Distribution and chemical speciation of arsenic and heavy metals in highly contaminated waters used for health care purposes (Srebrenica, Bosnia and Herzegovina)
Highlights
► Acid mine drainage type waters used for decades for healthcare purposes were analysed. ► Extremely high contents of As (up to 6.6 mg/L) and other heavy metals were registered. ► Acidic springs decreased pH of the river from 7.3 to 3.4 in only 1.5 km distance. ► Geochemical modelling revealed dominance of oxidized forms of all elements.
Introduction
Arsenic (As) is an element of environmental concern worldwide because of its potential toxicity to humans. Exposure to drinking waters with high arsenic levels (World Health Organization limit > 10 ppb; WHO Guidelines for Drinking-water Quality, 2011) have been associated with adverse health effects (Kaltreider and Hamilton, 2001, Nguyen et al., 2011). There is also scientific interest dedicated to the consequences of chronic ingestion (Kapaj et al., 2006, Liang et al., 2011, Mazumder and Dasgupta, 2011). Among the potential sources of arsenic in ecosystems, volcanism and related hydrothermal systems are of great importance (Nriagu, 1989). Ballantyne and Moore's (1988) study on arsenic aquatic geochemistry in hydrothermal stems showed the positive dependence of arsenic concentrations with reservoir temperature; a similar relation between arsenic and discharge temperatures has been reported in hotsprings (e.g., Aiuppa et al., 2003, Webster, 2003). Arsenic can also be associated with geothermal waters and has been reported in several regions, such as Iran, Greece or Italy (Aiuppa et al., 2006, Angelidis et al., 2007, Haeri et al., 2011). Geothermal waters are therefore known to be arsenic rich, but studies dedicated solely to arsenic, its concentration and its relationship to other metals in cold mineral waters are scarce.
The chemistry of As in aquatic systems is quite complicated and significantly differs from that of trace metals. In such environments, the arsenate (H2AsO4− and HAsO42 −) and arsenite (H3AsO3) species are usually predominant (Chakravarty et al., 2002). These species have different mobility and toxicity to humans (Lenoble et al., 2002, Dixit and Hering, 2003). Their proportion is closely linked to the redox potential of the ecosystem (Masscheleyn et al., 1991, Katsoyiannis et al., 2007, Garnier et al., 2010, Weigand et al., 2010). The governing mechanisms concerning As in environment submitted to significant Eh gradient (e.g. at the water/sediment interface, AMD, …) depend mainly on the geochemistry of the considered ecosystem. The most significant are i) release into the water through the dissolution of arsenic-bearing phases, ii) or retention onto oxides (Wang and Mulligan, 2006, Amstaetter et al., 2010).
Central Europe is one of the many parts of the world facing natural water arsenic contamination (Krüger et al., 2005, Dangić, 2007, Kristoforović-Ilić et al., 2009, Ravenscroft et al., 2009, Ujević et al., 2010). Srebrenica area (eastern Bosnia and Herzegovina) is well known for its long mining history, as well as for its mineral waters of specific composition (Dangić and Dangić, 2007). Recent sediment analysis from one of these water springs, Ljepotica (Dangić and Dangić, 2001), showed that they are very rich in arsenic, lead and iron. These mineral springs have a very low pH, caused by the oxidation of sulphides to sulphate. Such low pH leads to the dissolution of minerals, which then enriches the water with different elements and can lead to excessive concentrations (Casiot et al., 2009). This is the common scenario in active or abandoned mines with acid mine drainage waters (AMD), which are considered to have such harmful effects on aquatic life that only adapted microorganisms can be encountered (Bruneel et al., 2006). However, unlike AMD, Srebrenica waters were used for decades, and continue to be used, for health-care purposes despite evidence of high arsenic and iron(II) content (Dangić, 2007). Still, no studies have surveyed the co-existing elements and their relationship to such extreme physical chemical parameters.
The extreme chemical changes apparent in this study are also of interest as the element composition varies from “normal” river water composition to an abnormal environment (similar to AMD), within a very short distance (1.5 km). Thus, the aims of this study were to provide i) a detailed chemical composition (especially of arsenic and other metals) of the river and its associated springs ii) to assess chemical speciation, as well as the dynamic behaviour of elements using PHREEQC (Parkhurst and Appelo, 1999) and WHAM-VI (Tipping, 1998) speciation codes.
Section snippets
Historical background of Srebrenica
“Srebro” means “silver”. Since the fourth century AD, Romans called Srebrenica “Argentaria” after the silver ore. After the Romans, Turks and Austrians exploited the local mineral ores and left behind many mining trenches, which favoured the gradual formation of mineral springs. Evliya Çelebi, the famous Turkish traveller, was the first to publish information regarding mineral water from this area in the second half of the 17th century (Pašagić, 2008). The Austro-Hungarian physician Dr. Hans
Experimental
Water samples were filtered on-site by 0.45 μm syringe filters (Sartorius), immediately acidified with HNO3 to pH < 2 and stored in precleaned (washed with 10% HNO3 then thoroughly MilliQ water rinsed) HDPE bottles. Unfiltered samples were also acidified on-site and filtered through a 0.45 μm syringe filter just before measurement (ca. three months later) in order to remove potential small particles present in sample which are undesirable for ICP-MS measurement. Through acidification, elements
Major components, physico-chemical parameters and fluorescence measurements
The concentration of some of the major cations and anions varied between different springs by almost one order of magnitude. Numerical data for all measurements are given in the Supporting information document (SI). The highest concentrations of SO42 − (2.5 g L− 1) and K (29 mg L− 1) were measured at spring S1, whilst Ca was highest at springs S4 and S5 (~ 120 mg L− 1). High sulphate concentration, originating from sulphide oxidation, results in the low pH of these spring waters (Rimstidt and Vaughan, 2003
Environmental and health considerations
The presence of high to very high levels of arsenic does not modify the taste, colour or odour of water. Consumption of high to extreme levels of As can lead to potential chronic or acute toxicity. Chronic toxicity is still not fully understood, and remains the focus of a great deal of research due to the global populations at risk (Mazumder and Dasgupta, 2011). The Bijela Rijeka River springs are mainly used by humans for external use (e.g. bathing), which is thought to be the least dangerous
Conclusions
Arsenic and heavy metal contents as well as their distributions and chemical speciation were studied in river waters and in five connected acidic spring waters near Srebrenica town (Bosnia and Herzegovina). These spring waters are known as arsenical-ferrous waters, having an acidic pH (down to 2.2). This natural water system is of research interest as it represents chemistry ranging from normal river water to an effluent similar to typical acid mine drainage waters. Furthermore, these highly
Acknowledgements
This work was financially supported by a PHC ECONET (project 18842QB) project and by the Croatian Ministry of Science, Education and Sport project no. 098-0982934-2720. The authors would like to thank the Mayor of Srebrenica Mr Osman Suljić and Head of spatial planning Mr Senad Subašić, for their cooperation and hospitality during the sampling. The authors wish also to thank Dr. Kristopher Gibbon-Walsh for the attentive linguistic corrections throughout the article.
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