ARSENIC IN THERMAL WATERS OF GREECE

Abstract

The diffuse occurrence of As in natural waters, its relevant geochemical mobility in aqueous systems and its toxicity to human beings when consumed in enhanced doses, make this element one of the most problematic challenges of present water research. Arsenic in groundwater is often associated with geologic sources, but in some locations anthropogenic inputs can be extremely important. Volcanic degassing represents an important natural source of As to shallow aqueous systems. Arsenic is a minor but recurrent constituent of volcanic gases and geothermal fluids. It is also widely found in epithermal sulphide ore deposits, either as a major constituent (arsenopyrite, orpiment, realgar) or as a minor element in pyrite. As a result of the interaction with deep-rising fluids or leaching of ore deposits, groundwaters circulating in active volcanic-geothermal areas may contain high amounts of As. Arsenic in groundwater represents one of the major global health issues exposing millions of people to the risk of cancer and other As-related diseases, especially in southern Asia. Furthermore, previous studies evidenced that widespread areas in northern Greece display As concentrations above the European Maximum Admissible Concentration (MAC) of 10 µg/l. In this study As concentration were determined in 104 water samples collected in whole Greece. Forty-five of the samples are thermal waters (T > 30°C), 24 are hypothermal waters (T 20-30°C) and 35 are cold waters (T < 20°C). Arsenic concentrations span over 4 orders of magnitude ranging from < 0.2 to 5700 µg/l. They show a fair positive correlation with sampling temperature and cold waters exceed the MAC only in few cases. The contribution of geothermal activity to the As concentration of the studied groundwaters is further evidenced by the positive correlation between As and thermal-related elements like B, Li and F. The samples are too few to highlight a clear geographic distribution and high As values (> 100 µg/l) are found both in continental Greece (Chalkidiki, Sidirocastro in the north; Thermopyles, Edipsos in the central part; Kaiapha in the Peloponnesus) and along the South Aegean volcanic arc (Methana, Nysiros).