Determinação de metais em água doce superficial por MIP OES com sistema multimode

Abstract

Surface fresh water represents a smaller portion of water on the planet and the most important in terms of water resources. The quality of the natural waters is a subject of great relevance, especially of those with multiple uses such as the San Gonçalo Channel, a natural channel that borders the city of Pelotas and that suffers a strong impact of the anthropic actions, being emphasized the eviction of domestic wastewater and the surface outflow of agrochemicals in a large area of the hydrographic basin where the channel is located. An analytical methodology employing the MIP OES with multimode system in was developed and validated for the determination multielement of fifteen metals in surface fresh water. The metals studied were Al, Ba, Bi, Cd, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sb, Sn and Zn. This methodology was applied to samples of water from the São Gonçalo Channel, collected in four collection points, in eight sampling series. Optimized conditions were concentration of HCl (0.5%) and NaBH4 (0.5%). The detection limits of the method ranged from 0.07 to 7.6 μg L-1 while the limit of quantification ranged from 0.2 to 25.3 μg L-1. The method presented good linearity with R2 higher than 0.99. Accuracy was assessed through the analysis of certified reference material, recovery assays and comparison of the results obtained by introducing samples in conventional nebulizator in MIP OES. The CRM analysis showed good agreement with the certified values, obtaining recoveries of 90 to 121%. In the recovery assays, values ranged from 84 to 120%, and the comparison between the methods demonstrated concordant results for the studied analytes. When the developed method was applied in samples of the São Gonçalo Channel, the concentration of Hg, Mo and Sn was below the LQ. The concentration of Sb was above the LQ in only three samples, being two of them with concentration higher than the limit established by the legislation. Concentrations above the LQ for Bi were found in some samples, however there is no limit to this metal in the legislation. The metals Ba, Cu, Cr, Ni and Zn were found in the analyzed samples at levels above the LQ, but did not exceed the reference values of the 357/2005 CONAMA resolution. Al, Cd, Fe and Pb showed concentrations above the limit of legislation for class 2 waters. Seasonal assessment of these four metals demonstrated the significant difference (p < 0,05) in Pb concentrations between dry and rainy periods, while for Cd, Al and Fe there was no significant difference. These results can establish a relation between sources of pollution, being attributed the discharge of wastewater in the water as the main contamination factor, followed by surface outflow.