U-isotopes and weathering rates in watersheds of Araxá city, Minas Gerais State, Brazil.

This work was conducted at Araxá city, Minas Gerais State, Brazil. The aim was to characterize by different approaches weathering rates at six watersheds occurring there. The study area is well-known in the country due to economic and touristic reasons. Beginning in the 1960's and 1970's, nowadays huge mining activities for niobium and phosphate fertilizer exploitation by different companies are taking place there along with the use of natural mineral waters for health treatment, following a tradition that started in the 19th century for tuberculosis treatment. The dataset utilized in this investigation comprised results obtained in the analysis of distinct geochemical compartments, i.e. rocks, soils, bottom sediments, rainwater and surface waters from small hydrographic basins. The waters of three catchments are extensively used by water-supply systems of Araxá city in order to meet the demand of this resource as a possible supply of drinking water for the local community. Hydrochemical (major and trace constituents) and radionuclides (238U, 234U, and 210Po) analyses of rainwater and water bodies samples allowed estimates of the fluxes in each drainage. These fluxes were subtracted from rainfall deposition, yielding positive net values only for bicarbonate and U-isotopes as natural tracers in all watersheds, which allowed to calculate chemical weathering rates of 2.6-38.9 ton/km2yr (bicarbonate) and 0.09-19.8 ton/km2yr (U-isotopes). Physical weathering rates were obtained from 210Pb data in bottom sediments and exceeded 200 to 1.3 × 105 times the chemical weathering rates evaluated by the U-isotopes approach, a finding compatible with others reported in literature but adopting a diverse conceptual framework. Thus, the development of all analytical protocols along this investigation permitted an integrated appraisal of distinct approaches applied to the same selected site, as well as a comparison of weathering rates with other values reported in the literature, improving the knowledge about this subject in Araxá city watersheds. The novel dataset reported in this paper constitutes an aid to the already existing number of weathering rates elsewhere, helping modellers engaged on predicting future landscape changes.

Hydrochemical and radiometric evaluation of fresh and thermal waters from Araxá city (Minas Gerais, Brazil).

This paper reports the hydrochemistry and activity concentration of the natural radionuclides 238U, 234U, and 210Po for three compartments of the hydrological/hydrogeological system in Araxá city, Minas Gerais State, Brazil: 1) mineral waters from the prominent springs Dona Beja (DBS) and Andrade Júnior (AJS), occurring at Barreiro area; 2) surface waters from Barreiro area and vicinity; and 3) rainwater. According to the Rule for Mineral Waters in Brazil (Register 7841) for temperature, the DBS water is cold (< 25 °C), while AJS is hypothermal (25-33 °C). The TDS (Total Dissolved Solids) concentration of DBS is low (70 mg/L), but high in AJS (2898 mg/L). The hydrogeochemical facies corresponded to sodium-(bi)carbonate for AJS and sodium/potassium-bicarbonate for DBS. The hydrochemical differences of DBS and AJS waters reflect the distinct characteristics of their respective aquifer systems. The DBS classification for TDS is the same of the Barreiro basin surface waters (mean TDS = 102 mg/L). Such value is somewhat higher than that of the rainwater and surface waters used for human consumption at Araxá city (TDS < 50 mg/L). The dataset reported in this paper indicated that fluoride and barium exceeded the WHO limits proposed in 2011 for drinking water. Among the natural radionuclides analyzed here that offer potential hazards for the human health is 210Po, whose WHO's limiting value of 100 mBq/L in drinking water was exceeded in rainwater, thus, restricting the use of this resource as a possible supply of drinking water for the local community.

Tracking pollutants in selected Brazilian drainages from araxá city.

Sediments geochemical data from Araxá city, Minas Gerais State, Brazil, have provided new insights on the pollutants inputs in different drainage systems of Araxá city, Minas Gerais State, Brazil. The sediments profiles (6) provided from a lake (Grand Hotel) and streams (Sal, Areia, Fundo, and Feio). The local municipality uses some waters (Areia, Fundo, and Feio streams) in water-supply systems. Because of the Brazilian environmental agency does not establish concentration guidelines for several heavy metals occurring in freshwater sediments, the values reported in this paper were compared with limits proposed elsewhere. Enrichment Factor (EF) values of 20-40 (very high enrichment) and EF > 40 (extremely high enrichment) were found for Ba (in two sediment core), Nb (in three sediment core) and Se (in four sediment core). The 210Pb chronological method was useful for tracking some major events that occurred in the history of Araxá city, showing concentration peaks around 1962 and 1993 for BaO, Nb2O5, Fe2O3, P2O5, SO3, SrO and CeO2 and around 1972 and 1999 for SeO2.