Especiação de antimônio em amostras de água mineral e especiação de cromo em águas naturais empregando métodos de microextração e espectrometria de absorção atômica

Abstract

Antimony and chromium are elements present in the environment naturally or due to anthropic activities. The behavior, bioavailability, toxicity and transport of these elements are dependent on their specific forms, i.e., their speciation. Thus, it is important to know the different species of this element in a specific medium. Thereby, this work proposes to implement and validate in laboratory analytical protocols for the study of Sb and Cr speciation in mineral and natural water, employing extraction technique with detection by atomic absorption. The Sb speciation by cloud point extraction involved the selective extraction of Sb(III) at pH 2, with ammonium pyrrolidinedithiocarbamate - APDC (complexing agent) in surfactant medium (Triton X-114). By the same procedure was performed the determination of the total Sb content, however after reduction of Sb (V) to Sb (III) using L-cysteine. This protocol made possible an extensive study of the presence of Sb(III) and Sb(V) in Brazilian samples of bottled mineral water with PET. The mean concentration of Sb (total) for 39 freshly packaged samples was 4 ± 1.4 μg L-1, and 70% of the samples were within the limits acceptable by ANVISA (5.0 μg L-1). The majority species in the samples was Sb(III) with 53 to 79% of the total Sb content, suggesting the migration of Sb2O3 from PET to the beverage. With five brands of bottled mineral water was conducted a study, with samples analyzed for six months. Sb(total) content in mineral water increased from 2 to 27% after 6 months of storage. These results indicate that migration of the Sb present in the PET to the bottled beverage occurs. The migration of Sb from PET to mineral water was evaluated under different storage conditions (time, temperature, sun exposure) using the beverage as simulant and with food simulants (ultrapure water and acid solution). In these tests, when storage temperature increased to 80 °C was observed an increase of up to 214% in Sb content. When samples were exposed for 7 days to solar radiation was observed an increase of up to 323% in Sb content and when packaging were maintained for 10 days with acetic acid simulant was observed an increase of up to 600%. Regarding the distribution of species, the species that presented the most significant increase was Sb(III). The Cr speciation by ultrasound emulsification microextraction involved the selective extraction of Cr (VI) and preconcentration with organic extractor solvent, tributylphosphate (TBP), in HCl and NaCl medium. . It was performed the dispersion of the extractive solution with an ultrasonic bath in place of a dispersing solvent. By the same procedure, the determination of the total Cr(III) content was performed, but after oxidation of Cr(III) to Cr(VI) using KMnO4. A Cr speciation study in samples of natural water from the West, Center-West and Campos Gerais from the State of Paraná, Brazil was carried out. The total concentrations of Cr were less than 1.0 μg L-1,therefore, these levels are compatible with uncontaminated water. Cr dissolved was the largest fraction for the samples, indicating that Cr may have a greater mobility capacity and possible bioavailability in these waters. Regarding the distribution of Cr in the dissolved fraction, the majority fraction was Cr(VI). This is the more toxic specie and more expected form in oxygenated natural waters. The variability in the results shows the need for monitoring of the total concentrations of theses elements and their speciation in aquatic environments and bottled waters, as a way to evaluate their toxicity and guarantee social and environmental security.