ABSTRACT

High natural fluoride (up to 6.1 mg/l) and boron (up to 2.1 mg/l) concentrations in groundwater are recorded in western Estonia, where a carbonaceous Silurian-Ordovician aquifer system is the main source of drinking water. The aim of this study is to examine the dissolution of boron and fluoride from different carbonate rocks using batch dissolution tests. The total boron and fluorine concentration within carbonate rocks varies between 100-1000 and 5-150 mg/kg, respectively. Generally, boron and fluoride concentrations increase as the amount of terrigenous material in the rock increases. Laboratory leaching experiments showed that the amount of leached boron and fluoride was proportional to the content of these elements in the rock samples. Further, boron and fluoride concentrations in leachates were positively correlated with the amount of terrigenous material in rocks. Both boron and fluoride concentrations in leachates continually rose over 49 days of leaching. Long-term water-rock interaction is responsible for the high boron and fluoride contents in groundwater of western Estonia.