Naturally occurring arsenic in terrestrial geothermal systems of western Anatolia, Turkey: Potential role in contamination of freshwater resources

Abstract

h i g h l i g h t sPotential environmental impact of high arsenic from geothermal sources was identified. Geothermal waters from deep wells are characterized by Na-HCO 3 type. Hot spring fluids are characterized by Ca-HCO 3 type. As(III) is the dominant species in both deep wells and hot spring fluids. Mixing of geothermal waters containing As is responsible for environmental impact. Arsenic (As) contamination in terrestrial geothermal systems has been identified in many countries worldwide. Concentrations higher than 0.01 mg/L are detrimental to human health. We examined potential consequences for As contamination of freshwater resources based on hydrogeochemical investigations of geothermal waters in deep wells and hot springs collected from western Anatolia, Turkey. We analyzed samples for major ions and trace element concentrations. Temperature of geothermal waters in deep wells showed extreme ranges (40 and 230 • C), while, temperature of hot spring fluids was up to 90 • C. The Piper plot illustrated two dominant water types: Na-HCO 3 − type for geothermal waters in deep wells and Ca-HCO 3 − type for hot spring fluids. Arsenic concentration ranged from 0.03 to 1.5 mg/L. Dominance of reduced As species, i.e., As(III), was observed in our samples. The Eh value ranged between −250 and 119 mV, which suggests diverse geochemical conditions. Some of the measured trace elements were found above the World Health Organization guidelines and Turkish national safe drinking water limits. The variation in pH (range: 6.4-9.3) and As in geothermal waters suggest mixing with groundwater. Mixing of geothermal waters is primarily responsible for contamination of freshwater resources and making them unsuitable for drinking or irrigation.

Natural Arsenic in Global Groundwaters: Distribution and Geochemical Triggers for Mobilization

“…The potential risk of surface and groundwater contamination by As is associated mainly with the amounts of As present in soils, because As is more highly concentrated in soils than rock [8,33,44]. Arsenic may be found in soil as inorganic species as well as binding to organic compounds; however, it exists predominantly as inorganic species in soil.…”

“…Arsenic also may exist naturally in geothermal systems and springs as a result of the mobilization of As from rocks and mineral phases, and As-contaminated geothermal systems and springs are recognized in many areas around the world (Table 1) [3,8,10,91]. The mobilization of As from rocks into geothermal fluids takes place mainly through active tectonic plate boundaries [91].…”

“…The mobilization of As from rocks into geothermal fluids takes place mainly through active tectonic plate boundaries [91]. Arsenic from major geothermal reservoirs and related geothermal manifestations, such as hot springs, fumaroles, and solfataras, may directly enter cold aquifers, the vadose zone, and surface waters [8,10]. Many volcanoes, hot springs, fumaroles, and geothermal wells may be found in the Pacific region of Latin America, and these geothermal systems are widely contaminated by As at elevated concentrations [91].…”

“…The primary source of As is natural, derived mainly from the interactions between groundwater and aquifer sediments and hard rocks of minerals, particularly pyrite (FeS 2 ), arsenopyrite (FeAsS), and other unspecified sulfide minerals [4][5][6], as well as secondary As-bearing minerals or mineral coatings, whereas industrial uses, agricultural activities, coal and oil exploitation and combustion, and mining of metal ores are anthropogenic sources that release As into groundwaters [7,8].…”

Arsenic ecotoxicology: The interface between geosphere, hydrosphere and biosphere

“…Neidhart et al [22] showcased their research results on how groundwater extraction has impacted As concentration distributions in groundwater of West Bengal (India). The article by Bundschuh et al [23] addresses geochemical processes related to geothermal activity which showed potential impacts on freshwater resources in Western Turkey. The last article of this section by Alarcón-Herrera et al [24] addresses the co-occurrence of As and fluoride in semi-arid regions of Latin America and they provided a detailed assessment of genesis, mobility and remediation options.…”