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.

Synthesis of zeolites from volcanic ash (Tajogaite, Spain) for the remediation of waters contaminated by fluoride.

In the eruptive event of Tajogaite (2021) in La Palma, Canary Islands, large quantities of volcanic ash were accumulated, affecting the local environment and urban areas. In this study, volcanic ash sampled from urban areas (catalogued as municipal waste (20 03 03) by the European Wastes Catalogue) were converted into zeolites by hydrothermal synthesis at 100 °C with previous alkaline fusion at 550 °C with distilled water. During this process, new phases of zeolite principally type X and sodalite have been identified by XRD at 2 h of incubation. These zeolites, with the course of incubation time, present competitive processes where the transformation into sodalite develops after 24 h as the predominant phase. The synthesized zeolitic material presents a high concentration as impurities in Fe2O3 (13.70 wt%), Na2O (12.70 wt%), CaO (11.65 wt%), and TiO2 (3.89 wt%) coming from the volcanic ash and NaOH introduced in the synthesis methodology. These impurities impart different physicochemical capabilities to the zeolitic material. The application of zeolites obtained in a preliminary fluoride adsorption experiment with volcanic leachate water rich in fluoride has been tested in a novel way. Removal efficiencies of 41.4% at acidic pH (5.77) have been obtained with 2 g L-1 adsorbent zeolitic material doses. A value-added material is obtained and applied in a preliminary way to solve a problem generated by the volcanic ash itself, allowing the End of Waste status and meeting different objectives of the sustainable development goals of the UN Agenda 2030.

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.

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.

Soil and Freshwater Bioassays to Assess Ecotoxicological Impact on Soils Affected by Mining Activities in the Iberian Pyrite Belt.

This study aims to use geochemical, mineralogical, ecotoxicological and biological indicators for a comprehensive assessment of the ecological risks related to the mobility, ecotoxicity and bioavailability of potentially harmful elements in the Lousal mining district. Particularly, toxicity was evaluated using four assays: algae, cytotoxicity assays with HaCaT cell line (dermal), earthworms and Daphnia magna. The geochemical and mineralogical characterization of the studied area shows that the mine wastes underwent intense weathering processes, producing important contamination of the adjacent soils, which also led to the release and mobilization of PHEs into nearby water courses. Total PTE results indicate that the soils affected by mining activities were highly contaminated with As and Cu, while Zn and Pb content ranged from low to very high, depending on the analyzed samples. Cadmium levels were found to be very low in most of the soil samples. The test using Daphnia magna was the most sensitive bioassay, while the Eisenia foetida test was the least sensitive. Except for the LOS07 soil sample, the rest of the soils were classified as "High acute toxicity" and "Very high acute toxicity" for aquatic systems. The results in HACaT cells showed results similar to the ecotoxicological bioassays. The application of biotests, together with geochemical and mineralogical characterization, is a very useful tool to establish the degree of contamination and the environmental risk of potentially harmful elements.

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.

Feasibility study of fluorescent lamp waste recycling by thermal desorption.

The proposed Minamata Convention ban on the use of fluorescent lamps at the end of 2020, with a consequent reduction in mercury (Hg) light products, is expected to produce large amounts of discarded fluorescent bulbs. In this context, the most effective recycling options are a thermal mercury recovery system and/or aqueous solution leaching (lixiviation) to recover rare earth elements (REEs). Due to the heterogeneous nature of these wastes, a complete characterization of Hg compounds in addition to a determination of their desorption temperatures is required for their recycling. The objective of this study is to assess the feasibility of a fast cost-effective thermal characterization to ameliorate recycling treatments. A pyrolysis heating system with a heat ramping capability combined with atomic absorption spectrometry makes it possible to obtain residue data with regard to the temperature ranges needed to achieve total Hg desorption. The major drawback of these heat treatments has been the amount of Hg absorbed from the residue by the glass matrices, ranging from 23.4 to 39.1% in the samples studied. Meanwhile, it has been estimated that 70% of Hg is recovered at a temperature of 437 °C.

Ecological and Health Risk Assessments of an Abandoned Gold Mine (Remance, Panama): Complex Scenarios Need a Combination of Indices.

The derelict Remance gold mine is a possible source of pollution with potentially toxic elements (PTEs). In the study area, diverse mine waste has been left behind and exposed to weather conditions, and poses risks for soil, plants and water bodies, and also for the health of local inhabitants. This study sought to perform an ecological and health risk assessment of derelict gold mining areas with incomplete remediation, including: (i) characterizing the geochemical distribution of PTEs; (ii) assessing ecological risk by estimating the pollution load index (PLI) and potential ecological risk index (RI); (iii) assessing soil health by dehydrogenase activity; and iv) establishing non-carcinogenic (HI) and carcinogenic risks (CR) for local inhabitants. Soil health seems to depend on not only PTE concentrations, but also on organic matter (OM). Both indexes (PLI and RI) ranged from high to extreme near mining and waste accumulation sites. As indicated by both the HI and CR results, the mining area poses a health risk for local inhabitants and particularly for children. For this reason, it will be necessary to set up environmental management programs in the areas that are most affected (tailings and surrounding areas) and accordingly establish the best remediation strategies to minimize risks for the local population.

Biomonitoring of Hg0, Hg2 and Particulate Hg in a Mining Context Using Tree Barks.

The biomonitoring of atmospheric mercury (Hg) is an important topic in the recent scientific literature given the cost-benefit advantage of obtaining indirect measurements of gaseous Hg using biological tissues. Lichens, mosses, and trees are the most commonly used organisms, with many standardized methods for some of them used across European countries by scientists and pollution regulators. Most of the species used the uptake of gaseous Hg (plant leaves), or a mixture of gaseous and particulate Hg (mosses and lichens), but no method is capable of differentiating between main atmospheric Hg phases (particulate and gaseous), essential in a risk assessment. The purpose of this work was to evaluate different uptake patterns of biological tissues in terms of atmospheric Hg compounds. To accomplish this, the feasibility of two plant tissues from a tree commonly found in urban environments has been evaluated for the biomonitoring of gaseous Hg species in a Hg mining environment. Sampling included leaves and barks from Platanus hispanica and particulate matter from the atmosphere of the urban area around Almadén (south-central Spain), while analytical determinations included data for total Hg concentrations in biological and geological samples, Hg speciation data and total gaseous Hg (TGM). The results allowed us to identify the main Hg compounds in leaves and bark tissues and in atmospheric particulate matter, finding that leaves bioaccumulated only gaseous Hg (Hg0 and Hg2+), preferably during daylight hours, whereas the barks accumulated a combination of TGM and particulate bound Hg (PBM) during the day and at night. Subsequent merging of the atmospheric Hg speciation data obtained from leaves and barks allowed indicative maps of the main sources of TGM and PBM emissions to be obtained, thereby perfectly delimiting the main TGM and PBM sources in the urban area around Almadén. This method complements TGM biomonitoring systems already tested with other urban trees, adding the detection of PBM emission sources and, therefore, biomonitoring all Hg species present in the atmosphere. Scenarios other than mining sites should be evaluated to determine the utility of this method for Hg biospeciation in the atmosphere.

Occurrence and environmental constraints of gray monazite in red soils from the Campo de Montiel area (SW Ciudad Real province, south central Spain).

Monazite ((Ce, La, Nd, Th) PO4) is a rare and strategic mineral that occurs naturally as an accessory and minor mineral in diverse igneous and metamorphic rocks. This mineral does not frequently form mineable ore deposits and it has different typologies, including those formed by endogenous processes (generally "yellow monazite" mineralizations) and those formed by exogenous processes ("gray monazite" mineralizations). The mineral is an important ore of Rare Earth Elements (REEs), which have been identified by the European Union as critical raw materials. Monazite can be considered a weathering-resistant mineral, and the mobility of the REE and associated elements is low. The study reported here concerns a mineralogical and geochemical assessment of the occurrence and risks associated with the presence of concentrations of monazite in a typical, well-developed, and representative red Mediterranean soil, in order to establish the associated risk with their future mining. The results confirmed that monazite ore is particularly poor in radioactive elements, and it is concentrated in the most surficial soil horizons. The chemical mobility of REEs present in the soil, as assessed by selective extraction with ammonium acetate in acidic media, follows the order Y > Dy > U > Tb > Gd > Eu > Sm > La > Th > Ce. The mobility of REEs contained in monazite proved to be higher than that of the REE compounds in the upper horizons of the soil profile suggesting the immobilization in other REE-containing minerals, while light REEs show lower mobility rates than heavy REEs, due to an immobilization of LREE by sorption with iron oxy-hydroxides. Further studies are required in order to obtain better speciation data for REEs in soils aimed to identify soluble and insoluble compounds.

Microbial diversity and activity assessment in a 100-year-old lead mine.

Mining activities frequently leave a legacy of residues that remain in the area for long periods causing the pollution of surroundings. We studied on a 100 year-old mine, the behavior of potentially toxic elements (PTEs) and their ecotoxicological impact on activity and diversity of microorganisms. The PTEs contamination assessment allowed the classification of the materials as highly (reference- and contaminated-samples) and very highly polluted (illegal spill of olive mill wastes (OMW), tailings, and dumps). OMW presented the lowest enzymatic activities while tailings and dumps had low dehydrogenase and arylsulfatase activities. All the α-diversity indices studied were negatively impacted in dumps. Tailings had lower Chao1 and PD whole tree values as compared to those of reference-samples. ß-diversity analysis showed similar bacterial community composition for reference- and contaminated-samples, significantly differing from that of tailings and dumps. The relative abundance of Gemmatimonadetes, Bacteroidetes, and Verrucomicrobia was lower in OMW, tailings, and dumps as compared to reference-samples. Fifty-seven operational taxonomic units were selected as responsible for the changes observed between samples. This study highlights that assessing the relationship between physicochemical properties and microbial diversity and activity gives clues about ongoing regulating processes that can be helpful for stakeholders to define an appropriate management strategy.

Evolution of the Speciation and Mobility of Pb, Zn and Cd in Relation to Transport Processes in a Mining Environment.

Elements in mining extracts can be potentially toxic if they are incorporated into soils, sediments or biota. Numerous approaches have been used to assess this problem, and these include sequential extractions and selective extractions. These two methods have limitations and advantages, and their combined use usually provides a rough estimate of the availability or (bio)availability of potentially toxic elements and, therefore, of their real potential as toxicants in food chains. These indirect speciation data are interesting in absolute terms, but in the work described here, this aspect was developed further by assessing the evolution of availability-related speciation in relation to the transport processes from the emission source, which are mainly fluvial- and wind-driven. This objective was achieved by characterizing tailings samples as the source of elements in soils and sediments at increasing distances to investigate the evolution of certain elements. The standard procedures employed included a sequential five-step extraction and a selective extraction with ammonium acetate. The results show that the highest percentages of Zn and Pb in tailings, soils and sediment samples are associated with oxyhydroxides, along with a significant presence of resistant mineralogical forms. In the case of Cd, its association with organic matter is the second-most important trapping mechanism in the area. The physicochemical mechanisms of transport did not transform the main mineralogical associations (oxyhydroxides and resistant mineralogical forms) along the transects, but they produced a chaotic evolution pattern for the other minor matrix associations for Zn and a decrease in exchangeable and carbonate-bound forms for Pb in soils. Interestingly, in sediments, these mobile forms showed a decrease in Zn and a chaotic evolution for Pb. The most probable reason for these observations is that Zn2+ can form smithsonite (ZnCO3) or hydrozincite (Zn5(CO3)2(OH)6), which explains the retention of a carbonate-bound form for Zn in the soil transect. In contrast, Pb and Cd can appear as different mineral phases. The order of (bio)availability was Pb > Zn > Cd in tailings but Cd > Pb > Zn in soils. The physicochemical processes involved in transport from tailings to soils produce an increase in Cd (bio)availability. The trend is a decrease in bioavailability on moving away from the source (tailings), with maximum values obtained for Cd near to the source area (200-400 m).

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.

Factors influencing mercury uptake by leaves of stone pine (Pinus pinea L.) in Almadén (Central Spain).

The use of trees for biomonitoring of mercury (Hg) and other atmospheric pollutants is of increasing importance today. Leaves from different species have been the most widely used plant organ for this purpose, but only pine bark, and not leaves, was used to monitor Hg pollution. In Almadén (South Central Spain), the largest cinnabar (HgS) deposits in the world have been mined for over 2000 years to obtain metallic Hg and this activity has caused the widespread dispersion of this toxic element in the local environment. A strip of pine trees, 2750 m in length, adjacent and to the South of the mining town has been studied in order to evaluate pine tree needles as monitors for Hg contamination in this heavily polluted area. The study involved the collection of pine tree leaves from several discrete sites along the strip, as well as samples from other nearby locations, together with soil samples and monitoring of atmospheric Hg in the area during both the day and night. Leaves and soils were analyzed for total Hg concentration by means of atomic absorption spectrometry; the leachable fraction of soil Hg was also analyzed by the CV-AFS technique. The results indicate that soils from the investigated area were not directly affected by mining related pollution, with low total Hg levels (3-280 mg kg-1) found in comparison with the nearby Almadén metallurgical precinct and very low leachable Hg contents (0.27-59.65 mg kg-1) were found. Moreover, pine tree needles have a low uptake capacity, with lower THg levels (0.03-6.68 mg kg-1) when compared to those of olive trees in Almadén. However, pine needles do show significant variability with regard to the distance from the source. Gaseous Hg exhibits a similar pattern, with higher levels close to the source, especially during night time (225 ng m-3). A multiple linear regression analysis (MLRA) revealed that gaseous Hg in the nocturnal period is the prime factor that influences the amount of Hg uptake by pine tree needles. This finding makes pine needles a promising candidate to biomonitor gaseous Hg on a local or regional scale worldwide. Almadén pine tree needles have been exposed to a number of different Hg sources, including the primary one, namely the old mine dump, and secondary sources such as polluted roads or illegal urban residual waste. The secondary sources cause some minor discrepancies in the model established by the MRLA. The biomonitoring capacity of pine needles needs to be evaluated in areas far from the source. The process involved in gaseous Hg uptake by pine needles appears more likely to involve sorption in the external part of the needle than uptake through stomas, thus making this process strongly dependent on high atmospheric Hg concentrations.

Geochemical distribution of major and trace elements in agricultural soils of Castilla-La Mancha (central Spain): finding criteria for baselines and delimiting regional anomalies.

Castilla-La Mancha (central Spain) is a region characterized by significant agricultural production aimed at high-quality food products such as wine and olive oil. The quality of agricultural products depends directly on the soil quality. Soil geochemistry, including dispersion maps and the recognition of baselines and anomalies of various origins, is the most important tool to assess soil quality. With this objective, 200 soil samples were taken from agricultural areas distributed among the different geological domains present in the region. Analysis of these samples included evaluation of edaphological parameters (reactivity, electrical conductivity, organic matter content) and the geochemistry of major and trace elements by X-ray fluorescence. The dataset obtained was statistically analyzed for major elements and, in the case of trace elements, was normalized with respect to Al and analyzed using the relative cumulative frequency (RCF) distribution method. Furthermore, the geographic distribution of analytical data was characterized and analyzed using the kriging technique, with a correspondence found between major and trace elements in the different geologic domains of the region as well as with the most important mining areas. The results show an influence of the clay fraction present in the soil, which acts as a repository for trace elements. On the basis of the results, of the possible elements related with clay that could be used for normalization, Al was selected as the most suitable, followed by Fe, Mn, and Ti. Reference values estimated using this methodology were lower than those estimated in previous studies.

Heavy metal contamination in sediments of an artificial reservoir impacted by long-term mining activity in the Almadén mercury district (Spain).

Sediments from the Castilseras reservoir, located downstream on the Valdeazogues River in the Almadén mercury district, were collected to assess the potential contamination status related to metals(oids) associated with river sediment inputs from several decommissioned mines. Metals(oids) concentrations in the reservoir sediments were investigated using different physical and chemical techniques. The results were analyzed by principal component analysis (PCA) to explain the correlations between the sets of variables. The degree of contamination was evaluated using the enrichment factor (EF) and the geoaccumulation index (Igeo). PCA revealed that the silty fraction is the main metals(oids) carrier in the sediments. Among the potentially harmful elements, there is a group (Al, Cr, Cu, Fe, Mn, Ni, and Zn) that cannot be strictly correlated to the mining activity since their concentrations depend on the lithological and edaphological characteristics of the materials. In contrast, As, Co, Hg, Pb, and S showed significant enrichment and contamination, thus suggesting relevant contributions from the decommissioned mines through fluvial sediment inputs. As far as Hg and S are concerned, the high enrichment levels pose a question concerning the potential environmental risk of transfer of the organic forms of Hg (mainly methylmercury) from the bottom sediments to the aquatic food chain.

Mercury transfer from soil to olive trees. A comparison of three different contaminated sites.

Mercury contents in soil and olive tree leaves have been studied in 69 plots around three different source areas of this element in Spain: Almadén (Ciudad Real), Flix (Tarragona) and Jódar (Jaén). Almadén was the world's largest cinnabar (HgS) mining district and was active until 2003, Flix is the oldest Spanish chlor-alkali plant (CAP) and has been active from 1898 to the present day and Jódar is a decommissioned CAP that was active for 14 years (1977-1991). Total mercury contents have been measured by high-frequency modulation atomic absorption spectrometry with Zeeman effect (ZAAS-HFM) in the soils and olive tree leaves from the three studied areas. The average soil contents range from 182 µg kg(-1) in Flix to 23,488 µg kg(-1) in Almadén, while the average leaf content ranges from 161 µg kg(-1) in Jódar to 1213 µg kg(-1) in Almadén. Despite the wide range of data, a relationship between soil-leaf contents has been identified: in Almadén and Jódar, multiplicative (bilogarithmic) models show significant correlations (R = 0.769 and R = 0.484, respectively). Significant correlations were not identified between soil and leaf contents in Flix. The continuous activity of the Flix CAP, which remains open today, can explain the different uptake patterns for mercury, which is mainly atmospheric in origin, in comparison to the other two sites, where activity ceased more than 10 years ago and only soil uptake patterns based on the Michaelis-Menten enzymatic model curve are observed.

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.