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Arsenic-rich geothermal fluids as environmentally hazardous materials – A global assessment
Abstract
Arsenic-rich geothermal fluids are hazardous materials of global impact, affecting different environments (groundwater, surface water, seawater, sediments, soils, atmosphere) and human and animal health. They can be released naturally or through human activities. For the first time, a systematic global assessment of geothermal arsenic (As) in fluids of the six principal types of geothermal reservoirs and their environmental impact (e.g. freshwater sources used for drinking and irrigation), distinguishing between different uses (if any), was performed based on research of the geochemical characteristics and geotectonic setting of the formation of natural geothermal reservoirs worldwide. This will assist to further improve the sustainability of geothermal energy use, which can be an excellent environmental friendly renewable energy resource for electric power production and direct heat use. Arsenic in geothermal fluids (up to several tens of mg/L) originates especially in deep seated (several kilometers) reservoirs. Proper management of geothermal fluids during exploration, exploitation, use and disposal of resulting waste products through sustainable As mitigation strategies are essential. However, more research about As speciation and volatile As is necessary to fulfil this aim. Therefore As (and its principal species) needs to be included as parameter for standard analysis and monitoring program in any project using geothermal fluids from exploration to management of resulting wastes as base to define appropriate mitigation actions.
... The combustion of coal for power generation and the utilization of coal combustion residues are recognized as potential sources of arsenic contamination [14]. Geothermal systems have also emerged as potential sources of arsenic contamination [15]. Faults can serve as conduits for the ascent of geothermal water, transporting arsenic into aquifers [16]. ...
... 3.3.2. Analysis of arsenic variation based on the distance from geothermal systems and soil layer depths Arsenic is found in geothermal systems and holds the potential to be a source of arsenic contamination in the environment [15,43]. In the study area, there lies the geothermal area of Wayang Windu, precisely located in Pangalengan [44]. ...
... El MOE o coeficiente de peligrosidad por municipio de arsénico y fluoruros, evaluadas y asociadas con exposiciones y riesgos que posiblemente suscitan preocupación en salud pública se presentan en las tablas 2 y 3. Antioquia natural o antropogénica con arsénico, esta contaminación de origen natural afecta principalmente a los departamentos ubicados en la cordillera central y en la occidental cerca de las zonas de volcanes, en estas áreas el arsénico procede de yacimientos que contienen arsenopirita u otros minerales con trazas de este metaloide (6). Asimismo, el arsénico se encuentra naturalmente en los fluidos de los yacimientos geotérmicos y en manifestaciones superficiales, como, por ejemplo, manantiales, sin embargo, el agua subterránea tiende a ser más susceptible a su contaminación debido a la interacción de fluidos geotérmicos con minerales de roca y el mayor potencial en acuíferos en los que se crean condiciones fisicoquímicas que favorecen la liberación del metaloide el cual que puede ser vehiculizado al agua empleada para potabilización (15). Mientras que, las concentraciones más altas en suelo, sedimentos, agua y la cadena alimentaria podrían estar asociadas con la contaminación de origen antrópico, en regiones mineras, en particular en las que se practica la minería de oro artesanal o a pequeña escala (16). ...
Introducción. El agua es fundamental para la vida, salud y desarrollo socioeconómico de una población, sin embargo, también puede ser un vehículo de contaminantes bien sea de origen natural, debido a la hidrogeología y características geoquímicas de las zonas cercanas a la fuente de agua o relacionada con las actividades antropogénicas. El objetivo de este artículo fue evaluar el riesgo asociado a la exposición a arsénico, fluoruros y mercurio reportados ante el Sistema de Información de la Vigilancia de la Calidad del Agua para Consumo Humano (SIVICAP) durante los años 2019 a 2023 en Colombia. Metodología. Se realizó un estudio transversal empleando las concentraciones de arsénico, fluoruros y mercurio reportadas para agua de consumo humano en SIVICAP, durante 2019 a 2023 y se evaluó el riesgo por exposición a estos compuestos, mediante la metodología de evaluación de riesgos en inocuidad de alimentos y agua, empleando el programa Excel. Resultados. El 99,2 % de las muestras analizadas para arsénico y el 0,22 % de las muestras de fluoruros reportadas durante 2019 a 2023 presentan exposiciones que pueden suscitar preocupación en salud pública. Por el contrario, las exposiciones relacionadas con las concentraciones de mercurio reportadas durante este periodo no suscitan preocupación en salud pública. Conclusión. De acuerdo con la evaluación realizada las exposiciones calculadas para arsénico suscitan preocupación en salud en Atlántico, Antioquia y Cundinamarca durante 2019 a 2023, para los demás departamentos no se calculó el riesgo debido a la carencia de datos. La exposición oral crónica a fluoruros a través del agua para consumo humano en municipios de Nariño, Casanare y Huila suscitan preocupación en salud pública por posible aumento de fluorosis dental y aumento de riesgo de fractura ósea y, para este periodo de análisis, la exposición a mercurio no suscita preocupación en salud.
... Arsenic has an abundance in the Earthʼs crust of 5 × 10 -4 , its concentration levels vary in the environment due to the oxidation state in which it occurs (3-, 0, 3+, 5+) either in water, soil and/or rocks (Adrianno, 2001), it is present in more than 245 minerals of primary or secondary formation, either in the form of arsenates (60%), as sulfides (mainly pyrite, arsenopyrite, and sulfosalts) (20%) and other forms such as arsenides, arsenites, oxides and silicates (20%) (Mandal and Suzuki, 2002). Pyrite and arsenopyrite are the most abundant metallic sulfides in nature with a high As content, is common to find them in hydrothermal systems, in metasediments with mineralized veins, volcano-sedimentary or sedimentary environment, in ore deposits and Neogene or Quaternary alluvial basins, etc. (Chen et al., 2022;Mandal and Suzuki, 2002), geothermal fluids close to active geological and tectonic setting are a very important natural source of As in entire regions that pollute groundwater and surface water in addition to soils and sediments (Morales-Simfors and Bundschuh, 2022). Other arsenicbearing minerals are iron, magnesium, and aluminum oxides and hydroxides, either absorbed or forming part of the ore (Smedley and Kinniburgh, 2002). ...
Several aquifers located in North-Central Mexico have natural arsenic (As) concentrations higher than those allowed by national and international regulations; these aquifers are usually located in fractured volcanic environments that interact with sedimentary basins and have a carbonate basement. In this study, an evaluation of As in volcanic and sedimentary rocks collected at 13 sampling sites along the Sierra de Codornices (Guanajuato State, Central Mexico) was carried out. These geologic materials are representative of the dominant hydrogeologic environment. The As content is disseminated in volcanic rocks and the highest contents were obtained in felsic rocks; this information served to identify the hydrogeochemical processes related to the mobilization and transport of arsenic in the aquifer. The mobilization of As is a product of the dissolution of volcanic glass, a process involved in the alkaline desorption that occurs on As-containing mineral surfaces and possibly by the dissolution/desorption of Fe minerals and some clays, all these processes may be accelerated by the geothermal characteristics of the groundwater in the study area.
... In these regions, rapid water evaporation leads to the gradual concentration of dissolved solids, including arsenic, in salt lakes or groundwater [39]. Hot springs and geothermal springs are also significant natural sources of arsenic, especially in regions with frequent geothermal activity [40]. The water from hot springs and geothermal springs dissolves a large amount of minerals, including arsenic, as it passes through deep crustal layers [41]. ...
Arsenic contamination in sludge and sediment has emerged as a pressing environmental issue with far-reaching implications. This review delves into the multifaceted problem of arsenic contamination, focusing on its complex interactions with microbial resistance genes (MRGs). It explores the key role of microorganisms in the biogeochemical cycling of arsenic, including processes such as reduction, oxidation, methylation, and volatilization. It describes how microorganisms resist arsenic through resistance genes that encode proteins such as efflux pumps, enzymatic detoxification, and intracellular sequestration. Arsenic, a naturally occurring element, can enter sludge and sediment through various natural and anthropogenic pathways, leading to detrimental effects on environmental quality. Understanding the role of microorganisms in arsenic mobilization, transformation, and their ability to resist arsenic toxicity through MRGs is essential for effective mitigation and remediation strategies. This review discusses the sources and distribution of arsenic in sludge and sediment, the intricate mechanisms of microbial arsenic resistance, and the potential implications for environmental management and human health. It also examines current research trends and identifies areas requiring further investigation. By unraveling the interplay between arsenic contamination, microorganisms, and MRGs, this review aims to contribute to a deeper understanding of the issue and guide future research and environmental protection efforts.
... metals, bacteriological parameters, as well as the physico-chemistry of major ions, metals, and other trace elements [3][4][5][6][7][8]. In this context, synthetic mapping of drinking water quality requires strategic choices. ...
Groundwater, widely used for supplying drinking water to populations, is a vital resource that must be managed sustainably, which requires a thorough understanding of its diverse physico-chemical and bacteriological characteristics. This study, based on a 27-year extraction from the Sise-Eaux database (1993–2020), focused on the island of Corsica (72,000 km²), which is diverse in terms of altitude and slopes and features a strong lithological contrast between crystalline Corsica and metamorphic and sedimentary Corsica. Following logarithmic conditioning of the data (662 water catchments, 2830 samples, and 15 parameters) and distinguishing between spatial and spatiotemporal variances, a principal component analysis was conducted to achieve dimensionality reduction and to identify the processes driving water diversity. In addition, the spatial structure of the parameters was studied. The analysis notably distinguishes a seasonal determinism for bacterial contamination (rain, runoff, bacterial transport, and contamination of catchments) and a more strictly spatial determinism (geographic, lithological, and land use factors). The behavior of each parameter allowed for their classification into seven distinct groups based on their average coordinates on the factorial axes, accounting for 95% of the dataset’s total variance. Several strategies can be considered for the inventory and mapping of groundwater, namely, (1) establishing quality parameter distribution maps, (2) dimensionality reduction through principal component analysis followed by two sub-options: (2a) mapping factorial axes or (2b) establishing a typology of parameters based on their behavior and mapping a representative for each group. The advantages and disadvantages of each of these strategies are discussed.
... Today, thermal waters are used in a variety of ways. While tourists still seek the relaxing and therapeutic properties [3][4][5][6], investment in geothermal energy potential is increasing [7,8], with a growing awareness of the need to protect these natural resources and minimize their negative impact on the environment, such as noise from power plants, risks of water pollution by saline fluids rich in elements such as boron, fluorine and arsenic, and the accumulation of heavy metal sulfides in river sediments [9][10][11]. ...
Hydrothermal units are characterized by the emergence of several large-flow thermo-mineral springs (griffons), each with varying temperature and physico-chemical characteristics depending on the point of emergence. It seems, however, that there is variability between the different systems, although it is not easy to characterize it because the variability within each system is high. The regional dimension of the chemical composition of thermal waters is, therefore, an aspect that has received very little attention in the literature due to the lack of access to the deep reservoir. In this study, we investigated the spatial variability, on a regional scale, in the characteristics of thermal waters in northeastern Algeria, and more specifically the hydrothermal systems of Guelma, Souk Ahras, Khenchela and Tébessa. Thirty-two hot water samples were taken between December 2018 and October 2019, including five samples of low-temperature mineral spring water. Standard physico-chemical parameters, major anions and cations and lithium were analyzed. The data were log-transformed data and processed via principal component analysis, discriminant analysis and unsupervised classification. The results show that thermal waters are the result of a mixture of hot waters, whose chemical profile has a certain local character, and contaminated by cold surface waters. These surface waters may also have several chemical profiles depending on the location. In addition to the internal variability in each resource, there are differences in water quality between these different hydrothermal systems. The Guelma region differs the most from the other thermal regions studied, with a specific calcic sulfate chemical profile. This question is essential for the rational development of these regional resources in any field whatsoever.
... However, geothermal energy production plants could have also an impact on environment [7] and on human health due to the presence of some chemical hazards, such as mercury, hydrogen sulphide [8] and arsenic [9]. Moreover, the presence of naturally occurring radioactive materials (NORM) can also be of concern for workers and population living nearby. ...
In the present paper, the general methodological approach developed to manage legislative requirements for NORM involving industries was fitted to the geothermal industrial sector, which is in the indicative list of the European Directive 2013/59/Euratom (EU-BSS). A review of the state of the art about the radiological characterization of NORM in geothermal plants have been performed with the aim to identify matrices and exposure scenarios of radiological concern. From the analysis of collected data, it results that radiological content of NORM residues generally depends on the characteristics of the geothermal fluid as well as on the type of the plants. In several plants, residues (both scales and filtering materials) show generally high activity concentrations, especially for Ra-226 and Ra-228 decay segments, exceeding Exemption Levels of the EU-BSS. Several tables have been presented as tools to support the stakeholders in the application of the legislative requirements regarding radiation protection in the geothermal sector.
... In both aquifers, the most degraded quality characteristics appear around the villages of Chrisochori and, secondarily, Chrisoupoli, which coincides well with the documented geothermal field of Nestos basin [38]. Hence, the elevated concentrations of these parameters may well be linked to the geological structure and the low enthalpy fields documented, as suggested in several cases of such fields across the world [39][40][41]. As already discussed, in applying the PoS methodology, a set of reference values needs to be considered, which, in our case, is the potability set of criteria, as practiced in many analogous applications. ...
The Nestos River delta is one of the most important and sensitive basins in Greece and Europe due to its ecosystem functions, combining intensive agricultural production with low-enthalpy geothermal energy and important ecotopes. High water quality is of paramount importance to the sustainability of the system. Systematic and continuous assessment of water quality needs to be carried out in a way that is easy and quick for decision makers and non-expert societal partners to comprehend. In this way, decisions may be made more rapidly, and involved water users may be sensitized to rational water use. To this end, this paper presents the assessment of groundwater quality in the Nestos River’s western delta with the use of Poseidon (PoS), a versatile, index-based method. Groundwater samples collected from 24 and 22 wells tapping the unconfined and the confined aquifers, respectively, in four time periods (May and October 2019 and 2020) were analyzed. Using the PoS index, groundwater samples were classified according to their quality status, highlighting the parameters driving quality degradation issues, thus assisting water managers in obtaining an overview of quality status and evolution through datasets that were often large. PoS index is applied in the study area for the first time and provides a groundwater quality assessment through a unique score representative of the overall water quality status regardless of processes (anthropogenic or natural) or any kind of pressures.
... Arsenic (As) is a geogenic pollutant that is broadly distributed in rocks, sediments and water [1]. The two most important and wellrecognized natural sources of this metalloid are volcanism and geothermalism [2,3]. However, anthropogenic activities such as mining and agricultural activities, hydrocarbon and geothermal exploitation, strongly accelerated As release from geogenic sources and contributed to high As concentrations in drinking waters [4]. ...
... These PTEs can enter the human body mainly through direct ingestion and dermal contact during bathing and balneology [21,22]. The discharge of geothermal waters in the environment may also pose a serious threat to human health and ecosystems through the contamination of aquatic ecosystems (groundwater and stream water) [20,23]. Therefore, in other countries, some studies based on the hydrochemistry of geothermal water have been conducted for environmental surveys rather than for mineral exploration purposes [24,25]. ...
A comprehensive hydrogeochemical survey of the geothermal waters from the Nappe Zone (Maghrebides fold-and-thrust belt) was undertaken to determine the origins of geothermal waters and to assess the health risks associated with their potentially toxic elements. A total of 11 geothermal water and 3 stream water samples were collected and analysed for major and trace elements (As, B, Ba, Fe, Mn, Pb, Sr, Zn). Two main geothermal water groups were highlighted by hydrogeochemical diagrams and multivariate analyses (PCA, HCA): the first group is the Na−Cl type, TDS > 10 g/L, controlled by deep circulation, while the second group is the Na-Cl−HCO3 type, TDS < 2 g/L, and controlled by shallow circulation. A curved hydrogeochemical evolution path, observed from mixed bicarbonate shallow groundwater to chloride geothermal water, indicates that the interaction with evaporites drives the chemistry of the geothermal samples. On these, the As enrichments come from sulphide oxidation polymetallic mineralisation during the upwelling to the surface from E–W major lineaments. Therefore, E–W lineaments are potential areas for mineral prospecting. The health risk assessment reveals that the concentration of potentially toxic elements in geothermal waters are lower than the guideline values for the protection of freshwater aquatic life and dermal exposure (bathing or balneology).
... For example, matters as the use of land are strongly discussed, as well as the use of water resources (which does not account for the difference between deep and surface water, which is a key issue in geothermal energy as the two streams must be kept separate as far as possible). Moreover, the direct contribution of species such as H 2 S to acidification is currently being questioned [23] and the ecotoxicity of substances like heavy metals [24] or hazardous materials [25] is subject to high uncertainty. The recent publication of LCA guidelines in the GEOENVI H2020 project [26] has allowed to identify what are the major environmental impact categories and has confirmed the high attention to GHG global emissions. ...
... Vol:. (1234567890) Geothermal water is a very important natural source of PTEs (especially As and F) (Aksoy et al., 2009;Kayastha et al., 2022;Maitra et al., 2021;Sracek et al., 2015;Wang et al., 2021;Webster & Nordstrom, 2003), which has impacted the environment (such as freshwater source and agricultural soil), human health, and economy globally (Di Marzio et al., 2019;Morales-Simfors & Bundschuh, 2022;Raju, 2022;Ramos et al., 2021;Wang et al., 2021). Knappett et al. (2020) found that the concentration of As in an inter-montane aquifer system in central Mexico raised from 20 to 40 μg/L over 17 years because of the geothermal impact. ...
Potentially toxic elements from geothermal springs can cause significant pollution of the surrounding environment and pose potential risk to the ecosystem. The fate of potentially toxic elements in the water–soil–plant system in the Yangbajain geothermal field on the Tibetan Plateau, China was investigated to assess their impact on the eco-environment. The concentrations of Be, F, As, and Tl were highly elevated in the headwaters of the Yangbajain geothermal springs, and their concentrations in the local surface water impacted by the geothermal springs reached 8.1 μg/L (Be), 23.9 mg/L (F), 3.83 mg/L (As), and 8.4 μg/L (Tl), respectively, far exceeding the corresponding thresholds for surface and drinking water. The absence of As–Fe co-precipitation, undersaturated F⁻, and weak adsorption on minerals at high geothermal spring pH may be responsible for the As- and F-rich drainage, which caused pollution of local river. As concentrations in the leaves of Orinus thoroldii (Stapf ex Hemsl.) Bor were up to 42.7 μg/g (dry weight basis), which is an order of magnitude higher than the allowable limit in animal feeds. The locally farmed yaks are exposed to the excessive amount of F and As with high exposure risk through water-drinking and grass-feeding.
... Arsenic (As) is a natural trace element commonly found in groundwater (Hem, 1985;Herath et al., 2016;Mattheβ, 1994;Ravenscroft et al., 2009;Smedley and Kinniburgh, 2002) with concentrations in many aquifers below drinking water standards (<10 μg/L). Elevated concentrations (up to several thousands of μg/L) are observed in specific environments, notably in thermal groundwater (Morales-Simfors and Bundschuh, 2022;Webster and Nordstrom, 2003;Welch et al., 2000;Xing et al., 2022), groundwater affected by mining activities (Coudert et al., 2020;Paktunc, 2013;Smedley et al., 1996;Williams et al., 1996), groundwater in tuffaceous rock (Johannesson and Tang, 2009), groundwater in closed basins with high evaporation rates (Dehbandi et al., 2019;Jia et al., 2017;Ortega-Guerrero, 2017;Welch et al., 2000) and in deltas (Postma et al., 2007;Smedley, 2008;Smedley and Kinniburgh, 2002;Wang et al., 2018). Most problematic are the deltas, like the ones in Bangladesh, West Bengal, Cambodia and Vietnam, because of widespread reliance on untreated groundwater as the main source of drinking water. ...
Arsenic is a common trace element in groundwater and its fate and transport are controlled by combination of (i) natural processes, including redox conditions, salinity and pH, (ii) sedimentary and geochemical environment, and (iii) anthropogenic influences such as groundwater extraction, managed aquifer recharge (MAR), Aquifer Thermal Energy Storage (ATES), and pollution. We investigated the relative influence of these processes by presenting 10 cases from The Netherlands. Our review showed that the primary controlling factor for arsenic mobility in natural coastal dune systems is the redox state of groundwater, with concentrations between 2 and 10 μg/L. Strongly reduced greensands (containing glauconite and, more importantly, associated minerals) exhibited elevated As concentrations, with concentrations up to 40 μg/L. Groundwater systems modified by MAR or those that are influenced by nitrate pollution (NP) showed elevated As concentrations (20–110 μg/L), as a result of either pyrite oxidation (MAR, NP) or reductive dissolution of iron(hydr)oxides (MAR). Increasing temperature at ATES systems may cause mobilization of As at temperatures beyond 25 °C. The highest As concentrations were observed at sites where muddy sediments were recently deposited in surface water bodies (200–820 μg/L), for example in dammed Rhine River tributaries and sand pit lakes south of the city of Amsterdam. The reduction of arsenate to arsenite and competitive desorption during intrusion of polluted water also form important As mobilizing processes. The data for the Netherlands show that high CH4 and NH4 concentrations may form a risk indicator of elevated As levels in some fresh groundwater systems.
... Therefore, understanding the hydrogeochemical controls on the enrichment and mobility of As and B is a crucial key for predicting geogenic As and B enrichment within the major river basin in the Tibetan Plateau, and could potentially contribute to the retardation of the ecotoxicological risks in the downstream Asian regions. There is a growing belief that several hydrogeochemical processes have influenced the spatial distribution of As and B in the major river basin within the Tibetan Plateau: 1) the active geothermal activities and the discharge of geothermal water into rivers (Guo et al., 2008(Guo et al., , 2015(Guo et al., , 2019Li et al., 2013Li et al., , 2014Liu et al., 2020;Morales-Simfors and Bundschuh, 2021;Yuan et al., 2014;Wang et al., 2018); 2) the re-distribution of As and B during the source-rock weathering in the river basins (Coomar et al., 2019;Qu et al., 2019;Zhang et al., 2021;Zheng et al., 2022;Zhou et al., 2022); 3) the variations in hydrologic regimes under the natural or anthropogenic disturbance (including flooding, dam constructions, and mining activities, etc.) (Gu et al., 2020;Xu et al., 2021;Zhao et al., 2020). In addition, these mechanisms may concurrently influence the enrichment of As and B in river basins, such as the Yalung Tsangpo River Zhou et al., 2022) and Singe Tsangpo River (Li et al., 2013;Zheng et al., 2022;Zhao et al., 2020Zhao et al., , 2021. ...
... It is a minor but ubiquitous element of the Earth's crust, and some chemical species are volatile and highly soluble in aquatic systems. In general, arsenite and arsenate minerals are highly soluble in aqueous solution, often proving to be sources of arsenic contamination [1][2][3][4][5]. ...
Arsenic is a well-known contaminant present in different environmental compartments and in human organs and tissues. Inorganic As(III) represents one of the most dangerous arsenic forms. Its toxicity is attributed to its great affinity with the thiol groups of proteins. Considering the simultaneous presence in all environmental compartments of other common functional groups, we here present a study aimed at evaluating their contribution to the As(III) complexation. As(III) interactions with four (from di- to hexa-) carboxylic acids, five (from mono- to penta-) amines, and four amino acids were evaluated via experimental methods and, in simplified systems, also by quantum-mechanical calculations. Data were analyzed also with respect to those previously reported for mixed thiol-carboxylic ligands to evaluate the contribution of each functional group (-SH, -COOH, and -NH2) toward the As(III) complexation. Formation constants of As(III) complex species were experimentally determined, and data were analyzed for each class of ligand. An empirical relationship was reported, taking into account the contribution of each functional group to the complexation process and allowing for a rough estimate of the stability of species in systems where As(III) and thiol, carboxylic, or amino groups are involved. Quantum-mechanical calculations allowed for the evaluation and the characterization of the main chelation reactions of As(III). The potential competitive effects of the investigated groups were evaluated using cysteine, a prototypical species possessing all the functional groups under investigation. Results confirm the higher binding capabilities of the thiol group under different circumstances, but also indicate the concrete possibility of the simultaneous binding of As(III) by the thiol and the carboxylic groups.
Geothermal ecosystems are defined by extreme environmental conditions, such as elevated temperatures, high concentrations of toxic chemicals, and fluctuations in abiotic stressors, which shape plant survival and adaptation. These unique ecosystems, found across various geothermal regions globally, support specialized plant communities that have developed distinctive morphological, physiological, and ecological adaptations. Indonesia, located on the Pacific Ring of Fire, is one of the world's richest geothermal nations, offering an important yet underexplored context for studying vegetation in geothermal zones. This review examines the environmental conditions of geothermal ecosystems, the adaptive strategies of vegetation, and patterns of plant diversity within Indonesian geothermal fields. It also explores ecological succession, community dynamics, and the potential use of geothermal vegetation as environmental indicators for biomonitoring. Despite growing interest, significant research gaps remain, particularly in long-term monitoring and the integration of molecular-level studies. Addressing these gaps is essential for enhancing scientific understanding and informing conservation and sustainable geothermal energy development in tropical regions. This review highlights the ecological significance of geothermal vegetation and underscores the need for research to support both biodiversity preservation and responsible energy exploitation.
High-arsenic (As) geothermal water has been found over the world. However, the spatial distributions of As contents and genesis in geothermal systems remain to be fully understood due to the complexity of the sources and processes associated with As. In this study, the hydrochemical and isotopic methods and the self-organized mapping (SOM) were employed to investigate the spatial distributions and enrichment mechanism of As in hot springs in the Red River Fault Zone, southwest China. The results showed that arsenic concentration is low (less than 10 µg/L) in hot springs in the south part of the fault, while it is relatively high with a mean value of 212.73 µg/L in the north part of the fault. The distinct spatial differences in arsenic concentration of hot springs may be attributed to the heterogeneity of lithologies along the fault zone, with sedimentary rocks dominated in the northern and metamorphic rocks dominated in the southern section of the fault. Two sources of arsenic can be identified in the study area: 1) As is correlated with typical geothermal species such as Li and B, indicating that rock leaching from deep geothermal reservoirs can be a dominant source of As; 2) high level of HCO3- and weak alkalinity condition caused the desorption of arsenic from the sediment surface. In addition, the mixing with shallow groundwater also affects the As contents in hot springs. This study provides an insight into the formation and controls on high-arsenic geothermal water.
The Salton Sea has experienced significant recession over the past two decades due to changes in the diversion of Colorado River water to the Salton Trough for agricultural irrigation. As a result, wetlands have emerged in some exposed playa areas along the Salton Sea, primarily in regions with extensive agricultural return flows and agricultural drainage. One notable wetland system, known as the Bombay Beach Wetlands, has formed on the north shore of the Salton Sea, in an area devoid of agriculture. In many other areas with limited or no agriculture, wetlands have failed to develop, leaving exposed playa surfaces as the Salton Sea recedes. These dry playa surfaces pose a significant threat to the health of local residents due to the presence of toxins contained in windblown dust associated with playa deposits. In this study, stable water isotope data, combined with other hydrological information, led to identification of two potential water sources for the Bombay Beach Wetlands. The first possibility proposes that thermal artesian waters alone contribute to the wetlands' water source, while the second hypothesis involves a combination of drainage from Salton Sea bank storage water mixing with the thermal artesian water. The thermal artesian water discharges into drainage channels that flow towards the Bombay Beach Wetlands, initially devoid of possible groundwater baseflow until reaching the wetlands. Studies were subsequently done along the full reach of the drainage channels receiving thermal artesian water. Dissolved solids content, P and N nutrients, arsenic, and stable water isotopes were tested synoptically along the drainage channels. Channel investigations led to the development of a novel model of salinization, which is linked to channel discharge, channel morphometrics, and channel incision.
Microbially mediated arsenic methylation, crucial for arsenic biogeochemical transformation, remains understudied in subgeothermal environments. This study aimed to investigate the activity and diversity of arsM-carrying microorganisms in sediment samples (termed YC1, YC2, and YC5) from a low-temperature hot spring. Microcosm assays revealed that only YC1 and YC2 exhibited limited As-methylating activities, generating a maximum of 2.3–3.5 μg/L methylarsenate (MMA) and 2.2–2.8 μg/L dimethylarsenate (DMA). The addition of lactate and arsenite significantly promoted these activities, increasing the concentrations to 26.1–184.0 μg/L MMA and 36.5–204.0 μg/L DMA. The arsM gene abundance also increased by 85–195%, indicating that lactate can activate arsenite methylation. YC1 and YC2, which were closer to the hot spring hole than YC5 was, had similar patterns, and shared a similar arsM community structure, dominated by Actinobacteriota, Firmicutes, and Proteobacteriota on days 7 and 21. In contrast, at YC5, the sampling site far from the spring hole, representatives of Acidobacteriota were dominant on day 7, whereas those of Actinobacteriota were prevalent on day 21. Acidobacteriota co-occurred with dimethylarsenate production, and Mycobacterium co-occurred with DMA demethylation. These findings suggested that the low-temperature arsenic hot spring possessed diverse arsenic-methylating species, whereas demethylating bacteria preferred to inhabit niches farther from the hot spring.
Abstract
The gamut of geothermal energy research encompasses the studies aimed at harnessing the abundant and inexhaustible thermal energy within the Earth, and it ranges from heat transfer to the activity of thermophilic microorganisms, 3D printing, and additive manufacturing and impacts the NET ZERO endeavour of humanity. In this paper, computational social network analysis has been employed to discover the subfield clusters of geothermal energy research and further trace the key evolutionary routes from the research corpus. The development, limitations, and opportunities of each cluster are examined, and it becomes evident that the focus of research ranges from geothermal evaluation, long-term effects of borehole heat exchangers, shallow systems that employ urbanisation’s ground heating, enhanced geothermal systems (EGS) for district heating, combined and hybridised geothermal power generating models, including multi-generation and poly-generation, geothermal fluids, reinjection and their dual nature, environmental effects in geothermal water and mineral scaling, enhanced geothermal systems aiming to increase permeability without causing seismicity, and finally to social acceptability. We address significant questions, such as whether the waste heat is compatible with the idea of green geothermal heat and the elimination of pollutants and find that further R&D and technological advancements are required for this ubiquitous clean energy to get wider acceptance and employment. The future of this energy depends on the rational and scientifically sound exploration and use of the resources, just as in the case of fossil fuels, and thus precludes geothermal energy as a win-all solution to the energy needs of the whole world.
Geothermal utilization is generally used as clean green energy because of its contribution to gradually eliminating high carbon energy. However, in practice, geothermal damage to the environment, even regulation of its utilization does not guarantee environmental justice. This research study aims to determine environmentally just geothermal regulations to eliminate negative environmental impacts and public rejection of geothermal utilization. This study uses normative legal research. The results of this study indicate that geothermal potential can replace high-carbon energy even though it still has a damaging impact on the environment. Community rejection occurs in various areas where geothermal exploitation occurs in conservation forest areas. Geothermal energy regulation in Indonesia is no more pro-ecological than in the USA. Based on the analysis of the legal gap between the theory of ecological justice and the legal triangle and energy policy, it is found that the principles of geothermal regulation must prioritize ecology, not mere exploitation. The findings of this study are strengthening the principles of geothermal regulation based on ecological justice. Standardization of handling and monitoring of environmental impacts must be carried out in an integrated manner based on area category to avoid the widening of the ecological impact of geothermal utilization which results in rejection of the next project.
In order to protect both themselves and their property, in short, their material and moral interests, people created a common tool called insurance. As a result of the researches, it was determined that the basis of insurance arises from the creation of people's personal property.
In the Middle Ages, the insurance business was formed as an institution. In the market economy environment, no commercial contract is signed and no company operates without insurance in the advanced countries of the world. In these countries, every citizen and person has an insurance certificate related to property, life, and health.
In modern times, interest in insurance is increasing in our republic. Regardless of the existence of different views on insurance, what is necessary is that the insured person gets the chance to receive the insurance payment, that is, the economic compensation. The insurance certificate does not exclude the dangers that may occur in the insured person's life, but prevents and protects against negative consequences. In simple terms, insurance is related to the payment of damages, it is a means of protecting the property interests of the insured people.
There are different types and forms of insurance. According to the Law of the Republic of Azerbaijan "On Insurance", insurance consists of two main parts: life and non-life insurance.
One of the types of voluntary insurance in the field of non-life insurance is health insurance. Medical insurance - provides full or half compensation of the costs incurred in connection with the examination and treatment of medical institutions, as well as the purchase of medicines, based on the fact that the insured person suffers from a disease specified in the insurance contract.
Thus, in the conditions of market relations, insurance fields, especially health insurance, which is one of their types, play a special role. It is required to determine the role of health insurance, its place in the health care system.
Environmental context
High-quality ecotoxicology data are required to derive reliable water quality guideline values that ensure long-term protection of marine biota from arsenate. Tropical and temperate marine biota have sensitivity to arsenate covering three to four orders of magnitude due to the range of arsenate detoxification mechanisms used to reduce toxicity. The water quality guideline values derived in this study will contribute to robust risk assessments of arsenate in marine environments.
Rationale
There are very few high-quality chronic inorganic arsenate (AsV) toxicity data to assess the risks to marine ecosystems. We aimed to determine the range in chronic toxicity of AsV to marine biota and derive reliable water quality guideline values (GVs) for the long-term protection of marine ecosystems.
Methodology
We generated chronic toxicity data based on measured dissolved (<0.45 µm filtered) AsV concentrations for 13 marine species representing seven taxonomic groups from temperate and tropical environments. Effect concentrations at the 10% level (EC10) were used in a species sensitivity distribution (SSD) to derive water quality GVs.
Results
The range of concentrations causing chronic 10, 20 and 50% adverse effects were 13–26 000, 18–34 000 and 32–330 000 µg AsV L–1, respectively. Increased phosphate and nitrate concentrations were found to reduce the toxicity of AsV to certain microalgal, sea urchin and bivalve species. The range in effect concentrations for tropical versus temperate species overlapped at all effect levels. The GVs for the long-term protection of 80, 90, 95 and 99% of marine biota were: 48, 22, 12 and 4.8 µg AsV L–1, respectively.
Discussion
Recommendations on performing toxicity tests with arsenic to prevent artefacts associated with arsenic speciation were made to improve future research on arsenic toxicity. The new data will improve the reliability status of the Australian and New Zealand AsV GVs for marine water quality and fill a data gap for global risk assessments of AsV for marine biota.
Simav geothermal field is located in Simav graben within the Menderes Massif in Western Anatolia, Turkey. The geothermal waters in marbles, limestones and basalts can be classified as Na-HCO3-SO4 type exchange waters with the dominant cations in increasing order of Na+K>Ca>Mg while the anions are HCO3>SO4>Cl. The Cl-SO4-HCO3 ternary diagram shows that the waters are peripheral/immature and more likely related to groundwaters heated by steam from deeper reservoirs. Quartz, aragonite, calcite and chalcedony are oversaturated at discharge temperatures while at a recomputed temperature according to the reservoir composition, only quartz, dolomite and chalcedony are oversaturated. The silica thermometer shows reservoir temperatures between 83 and 182⁰C. The Na-K-Ca-Mg correction cation thermometers give reservoir temperatures close to the measured reservoir temperature on site in Eynal which is between 148 and 163 ⁰C. The waters plot along the meteoric water line suggesting the source from local meteoric water and are rich in δ¹⁸O. This situation points to the existence of water-rock interaction in the system and/or boiling due to the high temperatures in the reservoir.
This study investigate concentrations of heavy metals (Pb, Cd, Hg and As) in water and muscle fish collected from three different sites (Aden, Al-Hodeidah and AL-Mukalla ) of the Red Sea and the Gulf of Aden in Yemen’s coastal. Fresh samples were purchased from near the sea public auction site locations. The four species of fish (emperor) Lethrinus mahsena, (Longtail tuna) Thunnus tonggol, (Pickhandle Barracuda) Sphyraena jello and (Areolate grouper) Epinephelus areolatus were collected and analyzed, 81 samples of Seawater and 108 samples of muscle Fish were digested using suitable procedures. The heavy metal concentrations in the samples were measured using the Atomic Absorption Spectrophotometer. The obtained results showed that the concentration (mg/l) of the heavy metal in seawater (Pb-0.061±0.005, Cd-0.007±0.001, Hg-0.007±0.0005 and As-0.008±0.0003) was lower than that of the concentration (µg/g) of heavy metal in muscle (Pb-0.101±0.012, Cd-0.046±0.010, Hg-0.058±0.002 and As-0.089±0.002). The results showed that, the heavy metals concentrations were high in stations AL- Hudaydah and AL- Mukalla and low in station of Aden. The highest mean concentration of Pb, Cd and As a in the muscles of the four studied fish species was 0.137± 0.014 and 0.069±0.021 µg/g dry wt in large Epinephelus areolatus ; 0.106±0.007 µg/g dry wt in large Lethrinus mahsena At Site AL- Hudaydah in Summer. The highest mean concentration of Hg a in the muscles of the four studied fish species was 0.071±0.012 µg/g dry wt in large Epinephelus areolatus At Site Aden in Summer. Positive relationships were found between metal levels and fish size. From these results, we conclude that the heavy metals (Pb, Cd, Hg and As) in the muscles of fish and seawater, at Yemen’s coastal were still in range scale of international pollution standard However, the study recommends continuing the study of these pollutants and other contaminants and their impact on the environment and marine life.
Keywords: Fish, Heavy Metals, Water, Aden, Al-Hodeidah , AL-Mukalla, Red Sea, Gulf of Aden, Yemen.
The agricultural sector, which is highly dependent on water, is urged to build on improved water management practices and explore available options to match supply and demand because of the water scarcity risks and a sustainable and productive agri-food chain. Geothermal water is an energy source used to generate electricity and/or heat. After harnessing its energy, the remaining water can be used as a water source for irrigation following treatment because of its high ionic content. Geothermal fields are mostly located in rural areas where agricultural activities exist. This would be a good match to decrease the transportation cost of irrigation water. The energy demand of the desalination process for agriculture is higher, requiring additional post-treatment processes. Fossil fuels to fulfill the energy requirements are becoming expensive, and greenhouse gas emissions are harmful to the environment. Thus, efforts should be directed towards integrating renewable energy resources into desalination process. This work focuses on presenting a comprehensive review of geothermal water desalination which is powered by renewable energy and provides specific cases from Turkey and Poland. Furthermore, possible new generation renewable energy systems in desalination are introduced, considering their potential application in the desalination of geothermal water for agricultural irrigation.
1] Geochronologic and geological data define a 600 ka age for the current volcanic front in Costa Rica. In Nicaragua, this age is less constrained but is likely within the range 600 ka to 330 ka. In Costa Rica, the new geochronologic data significantly improve estimates of the volumes of the volcanoes because they define the contact between the active volcanoes and the previous volcanic front, which is substantially older (2.2 to 1.0 Ma). In addition, the contrast in extrusive volcanic flux between western Nicaragua (1.3 Â 10 10 kg/m/Myr) and central Costa Rica (2.4 Â 10 10 kg/m/Myr) is greatly reduced from previous estimates and now within the range of error estimates. We estimate the subducted component of flux for Cs, Rb, Ba, Th, U, K, La, Pb, and Sr by subtracting estimated mantle-derived contributions from the total element flux. An incompatible element-rich OIB source for the Cordillera Central segment in Costa Rica makes the subducted element flux there highly sensitive to small changes in the modeled mantle-derived contribution. For the other three segments studied, the estimated errors in concentrations of highly enriched, subduction-derived elements (Cs, Ba, K, and Pb) are less than 26%. Averaged over the time of the current episode of volcanism, the subduction-derived fluxes of Cs, Ba, K, Pb, and Sr are not significantly different among the four segments of the Central American volcanic front in Nicaragua and Costa Rica. The subduction-derived fluxes of Th and La appear to increase to the SE across Nicaragua and Costa Rica, but the estimated errors in their subduction-derived concentrations are very high, making this variation questionable. The lack of change in the fluxes of Cs, Ba, K, Pb, and Sr argues that the well-defined regional variation in Ba/La is the result of changes in the mode or mechanics of fluid delivery into the mantle wedge, not the total amounts of fluids released from the slab. Concentrated or focused fluids in Nicaragua lead to high degrees of melting. Diffuse fluids in Costa Rica cause lower degrees of melting. Components: 12,742 words, 11 figures, 5 tables.
Geothermal energy is a low-pollution energy source. However, air, soil, and water near geothermal plants may be affected by their operation. One of the largest geothermal energy sources in the world, Cerro Prieto, has a capacity of 720 MW and is located in northwest Mexico near an agricultural area. The abstracted geothermal fluids, which are enriched with arsenic (As), boron (B), lead (Pb), cadmium (Cd), and other heavy metals, are either reinjected into the aquifer or sent to an evaporation pond located in the geothermal plant. Because spills have occurred in other geothermal zones, it is important to evaluate the effect of those contaminants on the soils of the surrounding area and their possible infiltration into shallow groundwater. To that aim, soils (one chromic Vertisol and two calcic Regosols) from three sites near the Cerro Prieto Geothermal Plant were sampled to evaluate their behavior regarding As, Pb, and B retention. Batch experiments were carried out using the soils as the sorbent and geothermal water from three geothermal production wells as the sorbate. Raw water concentrations in each well were as follows: As: 0.2442 mg/L, 0.2774 mg/L, and mg/L; B: 18.409 mg/L, 13.5075 mg/L, and 16.646 mg/L; and Pb: 0.22 mg/L, 0.13 mg/L, and 0.26 mg/L. The physicochemical characteristics of the soils were determined and compared to the experimental results. A good adjustment of the chromic Vertisol sample to Freundlich isotherms was observed for As (r² > 0.9), followed by Pb (r² = 0.61), and B (r² > 0.5). As retention also showed a good adjustment to the Langmuir model (r² > 0.9). The retention followed the order Pb >As ≫B in one of the two calcic Regosols, while the other only retained Pb ≫ As. Cationic exchange capacity; clay minerals; carbonate; organic matter; and iron, aluminum, and manganese amorphous and crystalline oxides influenced the soils’ retention capacities. Irrigation with geothermal water could not imply a toxicity risk to plants grown in the chromic Vertisol soil due to its high Pb and As sorption capacity. Pb concentration could not be a toxicity issue in the calcic Regosols for the same reason, but As and B could be. B would be a hazard to vegetables and water due to its low or lack of retention in the three soils and also for its possible infiltration into shallow groundwater used for irrigation in the area. This study highlights the importance of maintaining adequate operation and control of the disposal of geothermal fluids in geothermal plants.
This paper presents a review of the worldwide applications of geothermal energy for direct utilization and updates the previous survey carried out in 2015. We also compare data from WGC1995, WGC2000, WGC2005, WGC2010, and WGC2015 presented at World Geothermal Congresses in Italy, Japan, Turkey, Indonesia and Australia. As in previous reports, an effort is made to quantify geothermal (ground-source) heat pump data. The present report is based on country update papers received from 62 countries and regions reporting on their direct utilization of geothermal energy. Twenty-six additional countries were added to the list based on other sources of information. Thus, direct utilization of geothermal energy in a total of 88 countries is an increase from 82 in 2015, 78 reported in 2010, 72 reported in 2005, 58 reported in 2000, and 28 reported in 1995. An estimation of the installed thermal power for direct utilization at the end of 2019 is used in this paper and equals 107,727 MWt, a 52.0 % increase over the 2015 data, growing at a compound rate of 8.73 % annually. The thermal energy used is 1,020,887 TJ/yr (283,580 GW h/yr.), a 72.3 % increase over 2015, growing at a compound rate of 11.5 % annually. The distribution of thermal energy used by category is approximately 58.8 % for geothermal (ground-source) heat pumps, 18.0 % for bathing and swimming (including balneology), 16.0 % for space heating (of which 91.0 % is for district heating), 3.5 % for greenhouse heating, 1.6 % for industrial applications, 1.3 % for aquaculture pond and raceway heating, 0.4 % for agricultural drying, 0.2 % for snow melting and cooling, and 0.2 % for other applications. Energy savings amounts to 596 million barrels (81.0 million tonnes) of equivalent oil annually, preventing 78.1 million tonnes of carbon and 252.6 million tonnes of CO2 from being released to the atmosphere. This includes savings for geothermal heat pumps in the cooling mode, compared to using fuel oil to generate electricity. Since it is almost impossible to separate direct-use from electric power generation for the following, they are combined: approximately 2647 wells were drilled in 42 countries, 34,500 person-years of effort were allocated in 59 countries, and US $22.262 billion invested in projects by 53 countries.
Drinking water sources in the southeastern part of Lake Titicaca (Lower Katari Basin: LKB) and the southern part of Lake Poopó (Southern Poopó Basin: SPB) have high concentrations of arsenic (As), >10 μg/L compared to the WHO and NB-512 guideline value. These regions belong to the Bolivian Altiplano and are characterized by a semiarid climate, slow hydrological flow, with geological formations of volcanic origin, in addition to brines and other mineral deposits. The present study is focused on comparing the geochemical processes of As in relation to the sources and mobilization in groundwater (GW) in LKB and SPB. Groundwater, surface water and sediment samples were collected from both basins. The As (LKB: 0.8–288 μg/L and SPB: 2.6–207 μg/L), boron (B) (LKB: 96–2473 μg/L and SPB: 507–4359 μg/L), manganese (Mn) (LKB: 0.6–7259 μg/L) and salinity (LKB: 125–11740 μS/cm) were found to be higher than the WHO guideline limit, which is a serious concern about the GW quality for human consumption. The dissolution and exchange of bases are the processes that govern the mineralization of GW. Load of solids and liquids of anthropogenic origin in surface water (LKB) represents an environmental problem for communities on river banks. The spatial distribution of As was attributed to the geology of both the basins and the heterogeneously distributed evaporites in the sediments. The highest As concentrations are found in alluvial sediments of the northern region of LKB and the “PACK belt” (an approximately 25 km long belt stretching along the southern shores of the Lake Poopó, between the villages of Pampa Aullagas and Condo K) in SPB. Sequential extraction of sediment and mineral saturation indices indicate that iron (Fe) and aluminum (Al) oxides as well as hydroxides are the most predominant mineral phases as potential sorbents of As.
Uranium and thorium decay series disequilibria in deep geothermal brines are a result of water-rock interaction processes. The migratory behavior of radionuclides provides valuable site-specific information and can therefore be an important tool for reservoir characterization and sustainable management of geothermal sites.
In this study, we present data from long-term monitoring of naturally occurring 238 U, 232 Th and 235 U series radionuclides analyzed in brine samples collected from the Permo-Triassic sedimentary reservoir rock at the Bruchsal geothermal site (SW Germany). The results show that radionuclides of the elements radium ( 226 Ra, 228 Ra, 224 Ra, 223 Ra), radon ( 222 Rn), and lead ( 210 Pb, 212 Pb) are rather soluble in brine, while isotopes of uranium ( 238 U, 234 U, 235 U), thorium ( 232 Th, 228 Th, 230 Th), polonium ( 210 Po), and actinium ( 227 Ac, 228 Ac) have low solubilities and are mostly immobile. Activities of radium isotopes in the geothermal brine exceed those of their thorium progenitors (average 226 Ra = 29.9 Bq kg -1 , about 10 3 times that of its 230 Th parent).
Modelling the observed disequilibria allows the following conclusion on water-rock interaction processes: (1) Supply from alpha recoil depends on isotope half-life because it is limited by the rate of diffusion through microfractures causing isotopic fractionation. (2) Radium retardation due to adsorption is low ( 226 Ra/ 222 Rn = 1.3) resulting in adsorption-desorption rate constants in the order of 10 -10 s -1 for k 1 and 10 -9 for k 2 . (3) Scavenging of 226 Ra from brine can best be explained by co-precipitation with barite resulting in an observed 226 Ra anomaly in the solids of the reservoir section. The precipitation rate constant amounts to ca. 3.4 x 10 -8 s - 1 corresponding to a mean removal time of radium from brine by mineral precipitation to approximately one year.
Today (year 2020), the globally recognized problem of arsenic (As) contamination of water resources and other environments at toxic levels has been reported in all of the 20 Latin American countries. The present review indicates that As is prevalent in 200 areas across these countries. Arsenic is naturally released into the environment and mobilized from geogenic sources comprising: (i) volcanic rocks and emissions, the latter being transported over thousands of kilometers from the source, (ii) metallic mineral deposits, which get exposed to human beings and livestock through drinking water or food chain, and (iii) As-rich geothermal fluids ascending from deep geothermal reservoirs contaminate freshwater sources. The challenge for mitigation is increased manifold by mining and related activities, as As from mining sites is transported by rivers over long distances and even reaches and contaminates coastal environments. The recognition of the As problem by the authorities in several countries has led to various actions for remediation, but there is a lack of long-term strategies for such interventions. Often only total As concentration is reported, while data on As sources, mobilization, speciation, mobility and pathways are lacking which is imperative for assessing quality of any water source, i.e. public and private.
In the Main Ethiopian Rift (MER) area, rural populations often use water that exceeds the World Health Organization thresholds for fluoride (F–) and arsenic (As), two elements that are hazardous for human health. In this study, twenty-nine water samples were collected from lakes and hot and cold springs in southern MER to investigate source(s) and health-risk of the F– and As contamination. According to major ion and trace element analyses, only cold spring water is safe for consumption, whereas hot spring water is the most contaminated. Leaching tests performed with the MER rhyolitic volcanic rocks and their weathered products (fluvio-lacustrine sediments) demonstrate that the main cause of the F– and As release is geogenic, i.e., not related to anthropogenic activities. The weathering of volcanic glass and minerals (apatites, clays, hydro-oxides) by CO2-bearing alkaline water induces the mobilisation of F– and As from solid to liquid phase. This process is particularly fast, when fluvio-lacustrine sediments are involved, and can be further enhanced by hot groundwater leaching. This study, investigating the distribution, sources, and mechanisms of F– and As release in MER water, could be of interest also for other sectors of the East African Rift and other similar volcano-tectonic settings.
[ES] Resumen Unos dos millones de personas en un área de un 1,7 x 10 6 km 2 en el Cono Sur americano están potencialmente expuestos a la ingestión de agua con más de 50 µg/l de arsénico y consecuentemente tienen un riesgo elevado de padecer arsenicismo. El área afectada se extiende en un continuo noroeste-sureste desde la costa pacífica a la costa atlántica. El límite meridional aproximadamente corresponde a los 30 o S en Chile y a los cursos de los ríos Desaguadero y Colorado en Argentina. El límite septentrional provisionalmente se ha fijado en el borde norte del Altiplano, y los cursos de los ríos Bermejo y Paraná. Por lo que respecta al arsénico en el agua, esta gran zona se puede subdividir en: 1) zona cordillerana, incluye el Altiplano y la Puna, y áreas limítrofes, 2) zona pericordillerana, y 3) zona pampeana. Salvo casos locales de contaminación (explotaciones mineras, fundiciones), el origen del arsénico es natural y está relacionado con el volcanismo y la actividad hidrotermal asociada de la cordillera de los Andes entre 14 y 28 o S. La dispersión secundaria a través de aguas superficiales ha sido el mecanismo dominante que ha llevado el arsénico hasta las costas pacífica y atlántica. La movilidad del arsénico está condicionada por las condiciones redox y el pH. En el contexto de la región arsenical del Cono Sur, prevalecen las condiciones oxidantes, estando el arsénico mayoritariamente disuelto en forma de especies con As(V), y el pH es neutro o tiende a la alcalinidad. La gestión del abastecimiento con agua de calidad en esta zona debe tener en cuenta además del estado de oxidación del arsénico en el agua, la existencia frecuente de salinidades elevadas y la presencia de concentraciones que superan los límites admisibles en agua para consumo humano de otros elementos potencialmente tóxicos (p. ej., flúor) y la baja calidad microbiológica. Las necesidades abarcan desde el suministro rural familiar hasta el de ciudades con varios cientos de miles de habitantes. Las soluciones pasan por el abastecimiento de fuentes alternativas sin arsénico o, cuando no sea posible, el tratamiento mediante plantas potabilizadoras convencionales optimizadas, tecnologías desmineralizadoras, bioremoción y utilización de métodos muy simples en el punto de uso.
[EN] Approximately two million inhabitants in an area of 1.7 x 10 6 km 2 in the South American Cone are potentially exposed to drinking water with arsenic concentrations exceeding 50 µg/l and, consequently, have a high risk of arsenicosis. The affected area extends NW-SE from the Pacific coast to the Atlantic coast. The southern border is a line at 30 o S in Chile that follows the rivers Desaguadero and Colorado in Argentina. A provisional northern border has been established through the north of the Altiplano and the rivers Bermejo and Paraná. In relation to arsenic, this large zone has been subdivided in: 1) cordilleran zone (includes the Altiplano and the Puna) and neighboring areas, 2) pericordilleran zone, and 3) pampean zone. Except for local contamination of mining and smelters, the arsenic source is natural and is related to the volcanism and associated hydrothermal activity of the Andes Cordillera between 14 y 28oS. The secondary dispersion by means of surface waters is the main process implied in the arsenic transport to the Pacific and Atlantic coasts. Arsenic mobility is controlled by redox
conditions and pH. Oxidizing conditions prevail in the South American Cone and arsenic is
dominantly present as dissolved species of As(V), while pH is near neutral to slightly alkaline. Water management in this area is conditioned by the oxidation state of arsenic, but also by the frequent high salinity and high concentrations of potentially toxic trace elements (e.g., fluorine) and the low microbiological quality. Water supply needs varie from rural families to cities. A possible solution is the use of alternative water sources. If this is not possible, water treatment using optimized conventional processes, demineralization technologies, bioremoval methods, and point of use technologies are alternatives for arsenic removal in water.
Geothermal brines can be a resource of energy, freshwater and minerals. Even when rejected after their exploitation to produce energy in a power plant, the brines can be a source of freshwater and minerals, and can have a residual enthalpy that can be recovered to produce additional power. The different reuse scenarios of these wasted brines depend on the composition and temperature at which they must be reinjected into the wells. On this basis, geothermal energy production is a perfect case study to investigate the water–energy nexus and to optimize the integrated energy- and water-production processes. In this paper, two case studies of brine reuse for both energy and water production are presented with the related process analysis, basic design and technical–economic analysis. A methodology to evaluate the exergy efficiency of the processes is presented by analyzing minimum work of separation, the maximum achievable work and the additional primary energy required for integrated production. The novel approach to estimate the process efficiency for integrated geothermal energy and desalination plants is applied to the case studies and discussed in light of literature results.
Studies conducted over the past eight years in Latin America (LA) have continued to produce new knowledge regarding health impacts of arsenic (As) in drinking water. We conducted a systematic review of 92 peer-reviewed English articles published between 2011 and 2018 to expand our understanding on these health effects. Majority of the LA studies on As have been conducted in Chile and Mexico. Additional data have emerged from As-exposed populations in Argentina, Bolivia, Brazil, Colombia, Ecuador, and Uruguay. The present review has documented recent data on the biomarkers of As exposure, genetic susceptibility and genotoxicity, and risk assessment to further characterize the health effects and exposed populations. Some recent findings on the associations of As with bladder and lung cancers, reproductive outcomes, and declined cognitive performance have been consistent with what we reported in our previous systematic review article. We have found highly convincing evidence of in utero As exposure as a significant risk factor for several health outcomes, particularly for bladder cancer, even at moderate level. New data have emerged regarding the associations of As with breast and laryngeal cancers as well as type 2 diabetes. We observed early life As exposure to be associated with kidney injury, carotid intima-media thickness, and various pulmonary outcomes in children. Other childhood effects such as low birth weight, low gestational age, anemia, increased apoptosis, and decreased cognitive functions were also reported. Studies identified genetic variants of As methyltransferase that could determine susceptibility to As related health outcomes. Arsenic-induced DNA damage and alteration of gene and protein expression have also been reported. While the scope of research is still vast, the substantial work done on As exposure and its health effects in LA will help direct further large-scale studies for more comprehensive knowledge and plan appropriate mitigation strategies.
Aluto-Langano in the Main Ethiopian Rift Valley is currently the only producing geothermal field in Ethiopia and probably the best studied prospect in the Ethiopian Rift. Geoscientific exploration began in 1973 and led to the siting of an exploration well LA3 on top of the volcanic complex. The well was drilled in 1983 to a depth of 2144m and encountered temperatures of 320°C. Since 1990 Aluto has produced electricity, albeit with interruptions. Currently it is undergoing a major expansion phase with the plan to generate about 70MWe from eight new wells, until now two of them have been drilled successfully. Geophysical exploration at Aluto involved magnetotelluric (MT) soundings, which helped delineate the clay cap atop of the hydrothermal reservoir. However, until now geophysical studies did not succeed in imaging the proposed magmatic heat source that would drive the observed hydrothermal convection. For this study, we inverted 165 of a total of 208 MT stations that were measured over the entire volcanic complex in three independent surveys by the Geological Survey of Ethiopia and ETH Zurich, Switzerland. For the inversion, we used a novel 3-D inverse solver that employs adaptive finite element techniques, which allowed us to accurately model topography and account for varying lateral and vertical resolution. We inverted MT phase tensors. This transfer function is free of galvanic distortions that have long been recognized as an obstacle in MT inversion. Our recovered model shows, for the first time, the entire magmatic-hydrothermal system under the geothermal field. The up-flow of melt is structurally controlled by extensional rift faults and sourced by a lower crustal basaltic mush reservoir. Productive wells were all drilled into a weak fault zone below the clay cap. The productive reservoir is underlain by an electrically conductive upper-crustal feature, which we interpret as a highly crystalline rhyolitic mush zone, acting as the main heat source. Our results demonstrate the importance of a dense MT site distribution and state-of-the-art inversion tools in order to obtain reliable and complete subsurface models of high enthalpy systems below volcanic geothermal prospects.
The total discharge and thermal output from the numerous hydrothermal features in Yellowstone National Park (YNP) can be estimated from the chloride (Cl) flux in the Madison, Yellowstone, Falls, and Snake Rivers. Monitoring the Cl flux in these four major rivers provides a holistic view of the hydrothermal output from YNP and changes in the Cl flux may indicate changes in geothermal or magmatic activity. In this study, the source, fate, and flux of geothermal solutes in the Yellowstone River and Gardner Rivers were determined. Beginning in 2012, the fluxes of geothermal solutes, including Cl, were determined at monitoring sites in the Yellowstone and Gardner Rivers downstream of geothermal inputs within YNP. A method was developed using specific conductance as a surrogate measure for solute concentrations at these monitoring sites. Combining continuous (15-min) specific conductance and discharge data, Cl and other geothermal solute fluxes were determined and approximately 32% of the Cl flux exiting YNP is from the Yellowstone River watershed. Synoptic sampling of river water and discharge measurements were performed during low-flow conditions of September 2014 allowed for the determinations of geothermal solute sources and their downstream fate. Thus, the contribution of geothermal solutes from the various geothermal areas at the downstream monitoring sites was quantified. The thermal features draining into Yellowstone Lake account for 34% of the Cl flux at the Yellowstone River monitoring site which is located approximately 5 km north of YNP. The Gardner River, which captures geothermal water from Mammoth Hot Springs, is responsible for 22% of the Cl at the Yellowstone River monitoring site. Because the Yellowstone River watershed is large and contains numerous thermal areas, knowing the source and fate of geothermal solutes is import baseline information that can be used to identify future changes in thermal activity.
Geothermal resources provide green, low‐carbon, and renewable clean energy, with abundant reserves and massive potential for application. The in‐depth analysis of geothermal resources in China, including their distribution and breakdown by shallow, hydrothermal, and hot dry rock (HDR) resources, is made in this study. Using the recent economic reports and state‐of‐the‐art technological solutions, this survey outlines the latest trends in the geothermal power generation in China. The application of geothermal power generation in China is still at an early stage, with the total installed capacity of 27.78 MW. The geothermal power generation technologies, such as dry steam technology, flash technology, binary cycle technology, and enhanced geothermal system (EGS), are briefly discussed and linked to their lucrative implementation sites. In particular, Tibet's Yangbajing is considered to be the most lucrative site for the EGS pilot project. The comparative analysis of low‐cost/large‐scale geothermal power generation technologies, such as low‐ to medium‐temperature one, solar‐geothermal hybrid one, and geothermal power generation in mines, was made, whose results strongly indicated the EGS technical and economical advantages. The concentration of 96% of China's population in the area to the east of Hu line affects the perspectives of high‐cost geothermal projects and has to be accounted in the comprehensive analysis of available data. Based on the revealed trends of geothermal resources’ development in China, the following guidelines are strongly recommended: comprehensive incorporation of geothermal energy generation into China's national energy and climate improvement plans, the rapid implementation of HDR technology, as well as comprehensive adaptation of the geothermal‐related projects to the local conditions/biased distribution of power consumers and state‐of‐the‐art challenges of power consumption.
Arsenic is a carcinogen known for its acute toxicity to organisms. Geothermal waters are commonly high in arsenic, as shown at the Bjarnarflag Power Plant, Iceland (∼224 μg/kg of solvent). Development of geothermal energy requires adequate disposal of arsenic-rich waters into groundwater/geothermal systems. The outcome of arsenic transport models that assess the effect of geothermal effluent on the environment and ecosystems may be influenced by the sensitivity of hydraulic parameters. However, previous such studies in Iceland do not consider the sensitivity of hydraulic parameters and thereby the interpretations remain unreliable. Here we used the Lake Mývatn basaltic aquifer system as a case study to identify the sensitive hydraulic parameters and assess their role in arsenic transport. We develop a one-dimensional reactive transport model (PHREEQC ver. 2.), using geochemical data from Bjarnarflag, Iceland. In our model, arsenite (H 3 AsO 3 ) was predicted to be the dominant species of inorganic arsenic in both groundwater and geothermal water. Dilution reduced arsenic concentration below ∼5 μg/kg. Adsorption reduced the residual contamination below ∼0.4 μg/kg at 250 m along transect. Based on our modelling, we found volumetric input to be the most sensitive parameter in the model. In addition, the adsorption strength of basaltic glass was such that the physical hydrogeological parameters, namely: groundwater velocity and longitudinal dispersivity had little influence on the concentration profile. © 2019 China University of Geosciences (Beijing) and Peking University
Los arroyos Covunco, Manchana Covunco y Aguas Calientes están localizados
sobre la margen Este del río Varvarco, en el NO de la provincia de Neuquén. Dichos
arroyos son parte de una extensa cuenca hidrográfica que atraviesa el campo geotermal
activo del Complejo Volcánico Domuyo, en donde parte de la recarga de los mismos es
aportada por una serie de surgencias subterráneas geotermales. El objetivo del trabajo es
realizar una caracterización hidroquímica de los arroyos que atraviesan el mencionado
complejo con el fin de evaluar la influencia que ejerce la descarga subterránea geotermal
en la química del agua superficial. A partir del análisis de imágenes satelitales se definió
una red de monitoreo de agua superficial y de las zonas de descarga subterránea
geotermal. En cada punto de muestreo se midieron in situ tanto el pH y la conductividad
eléctrica del agua con un equipo de campo, y se extrajeron muestras para la
determinación de iones mayoritarios mediante métodos estandarizados. Los datos
hidroquímicos relevados se volcaron en un sistema de información geográfica a fin de
interpretar las variaciones espaciales que ocurren en la química del agua superficial en
función de las descargas geotermales. Los resultados obtenidos evidencian que la
química del agua de los arroyos presentan variaciones al atravesar el campo geotermal
producto de la descarga de agua subterránea con alta carga iónica que existe en este
sector de la cuenca.
Offshore Geothermal Energy can be considered as a non-polluting source of renewable energy, in relation to harmful emissions that are associated with burning fossil fuels to generate electricity. The geothermal brines of the mid-ocean ridge hydrothermal vents are believed to be potential sources of offshore geothermal energy. These fluids represent one of the most abundant energy resources worldwide, due to their enormous quantity, infinite recharge, and high temperatures. However, all forms of electricity generation impact the environment in some way. The ecological and biological importance of the vents restricts the number of areas that can be utilized to produce electricity. Most of the marine areas with these vents are benefitted with some form of protection. Most of them are included in the networks of marine protected areas (MPAs), which stands as the foundation of marine conservation policies. While most of the scientific studies focused on quantifying the exploitable energy from the hydrothermal vents, the environmental impacts of harvesting the energy from these vents have not been explored till date and remained unanswered. For the offshore geothermal energy to develop, the uncertainties about the effects on the marine environment must be assessed. Therefore, this study attempts to assess the potential environmental impacts using the MOHID framework of hydrodynamic modelling along with some personal views and assumptions from various studies. ("Pedamallu et al.") This is the first of its kind of study in the offshore geothermal energy production, and the results demonstrate the marine ecological footprint that could quantify the impact on the marine environment by exploiting hydrothermal vents for energy production.
The toxicity of arsenic (As) towards life on Earth is apparent in the dense distribution of genes associated with As detoxification across the tree of life. The ability to defend against As is particularly vital for survival in As-rich shallow submarine hydrothermal ecosystems along the Hellenic Volcanic Arc (HVA), where life is exposed to hydrothermal fluids containing up to 3000 times more As than present in seawater. We propose that the removal of dissolved As and phosphorus (P) by sulfide and Fe(III)(oxyhydr)oxide minerals during sediment–seawater interaction, produces nutrient-deficient porewaters containing < 2.0 ppb P. The porewater arsenite-As(III) to arsenate-As(V) ratios, combined with sulfide concentration in the sediment and/or porewater, suggest a hydrothermally-induced seafloor redox gradient. This gradient overlaps with changing high affinity phosphate uptake gene abundance. High affinity phosphate uptake and As cycling genes are depleted in the sulfide-rich settings, relative to the more oxidizing habitats where mainly Fe(III)(oxyhydr)oxides are precipitated. In addition, a habitat-wide low As-respiring and As-oxidizing gene content relative to As resistance gene richness, suggests that As detoxification is prioritized over metabolic As cycling in the sediments. Collectively, the data point to redox control on Fe and S mineralization as a decisive factor in the regulation of high affinity phosphate uptake and As cycling gene content in shallow submarine hydrothermal ecosystems along the HVA.
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As well as gases that regulate climate over geological time, volcanoes emit prodigious quantities of metals into the atmosphere, where they have key roles as catalysts, pollutants and nutrients. Here we compare measurements of arc basaltic volcano metal emissions with those from hotspot settings. As well as emitting higher fluxes of metals (similar to those building ore deposits), these arc emissions possess a distinct compositional fingerprint, particularly rich in tungsten, arsenic, thallium, antimony and lead when compared with those from hotspots. We propose that volcanic metal emissions are controlled by magmatic water content and redox: hydrous arc magmas that do not undergo sulfide saturation yield metal-rich, saline aqueous fluid; shallow degassing and resorption of late-stage sulfides feeds volcanic gases in Hawai’i and Iceland. Although global arc magma chemistries vary considerably, our findings suggest that volcanic emissions in arcs have a distinct fingerprint when compared with other settings. A shift in global volcanic metal emissions may have occurred in Earth’s past as more oxidized, water-rich magmas became prevalent, influencing the surface environment.
Study region: Latin America. Parana Basin. Argentina, Brazil, Paraguay, Uruguay. Study focus: This article traces the trajectory of transboundary cooperation over the past fifteen years for the Guarani Aquifer System. A new insight for the region: The Guarani Aquifer System is a transboundary aquifer shared by Argentina, Brazil, Paraguay, and Uruguay. It stands as one of the largest reservoirs of freshwater worldwide and is one of the few transboundary aquifers whose management is regulated by an international treaty, the Guarani Aquifer Agreement (GAA). The latter is also the first to refer in its preamble to the UN International Law Commission Draft Articles on the Law of Transboundary Aquifers. A first period (2002–2010) of positive collaboration in which the four countries actively moved forward towards a better understanding of the aquifer, culminated with the adoption of the GAA in August 2010. A second period (2010–2017) has been marked by a slowdown in transboundary cooperation, limited in this period to sporadic cross-border projects and initiatives linked to past and existing international projects. In this period, Argentina and Uruguay, and more recently Brazil have ratified the GAA. A third phase seems to be emerging in 2017 due to the possibility that finally Paraguay ratifies the GAA allowing it to enter into force. This article argues that in the future implementation of the agreement countries should build on the good practices, both substantive and institutional, stemming from the first period of transboundary cooperation.
Germanium is considered to be a non-essential element; however, little is still known about its significance for living organisms. It exerts prophylactic and therapeutic effects in the treatment of serious diseases such as cancer, HIV infection, and others. Germanium does not exhibit acute toxicity, but, as it tends to accumulate in various organs and tissues, undesirable and even dangerous side effects have been reported after prolonged and/or high dosage application. In general, inorganic compounds of germanium are more toxic than its organic compounds. Further studies should be performed to elucidate the exact molecular mechanism of germanium action, to determine the safe and effective dose of germanium via curative/mineral waters, and to understand the applications and benefits of using germanium-enriched waters in balneotherapy. The geochemistry of curative (cold CO2-rich, thermal) waters from spas in the Sudetes (Poland) was clarified in terms of components and mineral phases which might govern germanium. Germanium and silicon in thermal (above 20 °C) waters presumably result from the solubility of silicates in crystalline (granites, gneisses) aquifer rocks and might be controlled by neo-formed quartz. The cold CO2-rich waters revealed a significant diversity of aqueous chemistry and relationships of germanium with iron, silicon, or arsenic. Locally, both in sedimentary (sandstones) and metamorphic (gneisses) aquifer rocks, primary (silicates) and/or secondary (oxides) iron-containing minerals likely release germanium into solution. In the CO2-rich waters of the western part of the Kłodzko Region, germanium distinctly correlates with arsenic. It is hypothesized that both elements are co-sourced from crystalline basement and/or migration of substances of post-magmatic origin along deep-seated dislocations related to the seismically active Poříčí-Hronov fault zone. This area was proposed as the most prospective one for finding waters rich in germanium in the Sudetes.
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To determine the main hydrogeochemical processes affecting the migration and enrichment of arsenic in the high arsenic geothermal water in the Batang area of Sichuan Province, the hydrogeochemistry and whole rock geochemistry of groundwater and aquifer sediments were studied. The results show that the groundwater has an arsenic concentration of 3.1 to 80.8 μg L ⁻ ¹, which is mainly present in the form of arsenate. The arsenic concentration in this groundwater system is correlated with the presence of fluoride ions and the temperature. The thermal storage temperature and cycling depth are significantly correlated with the arsenic concentration. The thermal storage temperature in the Batang area is relatively high (220 °C to 260 °C). When cold water mixing takes place, the temperature falls to 76.56–177.51 °C, the proportion of cold water mixing ranges from 67% to 79%, and the circulation depth reaches 1318.11 to 3443.37 m. The temperature of the groundwater, the competitive adsorption of HCO3⁻, and the pH level also affect the arsenic concentration. The above results indicate that the alkaline reducing environment in the Batang area of Western Sichuan is beneficial to the enrichment of arsenic in the groundwater. The desorption of the arsenic adsorbed on the surface of Fe oxide/hydroxide minerals is the main route by which arsenic enters the geothermal water. These results provide guidance for the exploitation and utilization of geothermal water in the Batang area.
The paper presents the results of research on the desalination of geothermal wastewater for further environmentally friendly use of the concentrate streams obtained. Three geothermal waters previously used for heating purposes were desalinated. They are 1) lightly mineralised geothermal water (LM-GT), 2) moderately mineralised geothermal water (MM-GT) and 3) heavily-mineralised (HM-GT) geothermal water. The analysis is based on six technical experiments. The results indicated that geothermal wastewater desalination system can provide satisfactory fresh water which can be used for drinking or economic purposes. At the same time high-quality concentrate was obtained which can potentially be used for: 1) balneotherapy treatment – all concentrates; 2) drinking and inhalations – LM-GT; 3) therapeutic purposes – MM-GT. The raw MM-GT product can, for instance, also be considered as medicinal solution, like silica water, due to the high metasilicic acid content. Other concentrates analysed can also be recommended for the treatment of various diseases or cosmetic purposes based on their specific composition. The high boron concentration and elevated chromium content in MM-GT and HM-GT concentrates require additional treatment due to the requirements of some therapeutic instructions and this may limit the possibility of their use as base substance for cosmetic or therapeutic product.
Arsenic is a well-recognized environmental contaminant that occurs naturally through geogenic processes in the aquifer. More than 200 million people around the world are potentially exposed to the elevated level of arsenic mostly from Asia and Latin America. Many adverse health effects including skin diseases (i.e., arsenicosis, hyperkeratosis, pigmentation changes), carcinogenesis, and neurological diseases have been reported due to arsenic exposure. In addition, arsenic has recently been shown to contribute to the onset of non-communicable diseases, such as diabetes mellitus and cardiovascular diseases. The mechanisms involved in arsenic-induced diabetes are pancreatic β-cell dysfunction and death, impaired insulin secretion, insulin resistance and reduced cellular glucose transport. Whereas, the most proposed mechanisms of arsenic-induced hypertension are oxidative stress, disruption of nitric oxide signaling, altered vascular response to neurotransmitters and impaired vascular muscle calcium (Ca2+) signaling, damage of renal, and interference with the renin-angiotensin system (RAS). However, the contributions of arsenic exposure to non-communicable diseases are complex and multifaceted, and little information is available about the molecular mechanisms involved in arsenic-induced non-communicable diseases and also no suitable therapeutic target identified yet. Therefore, in the future, more basic research is necessary to identify the appropriate therapeutic target for the treatment and management of arsenic-induced non-communicable diseases. Several reports demonstrated that a daily balanced diet with proper nutrient supplements (vitamins, micronutrients, natural antioxidants) has shown effective to reduce the damages caused by arsenic exposure. Arsenic detoxication through natural compounds or nutraceuticals is considered a cost-effective treatment/management and researchers should focus on these alternative options. This review paper explores the scenarios of arsenic contamination in groundwater with an emphasis on public health concerns. It also demonstrated arsenic sources, biogeochemistry, toxicity mechanisms with therapeutic targets, arsenic exposure-related human diseases, and onsets of cardiovascular diseases as well as feasible management options for arsenic toxicity.
Arsenic has a natural cycle as it travels underground. It can mix with geothermal fluid in different ways under the control of magmatic and tectonic processes. Geogenic arsenic is present in many geothermal fields in the world at concentrations above the limits set for human health. The arsenic content of geothermal fluids is also related to the concept of geothermal play type, which forms geothermal systems, because the natural processes that form the geothermal system also control the arsenic cycle.
In this study, an attempt is made to explain the relationship between the geothermal play type concept and geothermal arsenic circulation. For this purpose, geothermal field examples are given from around the world and Turkey. The result shows that arsenic concentrations can reach significant levels along with plate tectonic boundaries in the world. When arsenic concentrations were evaluated, the effect of major faults on the Anatolian Plate was clearly seen. Also, in the Anatolian plate where volcano-sedimentary units are common, geothermal fluids caused more effective alteration along with structural control and increased arsenic concentrations in geothermal systems.
This interaction between structural elements, geothermal fluid, and the arsenic cycle shows that the concept of play type in geothermal systems should also be taken into consideration. It was determined that the places with high arsenic values are located within the convective-non-magmatic extensional geothermal play types such as Western Anatolian Extensional System and the North Anatolian Fault. The concept of play type in geothermal systems includes all systematic and external factors that make up these processes. For this reason, it is very important to evaluate the play type classification together with the arsenic cycle.
One of the factors that determine agricultural crops' yield is the quality of water used during irrigation. In this study, we assessed the usability of spent geothermal water for agricultural irrigation after membrane treatment. Preliminary membrane tests were conducted on a laboratory-scale set up followed by mini-pilot scale tests in a geothermal heating center. In part I, three commercially available membranes (XLE BWRO, NF90, and Osmonics CK- NF) were tested using a cross-flow flat-sheet membrane testing unit (Sepa CF II, GE-Osmonics) under constant applied pressure of 20 bar. In part II, different spiral wound membranes (TR-NE90-NF, TR-BE-BW, and BW30) other than the ones used in laboratory tests were employed for the mini-pilot scale studies in a continuous mode. Water recovery and applied pressure were maintained constant at 60% and 12 bar, respectively. Performances of the membranes were assessed in terms of the permeate flux, boron and arsenic removals. In laboratory tests, the permeate fluxes were measured as 94.3, 87.9, and 64.3 L m-2 h-1 for XLE BWRO, CK-NF and NF90 membranes, respectively. The arsenic removals were found as 99.0%, 87.5% and 83.6% while the boron removals were 56.8%, 54.2%, and 26.1% for XLE BWRO, NF90 and CK-NF membranes, respectively. In field tests, permeate fluxes were 49.9, 26.8 and 24.0 L m-2 h-1 for TR-NE90-NF, BW30-RO and TR-BE-BW membranes, respectively. Boron removals were calculated as 49.9%, 44.1% and 40.7% for TR-BE-BW, TR-NE90-NF and BW30-RO membranes, respectively. Removal efficiencies of arsenic in mini-pilot scale membrane tests were all over 90%. Quality of the permeate water produced was suitable for irrigation in terms of the electrical conductivity (EC) and the total dissolved solids (TDS) for all tested membranes with respect to guidelines set by the Turkish Ministry of Environment and Urbanisation (TMEU). However, XLE BWRO, CK-NF and NF90 membranes failed to meet the required limits for irrigation in terms of boron and arsenic concentrations in the product water. The permeate streams of TR-BE-BW, TR-NE90-NF and BW30-RO membranes complied with the irrigation water standards in terms of EC, TDS and arsenic concentration while boron concentration remained above the allowable limit.
The compilation of water, sediment, rock, and condensed gas data of arsenic (As) in the Altiplano-Puna of Chile reveals a link between its natural enrichment and volcanic activity, high crustal thicknesses, and regional structures. Two zones were studied which encompass the Altiplano-Puna and western lowlands of Chile: the Northern Zone (including Los Pintados, Surire, and Huasco) and Southern Zone (including Pedernales, Grande, and Laguna Verde). A positive correlation was found between average As concentrations in saline and brackish water of salt flats and crustal thicknesses of the two studied zones with heightened values to the east (up to 25 mg･L−1 of dissolved As in water and a 64 km depth to the Mohorovicic discontinuity). Furthermore, in the studied Altiplano-Puna salt flats, surrounding Mio-Pliocene to Quaternary felsic and intermediate volcanic outcrops are abundant and As is well correlated with other dissolved components (e.g. Li and B). Sediments show extreme As values at punctual locations within the Altiplano-Puna, where the crust is thick, recent volcanic and hydrothermal activity is present, and regional faults are found. Volcanic rocks and condensed gas in the Altiplano-Puna are also enriched with As (up to 221 and 1234 mg･kg−1 respectively). In this tectonic environment, it is hypothesized that volcanism represents an important source of As and the thick continental crust can provide a large reservoir of As that can be leached by rising thermal fluids. Regional scale fault systems also can allow for preferential upwelling and the heightened concentration of As in fractures. Hydrological processes at the surface transport dissolved As to lower elevation regions through groundwater in aquifers and surface water in perennial rivers, creeks, and gorges, diluting element concentrations where significant evapoconcentration is not present.
The aim of this study is to investigate the performances of new N-methyl-D-glucamine functionalized resins revealing gel (1JW), expanded gel (2JW) and epidermal-like structure (2PTN) for simultaneous removal of boron and arsenic from saline geothermal water by means of adsorption-membrane filtration hybrid process. The effects of adsorbent concentration and resin replacement rate were particularly studied for boron removal from geothermal water. Boron removal with 1JW resin increased from 66% to 86% by doubling the resin concentration while the respective values found for 2PTN resin were 61% and 73%. In the case of the microporous 2PTN resin, due to its epidermal-like structure, the efficiency of the hybrid process was improved by increasing the replacement rate of fresh and saturated resins. Unlike the 2JW resin as the most efficient resin for boron removal among novel resins, the maximum arsenic removal of 35.8% was obtained by the 1JW resin using a resin concentration of 4 g/L. The Dowex XUS 43594.00 resin exhibited lower arsenic removal of 21.5% than 2PTN (4 g/L) and 2JW (2 g/L) giving arsenic removals of 22.4% and 28.8%, respectively.
Geothermal waters often are enriched in trace metal(loid)s, like arsenic, antimony, molybdenum, and tungsten. Presence of sulfide can lead to formation of thiolated anions, however, their contributions to total element concentrations typically remain unknown because non-suitable sample stabilization and chromatographic separation methods convert them to oxyanions. Here, the concurrent widespread occurrence of thioarsenates, thiomolybdates, thiotungstates, and thioantimonates, in sulfide-rich hot springs from Yellowstone National Park and Iceland is shown. More thiolation was generally observed at higher molar sulfide to metal(loid) excess (Iceland>Yellowstone). Thioarsenates were the most prominent and ubiquitous thiolated species, with trithioarsenate typically dominating arsenic speciation. In some Icelandic hot springs, arsenic was nearly quantitatively thiolated. Also for molybdenum, thioanions dominated over oxyanions in many Icelandic hot springs. For tungsten and antimony, oxyanions typically dominated and thioanions were observed less frequently, but still contributed up to a few tens of percent in some springs. This order of relative abundance (thioarsenates>thiomolybdates>thiotungstates≈thioantimonates) was also observed when looking at processes triggering transformation of thioanions like mixing with non-geothermal waters or H2S-degassing and oxidation with increasing distance from a discharge. Even though to different extents, thiolation contributed substantially to speciation of all four elements studied, indicating their analysis is required when studying geothermal systems.
Arsenic (As) is an important component in thermal springs, which can reach water sources constituting an important hazard for both the environment and people. For this reason, the aim of this paper is to analyze the geologic and geochemical processes that determine the presence and concentration of As in wet-meadows associated to a geothermal field in Patagonia (Argentina) which is used as water supply. To achieve this, during field surveys temperature, pH and electrical conductivity were measured and water and rock samples were taken. Major ions and stable isotopes were determined in water samples while As content was analyzed in both water and rock samples. Due to geological control and chemical analyses, three areas were recognized with respect to major streams in the geothermal field: wet-meadows at headwaters, thermal springs at mid basin and wet-meadows at down basin. Even though, water in wet-meadows have the same origin the obtained results evidence how thermal springs at mid-basin influence the chemistry of these wetlands, particularly those at down basin. In the latter, As raises over two orders of magnitude than the ones at headwaters which surpasses the reference limit, proving that thermal springs are also responsible for the increase of the As content in water changing its quality as a source of potable water. The concentration of this metalloid could be higher but it is retained in travertine and sinter deposits formed near the geothermal discharge area. Understanding processes controlling water quality and the chemistry of As in this type of wetlands is of vital importance, mainly in an arid region where water supply sources are scarce.
The challenge for many communities in Latin America is to find adequate solutions which are feasible given the local economic and technical conditions and which enable them to source water with arsenic concentrations below the WHO guideline value for drinking water (<10 μg/L) of arsenic (As) pollution, suitable for human consumption and the irrigation of crops. Three regions where geothermal fields are present were selected for study out of the several hundred locations in Latin America where the water environment is contaminated with As and where there is a critical water shortage problem. These are Cerro Prieto in Mexico, Momotombo in Nicaragua and Lake Poopó in Bolivia. The paper presents the results of research on the use of low-enthalpy geothermal energy sources and waste heat from geothermal power plants in membrane distillation (MD) processes, which is the only heat-powered membrane technology, in order to obtain potable water and/or water for crop irrigation. It was concluded that MD could be considered as a solution for obtaining water of good quality with a high retention of toxic solutes such as As as well as other different species found in groundwater. In addition, it is not only geothermal energy, but also the geothermal water itself that can be considered as a source of freshwater produced through the MD process, a process which is most suitable to be used in areas where cheap sources of heat are available.
In contrast to other Latin American countries, where the presence of arsenic (As) in drinking water sources and related adverse human health impacts are well-known, little is internationally known from Nicaragua. However, the As problem is of high relevance as numerous assessments by national research, governmental and non-governmental institutions have proven. To assess for the first time and globally disseminate this predominantly nationally originated information is the aim of this review. In Nicaragua, >1000 water samples have been analyzed for total As from 1991 to 2017. By today, 144 communities distributed within 12 departments and one autonomous region (RACCS) are impacted with As. At least 55,700 people are exposed to drinking water with As (n = 173; range: 10-1320 μg/L, mean: 48.30 μg/L; 21.95%). Arsenic in surface water ranged from 0.99 to 2650 μg/L (n = 124, mean: 65.62 μg/L, 62.9% < 10 μg/L); and in groundwater from 0.10 to 1320 μg/L [n = 624, mean: 20.86 μg/L (70.7% < 10 μg/L)]. The highest As concentration was recorded from a well of the El Zapote community in 1996 (1320 μg/L), alerting national authorities and academic's to research As in water sources and health risks. Since then, 10 μg As/L has been the national regulatory limit for drinking water supplies. Occurrence of high As levels is linked to three geoenvironments: (i) Paleocene-Mesozoic metamorphic rocks (Northern Highlands) where As is present in epithermal veins, (ii) Tertiary volcanic rocks (Central Plateau) where As is related to fossil hydrothermal/volcanic systems, (iii) Quaternary rocks (Nicaragua Depression) where As is caused by active geothermal/volcanic activities. No mitigation measures have been implemented. Incipient water treatment efforts (Kanchan filters activated carbon) have failed because they were not socially accepted. More integrated, cross-sectorial research on genesis, health impacts and problem mitigation is needed. Provision of water treatment units for As removal on a single-household and community scale is needed, calling for the cooperation of national entities with communities in problem detection and solving.
Elevated Arsenic (As) and Fluoride (F) concentrations in groundwater have been studied in the shallow aquifers of northeastern of La Pampa province, in the Chaco-Pampean plain, Argentina. The source of As and co-contaminants is mainly geogenic, from the weathering of volcanic ash and loess (rhyolitic glass) that erupted from the Andean volcanic range. In this study we have assessed the groundwater quality in two semi-arid areas of La Pampa. We have also identified the spatial distribution of As and co-contaminants in groundwater and determined the major factors controlling the mobilization of As in the shallow aquifers. The groundwater samples were circum-neutral to alkaline (7.4 to 9.2), oxidizing (Eh ~0.24 V) and characterized by high salinity (EC = 456-11,400 μS/cm) and Na+-HCO3- water types in recharge areas. Carbonate concretions ("tosca") were abundant in the upper layers of the shallow aquifer. The concentration of total As (5.6 to 535 μg/L) and F (0.5 to 14.2 mg/L) were heterogeneous and exceeded the recommended WHO Guidelines and the Argentine Standards for drinking water. The predominant As species were arsenate As(V) oxyanions, determined by thermodynamic calculations. Arsenic was positively correlated with bicarbonate (HCO3-), fluoride (F), boron (B) and vanadium (V), but negatively correlated with iron (Fe), aluminium (Al), and manganese (Mn), which were present in low concentrations. The highest amount of As in sediments was from the surface of the dry lake. The mechanisms for As mobilization are associated with multiple factors: geochemical reactions, hydrogeological characteristics of the local aquifer and climatic factors. Desorption of As(V) at high pH, and ion competition for adsorption sites are considered the principal mechanisms for As mobilization in the shallow aquifers. In addition, the long-term consumption of the groundwater could pose a threat for the health of the local community and low cost remediation techniques are required to improve the drinking water quality.
Due to the utilization of landfill technology and geothermal energy production in Tibet, the contamination of the soils and underground water by trace element has currently become a serious problem, both ecologically and to the human health point of view. However, relevant studies concerning this critical problem, particularly in the Tibet area has not been found. Therefore, this study investigated the soil contamination and the spatial distribution of the trace elements in the areas surrounding the Tibetan landfill sites (LS) and geothermal sites (GS) through several pollution evaluation models. In addition, the possible sources of trace elements and their potential impact on public health were also investigated. Results showed that the trace elements in soils nearby LS and GS had moderate to high contamination risk. In soils surrounding LS, mercury had the highest concentration of 0.015 mg/kg and was 6 times higher than the background value of 0.008 mg/kg while in GS, arsenic had the highest concentration of 66.55 mg/kg, and exceeded the soil contamination risk value of 25 mg/kg. Maizhokunggar LS was the most polluted site with an average pollution load index value of 2.95 compared to Naqu, Nyingchi, Shigatse, and Lhasa. 42% of LS were with considerable ecological risk, and all GS had low ecological risk. Both carcinogenic and non-carcinogenic risk for children and adults (male, female) were within the acceptable range. According to the source analysis, unscientific anthropogenic activities including accumulated MSW, industrial discharges, and vehicle emissions significantly contributed 51.83% to soil trace element contamination. Considering that Tibet is an environment-ecologically vulnerable region with very weak self-adjustment ability, accumulated municipal solid waste in the landfill sites should be well disposed of, and even soil remediation should be well implemented.
As a potential source of arsenic (As) for the downstream region of the South and East Asia, the As contamination in the Qinghai-Tibet Plateau (QTP) still needs more investigation. In this study, As concentrations in the surface water, lake sediments, and fish of lakes and endorheic rivers in the central Tibet Plateau (CTP) were investigated for the better understanding of As fate in the CTP. Extremely high levels of As in saline lakes water were found with concentrations up to 10,775.40 μg/L, while the lowest level of As was found in freshwater lakes with a concentration of only 1.80 μg/L. Natural loading and evaporation concentration were the main reasons for As accumulation in saline lakes in the CTP. Rock weathering and terrestrial ecosystem could affect the As level in the lake. As contents in lake sediments significantly positive related to the As/EC ratios but showed no correlation with As concentrations in the water. Although As levels in the fish were higher in lakes with higher As concentrations, they were still lower than those of the fish from As-contaminated lakes in other studies. Results of this study indicate that hot spots of As in the CTP require more in-depth attention and studies in the future to better understand their influence on the fragile CTP aquatic ecosystem.
Geothermal fluids and volcanic emissions are important sources of arsenic (As), resulting in elevated concentrations of As in ground-, surface-water and soil, which may adversely affect the environment. Arsenic originating from geothermal features and volcanic activities is common in Latin America forming a serious threat to the livelihoods of millions of people. This review attempts to provide a critical overview of the geochemistry of As originating from these sources in Latin America to understand what information exists about and what future research needs to be undertaken. This study evaluated 15 countries in Latin America. In total, 423 sites were characterized with As originating from geothermal sources, mostly related to present volcanic activity (0.001 < As<73 mg/L, mean: 36.5 mg/L) and the transboundary Guarani Aquifer System (0.001 < As<0.114 mg/L, mean: 0.06 mg/L). Many of the geothermal systems and volcanoes discussed in this study are close to densely populated cities, including Bogota, Managua, San José, Guatemala City and Mexico City, where total As concentrations in natural ground- and surface- water exceed the safe drinking water guideline of 0.01 mg/L, recommended by the World Health Organization (WHO). However, the wide geographical occurrence of As in geothermal fluids and volcanic emissions of this region is by far not fully understood, so that development of geographical maps based on geographic information system (GIS) is an urgent necessity to understand the real nature of the problem. The assessment of environmental risks and the potential impacts on human health both inadequate and scarce and hence, these gaps need to be addressed by future research. The present holistic assessment of As originating from geothermal features and volcanic emissions would be a driving force to formulate a plan for establishing a sustainable As mitigation in vulnerable areas of Latin America in the near future. An assessment of the geochemistry, mobility and distribution of As would augment the effectiveness of the plan.
In New Zealand and internationally, two deleterious constituents in geothermal fluids are silica and arsenic. Silica because scaling is a significant limiting factor for effective geothermal energy production and arsenic due to its potential groundwater contamination. Electrocoagulation treatment offers a simple and cost-effective method of removing both constituents, compared to the traditional treatment methods of coagulation and flocculation. It is an electrochemical process that uses direct current to remove a wide range of contaminants. This method has the potential to allow efficient downstream utilization of heat in low enthalpy fluids through cascaded direct use applications and can provide a more cost-effective disposal option than reinjection.
Laboratory and field experiments have shown that the process can remove both silica and/or arsenic rapidly from aged geothermal water, leaving a floc which readily settles on standing. In aged water, iron electrodes were most efficient at reducing arsenic levels from approximately 4 mg L⁻¹ to < 0.1 mg L⁻¹, while aluminium electrodes were the most effective method for reducing silica levels from approximately 600 mg L⁻¹ to < 100 mg L⁻¹. In a full-scale process, the silica and arsenic can be removed as two separate components, leaving an arsenic-free silica sludge to be disposed of in a landfill and a much smaller arsenic / iron fraction to be further treated or disposed of by reinjection.
Evidence for low-dose health effects of Arsenic (As) in humans is still controversial and presents a major public health issue in several countries worldwide. It is not clear yet, whether there is a lower safe threshold for arsenic in drinking water among other possible sources such as food, below which, exposures are not harmful.
In Uruguay, safe drinking water is supplied to 94% of the population by a state company (OSE) and As levels in workplaces and food are officially regulated.
This paper aims to present and discuss the issues regarding arsenic exposure risks to the environment and human population, which are being addressed in a multidisciplinary manner in Uruguay since 2007. An overview is given on both the background and the current situation, presenting reports and research studies conducted on these problems by various academic, state, and private institutions that deal with regulations, surveillance, and health care.
Scientific research on geogenic As levels in groundwater indicates As levels above those recommended by the WHO for drinking water (10 μg L⁻¹) in different Uruguayan aquifers. There is a lack of baseline studies concerning Uruguayan residents that are exposed to As in drinking water over time. Furthermore, there is a need for data on environmental chemical exposure that could be associated with disease or death in the country. In addition, only a few As risk exposure assessment studies in children, adults, and workers using biomarkers in urine are available.
Furthermore, this paper presents As levels in a rice growing region and the spatial distribution of groundwater arsenic data compared to a national cancer atlas database as ongoing research advances. Multidisciplinary research projects and local future actions are also described.
This contribution constitutes a first attempt to develop a feasible health risk assessment of low-dose arsenic exposure in this Latin-American country.
Tibet is characterized by extremely high terrestrial heat flow and widely distributed hydrothermal systems, among which many are discharging geothermal waters with extremely high arsenic concentrations from over 10 mg/L to up to 126 mg/L. The distribution of these high arsenic waters is basically in accordance with the location of the Indian continental subduction zone. A detailed analysis indicates that host rock leaching alone cannot explain the observed arsenic anomaly. Instead, substantial contribution of arsenic from the underlying magma chambers is postulated, which are likely mantle-derived intrusions that have been severely contaminated by the very thick crustal material below southern Tibet, possibly including deep-seated arsenic-rich sedimentary rocks. Alternatively, the partial melts at crustal depths reflected by the detected low-velocity and/or high-conductivity anomalies in southern Tibet, serving as the magmatic heat source of the high‑arsenic hydrothermal systems, may also form indirectly under the high-temperature conditions generated by mantle upwelling or due to crustal thickening. Low sulfide concentrations further promote high dissolved arsenic concentrations with little formation of thioarsenates and no precipitation of limiting arsenic-sulfide phases. In contrast, mantle magmas less affected by crustal contamination, serving as the heat source of many hydrothermal systems in rift zones and hot spots worldwide where the crust is thinner, are releasing magmatic fluids lower in arsenic and higher in mantle sulfur species. Overall, the existence of a magmatic heat source alone does not ensure the formation of geothermal waters with very high arsenic concentrations, and geothermal waters from sedimentary rock-hosted systems are neither necessarily arsenic-rich. The most critical factor controlling the arsenic concentration of geothermal water discharging from a magmatic hydrothermal system is the geological genesis of the magma fluid and its chemical composition.
The chemical composition, textures and mineral associations of pyrite provide key information that help elucidate the evolution of hydrothermal systems. However, linking the compositional and micro-textural features of pyrite with a specific physico-chemical process, e.g., boiling versus non-boiling, remains elusive and challenging. In this study we examine pyrite geochemical and micro-textural features and relate these results to pyrite-forming processes at the active Cerro Pabellón Geothermal System (CPGS) in the Altiplano of the northern Chile. We integrate electron microprobe analysis (EMPA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) data with micro-textural observations of pyrite and associated gangue minerals recovered from a ∼500 m long drill core that crosscuts the argillic, sub-propylitic and propylitic alteration zones of the CPGS. Additionally, we carried out a Principal Component Analysis (PCA) in order to inspect and understand the main data structure of the pyrite geochemical dataset. The concentrations of precious metals (Au and Ag), metalloids (As, Sb, Se, Bi and Tl), and base and heavy metals (Cu, Co, Ni and Pb) in pyrite from the CPGS are significant. Among the elements analyzed, As, Cu and Pb are the most abundant with concentrations that vary from a few parts per million (ppm) to wt% levels (up to 4.4 wt% of As, 0.5 wt% of Cu and 0.2 wt% of Pb). Based on contemporaneous gangue mineral associations and textures, the mechanisms of pyrite precipitation in the CPGS were inferred. Pyrite formed during vigorous boiling is characterized by relatively high concentrations of As, Cu, Pb, Ag and Au and lower concentrations of Co and Ni compared to pyrite formed under different conditions. These anhedral to euhedral pyrite grains display zones with a porous texture and abundant mineral micro- to nano-inclusions (mainly galena and chalcopyrite) indicating a formation by rapid crystallization. In contrast, pyrite formed under gentle boiling (more gradual cooling and less abrupt physico-chemical variations than in vigorous boiling) to non-boiling conditions is characterized by a higher concentration of Co and Ni, and relatively low concentrations of As, Cu, Pb, Ag and Au. Texturally, these pyrites form aggregates of euhedral and pristine pyrite crystals with scarce pores and mineral inclusions suggesting formation under steadier physico-chemical conditions. Our results show that pyrite can not only record the chemical evolution of hydrothermal fluids, but can also provide critical information related to physico-chemical process such as boiling and phase separation. Since boiling of aqueous fluids is a common phenomenon occurring in a variety of pyrite-forming environments, e.g., active continental and seafloor hydrothermal systems, and porphyry Cu-epithermal Au-Ag deposits, pyrite compositional and textural features are a valuable complement for discriminating and tracking boiling events in modern and fossil hydrothermal systems.
Arsenic (As) is a ubiquitous constituent in geothermal waters. Geothermal fluids with As concentrations ranging from 0.01 to tens of mg/L occur in different locations around the world, especially in geothermal systems along the boundaries of active plates. Leaching of reservoir rocks is the most important source of As in geothermal fluids. Arsenic exists in different As-bearing minerals in geothermal reservoirs with different temperatures, and the As concentrations in aqueous phase are affected by reservoir temperature to various degree. Arsenic concentration in geothermal waters depends on their genesis and geochemistry, with deep neutral chloride waters commonly containing much higher As concentrations than shallow acidic sulfate waters. During the upflow of geothermal fluids from the reservoir to the surface, As experiences a series of abiotic and biotic processes: oxidation, reduction, methylation and As-S redox cycling. Arsenic oxidation could happen under both aerobic and anaerobic conditions. Up till now a total of twelve aerobic As(III)-oxidizing bacteria have been isolated and thousands of clones harboring arsenite oxidase gene were detected in hot springs worldwide. As(III)-oxidizing rate of these isolates reached up to 1.27 μM/min. In situ microbial arsenate reduction in geothermal environment was found in the bottom water of Mono Lake fed by hot spring waters, and several arsenate reducers were reported in some geothermal waters as well. Inorganic As could be methylated in hot springs by biological activity. Arsenic and sulfur often coexist in geothermal environments and undergo similar chemical and microbial redox transformations. In sulfidic hot springs, thioarsenates/thioarsenites can be formed preferentially by replacing several hydroxyl groups in arsenate and arsenite with thiol groups, respectively, and thioarsenites/thioarsenates could be reciprocally transformed regardless of the presence of sulfur. Microorganisms in hot springs have been found to exert a profound influence on As and sulfur speciation by using them as both electron donors and acceptors, forming various thioarsenate species. Geothermal As from depth can be released into the surface or near-surface environments either via discharge of hot springs or geothermal wastewater, or via natural mixing of geothermal waters with local shallow groundwaters. Some rivers contaminated by geothermal As were estimated to discharge tens to more than one hundred tons of As per year. Understanding the biogeochemical behaviors of As in geothermal systems before and after mixing with shallow groundwaters and surface waters is therefore critical for the protection of water resources and the environment.
The geothermal provinces of the western Red Sea coast and East African countries have evolved synchronous with the evolution of the landmasses around the Red Sea. The Red Sea opening was initiated subsequent to the opening of the Aden Gulf that was triggered by the Afar plume. During the Late Oligocene, the Red Sea rift started extending from south towards north culminating into a failed arm near the Suez Gulf. The geothermal systems evolved due to shallow mantle below the Danakil depression and circulating seawater. Besides the volcanic flows, the regional sedimentary aquifers like the Wajid Sandstone and Amron limestone, that occur in Ethiopia, Egypt, Eritrea and Djibouti, that were deposited prior to the younger tectonic events that started at 31 Ma are the main geothermal reservoirs in these countries. In contrast, rain surface and evaporated lake water are the main sources for the Kenyan geothermal systems. Although these geothermal fluids show variation in their chemical components due to different recharging sources, all the geothermal systems are of high temperature, capable of generating electricity.
Thiolated arsenic compounds are the sulfur analogous substructures of oxo-arsenicals as the arsinoyl (As = O) is substituted by an arsinothioyl (As = S) group. Relatively brief history of thioarsenic research, mostly in the current decade has endeavored to understand their consequences in the natural environment. However, thioarsenic related aspects have by far not attached much research concern on global scale compared to other arsenic species. This review attempts to provide a critical overview for the first time on formation mechanisms of thioarsenicals, their chemistry, speciation and analytical methodologies in order to provide a rational assessment of what is new, what is current, what needs to be known or what should be done in future research. Thioarsenic compounds play a vital role in determining the biogeochemistry of arsenic in sulfidic environments under reducing conditions. Thioarsenic species are widely immobilized by naturally occurring processes such as the adsorption on iron (oxyhydr)oxides and precipitation on iron sulfide minerals. Accurate measurement of thioarsenic species is a challenging task due to their instability upon pH, temperature, redox potential, and concentrations of oxygen, sulfur and iron. Assessment of direct and indirect effects of toxic thioarsenic species on global population those who frequently get exposed to high levels of arsenic is an urgent necessity. Dimethylmonothioarsinic acid (DMMTAV) is the most cytotoxic arsenic metabolite having similar toxicological effects as dimethylarsinous acid (DMAIII) in human and animal tissues. The formation and chemical analysis of thioarsenicals in soil and sediments are highly unknown. Therefore, future research needs to be more inclined towards in determining the molecular structure of unknown thioarsenic complexes in various environmental suites. Contemporary approaches hyphenated to existing technologies would pave the way to overcome critical challenges of thioarsenic speciation such as standards synthesis, structural determination, quantification and sample preservation in future research.
The paper presents an innovative approach to freshwater production using geothermal aquifers as a water and energy source. The main parameters which can potentially influence the results of the analysis were selected to investigate their effect on the proposed schemes, e.g. feed water quality, quality of the geothermal resource, concentrate utilisation and cost of freshwater production. A technical and economic feasibility study demonstrates that effective use of geothermal resources can include direct utilisation of geothermal energy in the heating system and the use of the cooled water as a source of freshwater obtained in a desalination unit. The comparison of the costs of freshwater from current freshwater resources in Poland (groundwater and surface water) with those calculated for the geothermal option showed that the costs of the latter are equal to the former. The treatment of geothermal water can bring an improved water balance for drinking purposes. In areas of high water deficit, the solution presented is a good example of the rational management of geothermal resources.