Investigação de diferentes estratégias de preparo de amostras de sedimentos de rio para determinação de elementos-traço por espectrometria de absorção atômica

Abstract

The determination of trace elements in sediments has being receiving special attention in the field of ecology and environmental chemistry. Such species are not biodegradable and have a tendency to accumulate in living organisms and sediments, thus contaminating the entire ecosystem. Thus, sediment may act as a reservoir of these species and can be used to investigate the history of pollution in certain areas. Within this context, the aim of this study was to develop and optimize a method of ultrasound-assisted extraction for the determination of Cr, Cu, Zn, Cd and Pb in sediments by atomic absorption spectrometry. Several extraction procedures were studied. To optimize the extraction conditions a fractional factorial design were used. The optimum conditions for extraction were: 0.1 g of sediment, 7.0 mL concentrated HF, 3.0 mL concentrated HCl, 3 h of sonication time and ultrasound bath temperature equal to 60 ° C. The results obtained by external calibration and standard additions were consistent at 95% confidence level for all analytes. The pyrolysis and atomization temperatures for the determination of Cd and Pb by GF AAS were studied. In the determination of Pb was used the chemical modifiers (Pd and Mg). The proposed extraction method showed adequate results in terms of precision (RSD < 10% with F AAS and < 20% with GF AAS). The accuracy was confirmed by spike tests (with recoveries between 89107%) and by analyzing the certified reference materials Buffalo River and Marine Sediment (with recoveries in the range of 74 to 106%). Compared to the official method for the digestion of sediment samples, the preparation time was lower, thus favoring the analytical frequency, and the use of lower volume of acid, reducing costs and minimizing the generation of waste chemicals. The method was applied to the analysis of samples from the Rio Doce and Córrego Igrejinha. About the Rio Doce samples, the results were below those maximum permitted by legislation for all analytes, with the exception of Cr, which showed alarming values, very close to the maximum acceptable level (90 mg kg-1). About the samples from Córrego Igrejinha, all values were high, indicating a strong environmental impact in the region.