Mercury Speciation In Soils Research Articles

Mobility and speciation of mercury in soils from a mining zone in Villa Hidalgo, SLP, Mexico: A preliminary risk assessment

The mineralized district La Tapona in Villa Hidalgo SLP was widely known as a mercury producer at the end of the XIX century. Although primary production was stopped since 1994 in Mexico, the presence of mercury and the artisanal and small-scale mercury mining represents a risk to the local population living in the surrounding. Thus, the study aimed to determine the impact of Hg on the inhabitants of Villa Hidalgo, SLP, Mexico. Soil and groundwater samples were collected from seven localities in the autumn of 2016. In these communities, water is used for human activities, such as irrigation, housework, and human consumption. Total Hg was determined in local waters and soils; furthermore, Hg fractionation and Hg speciation (methyl mercury) were investigated in soils. The results were correlated to physicochemical parameters as well as mineralogy and main geochemistry. The total mercury (THg) content in water was lower than the threshold value at all the monitoring sites, whereas the THg content in the soil samples ranged from 0.34 to 41.76 mg kg−1, which exceeded the national regulations for a single site. In soil, the residual mercury was the main Hg fraction, and methylmercury was not detected. The most critical factors that affect soil fraction distribution and low Hg mobility in the studied area were the low organic carbon content, and high concentrations of iron, aluminum, and calcium. These results could indicate the association of mercury with sulfides and crystalline oxides of iron and manganese. Although low Hg mobility was detected, the children's population was more sensitive to the non-carcinogenic risk caused by Hg as corroborated with the results of the hazard indexes (HI: 0.11 – 3.90) being the soil ingestion the main route of exposure.

Thermo-desorption: A valid tool for mercury speciation in soils and sediments?

Mercury (Hg) speciation by thermo-desorption is considered an alternative to laborious sequential chemical procedures; hence its popularity has increased in the last years. In this work, steps were taken to improve the information obtained by Hg speciation through thermo-desorption, specifically to improve peak resolution and increase the number of species that can be identified. The thermo-desorption behavior of Hg bound to iron oxides was characterized, as well as a new Hg–humic acid synthetic standard material. In contrast to previous studies, the peak corresponding to the Hg fraction associated with humic acids was clearly separated from the mineral fraction, and identified in some natural samples. With increasing temperature, Hg species are released in the following order: HgCl2=Hg associated with Fe2O3<Hg associated with humic acids<HgS<HgO, with an overlap of HgCl2 and Hg associated with iron oxides.An evaluation of the effects of sample pre-treatment and storage on Hg speciation was also performed. It was found that sieving to <2mm improved the sample homogeneity. The importance of fast sample analysis was highlighted, given that after 10days of storage at room temperature, volatile Hg0 could no longer be identified in the sample. The suitability of thermo-desorption for mercury speciation in soils and sediments is discussed.

ChemInform Abstract: Chemical Speciation of Mercury in Soil and Sediment

AbstractReview: 117 refs.

Development and validation of a simple thermo-desorption technique for mercury speciation in soils and sediments

An innovative technique for rapid identification and quantification of mercury (Hg) species in soils and sediments was developed using a direct mercury analyser. Speciation was performed by the continuous thermal-desorption of mercury species (temperature range 76–770°C), in combination with atomic absorption spectrophotometry detection. Standard materials HgCl2, Hg bound to humic acids and HgS were characterized; thermo-desorption curves of each material showed a well-resolved peak at specific temperature intervals: 125–225°C, 100–250°C and 225–325°C, respectively. Certified reference materials (CRM) BCR® 142R, RTC® CRM 021, NRC® MESS-3 and PACS-2 were tested. Although the CRM were not certified for Hg species, the sum of Hg species obtained was compared to the certified value for total Hg; recoveries were 92%, 100%, 97%, and 95%, respectively. One sediment and three soil samples from mercury contaminated areas (total Hg concentrations 0.067–126mgkg−1) were analysed as well. It was possible to compare peaks of thermo-desorption curves from the samples with those from standard materials and thereby distinguish different Hg species in solid samples. Generally, Hg was present as bound to chloride or humic substances. The precision was satisfactory, as reflected by the relative standard deviations determined for standards and certified reference materials (<11%; n=10).

Speciation of mercury in mine waste: case study of abandoned and active gold mine sites at the Bibiani–Anwiaso–Bekwai area of South Western Ghana

Speciation determines toxicity, transport pathways and residence time of a metal in different compartments of the environment. This study investigated the speciation of mercury in soils, derived from sites known for dumping of mine wastes in the Bibiani-Anwiaso-Bekwai district, a gold mining community of the Western Region of Ghana. Soil samples were taken from the surface; depths of 20, 40 and 60 cm from mine waste at both abandoned and active mine sites. Each sample was analysed for total mercury, organic mercury and elemental mercury. After sample treatment, digestion and reduction with stannous chloride (SnCl(2)), total mercury content was determined using the Inductively Coupled Plasma-Optical Emissions Spectrometer (ICP-OES). Organic mercury content was determined employing a differential technique after disposing of elemental mercury by heating. Total mercury content in samples ranged from 0.067 to 0.876 mg/kg for surface soils. The same soil of depths 20, 40 and 60 cm had total mercury from 0.102 to 1.066, 0.037 to 4.037 and 0.191 to 4.998 mg/kg, respectively. For organic mercury, concentrations range from 0.012 to 0.260 mg/kg for surface soil. Soil depths of 20, 40 and 60 cm had organic mercury concentrations from 0.016 to 0.653, 0.041 to 1.093 and 0.101 to 2.546 mg/kg respectively. Elemental mercury concentrations in surface soils, soils at depths of 20, 40 and 60 cm ranged from 0.043 to 0.780; 0.017 to 0.749; 0.014 to 2.944 and 0.009 to 2.452 mg/kg respectively. Among the sites studied, only galamsey tailings (GM) showed a trend of increasing total mercury level with increasing depth. For the other sites, trends were not defined. There has been no defined trend for elemental mercury with depth at any of the sampling sites. Just as with total mercury, it was only GM that showed an increasing trend of organic mercury concentration with depth.

Distribution and speciation of mercury in soil in the area of an ancient mercury ore roasting site, Frbejžene trate (Idrija area, Slovenia)

In the initial period of mining activities in the Idrija basin (the16 th and the first half of the17 th centuries), Hg ore processing was performed at various small-scale roasting sites in the woods surrounding Idrija, by roasting ore in earthen vessels. The recovery rate of this method was very low; about half of Hg was lost, causing soil contamination and considerable amounts of waste material that could potentially leach Hg into the surrounding environment. The main aims of present geochemical study were to determine the contents, vertical distribution and speciation of Hg in soils at the roasting site at Frbejžene trate in order to verify the extreme pollution of ancient Hg ore roasting sites in the Idrija area and to establish their significance in the wider spatial contamination of soils and aquatic systems. Soil sampling was performed at the area of the former roasting site. The organic matter-rich surface soil layer (SOM) and underlying mineral soil were sampled at 63 sampling locations. Mercury speciation was performed using Hg thermo-desorption-AAS to distinguish cinnabar from potentially bioavailable forms. The results indicate extremely high Hg concentrations with a maximum of 37,000 mg/kg in SOM and 19,900 mg/kg in mineral soil. The established Hg median in soil was 370 mg/kg and in SOM 96.3 mg/kg. Spatial distributions of Hg in SOM and soil showed very high Hg contents in the central area and decreased rapidly with distance. The results of Hg thermo-desorption measurements indicated the presence of cinnabar (HgS) and Hg bound to organic or mineral soil matter. A significant portion (35–40%) of Hg in the investigated soil and SOM samples was comprised of non-cinnabar compounds, which are potentially bioavailable. It has been shown that soils contain high amounts of potentially transformable non-cinnabar Hg, which is available for surface leaching and runoff into the surrounding environment. Therefore, contaminated soils and roasted residues at the studied area are important for persistent Hg release into the aquatic ecosystem.

Mercury Distribution and Speciation in Soils Affected by Historic Mercury Mining

Vertical distribution and mercury speciation in soil profiles were studied to evaluate the extent of contamination and potential Hg mobility in a historical Hg mining area. Three sites were chosen for a case study of Hg contamination. One site was considered a low impact site located 400 m uphill from the mining activities and two sites were located in a presumably more highly impacted area. Mercury speciation was determined by thermo-desorption analysis. High impact soils in a close vicinity of the mine shaft exhibited relatively high Hg concentrations ranging from 8 to 10 μg g−1 in the surface (Ah) horizons and from 3 to 9 μg g−1 in the underlying mineral soils. Approximately 50–80% of total Hg in all soil horizons of high impact soils was present as relatively insoluble HgS. The remaining 20–50% of total Hg was attributed to Hg adsorbed on mineral surfaces, Fe-oxyhydroxides or clay minerals. The highest Hg concentration in the low impact soils was detected in the Ah horizon (7 μg g−1). Mineral soil horizons contained relatively low Hg concentrations (≤0.6 μg g−1). Over 40% of total Hg in the Ah horizon of the low impact soils was HgS, likely deposited as fine particles derived from past mining activities. The Hg in mineral horizons of low impact soils was exclusively Hg(II) weakly bound to mineral particles. Our study indicated that HgS contamination in the vicinity of a former mining area occurs in most Ah horizons of the area, but contamination of mineral soil horizons appears to be limited to the sites downhill from the mine shaft.

Mercury speciation in soils of the industrialised Thur River catchment (Alsace, France)

Methylmercury (MeHg) and total Hg (THg) concentrations in soil profiles were monitored in the Thur River basin (Alsace, France), where a chlor-alkali plant has been located in the city of Vieux-Thann since the 1930s. Three soil types were studied according to their characteristics and location in the catchment: industrial soil, grassland soil and alluvial soil. Contamination of MeHg and THg in soil was important in the vicinity of the plant, especially in industrial and alluvial soil. Concentrations of MeHg reached 27 ng g −1 and 29,000 ng g −1 for THg, exceeding the predictable no effect concentration. Significant ecotoxicological risk exists in this area and remedial actions on several soil types are suggested. In each type of soil, MeHg concentrations were highest in topsoil, which decreased with depth. Concentrations of MeHg were negatively correlated with soil organic matter and total S, particularly when MeHg concentrations exceeded 8 ng g −1. Under these conditions, MeHg concentrations in soil seemed to be influenced by THg, soil organic matter and total S concentrations. It was found that high MeHg/THg ratios (near 2%) in soil were mainly related to the combined soil environmental conditions such as low THg concentrations, low organic C/N ratios (<11) and relatively low pH (5–5.5). Nevertheless, even when the MeHg/THg ratio was low (∼0.04%), MeHg and THg concentrations were elevated, up to 13 ng g −1 and to 29,000 ng g −1, respectively. Thus, both THg and MeHg concentrations should be taken into account to assess potential environmental risks of Hg.

Quantification and speciation of mercury in soils from the Tripuí Ecological Station, Minas Gerais, Brazil

Contents of total mercury, organic carbon, total sulfur, iron, aluminum and grain size and clay mineralogy were used along with Pearson's correlation and Hg thermal desorption technique to investigate the presence, distribution and binding behavior of Hg in soils from three depths from the Tripuí Ecological Station, located near Ouro Preto, Minas Gerais State, Brazil. The soils studied had predominantly medium and fine sand texture (0.59–0.062 mm), acid character and Hg contents ranging from 0.09 to 1.23 μg/g. The granulometric distribution revealed that Hg is associated with coarse sand (2–0.59 mm) and silt and clay (< 0.062 mm) and presents similar Hg concentrations in both fractions. Mercury distribution in soil profiles showed that Hg was homogeneously distributed throughout the depths at most sites. Hg thermal desorption curves show that mercury occurs not only as Hg 2+ predominantly bound to organic components in most of the samples, but also in the form of cinnabar in some. Pearson's correlation confirmed that mercury is associated with organic matter and sulfur and possibly with sulfur-bearing organic matter in most samples.

An operationally defined method to determine the speciation of mercury.

This paper presents a modified method of an operationally determined speciation of mercury in soil. The analytical work was mainly concerned to suit properly with inductively coupled plasma-atomic emission spectrometry (ICP-AES). Soil samples analysed in this study were selected from open areas around a crematorium, a waste incinerator, and two power plants. Results show that both topsoil and subsoil samples were dominated by elemental mercury Hg(0) and mercuric sulphide (HgS). The significant correlation between sulphur concentration and HgS was found in topsoil samples.

Impacts of Mercury on Freshwater Fish-Eating Wildlife and Humans

This paper reviews the current state of knowledge of the toxic effects of mercury on fish-eating birds, mammals, and humans associated with freshwater ecosystems, including new information on the relative risk of elevated methyl Hg exposure for fish-eating birds inhabiting aquatic ecosystems impacted by mining/smelting activities and areas characterized by high geological sources of Hg. The influence of various environmental conditions such as lake pH, DOC, and chemical speciation of Hg, on fish-Hg concentrations and Hg exposure in fish-eating wildlife, are discussed. Although a continuing global effort to decrease the release of this nonessential metal into the environment is warranted, Hg methylation and biomagnification may be limited in some environments due to chemical speciation of mercury in soils and sediments (e.g., HgS) and water quality conditions (e.g., high alkalinity and pH) that do not facilitate high methylation rates. We have shown such limitations for a lake where historic Hg mining greatly increased sediment-Hg loadings, yet Hg increases in small fish of various species are currently lower than expected, and top predators (bald eagles), despite having elevated concentrations of Hg in their blood compared with individuals from nearby lakes, exhibit no Hg-related reproductive impairment or other signs of MeHg intoxication. Recent epidemiological studies have shown that fish-eating human populations may be exposed to Hg sufficient to cause significant developmental effects. However, for humans, we conclude that the current USEPA reference dose for MeHg may be too restrictive, particularly for the less sensitive adult. The health status of indigenous peoples relying on the subsistence harvest of wild foods may be negatively affected by such restrictions.

Mercury speciation in soils and river sediments of the industrialised Thur river catchment (Alsace, France)

The mobility of mercury (Hg), particularly organic Hg, has been studied in the Thur river basin using an ultra-sensitive and specific analytical equipment (High Performance Liquid Chromatography (HPLC) with on-line CVAFS detection). The Thur river, sub-tributary of the Rhine river is polluted by mercury since the beginning of the 20th century because of industrial effluents from chlorine and soda industry. This study allows to determine in different environmental compartments (soils and river sediments) the total mercury contents (THg) and, for the first time in such an industrialized catchment, the methyl mercury concentrations (MeHg). The ratio between MeHg and THg concentrations is higher in the grassland soils than in the industrial and alluvial soils even if MeHg and THg contents are higher in these latters. The highest MeHg/THg ratios can be observed for lowest C/N ratios and slightly acidic soils. MeHg/THg ratio is very low in the industrial channel despite high MeHg and THg concentrations. For river sediments, MeHg/THg ratios are higher in the suspended matters than in the bottom sediments. These first results are very helpful to better understand the transformation of Hg species in the different compartments and the processes of Hg transfer from one compartment to another.

Speciation of mercury in soil and sediment by selective solvent and acid extraction.

In order to characterize the mercury hazard in soil, a sequential extraction scheme has been developed to classify mercury species based on their environmental mobility and/or toxicity for either routine lab analysis or on-site screening purposes. The alkyl mercury species and soluble inorganic species that contribute to the major portion of potential mercury toxicity in the soil are extracted by an acidic ethanol solution (2% HCl+10% ethanol solution) from soil matrices as "mobile and toxic" species. A High-Performance Liquid Chromatography (HPLC) system coupled with Inductively Coupled Plasma Mass Spectrometry (ICP-MS) detection has been developed to further resolve the species information into soluble inorganic species (Hg(2+)), methylmercury(II) (MeHg(+)) and ethylmercury(II) (EtHg(+)) species. Alternatively, these species can be separated into "soluble inorganic mercury" and "alkyl mercury" sub-categories by Solid-Phase Extraction (SPE). A custom Sulfydryl Cotton Fiber (SCF) material is used as the solid phase medium. Optimization of the SCF SPE technique is discussed. Combined with a direct mercury analyzer (DMA-80), the SCF SPE technique is a promising candidate for on-site screening purposes. Following the ethanol extraction, the inorganic mercury species remaining in soil are further divided into "semi-mobile" and "non-mobile" sub-categories by sequential acid extractions. The "semi-mobile" mercury species include mainly elemental mercury (Hg) and mercury-metal amalgams. The non-mobile mercury species mainly include mercuric sulfide (HgS) and mercurous chloride (Hg(2)Cl(2)).

Mercury speciation in soils and attic dust in the Idrija area

Speciation of mercury in soils and attic dust in Idrija and its surroundings was studied by means of pyrolysis technique. The results show that soil and attic dust have similar course of Hg release. The samples show double peak curves with first maximum between 200 °C and 250 °C and a second one between 250 and 350 °C. The first peak (200-250 °C) indicates non-cinnabar Hg compounds. Compared to the standard Hg compounds curves and that of humic acid bound Hg of the forest soil sample, it is most reasonable that this peak represents Hg bound or sorbed to matrix components. The second peak, which occurs in the higher temperature range, indicates the presence of cinnabar. In areas close to the mine or tailings Hg occurs predominantly as cinnabar. In more distant areas, Hg is mainly bound to matrix components.

Speciation of mercury in soils and sediments by thermal evaporation and cold vapor atomic absorption

Evaporation studies of mercury in several chemical compounds, soils, and sediments with a high content of organic matter indicate that a quantitative release is possible at temperatures as low as 400°C. The desorption behaviour from a gold column is not influenced. Only from samples with a thermal prehistory, such as brown coal ash, did mercury evaporate at higher temperatures. Qualitative conclusions can be derived about the content of metallic mercury as well as mercury associated with organic matter or sulfide. A comparison of the analytical results obtained by using the evaporation technique or by dissolving using a mixture of conc. HCl and HNO3 shows good agreement; the advantages of the evaporation technique are obvious at very low mercury concentrations.