Mercury distribution in plants and soils from the former mining area of Abbadia San Salvatore (Tuscany, Central Italy).

The distribution of heavy metals in plants (Castanea sativa, Sambucus nigra, Verbascum thapsus, Popolus spp., Salix spp., Acer pseudoplatanus, Robinia pseudoacacia) growing in soils from active and abandoned mining areas is of scientific significance as it allows to recognize their ability to survive in a hostile environment and provide useful indications for phytoremediation operations. In this work, soils from the former Hg-mining area of Abbadia San Salvatore (Tuscany, Central Italy) were analyzed for total, leached Hg, % of organic and inorganic-related Hg. The dehydrogenase enzyme activity (DHA) was also measured with the aim to evaluate the status of the soil, being characterized by high Hg contents (up to 1068 mg kg-1). Eventually, the concentration of Hg in the different parts of the plants growing on these soils was also determined. Most studied soils were dominated by inorganic Hg (up to 92%) while the DHA concentrations were < 151 µg TPF g-1 day-1, suggesting that the presence of Hg is not significantly affecting the enzymatic soil activity. This is also supported by the bioaccumulation factor (BF), being predominantly characterized by values < 1. Sambucus nigra and Verbascum thapsus had the highest Hg contents (39.42 and 54.54 mg kg-1, respectively). The plant leaves appear to be the main pathways of Hg uptake, as also observed in other mining areas, e.g., Almadèn (Spain), indicating that particulate-Hg and Hg0 are the main forms entering the plant system, the latter derived by the GEM emitted by both the edifices hosting the roasting furnaces and the soils themselves.

Trace elements in farmland soils and crops, and probabilistic health risk assessment in areas influenced by mining activity in Ecuador.

Consumption of food grown in contaminated soils may be a significant human exposure pathway to pollutants, including toxic elements. This study aimed to investigate the pollution level of trace elements in farmland soil and crops collected in orchards from Ponce Enriquez, one of the Ecuador's most important gold mining areas. The concentration of arsenic (As), cadmium (Cd), chrome (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) was analyzed in soil and crop samples (celery, chives, corn, herbs, lettuce, turnips, green beans, cassava, and carrots). In addition, a probabilistic human health risk assessment, in terms of hazard quotients (HQ) and cancer risk (CR), was conducted to assess the potential risk related to local crop ingestion. The contents of As, Cr, Cu, and Ni in soils exceeded the Ecuadorian quality guidelines for agricultural soils. The trace elements concentration in local crops was higher than the maximum permissible levels set by the Food and Agriculture Organization of the United Nations (FAO). The HQ and CR of local crop ingestion were several orders higher than the safe exposure threshold, mainly for lettuce, chives, and turnips. Our results revealed that inhabitants of the study area are exposed to developing carcinogenic and non-carcinogenic effects due to long-term food consumption with high trace elements. This study sheds light on the need to assess further the quality of agricultural soils and crops grown in mining areas with signs of contamination to guarantee consumer food safety.

An approach for evaluating the bioavailability and risk assessment of potentially toxic elements using edible and inedible plants-the Remance (Panama) mining area as a model.

Mining affects the environment, particularly through the persistence of accumulation of tailings materials; this is aggravated under tropical climatic conditions, which favours the release of potentially toxic elements (PTEs) bioavailable to the local flora and fauna and supposing a risk to human health. The Remance gold mine (Panamá), exploited intermittently for more than 100 years, and has remained derelict for over 20 years. Within the area live farmers who carry out subsistence agriculture and livestock activities. The objective of this study has been to study the transference of PTEs in the local agricultural soil-plants system, with the goal of identifying their bioavailability to perform a human risk assessment. The results obtained of the Bioaccumulation coefficient in local plants show very weak to strong absorption of As (< 0.001-1.50), Hg (< 0.001-2.38), Sb (0.01-7.83), Cu (0.02-2.89), and Zn (0.06-5.32). In the case of Cu in grass (18.3 mg kg-1) and plants (16.9 mg kg-1) the concentrations exceed the maximum authorised value in animal nutrition for ruminants (10 mg kg-1). The risk to human health for edible plants exceeds the non-carcinogenic risk for rice, corn, cassava, and tea leaves for Sb (HQ 19.450, 18.304, 6.075, 1.830, respectively), the carcinogenic risk for Cu (CR = 2.3 × 10-3, 7.7 × 10 -4, 1.1 × 10-3, 1.0 × 10-3, respectively), and the carcinogenic risk for As in rice, corn and tea leaves (CR = 8 × 10-5, 3 × 10-5, 3 × 10-5, respectively). Urgent measures are needed to alleviate these effects.

Environmental challenges related to cyanidation in Central American gold mining; the Remance mine (Panama).

Mine tailings are a potential source of environmental pollution because they typically contain potentially toxic elements (PTEs) and the residue of chemical compounds used during extraction processes. The Remance gold mine (NW Panama) is a decommissioned mine with mining activity records dating from the 1800s and several periods of abandonment. Very little remediation work has been performed, and waste is exposed to climatic conditions. This study aimed to evaluate the PTEs and cyanide contents in mine waste after mining operations ceased some 20 years ago, and to evaluate the degree of pollution and the environmental risks they pose with the use of the Pollution Load Index (PLI) and the Ecological Risk Index (RI). Although the total cyanide (T-CN) concentration (1.4-1.9 mg kg-1) found in most of the study area falls within the limits of gold mining tailing values for American sites (1.5-23 mg kg-1), it is worth noting that the values of the tailings of the last used mining operation exceed it (25.2-518 mg kg-1) and persist at the site. The PLI and RI suggest that the tailings from the mine and mine gallery sediments represent a source of pollution for soils and surrounding areas given their high content of PTEs (As, Cu, Sb, Hg) and T-CN, which pose serious ecological risks for biota. Therefore, it is necessary to draw up a remediation plan for this area.

Characterization of the biochemical basis for copper homeostasis and tolerance in Biscutella auriculata L.

Biscutella auriculata L. is a plant that belongs to the Brassicaceae family and it has been found growing in a metal-contaminated area of the San Quíntín mine (Ciudad Real, Spain). The purpose of this work was to evaluate the mechanisms that allow this plant to tolerate high concentrations of copper. Seedlings were grown in a semi-hydroponic system for 15 days under 125 µM of Cu (NO3 )2 . Exposure to copper resulted in growth inhibition and reduction in the photosynthetic parameters. Copper was mainly accumulated in vascular tissue and vacuoles of the roots and only a minor proportion was transferred to the shoot. Biothiol analysis showed a greater enhancement of reduced glutathione in leaves and increases of phytochelatins (PC2 and PC3) in both leaves and roots. Copper treatment induced oxidative stress, which triggered a response of the enzymatic and non-enzymatic antioxidant mechanisms. The results show that B. auriculata is able to tolerate high metal levels through the activation of specific mechanisms to neutralize the oxidative stress produced and also by metal sequestration through phytochelatins. The preferential accumulation of copper in roots provides clues for further studies on the use of this plant for phytostabilization and environmental recovery purposes in Cu-contaminated areas.

Multi-pathway human exposure risk assessment using Bayesian modeling at the historically largest mercury mining district.

The largest mercury (Hg) mining district in the world is located in Almadén (Spain), with well-known environmental impacts in the surrounding ecosystem. However, the impact of mercury on the health of the inhabitants of this area has not been documented accordingly. This study aims to carry out a probabilistic human health risk assessment using Bayesian modeling to estimate the non-carcinogenic risk related to Hg through multiple exposure pathways. Samples of vegetables, wild mushrooms, fish, soil, water, and air were analyzed, and adult residents were randomly surveyed to adjust the risk models to the specific population data. On the one hand, the results for the non-carcinogenic risk based on Hazard Quotient (HQ) showed unacceptable risk levels through ingestion of Hg-contaminated vegetables and fish, with HQ values 20 and 3 times higher, respectively, than the safe exposure threshold of 1 for the 97.5th percentile. On the other hand, ingestion of mushrooms, dermal contact with soil, ingestion of water, dermal contact with water and inhalation of air, were below the safety limit for the 97.5th percentile, and did not represent a risk to the health of residents. In addition, the probabilistic approach was compared with the conservative deterministic approach, and similar results were obtained. This is the first study conducted in Almadén, which clearly reveals the high levels of human health risk to which the population is exposed due to the legacy of two millennia of Hg mining.

Experimental assessment of the daily exchange of atmospheric mercury in Epipremnum aureum.

Mercury (Hg) exchange at the plant leaf-atmosphere interface is an important issue when considering vegetation as a sink or source of this global pollutant. The aim of the study described here was to clarify this process by studying Hg exchange under laboratory conditions with a plant model, namely Epipremnum aureum. The desorption and absorption processes were studied under similar conditions in natural daylight. Hg exchange was measured at the foliar surface, and micrometeorological parameters and stomatal conductance were assessed. The results of the Hg exchange study showed different rhythms for the two processes, i.e. desorption (14-196 ng m-2 day-1) was slower than absorption (170-1341 ng m-2 day-1). The daily cycle was more complex in the desorption process, with a maximum when stomatal conductance was high but also with high values during nocturnal hours and a trend to absorption in the mornings. The daily absorption cycles were relatively simple, with values that coincided with positive stomatal conductance values and null values during nocturnal hours. The main factors involved in desorption were stomatal conductance and temperature, but other factors may need to be considered. The absorption process only involved total gaseous Hg, stomatal conductance and relative humidity. A net balance of the two experiments provided data on the amount of Hg transferred per unit leaf area (167 ng m-2 for desorption and 9213 ng m-2 for absorption), which implies total amounts of 23 ng of Hg desorbed and 1280 ng absorbed during the whole experiment. Finally, the reversible/non-reversible nature of the Hg exchange process must be reconsidered bearing in mind that Hg within the leaf can be emitted if changes in ambient conditions are appropriate to favour this process.

Biogeochemical assessment of the impact of Zn mining activity in the area of the Jebal Trozza mine, Central Tunisia.

Soil pollution associated with potentially toxic elements (PTEs) from mining residues is a significant problem worldwide. The decommissioned Jebal Trozza mine, located in central Tunisia, may pose a serious problem because of the possible high concentrations of PTEs present in its wastes. This mine is a potential source of contamination for agriculture in this area due to both direct causes (pollution of agricultural soils) and indirect causes (pollution of sediments that accumulate in a dam used for irrigation). The aim of the study reported here was to assess the effects of local mining activity in two respects: (1) in terms of soil quality, as determined by soil edaphological parameters and PTEs contents in the mining wastes and local soils; and (2) in terms of biological quality, as evaluated by quantification of enzymatic activity as an indicator of bacterial activity in soils and wastes. The mine tailings contained high levels of Pb (1.83-5.95%), Zn (7.59-12.48%) and Cd (85.95-123.25 mg kg-1). The adjacent soils were also highly contaminated with these elements, with average concentrations of Pb, Zn and Cd that exceeded the European standard values for agricultural soils (3, 300 and 300 mg kg-1 for Cd, Pb and Zn, respectively). Enzymatic dehydrogenase showed zero activity in waste piles and very low activity in PTE-contaminated soils, but this activity returned to normal values as the pollution decreased, thus demonstrating the effect that the contamination load had on the health of the studied soils. A Statistical Factor Analysis clearly distinguished three groups of samples, and these are related to the influence that mining on the soils and sediments had on the PTE concentrations and their effects on the biological quality of the soil. An environmental assessment based on the enrichment factor criteria indicated risk levels that varied from strongly to severely polluted. The risk appears to be greater close to the mine, where the highest PTE levels were determined.

Assessment of EDDS and vermicompost for the phytoextraction of Cd and Pb by sunflower (Helianthus annuus L.).

The effects of Ethylenediamine disuccinic acid (EDDS) (0 and 5 mmol·kg-1) as a synthetic chemical amendment, vermicompost (0 and 5%w/w) as an organic amendment and their combined application were evaluated for the phytoextraction by sunflower (Helianthus annuus L.) of cadmium (Cd) and lead (Pb) at three artificial contamination levels in soils (0, 50, and 100 mg·kg-1 for Cd and 0, 100, and 200 mg·kg-1 for Pb). The results showed that the application of EDDS was the most effective method to increase Pb and Cd concentrations in both parts of the plant. The results also showed that the application of EDDS increased 9.27% shoot Pb content at 200 mg·kg-1 but decreased 15.95% shoot Cd content at 100 mg·kg-1 contamination level with respect to the respective controls. The bioavailable concentrations of Cd at 100 mg·kg-1 and Pb at 200 mg·kg-1 contamination level in the soil at the end of experiment increased 25% and 26%, respectively after the application of EDDS but vermicompost decreased 43.28% the bioavailable Pb concentration relative to their controls. Vermicompost increased the remediation factor index of Cd, thus making it the best treatment for the phytoextraction of Cd. The combined application of EDDS and vermicompost was the best amendment for Pb phytoextraction.

Use of humic substances in froth flotation processes.

Continual growing demand for metals in regular and emerging markets has led to an increasing use of chemicals and reagents in ore processing. This trend force to incur in an increasing use of commodities which inevitable leads to higher operational costs and environmental concern. The chemicals and reagents used in flotation processes especially invoke high costs of handling and disposal due to their hazardous nature, but until now, few studies have been carried out to seek possible alternatives. In order to develop a cheaper and greener processes, these hazardous materials should be replaced by more sustainable products, by-products, or wastes generated by other industries. Biosolids, cheaper and greener than chemical frothers and collectors, have been tested successfully in flotation processes. Studies of removal rates and froth flotation kinetics have been carried out independently, nevertheless a deeper understanding of the tradeoffs involved between the rates and kinetics should be obtained. This work evaluates the use of different collectors (conventional collector (CC), biosolids (and their main components), and mixtures of CC and biosolids main components) in the froth flotation of copper sulfide ores. Tests were carried out in Denver Cells, at fixed collector, frother, and pH levels, in order to estimate metallurgical and kinetic parameters. In rougher flotation tests, biosolids show to be the most efficient non-CCs, achieving Cu recoveries of 64.1%. CC achieved 76.2% Cu recoveries while none of the pure biosolids main components achieved Cu recoveries over 60%. In the kinetics studies, only the partial replacement of CC (by 50% of Humic Acids (HAs) or biosolids) allowed a similar copper recovery once compared with CC (~81% Cu to be obtained with a fast kinetic constant of ~0.88 min-1). For molybdenum, partial replacement of CC produced better recovery and kinetics constants (k of 0.83 min-1 and R∞ of 66.10% for 50% CC - 50% HAs; k of 0.90 min-1 and R∞ of 61.79% for 50% CC - 50% biosolids). Results show that different combinations of biosolids - CC or HAs - CC could achieve optimal flotation conditions. As evaluated, an optimal combinations would allow considerable reductions in energy and chemical consumption.

The role of native lichens in the biomonitoring of gaseous mercury at contaminated sites.

Contamination by atmospheric mercury has been assessed in two different areas from Spain (Las Cuevas, Ciudad Real and Flix, Tarragona) using lichens as biomonitors. The relationship established between mercury contents in the soils and the gaseous mercury (GM) was also observed. It was found that the GM is highest in the vicinity of the source and it is dispersed depending on of the distance to the source and the wind directions. The mercury concentration in the gas phase in Flix was higher than that found in Las Cuevas and also higher than the value that the US EPA recommended. The mercury bioaccumulation in the native lichens from genders Ramalina and Xanthoria were used as biomonitors for absorbing mercury in Las Cuevas and Flix, respectively. The mercury uptake by Ramalina was higher than the amount accumulated by Xanthoria, a difference that was mainly due to the lichen characteristics. The content of mercury in lichens in relation to the mercury in gas was fitted by a Freundlich type equation, indicating that the equilibrium between both phases was established. Besides, transplanted Ramalina lichen in Las Cuevas allowed to obtain the kinetic of mercury uptake. A kinetic model of first order based on the equilibrium was proposed and the mass transfer constants for each sampling station were estimated. As it was expected, these values increased with the predominant wind flow direction.

Bioaccumulation of thallium and other trace metals in Biscutella laevigata nearby a decommissioned zinc-lead mine (Northeastern Italian Alps).

The mineral body exploited in Salafossa (Eastern Dolomites) was one of the largest lead/zinc-containing mineral deposits in Europe. Both metals were mainly present as sulphides (sphalerite, ZnS and galena, PbS). Mining activity started around 1550, but it was only around 1960 that the richest veins of the minerals were discovered. The mine closed in 1985, and concentrations of several trace metals, such as thallium (Tl), iron (Fe), manganese (Mn), lead (Pb) and zinc (Zn), were detected in the soils and plant samples (Biscutella laevigata L.) that were collected from eighteen sites selected outside the mine. B. laevigata is a pseudometallophyta species, and it often grows near mining areas where the soil's metal concentrations are significantly higher than those of soil with a natural geochemical background. The total metal concentrations in the plant tissue (roots and leaves of Biscutella laevigata) and in the soil samples - both bulk-soil and the B. laevigata root system (rhizo-soil) - were determined through Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The metal extractability and leachability of the soil samples were estimated using soil extractions with DTPA (Diethylenetriaminepentaacetic acid). In addition, metal mobility caused by rainwater runoff was estimated by using a leaching test with a dilute solution of H2SO4 and HNO3. The results showed that metals were present in a chemical form available for uptake by the plants' roots. In fact, high concentrations of the metals were also found in the plant tissue (roots and leaves) of B. laevigata, and these concentrations were higher than those whose soils present natural geochemical background levels in the corresponding rhizo-soil. Thus, B. laevigata has shown a marked ability to bioaccumulate trace metals, especially Tl and, to a lesser extent, Zn, Pb, Fe and Mn, and it can influence metal mobility in the rhizo-soil. To assess the uptake and translocation processes of the trace metals, resulting in their bioaccumulation, two different indices were calculated: the enrichment factor in roots (EFr), as the ratio between the metal concentration in belowground biomass and in the respective rhizo-soil, and the translocation factor (TF), as the ratio between the metal concentration in the leaves and the corresponding roots. For both indices, values > 1 denoted enrichment of the metal in the roots or its translocation to the upper tissues. The results showed that EFr and TF were considerably high only for Tl, reaching a maximum value of 60 for EFr and 11.6 for TF. Conversely, the other investigated metals did not show significant bioaccumulation (EFr < 1), and they showed TF > 1 only at a few sites.

Evaluation of mercury stress in plants from the Almadén mining district by analysis of phytochelatins and their Hg complexes.

To evaluate plant response to Hg stress, glutathione, phytochelatins, and their Hg complexes were analyzed using HPLC with amperometric detection in samples of Asparagus acutifolius grown in the Almadén mining district (Ciudad Real, Spain), one of the most Hg-contaminated sites in the world. Soils of the Almadén mining district, and specifically from the Almadenejos zone, are highly contaminated, with some zones having values above 4,000 µg Hg g(-1) soil. Although soils have an extremely high concentration of mercury, generally less than 2% is available for plants, as is shown by various soil extractions simulating bioavailability. In plants, Hg concentration increases depending on the content of Hg in soils. In addition, Hg levels in roots are higher than in aerial parts, which is a strategy of plants for protecting their more sensitive aerial parts from the deleterious effects of metal stress. The total content of phytochelatins (PCs) and their complexes are directly related with the amount of mercury in soils. These findings highlight the important role of thiol compounds and their metal complexes in capturing and fixing Hg from soils, giving plants the capacity to deal with the heavy metal toxicity of polluted soils.

A compilation of field surveys on gaseous elemental mercury (GEM) from contrasting environmental settings in Europe, South America, South Africa and China: separating fads from facts.

Mercury is transported globally in the atmosphere mostly in gaseous elemental form (GEM, [Formula: see text]), but still few worldwide studies taking into account different and contrasted environmental settings are available in a single publication. This work presents and discusses data from Argentina, Bolivia, Bosnia and Herzegovina, Brazil, Chile, China, Croatia, Finland, Italy, Russia, South Africa, Spain, Slovenia and Venezuela. We classified the information in four groups: (1) mining districts where this contaminant poses or has posed a risk for human populations and/or ecosystems; (2) cities, where the concentration of atmospheric mercury could be higher than normal due to the burning of fossil fuels and industrial activities; (3) areas with natural emissions from volcanoes; and (4) pristine areas where no anthropogenic influence was apparent. All the surveys were performed using portable LUMEX RA-915 series atomic absorption spectrometers. The results for cities fall within a low GEM concentration range that rarely exceeds 30 ng m(-3), that is, 6.6 times lower than the restrictive ATSDR threshold (200 ng m(-3)) for chronic exposure to this pollutant. We also observed this behavior in the former mercury mining districts, where few data were above 200 ng m(-3). We noted that high concentrations of GEM are localized phenomena that fade away in short distances. However, this does not imply that they do not pose a risk for those working in close proximity to the source. This is the case of the artisanal gold miners that heat the Au-Hg amalgam to vaporize mercury. In this respect, while GEM can be truly regarded as a hazard, because of possible physical-chemical transformations into other species, it is only under these localized conditions, implying exposure to high GEM concentrations, which it becomes a direct risk for humans.

Biogeochemical prospecting of metallic critical raw materials: soil to plant transfer in SW Ciudad Real Province, Spain.

The soil-plant transfer of trace elements is a complex system in which many factors are involved such as the availability and bioavailability of elements in the soil, climate, pedological parameters, and the essential or toxic character of the elements. The present study proposes the evaluation of the use of multielement contents in vascular plants for prospecting ore deposits of trace elements of strategic interest for Europe. To accomplish this general goal, a study of the soil-plant transfer of major and trace elements using Quercus ilex as a study plant has been developed in the context of two geological domains with very different characteristics in geological terms and in the presence of ore deposits: the Almadén syncline for Hg and the Guadalmez syncline for Sb. The results have made it possible to differentiate geological domains not only in terms of individual elements, but also as a combination of major and trace elements using Factor Analysis. The bioconcentration factors have demonstrated the uptake of macronutrients and micronutrients in very high concentrations but these were barely dependent, or even independent of the concentrations in the soil, in addition to high values of this factor for Sb. The Factor Analysis allowed for the differentiation of geogenic elements from other linked to stibnite ore deposits (Sb, S, and Cu). This element (Sb) can be uptake by Quercus ilex via the root and from there translocating it to the leaves, showing a direct relation between concentrations in soil and plants. This finding opens the possibility of using Quercus ilex leaves for biogeochemical prospecting of geological domains or lithological types of interest to prospect for Sb deposits.

Industrial and natural sources of gaseous elemental mercury in the Almadén district (Spain): an updated report on this issue after the ceasing of mining and metallurgical activities in 2003 and major land reclamation works.

Two events during the last decade had major environmental repercussions in Almadén town (Spain). First it was the ceasing of activities in the mercury mine and metallurgical facilities in 2003, and then the finalization of the restoration works on the main waste dump in 2008. The combination of both events brought about a dramatic drop in the emissions of gaseous elemental mercury (GEM) to the atmosphere. Although no one would now call the Almadén area as 'mercury-free', the GEM levels have fallen beneath international reference safety levels for the first time in centuries. This has been a major breakthrough because in less than one decade the site went from GEM levels in the order of "tens of thousands" to mere "tens" nanogram per cubic meter. Although these figures are per se a remarkable achievement, they do not mark the end of the environmental concerns in the Almadén district. Two other sites remain as potential environmental hazards. (1) The Las Cuevas mercury storage complex, a partially restored ex-mining site where liquid mercury is being stored. The MERSADE Project (LIFE-European Union) has tested the Las Cuevas complex as a potential site for the installation of a future European prototype safe deposit of surplus mercury from industrial activities. Despite restoration works carried out in 2004, the Las Cuevas complex can still be regarded as hotspot of mercury contamination, with high concentrations above 800µgg(-1) Hgsoil and 300ngm(-3) Hggas. However, as predicted by air contamination modeling using the ISC-AERMOD software, GEM concentrations fade away in a short distance following the formation of a NW-SE oriented narrow plume extending for a few hundred meters from the complex perimeter. (2) Far more dangerous from the human health perspective is the Almadenejos area, hosting the small Almadenejos village, the so-called Cerco de Almadenejos (CDA; an old metallurgical precinct), and the mines of La Nueva Concepción, La Vieja Concepción and El Entredicho. The CDA is an old metallurgical site that operated between 1794 and 1861, leaving behind a legacy of extremely contaminated soils (mean concentration=4220µgg(-1) Hg) and GEM emissions that in summer can reach levels up to 4,000-5,000ngm(-3). Thus the CDA remains the sole 'urban' site in the district surpassing GEM international reference safety levels. In order to prevent these emissions, the CDA requires immediate action regarding restoration works. These could involve the full removal of soils or their permanent capping to create an impermeable barrier.

Distribution of gaseous Hg in the Mercury mining district of Mt. Amiata (Central Italy): a geochemical survey prior the reclamation project.

The Mt. Amiata volcano is the youngest and largest volcanic edifice in Tuscany (central-northern Italy) and is characterized by a geothermal field, exploited for the production of electrical energy. In the past Mt. Amiata was also known as a world-class Hg district whose mining activity was mainly distributed in the central-eastern part of this silicic volcanic complex, and particularly in the municipality of Abbadia San Salvatore. In the present work we report a geochemical survey on Hg(0) measurements related to the former mercury mine facilities prior the reclamation project. The Hg(0) measurements were carried out by car for long distance regional surveys, and on foot for local scale surveys by using two LUMEX (915+ and M) devices. This study presents the very first Hg(0) data obtained with this analytical technique in the Mt. Amiata area. The facilities related to the mining areas and structures where cinnabar was converted to metallic Hg are characterized by high Hg values (>50,000ngm(-3)), although the urban center of Abbadia San Salvatore, few hundred meters away, does not appear to be receiving significant pollution from the calcine area and former industrial edifices, all the recorded values being below the values recommended by the issuing Tuscany Region authorities (300ngm(-3)) and in some cases approaching the Hg background levels (3-5ngm(-3)) for the Mt. Amiata area.

Mercury distribution in plants and soils from the former mining area of Abbadia San Salvatore (Tuscany, central Italy).

The distribution of heavy metals in plants growing in soils from active and abandoned mining areas is of scientific significance as it allows one to recognize their ability to survive in a hostile environment and to provide useful indications for phytoremediation operations. In this work, soils developed in the former Hg-mining area of Abbadia San Salvatore (Tuscany, Central Italy) were analyzed for total, leached Hg, % of organic- and inorganic-related Hg. The dehydrogenase enzyme activity (DHA) was also measured with the aim to evaluate the status of the soil, being characterized by high Hg content. Eventually, the concentration of Hg in the different parts of the plants growing on these soils was analyzed. The soils showed Hg content up to 1068 mg kg - 1 and in most of them is dominated by inorganic Hg (up to 92%). The DHA concentrations were < 151 µg TPF g - 1 day - 1 , suggesting that the presence of Hg is not significantly affecting the enzymatic soil activity. This is also supported by the bioaccumulation factor (BF) that is < 1 in most of the studied plants. Generally speaking, the plant leaves appear to be one of the main pathways of Hg uptake, as also observed in other mining areas, e.g. Almaden (Spain), suggesting that particulate-Hg and Hg 0 are the main forms entering the plant system, the latter derived by the GEM emitted by both the edifices hosting the roasting furnaces and the soils themselves.

Mobility of antimony in contrasting surface environments of a mine site: influence of redox conditions and microbial communities.

Microbial processes can influence the complex geochemical behaviour of the toxic metalloid antimony (Sb) in mining environments. The present study is aimed to evaluate the influence of microbial communities on the mobility of Sb from solid phases to water in different compartments and redox conditions of a mining site in southwest (SW) Spain. Samples of surface materials presenting high Sb concentrations, from two weathered mining waste dumps, and an aquatic sediment were incubated in slurries comparing oxic and anoxic conditions. The initial microbial communities of the three materials strongly differed. Incubations induced an increase of microbial biomass and an evolution of the microbial communities' structures and compositions, which diverged in different redox conditions. The presence of active bacteria always influenced the mobility of Sb, except in the neutral pH waste incubated in oxic conditions. The effect of active microbial activities in oxic conditions was dependent on the material: Sb oxic release was biologically amplified with the acidic waste, but attenuated with the sediment. Different bacterial genera involved in Sb, Fe and S oxidation or reduction were present and/or grew during incubation of each material. The results highlighted the wide diversity of microbial communities and metabolisms at the small geographic scale of a mining site and their strong implication in Sb mobility.

Evaluation of antimony availability in a mining context: Impact for the environment, and for mineral exploration and exploitation.

This work aims to establish Sb mobility, its transfer to biota and its effect on soil health in a semi-arid climate. The results show the presence of stibnite (Sb2S3) as the main primary Sb compound, bindhemite (Pb2Sb2O6(O,OH)), and minor proportions of stibiconite (Sb3+(Sb5+)2O6(OH)) as oxidised Sb species. This research also observes very high total Sb contents in mining materials (max: 20,000 mg kg-1) and soils (400-3000 mg kg-1), with physical dispersion around mining materials restricted to 450 m. The soil-to-plant transfer is very low, (bioaccumulation factor: 0.0002-0.1520). Most Sb remains in a residual fraction (99.9%), a very low fraction is bound to Fe and Mn oxy-hydroxides or organic matter, and a negligible proportion of Sb is leachable. The higher Sb mobility rates has been found under oxidising conditions with a long contact time between solids and water. The main factors that explain the poor Sb mobility and dispersion in the mining area are the low annual rainfall rates that slow down the Sb mobilisation process and the scarce formation of oxidised Sb compounds. All these data suggest poor Sb (III) formation and a low toxicological risk in the area associated with past mining activities. The low mobility of Sb suggests advantages for future sustainable mining of such ore deposits in a semi-arid climate and is also indicative of the limitations of geochemical exploration in the search for new Sb deposits.