Hydrogeochemistry of fluoride in the Quequen river basin: natural pollutants distribution in the argentine pampa |
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| Authors: | D E Martínez O M Quiroz Londoño H E Massone P Palacio Buitrago L Lima |
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| Institution: | 1.CONICET,Mar del Plata,Argentina;2.Instituto de Geología de Costas y del Cuaternario,Universidad Nacional de Mar del Plata,Mar del Plata,Argentina;3.Universidad de Antioquia,Medellin,Colombia |
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| Abstract: | Fluoride pollution is a widespread problem in Argentina, as it is in many areas of the World. Former investigations have demonstrated
that the dissolution of volcanic glass disseminated in the loess-like sediments is the main source of fluoride in the Argentine
pampas. Nevertheless, fluoride distribution is erratic and the factors controlling it are not yet well-known. A large amount
of hydrochemical data collected in the Quequen Grande river catchment is used in order to contribute to the understanding
of fluoride distribution and mobility in groundwater in the Argentine pampas. The Quequen Grande river catchment is 10,000 km2. It extends between two low hills ranges of Precambrian metamorphic rocks and sedimentary Paleozoic rocks, filled by a thick
sequence of Cenozoic sediments, mainly silts and silt-clayed, with sand layers. These sediments form a multilayer phreatic
aquifer, which is recharged from precipitation infiltration, discharging through streams directly into the sea. Fluoride concentration
in surface water (n = 353) ranges between 0 and 6.5 mg/l, with an average value of 2.14 mg/l. Groundwater concentration (n = 135) is from 0 up to 5.7 mg/l, with an average of 1.84 mg/l. Considering the statistic distribution of fluoride, two groups
of samples can be determined. A dominant group between 0 and 3 mg/l, with a mean value around 1.5 mg/l, corresponding to samples
widely distributed in the catchment; and a second one group with fluoride contents between 3 and 6 mg/l, corresponding to
a smaller area in the central-west border. Two different sources are proposed. Volcanic glass dissolution is responsible for
dominant values in the catchment, while the weathering of biotite from the Paleozoic bedrock can be assumed to account for
the higher concentrations in the second group. |
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