Abundance and distribution of fluoride concentrations in groundwater: La Ballenera catchment, southeast of Buenos Aires Province, Argentina

Abstract

High concentrations of fluoride have negative effects on human health, and it is one of the most widespread contaminants in groundwater, having being found in high concentrations in different countries over the entire world. Fluoride concentrations exceeding the drinking water levels are very frequent in the region known as Pampa Plain in Argentina, associated with loess-like sediments bearing volcanic shards and calcium carbonate concretions. In this study, the behavior of fluoride in the catchment of La Ballenera creek is performed to contribute to the understanding of the processes controlling its distribution at catchment scale. The catchment is around 100 km2, mostly in a flat landscape, outflowing into the Atlantic Ocean. The concentration of major ions, silica and fluoride was measured on 34 groundwater and 9 surface water samples obtained in October 2013. All the samples, both streamwater and groundwater, were sodium bicarbonate type with an average pH of 8 and 7.3, respectively. The fluoride concentrations in groundwater ranged between 1.1 and 2.5 mg/L with an average value of 1.9 mg/L. Fluoride concentrations in streamwater were close to groundwater concentrations indicating the predominance of baseflow on surface water composition. The variations in the contents of fluoride are due to two main factors, one geological?geomorphological and the other geochemical. The first one is related to the dominance of loess-like sediments formed by minerals bearing fluoride, and the second one is related to the control resulting on calcite precipitation adsorbing fluoride ions.