ARSENIC IN THE GROUNDWATER OF OURO PRETO (BRAZIL): ITS TEMPORAL BEHAVIOR AS INFLUENCED BY THE HYDRIC REGIME AND HYDROGEOLOGY

Abstract

In the city of Ouro Preto (MG), water catchment for public supply originates from superficial drainage, springs, old abandoned mines and some driven wells. In the rocks of the region, As is originally found in gold-enriched sulphide-bearing mineral deposits. The weathering process introduces As into the hydrological system by dissolution of this element into the leachate. Measurement of the As content in the groundwater of some catchments was carried out during 1year and these measurements demonstrated high As content—up to 224μgL−1 of As(V)—during the rainy season (the maximum concentration limit according to World Health Organization is 10μgL−1). Lower values were observed during the dry season and in some sampling stations, As was not even detected. The As concentration variability during 1year shows a strict and direct relationship to seasonal and hydrological conditions. For city authorities, responsible for public water supply, it is necessary to perform a complete inventory of the water sources used and constantly monitor the As content in the water.