Otimização das condições instrumentais e avaliação de interferências não espectrais para a determinação da concentração de metais em águas superficiais por MIP OES

Abstract

Water is an essential resource for both human life and aquatic ecosystems, with significant economic and social importance. The anthropogenic dissemination of potentially toxic metals in water resources is a major ecological and public health concern on a global scale. The contamination of aquatic ecosystems by residual metals is critical due to their toxicity and accumulation potential, representing a threat to biodiversity and human health. The São Gonçalo Channel, located in the Lagoa Mirim Hydrographic Basin and connecting the Patos Lagoon to Lagoa Mirim, is an important water body in southern Brazil, with notable environmental and economic value. In this context, the aim of this study was to optimize the instrumental parameters of Microwave-Induced Plasma Optical Emission Spectrometry (MIP OES) and to evaluate potential interferences from easily ionizable elements in the determination of Al, Ba, Ca, Cu, Fe, K, Li, Mg, Mn, Na, Si, and Zn in surface water samples from the municipality of Pelotas, RS. Four sampling campaigns were carried out at five distinct points between May 2023 and March 2024. To enable multielement determination in natural water samples, optimization of MIP OES instrumental parameters was necessary to identify the best analytical conditions for each element. The selection of optimized parameters resulted in increased signal intensities for some elements—over 50% in certain cases—compared to the conditions recommended by the manufacturer. The accuracy of the results was assessed by analyte spiking, with recovery rates ranging from 82% to 116%, and relative standard deviations (RSD) below 8.1%, indicating good precision. Among the evaluated interferents, potassium showed more significant ionization interferences than calcium and sodium, as expected due to its lower ionization energy, which results in higher electron density in the plasma. However, these effects were mitigated through sample dilution. Regarding the concentrations obtained, variations were observed throughout the sampling period. During wetter months, increased levels of Al, Fe, and Mn were detected, attributed to enhanced surface runoff transporting sediments and particles into the water bodies. Elements such as Al, Cu, Fe, and Mn showed elevated concentrations in most samples, exceeding the maximum limits established by CONAMA Resolution 357/2005 for Class 2 freshwater. Elements such as Ba and Li were detected above the quantification limits, though they remained within the regulatory thresholds. The impacts of anthropogenic activities on the São Gonçalo Channel highlight the importance of continuous monitoring and the need for public policies aimed at the preservation of water resources.