RESUMEN
Anomalous concentrations of hexavalent chromium have been detected in ground-water of the Adamantina Aquifer inat least 54 municipalities located in the northwestern region of the State of São Paulo, southeast Brazil, occasionallyexceeding the permitted limit for human consumption (0.05 mg.L-1). An investigation was conducted in the municipality of Urânia, where the highest concentrations of chromium were detected regionally. It was defined that the originof this contamination is natural, since high concentrations of chromium were detected in aquifer sandstones (averageof 221 ppm) and also in pyroxenes (6000 ppm), one of the main heavy minerals found in the sediments. Besides, noother possible diffuse or point sources of contamination were observed in the study area. Stratification of ground-waterquality was observed and the highest concentrations of Cr6+ were detected at the base of the aquifer (0.12 mg.L-1),where ground-water shows elevated values for redox potential (472.5 mV) and pH (8.61). The origin of Cr6+ in water may be associated with the weathering of pyroxene (augite), followed by the oxidation of Cr3+ by manganese oxides. The highest concentrations of Cr6+ are probably related to desorption reactions, due to the anomalous alkaline pHfound in ground-water at the base of the aquifer.
Concentrações anômalas de cromo hexavalente foram detectadas em águas subterrâneas do Aqüífero Adamantina em pelo menos 54 municipalidades localizadas na região noroeste do Estado de São Paulo, sudeste do Brasil, algumas vezes ultrapassando o limite máximo permitido para consumo humano (0,05 mg.L-1). Um estudo foi realizado no município de Urânia, onde as mais elevadas concentrações de cromo da região foram detectadas. A origem da contaminação foi definida como natural, pois foram detectadas concentrações de cromonos arenitos do aqüífero (média 221 ppm) e em piroxênios (6000 ppm), um dos principais minerais pesados encontrados nos sedimentos. Além disso, não foram observadas outras possíveis fontes de contaminação difusas ou pontuais naárea de estudo. Uma estratificação da qualidade da água no aqüífero foi observada e as mais elevadas concentrações de Cr6+ foram detectadas na base do aqüífero (0,12 mg.L-1), onde as águas subterrâneas apresentam valores elevados de potencial redox (Eh = 472,5 mV) e de pH (8,61). A origem do Cr6+ na água deve estar associada com o intemperismo do piroxênio (augita), seguida da oxidação do Cr3+ pelos óxidos de manganês. As maiores concentrações de Cr6+ estão provavelmente ligadas com reações de desorção, devido ao pH anomalamentealcalino da água subterrânea na base do aqüífero.
RESUMEN
El objetivo de la investigación fue determinar la presencia de fluoruros de aguas procedentes de vertientes y pozos cavados en la localidad de Rinconadillas de la Puna Jujeña. Dicha región fue seleccionada debido a que se quería corroborar la presencia de fluoruros, encontrados en la década del 80 por el organismo Agua Potable de la provincia de Jujuy, como así también ver si existía variación en la concentración de este contaminante natural en el transcurso del tiempo. La evaluación se realizó sobre 11 muestras de agua de vertientes y de pozos, que representan la totalidad de las fuentes en toda la localidad de Rinconadillas y alrededores. Otras 9 muestras fueron tomadas de Purmamarca, Tumbaya, Volcán, San Salvador de Jujuy y Palpalá, localidades que se alejan de Rinconadillas. Estas muestras consideradas testigos fueron seleccionadas sabiendo que, en estudios realizados anteriormente, no contenían fluoruros. De la totalidad de las muestras recolectadas en Rinconadillas, el 82 % superó el límite máximo recomendado por el Código Alimentario Argentino mientras que menos del 10% se encontraron por debajo de lo reglamentado. Las concentraciones de esta zona fueron superiores a las registradas en las muestras tomadas como referencias, determinándose diferencias significativas entre ambos grupos (p = 0,001). De las muestras testigos sólo una superó el límite superior recomendado por el Código Alimentario Argentino. Algunas de las concentraciones determinadas en el presente estudio fueron mayores a los registros de 15 años atrás y podrían indicar una variación creciente en el tiempo. Se ha observado que la población se ha dispersado en las cercanías a Rinconadillas con nuevas fuentes de aguas de bebida, que sólo reciben una eventual cloración. Se ha observado también en la población del lugar una marcada fluorosis dentalque debería ser evaluada clínica y epidemiológicamente.
The aim of this study was to determine the presence of fluorides in groundwaters from springs and wells belonging to Rinconadillas, a small town located in La Puna in the Province of Jujuy. This region was selected because fluoride has been detected during the '80 by Jujuy Water Agency and a comparative study of fluoride levels would provide information about the variation of concentrations of this natural contaminant along the time. In La Puna the study was conducted on eleven samples of groundwaters from springs and wells from Rinconadilllas and its surroundings. Nine further samples were obtained in Purmamarca, Tumbaya, Volcán, San Salvador de Jujuy and Palpalá, all ofthem far from Rinconadillas. Those samples were selected as prior studies determined that water from such towns does not contain fluoride. Eighty two percent of all the samples collected in Rinconadillas exceeded fluoride limits stated by Argentine Legislation (AL), while less than ten percent of the samples are below the stated values. Fluoride levels from this area were higher than the levels for the reference samples. For the blank samples, only one exceeds the maximum allowed level. Fluoride levels found in this study were higher than those coming from samples that have been analyzed 15 years ago indicating that fluoride levels in waters are increasing. It has also been observed that the population has moved to Rinconadillas surroundings having a drinking water form newsource that is only eventually chlorinated. A remarkable dental fluorosis is observed in the population, which should be clinically and epidemiologically assessed.