Stable isotope and chloride, boron study for tracing sources of boron contamination in groundwater: Boron contents in fresh and thermal water in different areas in Greece

Boron is biologically an essential element but is toxic at high concentrations to plants (above approximately 1 mg/L in irrigation water) and probably to humans: The EU Drinking Water Directive fixes a threshold of 1 mg/L and the World Health Organisation (WHO) set a recommended limit at 0.3 mg/L now increased to 0.5 mg/L. Because of this potential toxicity and the need of implementation of EU regulation on national level, the study of the boron levels in both ground- and surface water is of great significance for water management. In Greece, a significant number of thermal, mineral and superficial water springs are found especially in Northern Greece, that present high boron values rendering such water unacceptable according to the European standards. Nevertheless, such ground waters or borehole water with high temperature and high boron content are used for irrigation and drinking purposes, and could therefore have an antagonistic effect on crop yield and health. In order to study the boron contamination and to elucidate the origin of B, we collected a number of hot and fresh water all over Greece. In all the water sampled, the boron concentration exceeds the limit of 0.3 mg/L, which is the former recommended WHO limit. Moreover, in the irrigation water examined, the boron concentration exceeds the value of 0.75 mg/L, which is the limit for sensitive plants (for plants of moderate and plants of high tolerance, these values vary between 0.75-3 and > 3 mg/L respectively). In all cases, elevated boron could be attributed to natural sources, geothermal activity and/or seawater intrusion into the aquifers. This finding has important implications for water management: In a setting of high natural geochemical background values, source control of the pollution is not possible and water managers have to cope with a local to regional geochemical anomaly that implies boron specific water treatment or mixing with unpolluted resources to bring concentrations down.