Hydrochemical characterization of a mine water geothermal energy resource in NW Spain

Abandoned and flooded mine networks provide underground reservoirs of mine water that can be used as a renewable geothermal energy source. A complete hydrochemical characterization of mine water is required to optimally design the geothermal installation, understand the hydraulic behavior of the water in the reservoir and prevent undesired effects such as pipe clogging via mineral precipitation. Water pumped from the Barredo-Figaredo mining reservoir (Asturias, NW Spain), which is currently exploited for geothermal use, has been studied and compared to water from a separate, nearby mountain mine and a river that receives mine water discharge and partially infiltrates into the mine workings. Although the hydrochemistry was altered during the flooding process, the deep mine waters are currently near neutral, net alkaline, high metal waters of Na-HCO3 type. Isotopic values suggest that mine waters are closely related to modern meteoric water, and likely correspond to rapid infiltration. Suspended and dissolved solids, and particularly iron content, of mine water results in some scaling and partial clogging of heat exchangers, but water temperature is stable (22 °C) and increases with depth, so, considering the available flow (> 100 L s− 1), the Barredo-Figaredo mining reservoir represents a sustainable, long-term resource for geothermal use

Comparison of sediment bioavailable methods to assess the potential risk of metal(loid)s for river ecosystems

A heavily impacted river basin (Caudal River, NW Spain) by Hg and Cu mining activities, abandoned decades ago, was used to evaluate the environmental quality of their river sediments. The obtained results compared with reference values established by the US EPA and the Canadian Council of Ministers of the Environment for river sediments, have shown that the main elements of environmental concern are arsenic (As), mercury (Hg) and, to a lesser extent, copper (Cu), which reach concentrations up to 1080, 80 and 54 mg kg-1, respectively. To understand the role that river sediments play in terms of risk to ecosystem health, a comparison has been made between the total content of metal(oid)s in the sediments and the bioavailable contents of the same elements in pore water, passive DGT (Diffusive Gradients in Thin films) samplers and the sediment extractant using acetic acid. A good correlation between the As and Cu contents in the DGTs and the pore water was found, resulting in a transfer from the pore water to the DGT of at least 47% of the Cu and more than 75% of the As when the concentrations were low, with a deployment time of 4 days. When As and Cu concentrations were higher, their transfer was not so high (above 23.6% for As and 19.3% for Cu). The transfer of Hg from the pore water to the DGT was practically nil and does not seem to depend on the content of this metal. The fraction extracted with acetic acid, conventionally accepted as bioavailable, was clearly lower than that captured by DGTs for As and Cu (≤5% and ≤8.5% of the total amount, respectively), while it was similar for Hg (0.2%)

Study of the small mammals of Bronze Age layers from Arenaza I Cave (Galdames, Bizkaia)

Este trabajo recoge el estudio de los micromamíferos de los lechos superiores (ca. 3695-4414 cal BP) de la Cueva de Arenaza I (Galdames, Bizkaia), excavados entre 1991 y 1993 y recuperados recientemente del depósito provincial. El conjunto de restos corresponde al menos a 14 especies diferentes de micromamíferos, nueve de ellas pertenecientes al Orden Rodentia y cinco al Orden Eulipotyphla. Los datos paleoecológicos de los tres lechos indican un claro predominio de masas forestales, siendo el lecho 9 en el que mayor extensión presentan. Por ende, probablemente es en ese momento cuando tendrían lugar las condiciones ambientales más cálidas y húmedas de todo el registroThe study of the small mammals from the uppermost layers (ca. 3695- 4414 cal BP) from Arenaza I Cave (Galdames, Bizkaia) is reported in this paper. Even if the archaeological works were carried out between 1991 and 1993, the sediment has been recovered from the provincial deposit. A total of 14 species have been identified, nine belonging to the Order Rodentia and five to Order Eulipotyphla. Palaeoecological data obtained for the three layers indicate a clear predominance of forest, being the layer 9 where it was most extended. Therefore it was probably at that time when the most humid conditions and mild temperatures took plac

Occurrence and speciation of arsenic and mercury in estuarine sediments affected by mining activities (Asturias, northern Spain)

Sediments contaminated by Hg and As from two historical mining areas have been deposited in the Nalon estuary (Asturias, northern Spain) since 1850. Total mercury (Hgtotal) concentrations in the sediments range from 0.20 \u3bcg.g 121 to 1.33 \u3bcg.g 121 , most of it in the form of sulphides. Concentrations of methylmercury (303.20\u2013865.40 pg.g 121) are up to two orders of magnitude lower than the concentration of Hgtotal. Total As concentration (Astotal) is enriched compared to the background level for the area. The relative abundance of As(V) on As(III) in the sediments ranges from 97.6% to 100%, whereas inorganic Hg accounts for more than 99% of the total Hg. The occurrence of the most toxic species, inorganic As(III) and organic methylmercury, seem to be related to redox conditions together with the amounts of sulphur which act as natural barriers which inhibit the biological and chemical speciation processes. Despite the high amounts of Hg and As present in the sediments, their transference to the water column appear to be limited thus converting sediments in an effective sink of both elements. Special attention should be paid to potential variations of the environmental conditions which might increase the element mobility and exchange between sediments and the water column

The effects of resuspension on the fate of Hg in contaminated sediments (Nal\uf3n estuary, Spain)

Sediments of the Nal\uf3n estuary (Cantabrian Sea, Spain) are important repositories of mercury as a direct consequence of the runoffs from the historical Hg mining activity developed in the Nal\uf3n river basin. Previous studies have shown that sediment acts as secondary source of Hg species to the overlying water column in natural conditions. However, evidence for the effects of resuspension on the dynamics of Hg species is still lacking. The effect of resuspension on the cycling of inorganic mercury (IHg) and methylmercury (MeHg) between the sediment and water column was investigated in a mesocosm study. Two experiments were conducted in July 2017 based on unaltered material collected from sites heavily impacted by Hg and periodically subjected to dredging activities. Designed to mimic the resuspension of particles, both experiments revealed that the release of Hg species from the solid to the dissolved phase became negligible quickly after the event. MeHg values did not change according to total dissolved mercury (THg), suggesting that the enhancement of methylation processes may occur during this processes. The results reported in this research may be useful for the local fishing activities and environmental management, as well as for planning dredging activities on the area in order to decrease potential impacts on the aquatic environment

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 inhab-itants. 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 populatio

Empirical Model of Gaseous Mercury Emissions for the Analysis of Working Conditions in Outdoor Highly Contaminated Sites

The project SUBproducts4LIFE is a LIFE-funded research project that aims to demonstrate innovative circular economy concepts by repurposing industrial subproducts/waste (coal ash and gypsum from coal power plants, blast furnace slag, and steelmaking slag from steel factories) for the remediation of contaminated soils and brownfield areas associated with Hg mining on a large scale. Within the project, one of the objectives is related to worker safety by developing protocols and elaborating a guide of good practices to work under in these highly contaminated areas. The present research aims to assess the working conditions in an abandoned mine facility in terms of gaseous mercury in the environment, evaluating the main areas of the mine to ensure the health and safety of all workers and visitors. The study developed an empirical model for estimating the gaseous mercury concentration at any temperature with the target of scheduling the work to avoid occupational hazards. The research concluded that working without restrictions for temperatures under 15 °C in all the mine’s facilities is possible

MERCURY PARTITIONING IN THE WATER COLUMN OF EL ENTREDICHO OPEN-PIT (ALMAD\uc9N, SPAIN)

The Almad\ue9n mercury (Hg) mining district (Ciudad Real, central Spain) is located within the largest geochemical anomaly of this element in the world. The district includes a series of deposits that comprise a variety of structural and textural styles sharing a simple paragenesis, where a dominant cinnabar mineralization is associated with other accessory minerals but in very low proportions to be considered the deposits as monomineral. An intensive mining activity has been developed during more than 2000 years, leaving an important number of decommissioned mines and liabilities scattered in the area. Among the several sites of exploitation, El Entredicho (Fig. 1) is the most peculiar since it is an unusual open-pit mine which was in operation only for Hg extraction. It is the second mine in importance within the district which produced 290,000 flask of Hg in nineteen years of exploitation. As a consequence of the mine operations, a big hole was created (87,500 m2 of surface and 72 m of depth) which was restored by flooding with waters from the near Valdeazogues River in 1998. Today, this open-pit only receives waters from runoff without other inputs from ground or surface waters. Due to this unusual environmental setting, water column has evolved in isolation during the last seventeen years making this artificial lake a unique laboratory for investigating mercury biogeochemical processes in an isolated freshwater environment. This research focuses on a preliminary characterization of Hg abundance and fractionation in the water column of El Entredicho open-pit to understand the effects of physical and biogeochemical factors on the distribution of Hg specie

Heavy metal speciation and risk assessment in freshwater sediments of an artificial reservoir in the Almad\ue9n mining district, Spain

The Castilseras artificial water reservoir (Almad\ue9n, South Central Spain) is receiving runoff water from the most important Hg mines of the Almad\ue9n mining district and from other small Pb-Zn mines. This reservoir constitutes the only lentic medium located within the mining district and their sediments can be considered as a sink and/or source of contaminants in the aquatic ecosystem. Then, the ecological risk assessment of these sediments can be considered as priority target in order to assess the environmental quality of the fluvial ompartment and the potential uptake of heavy metals for the biota. For this objective, sediments collected in 12 sampling stations have been studied using the Sequential Extraction Procedure (SEP). Results were evaluated using Principal Component Analysis (PCA) and different risk criteria such as Pollution Degree, Mean Probable Effect Concentration Quotient, and Risk Index. general, the high contents in Hg and other elements such as As and Pb, can be attributed to environmental liabilities of decommissioned mines. The study of the different fraction steps and their statistical multivariate treatment by PCA, showed two differentiate groups of elements in the easily leachable fraction F1. This fact is indicative of the presence of sulfate salts and secondary precipitates of carbonates as the main sink for easily accessible metallic elements. In the reducible fraction F2, chemical analysis revealed a significant relationship between the majority of the analyzed elements and the Fe oxy-hydroxides, with exception of Co, Hg and Ni, which are preferentially associated with Mn oxy-hydroxides. In the oxidisable fraction (F3), a significant relationship between Cu, Fe, Hg and Zn (most representative metals of the ore deposits in the district) and sulfides/organic matter was observed. Finally, the residual fraction F4 showed a first group constituted by As, Ca, Co, Mg, Mn and Ni, elements which are related to the presence of silicates, and a second group related to sulfides or secondary sulfates. The environmental assessment based on the aforementioned criteria provides risk levels varying from moderate to high. The risk appears to be higher at the head of the reservoir, where the highest concentrations of heavy metals and metalloids in the sediment are due to a selective accumulation of fine-grained particles