, high industrial activity in İzmir, heavy metal and radioactive pollution in Manisa and Muğla. Moreover, the sources of the contamination are geothermal resources and transportation in Aydın and Denizli, respectively. However, soil pollution in Afyonkarahisar and Uşak provinces has not been discussed due to a lack of detailed reports and data in the literature. Besides, energy crops such as Zea mays, Ricinus communis, and Gossypium hirsitum were identified as appropriate candidates for İzmir, Denizli, Manisa, and Aydın due to being resistant to the arid climate. In Muğla province, Eucalyptus grandis and Eucalyptus bicostata can be cultivated because of having adaptation to moderate climatic conditions. Ricinus communis and Helianthus annuus were determined to be very suitable energy crops for the phytoremediation of many heavy metals in Kütahya. The review promotes the development of economic, environmental, and social benefits to regain the contaminated areas through phytoremediation. The findings of the study are important for creating sustainable solutions for remediation of polluted soils in Turkey, as well as for shedding light on the process of establishing appropriate policies to make soils contaminated suitable for agriculture.

Recent Advances in Enzymes for the Bioremediation of Pollutants

Nowadays, pollution of the environment is a huge problem for humans and other organisms' health. Conventional methods of pollutant removal like membrane filtration or ion exchange are not efficient enough to lower the number of pollutants to standard levels. Biological methods, because of their higher efficiency and biocompatibility, are preferred for the remediation of pollutants. These cost-effective and environment-friendly methods of reducing pollutants are called bioremediation. In bioremediation methods, enzymes play the most crucial role. Enzymes can remedy different types of organic and inorganic pollutants, including PAHs, azo dyes, polymers, organocyanides, lead, chromium, and mercury. Different enzymes isolated from various species have been used for the bioremediation of pollutants. Discovering new enzymes and new subtypes with specific physicochemical characteristics would be a promising way to find more efficient and cost-effective tools for the remediation of pollutants.

Contamination, exposure and risk assessment of mercury in the soils of an artisanal gold mining community in Ghana

Mercury pollution has pervaded many artisanal gold mining communities in the world, especially in developing countries. This study aimed to evaluate the potential risk of mercury pollution in soils in Gbani, an artisanal gold mining community in Ghana. Two hundred and thirty-seven soil samples were collected from within 0-10 cm depth, from active mining sites near residences, two transects in the community, waste soil from mining processing and the surroundings of the community. The measured mean mercury soil concentrations were 71 mg Hg/kg in active mining sites, and more moderate (2.7 mg Hg/kg) along transects through the community. Enrichment Factors classified the soils of the study area as being moderately to extremely severely contaminated with mercury. The spatial distribution shows the contamination of mercury is highest at residential facilities and decreases through the community to the outskirts covered by vegetation. Hazard quotients for non-cancer effects identified air-borne exposure pathways for humans to pose the largest risk, including the inhalation of vapour. The average hazard indices recorded were 0.5 (child) and 0.1 (adult) at the grid, 2 (child) and 0.3 (adult) at the transects, 1.6 (child) and 0.2 (adult) for waste soil and 76 (child) and 10.9 (adult) at the mining sites. The inhabitants of Gbani community are therefore at risk of non-cancer effects of mercury as the hazard quotients and hazard index were above one.

Enhancement of cement-based solidification/stabilization of a lead-contaminated smectite clay

The cement-based solidification/stabilization is commonly used to remediate heavy-metal-contaminated clayey soils. The major problem associated with this method is heavy-metal precipitation, which retards cement hydration. The objectives of this paper are to study the influence of pH-dependent lead solubility patterns on the solidification/stabilization of contaminated smectite and to overcome the problems associated with cement hydration in this process through NaOH treatment. A series of physicochemical experiments were performed on untreated and NaOH-enhanced samples. Contaminated smectite with 5-100 cmol/kg-soil of lead nitrate was solidified/stabilized by 10-50% cement. This research demonstrates that solidification/stabilization is a pH-dependent phenomenon. Enhancement increases the pH of contaminated soil in which lead components transfer to a soluble form. Hereafter, as the results of XRD reveal, a decrease in lead precipitation on cement components is observed. Consequently, a noticeable increase in CSH formation is detected. The capsulation of lead ions by CSH improves the setting-time and unconfined compressive strength of solidified/stabilized samples. Furthermore, the TCLP results show a significant reduction in samples' lead-leaching abilities. Therefore, enhancement has changed the governing retention phenomena from precipitation/stabilization in lead carbonate form to mainly capsulation/solidification by CSH. Moreover, the results show a noticeable reduction in the required cement content.