Mercury-contaminated Soil Research Articles

A risk assessment of human exposure to mercury-contaminated soil and household dust in the town of Idrija (Slovenia)

Exposure to soil and dust derived mercury (Hg), associated with a historical legacy of Hg mining in the city of Idrija in Slovenia, is evaluated using results from an earlier geochemical survey. An assessment of adverse health effects with regard to tolerable daily intake of inorganic Hg species is included. Analytical results of aqua regia soluble Hg concentrations, Hg binding forms (cinnabar and non-cinnabar) and Hg gastric bioaccessibility in topsoil and household dust were used to assess the potential adverse health effects of the exposure to Hg. Daily inhalation and ingestion doses were calculated using exposure parameters of different age groups: babies, general population of children, children who exhibit soil pica behaviour, pre-adults, adults and adult gardeners.The results of the risk assessment indicate that risk of increased Hg uptake is limited to the general population of children, and especially children who exhibit soil-pica behaviour, associated with ingestion of topsoil particles. The latter is the exposure pathway of most concern, so extra caution is recommended during outdoor activities in the urban green spaces of Idrija.

Screening of chelating ligands to enhance mercury accumulation from historically mercury-contaminated soils for phytoextraction

Screening of optimal chelating ligands which not only have high capacities to enhance plant uptake of mercury (Hg) from soil but also can decrease bioavailable Hg concentration in soil is necessary to establish a viable chemically-assisted phytoextraction. Therefore, Brassica juncea was exposed to historically Hg-contaminated soil (total Hg, 90 mg kg−1) to investigate the efficiency of seven chelating agents [ammonium thiosulphate, sodium thiosulphate, ammonium sulfate, ammonium chloride, sodium nitrate, ethylenediaminetetraacetic acid (EDTA), and sodium sulfite] at enhancing Hg phytoextraction; the leaching of bioavailable Hg caused by these chelating agents was also investigated. The Hg concentration in control (treated with double-distilled water) plant tissues was below 1 mg kg−1. The remarkably higher Hg concentration was found in plants receiving ammonium thiosulphate and sodium sulfite treatments. The bioaccumulation factors and translocation factors of ammonium thiosulphate and sodium sulfite treatments were significantly higher than those of the other treatments. The more efficient uptake of Hg by plants upon treatment with ammonium thiosulphate and sodium sulfite compared to the other treatments might be explained by the formation of special Hg-thiosulphate complexes that could be preferentially taken up by the roots and transported in plant tissues. The application of sulfite significantly increased bioavailable Hg concentration in soil compared with that in initial soil and control soil, whereas ammonium thiosulphate significantly decreased bioavailable Hg concentration. The apparent decrease of bioavailable Hg in ammonium thiosulphate-treated soil compared with that in sodium sulfite-treated soil might be attributable to the unstable Hg-thiosulphate complexes formed between thiosulphate and Hg; they could react to produce less bioavailable Hg in the soil. The results of this study indicate that ammonium thiosulphate may be an optimal chelating ligand for phytoextraction due to its great potential to enhance Hg accumulation in plants while decreasing bioavailable Hg concentration in the soil.

Organic and inorganic amendment application on mercury-polluted soils: effects on soil chemical and biochemical properties.

On the basis of a previous study performed in our laboratory, the use of organic and inorganic amendments can significantly modify the Hg mobility in soil. We have compared the effectiveness of organic and inorganic amendments such as digestate and fly ash, respectively, reducing the Hg mobility in Chernozem and Luvisol soils differing in their physicochemical properties. Hence, the aim of this work was to compare the impact of digestate and fly ash application on the chemical and biochemical parameters in these two mercury-contaminated soils in a model batch experiment. Chernozem and Luvisol soils were artificially contaminated with Hg and then incubated under controlled conditions for 21days. Digestate and fly ash were applied to both soils in a dose of 10 and 1.5%, respectively, and soil samples were collected after 1, 7, 14, and 21days of incubation. The presence of Hg in both soils negatively affected to processes such as nitrification, provoked a decline in the soil microbial biomass C (soil microbial biomass C (MBC)), and the microbial activities (arylsulfatase, and β-glucosaminidase) in both soils. Meanwhile, the digestate addition to Chernozem and Luvisol soils contaminated with Hg improved the soil chemical properties (pH, dissolved organic carbon (DOC), N (Ntot), inorganic-N forms (N-NH4 (+) and N-NO3 (-))), as consequence of high content in C and N contained in digestate. Likewise, the soil MBC and soil microbial activities (dehydrogenase, arylsulfatase, and β-glucosaminidase) were greatly enhanced by the digestate application in both soils. In contrast, fly ash application did not have a remarkable positive effect when compared to digestate in Chernozem and Luvisol soil contaminated with mercury. These results may indicate that the use of organic amendments such as digestate considerably improved the soil health in Chernozem and Luvisol compared with fly ash, alleviating the detrimental impact of Hg. Probably, the chemical properties present in digestate may determine its use as a suitable amendment for the assisted-natural attenuation of mercury-polluted soils.

Alleviation of Mercury Toxicity in Wheat by the Interaction of Mercury-Tolerant Plant Growth-Promoting Rhizobacteria

Heavy metal contamination of agricultural soils has increased along with industrialization. Mercury is a toxic heavy metal and a widespread pollutant in the ecosystem. Mercury-tolerant and plant growth-promoting rhizobacteria (PGPR) HG 1, HG 2, and HG 3 were isolated from the rhizosphere of plants growing in a mercury-contaminated site. These isolates were able to grow in the presence of mercury ranging from 10 to 200 µM in minimal medium and 25 to 500 µM in LB medium. The strains were characterized by morphological, biochemical, and plant growth-promoting traits. In the present study, these PGPR strains were analyzed for their involvement in metal stress tolerance in Triticum aestivum (wheat). Two bacterial strains, namely, Enterobacter ludwigii (HG 2) and Klebsiella pneumoniae (HG 3), showed better growth promotion of T. aestivum seedlings under metal stress. Different growth parameters like, water content and biochemical properties were analyzed in the PGPR-inoculated wheat plants under 75 µM HgCl2. Shoot length, root length, shoot dry weight, root dry weight and relative water content (RWC) were significantly higher in inoculated plants compared to uninoculated plants under stress condition. Proline content, electrolyte leakage, and malondialdehyde content (shoots and roots) were significantly lower in inoculated plants with respect to uninoculated plants under mercury stress. Therefore, it could be assumed that all these parameters collectively improve plant growth under mercury stress conditions in the presence of PGPR. Hence, these PGPRs can serve as promising candidates for increasing plant growth and also have immense potential for bioremediation of mercury-contaminated soils.

Thermogravimetric and XRD study of the effects of chloride salts on the thermal decomposition of mercury compounds

In this paper, the effects of chloride salt (MgCl2, CaCl2 or NaCl) addition on the thermal decomposition of five inorganic mercury compounds (HgCl2, HgS, Hg(NO3)2·H2O, HgO, and HgSO4) were investigated by thermogravimetric analysis. Mercury-contaminated soil samples collected from Inner Mongolia were used to verify the results. The desorption temperatures of the mercury compounds increased in the following order: HgCl = HgCl2 < HgS < Hg(NO3)2·H2O < HgO < HgSO4. Among the chloride salts, MgCl2 had the greatest effect on thermal desorption of the mercury compounds, with the greatest reduction in the initial temperature of thermal desorption. After MgCl2 treatment, the mercury removal rates for the soil were 65.67–81.35 % (sample A), 70.74–84.91 % (sample B), and 69.08 % (sample C). The increase in the mercury removal rate for sample C with addition of MgCl2 was particularly large (34.96–69.08 %). X-Ray diffraction analysis of white crystals from the thermal desorption with MgCl2 indicated that MgCl2 promoted conversion of the mercury compounds in the soil to mercury(II) chloride and dimercury dichloride. This transformation is beneficial for applying thermal desorption to remedy mercury-contaminated soils and treat of mercury containing waste.

Microarray analysis and real-time PCR assay developed to find biomarkers for mercury-contaminated soil.

The evaluation of mercury (Hg) toxicity in agricultural soil is of great concern because its bioavailability and bioaccumulation in organisms through the food chain can have adverse effects on human health. Therefore, the aim of this study was to develop sensitive biomarkers for Hg stress in agricultural soil. With the results obtained from a high-throughput cDNA microarray, 12 Hg-responsive genes were selected to examine their concentration-dependent responses to Hg stress at different Hg concentrations. The lowest observable adverse effect concentrations (LOAECs) of Hg were 0.8 mg kg-1 for seed germination, 1.6 mg kg-1 for root biomass, 0.8 mg kg-1 for root elongation, and 0.8 mg kg-1 for root morphology, respectively, whereas the lowest Hg treatments (0.1-0.4 mg kg-1) could generally induce differential expression of genes. These results indicated that the detection of Hg in soil at the molecular level is a highly sensitive method. Moreover, the Hg soil content exhibited a significant positive correlation with the relative expression of probable glutathione S-transferase parA (r = 0.637, p = 0.05), chlorophyll a-b binding protein 13, chloroplastic-like (r = 0.689, p = 0.05) and geranylgeranyl pyrophosphate synthase 1 (r = 0.682, p = 0.05), implying that the three genes are good candidates to detect Hg-contaminated soil.

Effects of incorporating differently-treated rice straw on phytoavailability of methylmercury in soil.

Differently-treated crops straw is being widely used to fertilize soil, while the potential impacts of straw amendment on the biogeochemistry and phytoavailability of mercury in contaminated soils are largely unknown. In the present study, differently-treated rice straw (dry straw, composted straw, straw biochar, and straw ash) was incorporated into mercury-contaminated soil at an environment relevant level (1/100, w/w), and mercury speciation, methylmercury (MeHg) phytoavailability (using ammonium thiosulfate extraction method, validated elsewhere) and bioaccumulation (in Indian mustard Brassica junceas) were quantified. Our results indicated that incorporating straw biochar or composted straw into soil would decrease phytoavailable MeHg levels, possibly due to the strong binding of MeHg with particulate organic matter in amended straw ('MeHg immobilization effect'). Consequently, MeHg accumulation in aboveground tissue of Indian mustard harvested from straw biochar-amended soil decreased by 20% compared to the control. Differently, incorporation of dry straw resulted in elevated MeHg levels in soil ('Mercury methylation effect'). Decomposition of amended dry straw in soil would evidently increase DOC levels (averagely 40%-195% higher than the control), which may subsequently mobilize MeHg in the soil ('MeHg mobilization effect'). Accordingly, incorporation of dry straw led to increased phytoavailable MeHg levels in the soil and doubled MeHg accumulation in Indian mustard. Our results provided the first evidence that incorporating differently-treated rice straw into soil could have diverse effects on mercury biogeochemistry and phytoavailability, which should be taken into account in risk assessment or soil remediation.

Uptake dynamics of inorganic mercury and methylmercury by the earthworm Pheretima guillemi.

Mercury uptake dynamics in the earthworm Pheretima guillemi, including the dissolved uptake rate constant (ku) from pore-water and assimilation efficiencies (AEs) from mercury-contaminated soil, was quantified in this study. Dissolved uptake rate constants were 0.087 and 0.553 L g(-1) d(-1) for inorganic mercury (IHg) and methylmercury (MeHg), respectively. Assimilation efficiency of IHg in field-contaminated soil was 7.2%, lower than 15.4% of spiked soil. In contrast, MeHg exhibited comparable AEs for both field-contaminated and spiked soil (82.4-87.2%). Within the framework of biodynamic model, we further modelled the exposure pathways (dissolved exposure vs soil ingestion) to source the accumulated mercury in Pheretima guillemi. The model showed that the relative importance of soil ingestion to mercury bioaccumulation depended largely on mercury partitioning coefficients (K(d)), and was also influenced by soil ingestion rate of earthworms. In the examined field-contaminated soil, almost (>99%) accumulated IHg and MeHg was predicted to derive from soil ingestion. Therefore, soil ingestion should be carefully considered when assessing mercury exposure risk to earthworms.

El Mercurio y la contaminación por actividad extractiva

ONTARE. REVISTA DE INVESTIGACIÓN DE LA FACULTAD DE INGENIERÍA&#x0D; Desde mucho antes de la “Locomotora Minera” del Plan Nacional de Desarrollo 2010-2014 de Colombia, las actividades vinculadas a la extracción de minerales han sido fuente de riqueza y problemas en diferentes partes del país. El presente artículo, recoge resultados sobre la investigación que desde 2014 hace la Universidad EAN para consolidar conocimiento sobre la situación de contaminación de suelos con Mercurio ocasionada por los procesos mal desarrollados de extracción de oro en Colombia (Martínez &amp; Uribe, 2014), buscando contribuir a la identificación de las soluciones para la recuperación de la matriz suelo contaminado con Mercurio.

Potential bioavailability of mercury in humus-coated clay minerals

It is well-known that both clay and organic matter in soils play a key role in mercury biogeochemistry, while their combined effect is less studied. In this study, kaolinite, vermiculite, and montmorillonite were coated or not with humus, and spiked with inorganic mercury (IHg) or methylmercury (MeHg). The potential bioavailability of mercury to plants or deposit-feeders was assessed by CaCl2 or bovine serum albumin (BSA) extraction. For uncoated clay, IHg or MeHg extraction was generally lower in montmorillonite, due to its greater number of functional groups. Humus coating increased partitioning of IHg (0.5%–13.7%) and MeHg (0.8%–52.9%) in clay, because clay-sorbed humus provided more strong binding sites for mercury. Furthermore, humus coating led to a decrease in IHg (3.0%–59.8% for CaCl2 and 2.1%–5.0% for BSA) and MeHg (8.9%–74.6% for CaCl2 and 0.5%–8.2% for BSA) extraction, due to strong binding between mercury and clay-sorbed humus. Among various humus-coated clay particles, mercury extraction by CaCl2 (mainly through cation exchange) was lowest in humus-coated vermiculite, explained by the strong binding between humus and vermiculite. The inhibitory effect of humus on mercury bioavailability was also evidenced by the negative relationship between mercury extraction by CaCl2 and mercury in the organo-complexed fraction. In contrast, extraction of mercury by BSA (principally through complexation) was lowest in humus-coated montmorillonite. This was because BSA itself could be extensively sorbed onto montmorillonite. Results suggested that humus-coated clay could substantially decrease the potential bioavailability of mercury in soils, which should be considered when assessing risk in mercury-contaminated soils.

In situ remediation technologies for mercury-contaminated soil

Mercury from anthropogenic activities is a pollutant that poses significant risks to humans and the environment. In soils, mercury remediation can be technically challenging and costly, depending on the subsurface mercury distribution, the types of mercury species, and the regulatory requirements. This paper introduces the chemistry of mercury and its implications for in situ mercury remediation, which is followed by a detailed discussion of several in situ Hg remediation technologies in terms of applicability, cost, advantages, and disadvantages. The effect of Hg speciation on remediation performance, as well as Hg transformation during different remediation processes, was detailed. Thermal desorption, electrokinetic, and soil flushing/washing treatments are removal technologies that mobilize and capture insoluble Hg species, while containment, solidification/stabilization, and vitrification immobilize Hg by converting it to less soluble forms. Two emerging technologies, phytoremediation and nanotechnology, are also discussed in this review.

Soil geochemistry and digestive solubilization control mercury bioaccumulation in the earthworm Pheretima guillemi

Mercury presents a potential risk to soil organisms, yet our understanding of mercury bioaccumulation in soil dwelling organisms is limited. The influence of soil geochemistry and digestive processes on both methylmercury (MeHg) and total mercury (THg) bioavailability to earthworms (Pheretima guillemi) was evaluated in this study. Earthworms were exposed to six mercury-contaminated soils with geochemically contrasting properties for 36 days, and digestive fluid was concurrently collected to solubilize soil-associated mercury. Bioaccumulation factors were 7.5–31.0 and 0.2–0.6 for MeHg and THg, respectively, and MeHg accounted for 17–58% of THg in earthworm. THg and MeHg measured in soils and earthworms were negatively associated with soil total organic carbon (TOC). Earthworm THg and MeHg also increased with increasing soil pH. The proportion of MeHg and THg released into the digestive fluid (digestive solubilizable mercury, DSM) was 8.3–18.1% and 0.4–1.3%, respectively. The greater solubilization of MeHg by digestive fluid than CaCl2, together with a biokinetic model-based estimate of dietary MeHg uptake, indicated the importance of soil ingestion for MeHg bioaccumulation in earthworms.

Phytoremediation of mercury-contaminated soils by Jatropha curcas

Jatropha curcas plants species were tested to evaluate their phytoremediation capacity in soils contaminated by different levels of mercury. The experimental treatments consisted of four levels of mercury concentrations in the soil – T0, T1, T5, and T10 (0, 1, 5, and 10μg Hg per g soil, respectively). The total mercury content absorbed by the different plant tissues (roots, stems and leaves) was determined during four months of exposure. The growth behavior, mercury accumulation, translocation (TF) and bioconcentration (BCF) factors were determined. The different tissues in J. curcas can be classified in order of decreasing accumulation Hg as follows: roots>leaves>stems. The highest cumulative absorption of the metal occurred between the second and third month of exposure. Maximum TF was detected during the second month and ranged from 0.79 to 1.04 for the different mercury concentrations. Values of BCF ranged from 0.21 to 1.43. Soils with T1 showed significantly higher BCF (1.43) followed by T10 (1.32) and T5 (0.91), all of them at the fourth month. On the other hand TFs were low (range 0.10–0.26) at the en of the experiment. The maximum reduction of biomass (16.3%) occurred for T10 (10μg Hg g−1). In sum, J. curcas species showed high BCFs and low TFs, and their use could be a promising approach to remediating mercury-contaminated soils.

Identification and in Vitro Effectivenesstest of Four Isolates of Mercury-resistant Bacteriaas Bioaccumulation Agents of Mercury

Bioaccumulation of mercury is one of the reclamation methods in ex-gold mining areas. Mercury-resistant bacteria canbe used as a mercury bioaccumulation agent. The previous study in Mandor District West Kalimantan has collected four mercury-resistant bacteria from 62 samples with isolates code: HgTA1, HgTL2, HgRL and HgRA. The purpose of this study is to identify and verify the in vitro effectiveness ofthese four mercury-resistant bacteria. Identification of the bacteria is performed using16SrRNAsequencinganalysis, while the in vitro effectiveness test of the bacteriais done by using Canstein's selective media.The results show that the identification of bacterial isolates finds that HgTA1 and HgTL2 are Bacillus subtilis, HgRL is Burkholderia cepacia, and HgRA is Burkholderia cenosepacia. These three species of bacteria belong to the class of bacteria that are resistant to extreme conditions. Thus, these bacteria have anability toaccumulatemercury. Meanwhile, based on the test results of colony growth, detoxification abilities, mercury accumulation and bioaccumulation levels,three out of the four bacterial isolates are proven to be effective and superior to accumulate mercury i.e. HgRA, HgTA1 and HgTL2 isolates. Furthermore, these three isolates can be used as bioacculation agents of mercury-contaminated soil.

Green waste compost as an amendment during induced phytoextraction of mercury-contaminated soil.

Phytoextraction of mercury-contaminated soils is a new strategy that consists of using the higher plants to make the soil contaminant nontoxic. The main problem that occurs during the process is the low solubility and bioavailability of mercury in soil. Therefore, some soil amendments can be used to increase the efficiency of the Hg phytoextraction process. The aim of the investigation was to use the commercial compost from municipal green wastes to increase the efficiency of phytoextraction of mercury-contaminated soil by Lepidium sativum L. plants and determine the leaching of Hg after compost amendment. The result of the study showed that Hg can be accumulated by L. sativum L. The application of compost increased both the accumulation by whole plant and translocation of Hg to shoots. Compost did not affect the plant biomass and its biometric parameters. Application of compost to the soil decreased the leaching of mercury in both acidic and neutral solutions regardless of growing medium composition and time of analysis. Due to Hg accumulation and translocation as well as its potential leaching in acidic and neutral solution, compost can be recommended as a soil amendment during the phytoextraction of mercury-contaminated soil.

Mercury removal from contaminated soil by thermal treatment with FeCl3 at reduced temperature

Thermal treatment has been used to remediate mercury-contaminated soils; however, existing thermal technologies use high temperatures (e.g., 600–800°C) and require high energy costs. Moreover, the treated soil is unfavorable for agricultural reuse. To address these issues, the present study developed a method for the thermal treatment of mercury-contaminated soils at a reduced temperature (400°C) by adding FeCl3. A FeCl3/Hg molar ratio of 100:1 in the soil was adopted as the optimum dosage of FeCl3 required to achieve maximum reduction of mercury. The mercury concentration in soils was successfully reduced to 0.8mgkg−1 when treated at 400°C for 60min and the treated soil retained most of its original soil properties. FeCl3 addition during thermal treatment not only accelerated the volatilization of mercury in the easily removed fraction but also reduced the volatilization temperature of mercury in the hardly removed fraction. The adsorbable organic halogens and PCDD/Fs formed during thermal treatment with FeCl3 would not affect the soil reuse in agriculture. The thermal decontamination method reduces energy costs and leads to agricultural soil reuse, thus providing a greener and more sustainable remediation method for treating mercury-contaminated soil in future engineering applications.

A plant species (Trifolium repens) with strong enrichment ability for mercury

This paper studied the absorption condition of mercury by Trifolium repens in medium with 10μgL−1 HgCl2. We compared the accumulation condition of roots, stems and leaves of the plant species in medium with 10μgL−1 HgCl2. The amount of mercury uptake by T. repens was determined by cold vapor atomic absorption spectrometry. The results demonstrate that the T. repens is extremely efficient in extracting mercury from 100% Hoagland solution with 10μgL−1 HgCl2 and translocating it into its above-solution biomass. This plant – which, to the best of our knowledge, has the strongest enrichment ability according to previous reports – has a significant advantage for the remediation of mercury-contaminated soils.

Impact of gold mining associated with mercury contamination in soil, biota sediments and tailings in Kenya.

This work considered the environmental impact of artisanal mining gold activity in the Migori-Transmara area (Kenya). From artisanal gold mining, mercury is released to the environment, thus contributing to degradation of soil and water bodies. High mercury contents have been quantified in soil (140 μg kg(-1)), sediment (430 μg kg(-1)) and tailings (8,900 μg kg(-1)), as expected. The results reveal that the mechanism for transporting mercury to the terrestrial ecosystem is associated with wet and dry depositions. Lichens and mosses, used as bioindicators of pollution, are related to the proximity to mining areas. The further the distance from mining areas, the lower the mercury levels. This study also provides risk maps to evaluate potential negative repercussions. We conclude that the Migori-Transmara region can be considered a strongly polluted area with high mercury contents. The technology used to extract gold throughout amalgamation processes causes a high degree of mercury pollution around this gold mining area. Thus, alternative gold extraction methods should be considered to reduce mercury levels that can be released to the environment.

Remediation of mercury-contaminated soil – a case study

Remediation of mercury-contaminated soil – a case study

Electrokinetic remediation of mercurycontaminated soil, from the mine El Alacran-San Jorge river basin, Cordoba- Colombia

The aim of this work was to evaluate the electrokinetic technique for remediation of mercury contaminated soils from the mine El Alacrán, located in the San Jorge river basin from Colombian's Córdoba department. KI andNaCl solutions were used as complexing agents for removing mercury at two concentrations 0.01 M and 0.05 M, by applying voltages of 30 and 40 V respectively. The best results were obtained when KI was used as complexing agent, reaching percentages of recovery up to 98.7%. The treatments where NaCl was used as complexing agent not achieved significant recoveries (&lt; 1%), except when was used a concentration of 0.05 M NaCl with an applied voltage of 40 V reaching a recovery of 38%. In all experiments, the mercury moved towards the anode due to complexation of anionic nature complex and was observed that increasing concentrations and voltages a more efficient and speedy removal of mercury in the soil was achieved. The results showed that the iodide has properties that make it a promising electrolyte solution for theremoval of mercury in the soil.