Mercury species in formerly contaminated soils and released soil gases

Tracing anthropogenic mercury in soils from Fe-Hg mining/smelting area: Isotopic and speciation insights

Mercury (Hg) stable isotope ratios supplemented by Hg solid speciation data were determined in soils in a former Fe-Hg mining/smelting area (Jedová hora, Czech Republic, Central Europe). The dominant Hg phase in the studied soils was found to be cinnabar (HgS). A secondary form of soil Hg(II) was represented by Hg weakly and strongly bound to mineral (micro)particles, as revealed by thermo-desorption analysis. These Hg species probably play a key role in local soil Hg processes and biogeochemical cycling. The Hg isotopic data generally showed small differences between HgS (-1.1 to -0.8‰; δ202Hg) and the soil samples (-1.4 to -0.9‰; δ202Hg), as well as limited isotopic variability within the two studied soil profiles. On the other hand, the detected negative δ202Hg shift (∼0.4‰) in organic horizons compared to mineral soils in the highly contaminated profile suggests the presence of secondary post-depositional Hg processes, such as sorption or redox changes. For the less contaminated profile, the observed Hg isotopic variation (∼0.3‰; δ202Hg) in the subsurface mineral soil compared to both overlying and underlying horizons is likely due to cyclic redox reactions associated with Hg isotopic fractionation. We assume that the adsorption of Hg(II) to secondary Fe(III)/Mn(III,IV)-oxides could be of major importance in such cases.

Significance of phosphorus deficiency for the mitigation of mercury toxicity in the Robinia pseudoacacia L.- rhizobia symbiotic association

Nitrogen (N2)-fixing legumes can be used for phytoremediation of toxic heavy metal Mercury (Hg) contaminated soil, but N2-fixation highly relies on phosphorus (P) availability for nodule formation and functioning. Here, we characterized the significance of P deficiency for Hg accumulation and toxicity in woody legume plants. Consequences for foliar and root traits of rhizobia inoculation, Hg exposure (+Hg) and low P (-P) supply, individually and in combination were characterized at both the metabolite and transcriptome levels in seedlings of two Robinia pseudoacacia L. provenances originating from contrasting climate and soil backgrounds, i.e., GS in northwest and the DB in northeast China. Our results reveal that depleted P mitigates the toxicity of Hg at the transcriptional level. In leaves of Robinia depleted P reduced oxidative stress and improved the utilization strategy of C, N and P nutrition; in roots depleted P regulated the expression of genes scavenging oxidative stress and promoting cell membrane synthesis. Rhizobia inoculation significantly improved the performance of both Robinia provenances under individual and combined +Hg and -P by promoting photosynthesis, increasing foliar N and P content and reducing H2O2 and MDA accumulation despite enhanced Hg uptake. DB plants developed more nodules, had higher biomass and accumulated higher Hg amounts than GS plants and thus are suggested as the high potential Robinia provenance for future phytoremediation of Hg contaminated soils with P deficiency.

Mercury speciation in selenium enriched wheat plants hydroponically exposed to mercury pollution

Mercury (Hg) pollution in agricultural soils and its potential pathway to the human food chain can pose a serious health concern. Understanding the pathway of Hg in plants and how the speciation may change upon interaction with other elements used for biofortification can be critical to assess the real implications for the final plant-based product. In that respect, selenium (Se) biofortification of crops grown in Se-poor soil regions is becoming a common practice to overcome Se deficient diets. Therefore, it is important to assess the interplay between these two elements since Se may form complexes with Hg reducing its bioavailability and toxicity. In this work, the speciation of Hg in wheat plants grown hydroponically under the presence of Hg (HgCl2) and biofortified with Se (selenite, selenate, or a 1:1 mixture of both) has been investigated by X-ray absorption spectroscopy at the Hg L3-edge. The main Hg species found in wheat grains was the highly toxic methylmercury. It was found that the Se-biofortification of wheat did not prevent, in general, the Hg translocation to grains. Only the 1:1 mixture treatment seemed to have an effect in reducing the levels of Hg and the presence of methylmercury in grains.

The transformation of soil Hg oxidation states controls elemental Hg release in the greenhouse with applying organic fertilizer

The foliage vegetables cultivated in greenhouse of Hg-contaminated regions suffer from severe Hg contamination issues because of soil elemental Hg (Hg(0)) release. Application of organic fertilizer (OF) is the indispensable part of farming, but its influences on soil Hg(0) release are unclear. A new method of thermal desorption coupled with cold vapor atomic fluorescence spectrometry was developed to measure transformations of Hg oxidation states to elucidate the impact mechanism of OF on Hg(0) release process. Our results showed that the soil Hg(0) concentrations can directly determine its release fluxes. The application of OF causes that oxidizing reactions of Hg(0)/Hg(I) and Hg(I)/Hg(II) are excited; then soil Hg(0) concentrations decreases. Besides, the elevated soil organic matter by amending OF can complex with Hg(II), resulting in that the reductions of Hg(II) to Hg(I) and Hg(0) are inhibited. Additionally, the OF can directly adsorb soil Hg(0), decreasing the removability of Hg(0). Subsequently, the application of OF can significantly inhibit soil Hg(0) release, resulting in a pronounced decrease in interior atmospheric Hg(0) concentrations. Our results provide a novel perspective for enriching the fate of soil Hg that transformation of soil Hg oxidation states plays a crucial role in affecting soil Hg(0) release process.

Retention and transformation of exogenous Hg in acidic paddy soil under alternating anoxic and oxic conditions: Kinetic and mechanistic insights

To estimate the risks and developing remediation strategies for the mercury (Hg)-contaminated soils, it is crucial to understand the mechanisms of Hg transformation and migration in the redox-changing paddy fields. In present study, a Hg-spiked acidic paddy soil (pH 4.52) was incubated under anoxic conditions for 40 d and then under oxic conditions for 20 d. During anoxic incubation, the water-soluble, exchangeable, specifically adsorbed, and fulvic acid-complexed Hg decreased sharply, whereas the humic acid-complexed Hg, organic, and sulfide-bound Hg gradually increased, which were mainly ascribed to the enhanced adsorption on the surface of soil minerals with an increase in soil pH, complexation by organic matters, precipitation as HgS, and absorption by soil colloids triggered by reductive dissolution of Fe(III) oxides. By contrast, after oxygen was introduced into the system, a gradual increase in available Hg occurred with decreasing soil pH, decomposition of organic matters and formation of Fe(III) oxides. A kinetic model was established based on the key elementary reactions to quantitatively estimate transformation processes of Hg fractions. The model matched well with the modified Tessier sequential extraction data, and suggested that large molecular organic matter and humic acid dominated Hg complexation and immobilization in acidic paddy soils. The content of methylmercury increased and reached its peak on anoxic 20 d. Sulfate-reducing bacteria Desulfovibrio and Desulfomicrobium were the major Hg methylating bacteria in the anoxic stage whereas demethylating microorganisms Clostridium_sensu_stricto_1 and Clostridium_sensu_stricto_12 began to grow after oxygen was introduced. These new dynamic results provided new insights into the exogenous Hg transformation processes and the model could be used to predict Hg availability in periodically flooded acidic paddy fields.

Gaseous mercury evasion from bare and grass-covered soils contaminated by mining and ore roasting (Isonzo River alluvial plain, Northeastern Italy)

High amounts of mercury (Hg) can be released into the atmosphere from soil surfaces of legacy contaminated areas as gaseous elemental mercury (Hg⁰). The alluvial plain of the Isonzo River (NE Italy) suffered widespread Hg contamination due to the re-distribution of Hg-enriched material discharged by historical cinnabar mining at the Idrija mine (Slovenia), but an assessment of Hg⁰ releases from the soils of this area is still lacking. In this work, Hg⁰ fluxes at the soil-air interface were evaluated using a non-steady state flux chamber coupled with a real-time Hg⁰ analyser at 6 sites within the Isonzo River plain. Measurements were performed in summer, autumn, and winter both on bare and grass-covered soil plots at regular time intervals during the diurnal period. Moreover, topsoils were analysed for organic matter content and Hg total concentration and speciation. Overall, Hg⁰ fluxes tracked the incident UV radiation during the sampling periods with daily averages significantly higher in summer (62.4 ± 14.5-800.2 ± 178.8 ng m^-2 h^-1) than autumn (15.2 ± 4.7-280.8 ± 75.6 ng m^-2 h^-1) and winter (16.9 ± 7.9-187.8 ± 62.7 ng m^-2 h^-1) due to higher irradiation and temperature, which favoured Hg reduction reactions. In summer and autumn significant correlations were observed between Hg⁰ fluxes and soil Hg content (78-95% cinnabar), whereas this relationship was not observed in winter likely due to relatively low emissions found in morning measurements in all sites coupled with low temperatures. Finally, vegetation cover effectively reduced Hg⁰ releases in summer (∼9-68%) and autumn (∼41-78%), whereas the difference between fluxes from vegetated and bare soils was not evident during winter dormancy due to scarce soil shading. These results suggest the opportunity of more extended spatial monitoring of Hg⁰ fluxes particularly in the croplands covering most of the Isonzo River alluvial plain and where bare soils are frequently disturbed by agricultural practices and directly exposed to radiation.

Mercury contamination in the riparian ecosystem during the reservoir discharging regulated by a mega dam

Mercury (Hg) is extremely poisonous and can be absorbed through touch, inhalation, or consumption. In the living environment, Hg in contaminated sediment can be transferred into grass by the direct absorption through the roots or shoots. The intake of Hg due to Hg emissions may pose a threat to living bodies especially to human beings. The present study aims to provide a novel insight about total mercury (THg) and methyl mercury (MeHg) in a riparian grass (Cynodon dactylon (L).Pers) and sediments during the discharging phase (summertime at 145 m water level) in Three Gorges Reservoir (TGR-China); where C. dactylon is a dominant perennial herb in the riparian zone. Yet, the potential risk of Hg contamination in the riparian ecosystem is not thoroughly assessed in the dam regulated reservoir. This study was conducted in the riparian zones of the reservoir formed by a mega dam (Three Gorge Dam) which regulates the water levels during the summer and winter period in the TGR. Our results showed that riparian sediments were acting as a sink for THg and MeHg. Insignificant correlation of THg and MeHg was found between the amphiphyte C. dactylon and its surrounding sediments in the TGR. Bioconcentration factors values for MeHg were found higher than 1 in all study locations in the riparian zones in TGR, which could be due to action of certain bacteria/purely chemical-based methylation on inorganic form of Hg. Additionally, translocation factor indices also highlighted that the amphiphyte C. dactylon was MeHg accumulator in riparian zones. These results suggested that since riparian sediment was found acting as the sink for THg and MeHg during discharging phase, MeHg contamination in the amphiphyte C. dactylon in riparian zones was not caused by the riparian sediments but by other factors, for instance, the anthropogenic activities in the TGR. Finally, this study leads to conclude that amphiphyte C. dactylon can be used as biomonitoring agent for Hg pollution in the TGR.

Mercury fractionation, bioavailability, and the major factors predicting its transfer and accumulation in soil-wheat systems

Soil mercury (Hg) and its bioaccumulation in food crops have attracted widespread concerns globally due to its harmful effects on biota. However, soil mercury fractionation, bioavailability, and the major factors predicting its transfer and accumulation in soil-wheat-systems have not been thoroughly explored. Twenty-one (21) soil samples collected throughout China with a wide spectrum of physico-chemical characteristics were contaminated with HgCl₂ and winter wheat (Triticum aestivum L.) was grown on the soils in a greenhouse pot-culture experiment for 180 days. A four-step sequential extraction was used segregating soil Hg into water-soluble (F1, 0.21 %), exchangeable (F2, 0.07 %), organically bound (F3, 16.40 %), and residual fractions (F4, 83.32 %). Step-wise multiple linear regression (SMLR) and path analysis (PA) were used to develop a prediction model and identify the major controlling factors of soil-wheat Hg transference. The SMLR results revealed that wheat Hg in leaves, husk, and grain was positively correlated with soil total and available Hg, and crystalline manganese (Cryst-Mn), while negatively correlated with soil pH, amorphous manganese (Amor-Mn) and crystalline aluminium (Cryst-Al). Bioconcentration factor (BCF) values were significantly higher in acidic soils (highest 0.05), with phytotoxic effects in some soils, as compared to alkaline soils (lowest 0.006). Furthermore, wheat grain Hg was significantly correlated with total (R² = 0.25), water-soluble (R² = 0.54) and NH₄Ac-extractable Hg (R² = 0.43) while also had a good correlation with soil pH (R² = -0.20). In conclusion, the soil total and available Hg (water-soluble + exchangeable fraction), pH, organic matter, and Amor-Mn are the most important soil variables that support Hg uptake in the wheat plants, which benefit managing Hg-enriched agricultural soils for safe wheat production.

Effect of inorganic carbonate and organic matter in thermal treatment of mercury-contaminated soil

Thermal treatment of mercury (Hg)-contaminated soil was studied to investigate the desorption behavior of Hg at different temperatures. The soil samples were collected from two locations with different land uses around the mine and industrial site. The effect of soil properties such as inorganic carbonate minerals and organic matter content on Hg desorption was investigated to understand the thermal desorption process. The effect of soil composition on Hg desorption showed that behavior at 100 °C was similar, but a different behavior could be found at 300 °C. The thermal desorption efficiency at 300 °C is affected by the thermal properties of soils and the Hg desorption capacity of the soils. The Hg from both soil types was removed above 300 °C, and Hg was effectively removed from mine soil due to the partial decomposition of carbonate in the soil composition, while industrial soil showed that desorption would be restrained by Hg organic matter complexes due to organic matter content. Despite a relatively higher concentration of Hg in the mine soil, Hg removal efficiency was greater than that in the industrial soil. Sequential extraction results showed that only the Hg fractions (residual fractions, step 6) in mine soil changed, while the industrial soil was affected by changes in Hg fractions (step 3 to step 6) at 300 °C. Changes in soil pH during thermal desorption are also influenced by heating time and temperature. Therefore, the mechanisms of Hg desorption during thermal treatment were observed by soil properties. The volatilization of Hg in the soil is induced by organic carbon, while soil Hg release is controlled by organic matter complexes.

Onshore mud volcanoes as a geological source of mercury: Case study from the Kerch Peninsula, Caucasus continental collision zone

Three mud volcanoes (MVs) in the Kerch Peninsula were studied as a geological source of mercury. The study focused on total mercury (THg) concentrations in MV waters, mud masses and plants colonizing MV areas; gaseous elemental mercury (GEM) in the atmosphere above MVs; and sulfide mercury (HgS) and HgCl₂ species in representative samples of mud masses. THg concentrations in the illite-smectite mud masses ranged from 38 to 920 ng/g. They contained up to 70% of total mercury in sulfide form (in pyrite and cinnabar), but lacked HgCl₂. THg values in MV waters of HCO₃-Cl/Na- and/or Cl-HCO₃/Na-types with рН = 7.4-9.5 mostly fell in a range of 79-440 ng/L, but rarely exceeded 600 ng/L, being comparable with those for geothermal systems. Another issue of interest was the distribution of THg in below- and above-ground parts of halophyte plant Limonium caspium. THg was incorporated into the plant roots, leaves and flowers; the roots exhibited higher concentrations of THg relative to the other organs. The Hg bioaccumulation factor ranged from 0.06 to 0.76. GEM concentrations measured over large bubbling MV pools and newly formed cracks showed values (50 to 520 ng·m^-3) higher than background values (≤3 ng·m^-3) associated with pristine test sites and background values measured within three MV areas of the Kerch peninsula that is slightly higher than background concentration for the Northern Hemisphere. Maximum GEM contents were comparable with the values found in geothermal and magmatic volcanic provinces.

Hyperspectral inversion of mercury in reed leaves under different levels of soil mercury contamination

High mercury (Hg) affects biochemical-physiological characteristics of plant leaves such as leaf chlorophyll, causing refractive discontinuity and modifications in leaf spectra. Furthermore, the hyperspectroscopy provides a potential tool for fast non-destructive estimation of leaf Hg. However, there are few studies that have investigated Hg for wetland plants via hyperspectral inversion. In this study, reeds (Phragmites australis) leaf Hg concentration and hyperspectra were measured under different soil Hg treatment. Hg-sensitive parameters were identified by basic spectral transformations and continuous wavelet transformation (CWT). Inversion models were developed using stepwise multiple linear regressions (SMLR), partial least square regression (PLSR), and random forest (RF) to estimate leaf Hg. The results indicated that CWT improved the correlation of hyperspectra and leaf Hg by 0.020-0.227, and R² of the CWT-related model increased by 0.0557-0.2441. In addition, Hg-sensitive bands were predominant at 600-750 (visible region) and 1500-2300 nm (mid-infrared), and Hg might modify leaves spectra primarily by affecting chlorophyll and water contents. Of the studied models, SMLR using normalized transformation (NR) and CWT (NR-CWT-SMLR) model (R² = 0.8594, RMSE = 0.0961) and RF using NR and CWT (NR-CWT-RF) model (R² = 0.8560, RMSE = 0.1062) suited for leaf Hg inversion. For Hg content < 1.0 mg kg^-1, the former model was more reliable and accurate. This study provided a method for the estimation of Hg contamination in wetland plant and indicated that model-based hyperspectral inversion was feasible for fast and non-destructive monitoring.

A critical review of mercury speciation, bioavailability, toxicity and detoxification in soil-plant environment: Ecotoxicology and health risk assessment

Environmental contamination by a non-essential and non-beneficial, although potentially toxic mercury (Hg), is becoming a great threat to the living organisms at a global scale. Owing to its various uses in numerous industrial processes, high amount of Hg is released into different environmental compartments. Environmental Hg contamination can result in food chain contamination, especially due to its accumulation in edible plant parts. Consumption of Hg-rich food is a key source of Hg exposure to humans. Since Hg does not possess any identified biological role and has genotoxic and carcinogenic potential, it is critical to monitor its biogeochemical behavior in the soil-plant system and its influence in terms of possible food chain contamination and human exposure. This review traces a plausible link among Hg levels, its chemical speciation and phytoavailability in soil, accumulation in plants, phytotoxicity and detoxification of Hg inside the plant. The role of different enzymatic (peroxidase, catalase, ascorbate peroxidase, superoxide dismutase, glutathione peroxidase) and non-enzymatic (glutathione, phytochelatins, proline and ascorbic acid) antioxidants has also been elucidated with respect to enhanced generation of reactive radicles and resulting oxidative stress. The review also outlines Hg build-up in edible plant tissues and associated health risks. The biogeochemical role of Hg in the soil-plant system and associated health risks have been described with well summarized and up-to-date data in 12 tables and 4 figures. We believe that this comprehensive review article and meta-analysis of Hg data can be greatly valuable for scientists, researchers, policymakers and graduate-level students.

From classic methodologies to application of nanomaterials for soil remediation: an integrated view of methods for decontamination of toxic metal(oid)s

Soil pollution with toxic elements is a recurrent issue due to environmental disasters, fossil fuel burning, urbanization, and industrialization, which have contributed to soil contamination over the years. Therefore, the remediation of toxic metals in soil is always an important topic since contaminated soil can affect the environment, agricultural safety, and human health. Many remediation methods have been developed; however, it is essential to ensure that they are safe, and also take into account the limitation of each methodology (including high energy input and generation of residues). This scenario has motivated this review, where we explore soil contamination with arsenic, lead, mercury, and chromium and summarize information about the methods employed to remediate each of these toxic elements such as phytoremediation, soil washing, electrokinetic remediation, and nanoparticles besides elucidating some mechanisms involved in the remediation. Considering all the discussed techniques, nowadays, different techniques can be combined together in order to improve the efficiency of remediation besides the new approach of the techniques and the use of one technique for remediating more than one contaminant.

A scoping study of component-specific toxicity of mercury in urban road dusts from three international locations

This scoping study presents an investigation of the total and bioaccessible mercury concentrations in road dust (RD) from three international urban sites, where a one-off sampling campaign was conducted at each. This was done to address the hypothesis that the matrix in which mercury is found influences its ability to become accessible to the body once inhaled. For that purpose, the samples were analysed for total and pulmonary bioaccessible mercury and the data compared to the chemical structure of individual particles by SEM. The results obtained from this study suggest that a high mercury content does not necessarily equate to high bioaccessibility, a phenomenon which could be ascribed to the chemical character of the individual particles. It was found that the Manchester samples contained more pulmonary soluble mercury species (as determined by elemental associations of Hg and Cl) in comparison to the other two samples, Curitiba, Brazil, and Johannesburg, South Africa. This finding ultimately underlines the necessity to conduct a site-specific in-depth analysis of RD, to determine the concentration, chemical structure and molecular speciation of the materials within the complex matrix of RD. Therefore, rather than simply assuming that higher bulk concentrations equate to more significant potential human health concerns, the leaching potential of the metal/element in its specific form (for example as a mineral) should be ascertained. The importance of individual particle behaviour in the determination of human health risk is therefore highlighted.

Mercury accumulation and transformation of main leaf vegetable crops in Cambosol and Ferrosol soil in China

Leaf vegetables serve as an important food for the local residents in China. This paper focuses on the uptake, accumulation, transfer, and mercury (Hg) sensitivity of leafy vegetables. Two types of soil (an alkaline Cambosol and an acid Ferrosol) and eleven species of leafy vegetable, namely, Spinach, Tung choy, Leek, Fennel, Coriander, Chinese flowering cabbage, Wuta-tsai, Pakchoi, Chicory, Crown daisy, and Lettuce, were selected to investigate their sensitivity to Hg accumulation in a greenhouse pot experiment. Three Hg concentration treatments were carried out as control (background values), low concentration (1.5 times standard value), and high concentration (2 times standard value) as adjusted by the soil pH. Hg concentrations of more than half vegetable samples grown in Cambosol (collected from Shandong Province) reached or exceeded the maximum permissible food safety levels (10 μg kg^-1) according to the General Standard of Contaminants in Food in China (GB 2762-2012), while only about 15% in Ferrosol (collected from Jiangxi Province). Meanwhile, Hg bio-concentration factors (BCF) in all treatments were < 1, while Hg translocation factors (TF) in most treatments were < 1. Correlation analysis among soil, root, and edible plant parts revealed that the principal source of Hg in leafy vegetables was most likely from Hg-contaminated soils. Species sensitivity distribution (SSD) models were constructed and their simulated curves indicated that sensitivity to Hg was highest in Pakchoi in low Hg-contaminated soils, and Chicory in highly Hg-contaminated soils. Therefore, Hg concentration is mostly accumulated in roots of leafy crops, which reduces the risk of Hg bioaccumulation in edible portion of vegetables, and (2) Brassicaceae vegetables are mostly less sensitive to soil Hg contamination. Our results provide effective guidance for the selection of leafy vegetables for cultivation and daily consumption that minimizes health risk.

Mercury speciation, transformation, and transportation in soils, atmospheric flux, and implications for risk management: A critical review

Mercury (Hg) is a potentially harmful trace element in the environment and one of the World Health Organization's foremost chemicals of concern. The threat posed by Hg contaminated soils to humans is pervasive, with an estimated 86 Gg of anthropogenic Hg pollution accumulated in surface soils worldwide. This review critically examines both recent advances and remaining knowledge gaps with respect to cycling of mercury in the soil environment, to aid the assessment and management of risks caused by Hg contamination. Included in this review are factors affecting Hg release from soil to the atmosphere, including how rainfall events drive gaseous elemental mercury (GEM) flux from soils of low Hg content, and how ambient conditions such as atmospheric O₃ concentration play a significant role. Mercury contaminated soils constitute complex systems where many interdependent factors, including the amount and composition of soil organic matter and clays, oxidized minerals (e.g. Fe oxides), reduced elements (e.g. S^2-), as well as soil pH and redox conditions affect Hg forms and transformation. Speciation influences the extent and rate of Hg subsurface transportation, which has often been assumed insignificant. Nano-sized Hg particles as well as soluble Hg complexes play important roles in soil Hg mobility, availability, and methylation. Finally, implications for human health and suggested research directions are put forward, where there is significant potential to improve remedial actions by accounting for Hg speciation and transportation factors.

Total mercury, chromium, nickel and other trace chemical element contents in soils at an old cinnabar mine site (Merník, Slovakia): anthropogenic versus natural sources of soil contamination

The aims of this study were to investigate the occurrence and distribution of total mercury (Hg) and other trace elements of environmental concern, such as arsenic (As), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), lead (Pb), zinc (Zn) and vanadium (V), in soils from the abandoned Merník cinnabar mine in eastern Slovakia. For this purpose, thirty soil samples from two depth intervals within the mine area (n = 60 soil samples) and additional sixteen soil samples from adjacent areas (n = 25 soil samples) were collected. Total Hg was measured by atomic absorption spectrometry, while As and other metals were analyzed using inductively coupled plasma atomic emission spectrometry. High mercury concentrations (> 100 mg/kg with a maximum of 951 mg/kg) were observed only in surface soils close to mine waste heaps and adits. Otherwise, Hg concentrations in the majority of surface soils were lower (0.14-19.7 mg/kg), however, higher than Hg in soils collected from sites outside the mine area (0.19-6.92 mg/kg) and even considerably higher than Hg in soils at sites not influenced by the Merník mine. Elevated Cr and Ni concentrations in soils regardless of their sampling sites (mean of 276 mg/kg and median of 132 mg/kg for Cr and 168 mg/kg and 81 mg/kg for Ni, respectively) were attributed to the lithology of the area; the soils are underlain by the sediments of the Central Carpathian Palaeogene, containing a detritus of ultrabasic rocks. As our geochemical data are compositional in nature, they were further treated by compositional data analysis (CoDA). Robust principal component analysis (RPCA) applied on centred (clr) log-ratio-transformed data and correlation analysis of compositional parts based on symmetric balances distinguished very well different sources of origin for the chemical elements. The following three element associations were identified: Hg association with the main source in mining/roasting, Cr-Ni association derived from bedrock and As-Cu-Mn-Pb-Zn-V association (natural background and minor sulphides/sulfosalts in mineralized rocks). The values of geoaccumulation index and enrichment factor suggested that concentrations of Hg in the soils were influenced by human industrial activities.

The soil-plant transfer of risk elements within the area of an abandoned gold mine in Libčice, Czech Republic

Abandoned gold mines are often suggested as potential sources of environmental pollution. Thus, the soils within the area of a gold mine in Libčice, Czech Republic, were monitored. Elevated element contents were found of As, Cd, Cu, Hg, Pb, and Zn. The risk assessment codes (RACs) indicated high environmental risk from soil Cd, and moderate risk from Zn, whereas the risk of As, Cu, and Pb was low. It was supported by the analysis of 134 samples of aboveground biomass of plants, where the levels of As and Pb were below the detection limit. For Cd, the plant uptake reflected the high mobility of this element, where the bioaccumulation factors (BAFs) varied in range 0.032 (Fragaria vesca) and 1.97 (Circia arvensis). For 11% of samples the BAF values for Cd exceeded 1. For Hg, although the maximum BAF did not exceed 0.37 (Lotus corniculatus), the Hg contents in plants occasionally exceeded the threshold limits for Hg contents in raw feedstuffs. The investigated gold mine does not represent a direct environmental risk, but the fate of Cd and Hg in the soils and plants suggests the necessity of a deeper understanding of the penetration of these elements into the surrounding environment.