This work reports an alternative, fast and robust method, for the determination of total As, As(III) and As(V) by HG-AAS without the use of prereductants. The method is based on the different rates of arsine formation of the inorganic As species and the effect of As(III) in the signal obtained for total As. Groundwater and mineral spiked waters were used to sample preservation evaluation. The method was validated by the determination of As in SRM 1640 and used in the determination of total As and its inorganic species in groundwater samples collected from mines in the Iron Quadrangle - MG.

No Quadrilátero Ferrífero (QF), o abastecimento público de água é feito principalmente com a captação de águas das bacias hidrográficas. Entretanto, em alguns locais, há a utilização de água subterrânea, proveniente de nascentes ou mesmo de minas abandonadas, para o abastecimento humano. As principais fontes naturais de As no QF estão relacionadas às rochas que hospedam depósitos auríferos sulfetados. As fontes antrópicas de As são as pilhas de rejeito, solos e sedimentos contaminados. Em águas coletadas em algumas minas auríferas subterrâneas e nascentes das regiões de Ouro Preto e Mariana, foram encontradas concentrações de As total variando de 2 a 2980µg/L e de As3+ de 1 até 86 µg/L. Com base nos estudos geológicos e hidrogeoquímicos da ocorrência de As, nas rochas e nas águas subterrâneas, observou-se que as maiores concentrações de As são encontradas nos aqüíferos hospedados em rochas que possuem sulfetos e carbonatos, embora as concentrações dos aqüíferos que possuem somente sulfetos também foram elevadas. O monitoramento de As na água subterrânea deve ser periódico, independentemente de sua ausência num primeiro momento, nos poços e em outras fontes de captações de águas subterrâneas atualmente em utilização no abastecimento público ou privado.

In the Iron Quadrangle region the public supply of water is done mainly by the impound of water of watersheds. However, in some places, the population use spring water or ground water from closed mines for human consumption. The main natural sources of As in the Iron Quadrangle are related to the rocks that contain lode gold deposits. The antropic sources of As are contaminated refuse piles, soil, and sediment. It was found total As concentration varying from 2 to 2,980 µg/L and As3+ from 1 to 86 µg/L in water samples collected in underground gold mines, artesian wells, and springs in Ouro Preto and Mariana counties. Based on geological and hydrogeochemical studies of the occurrence of As in rocks and groundwater, it was found that the highest As concentrations occurred in aquifers hosted in carbonate sulphide rich rocks. The As monitoring in underground water should be done periodically, independent of its absence in a first instance, in wells and other groundwater caption sources that are used nowadays for public or private suppliers.