Contaminação ambiental da Laguna Mundaú (Maceió-AL): determinação de mercúrio em amostras ambientais e biológicas

Abstract

The Mundaú Lagoon (Maceió - AL, Brazil) is part of the Mundaú- Manguaba lagoon estuarine complex (CELMM) and is considered to be an environment of socio-economic importance due to fishing for the local bivalve, the sururu (Mytella charruana). In this context, the inappropriate disposal of domestic and industrial waste increases the rate of environmental degradation in this ecosystem, including possible contamination by potentially toxic species, such as mercury. This study aimed to determine Hg in environmental (water, sediment, and sururu) and biological (blood and urine from local fishermen) matrices. Six sampling campaigns were conducted for the environmental samples from July 2021 to February 2023, each analyzing 11 sampling points. Cold vapor atomic fluorescence spectrometry (CV AFS) was used to determine Hg concentrations in the different types of samples. When necessary, the samples were acid-digested in a closed system. It is worth noting that in the water samples, the concentrations of total mercury (HgT), total dissolved mercury (HgDS), as well as the inorganic (Hgino) and organic (Hgorg) fraction of this element in the dissolved fraction were determined. In contrast, only the total mercury concentrations were determined in the other samples. The results obtained by this study concerning the environmental samples showed variations in the Hg concentration profiles between the samples, where from sample 1 to 3, there was a decrease in the concentrations obtained for HgT and HGDS in the water samples, and for HgT in the sediment and sururu samples. Thus, the concentration ranges (μg L-1) of HgT, HgDS, Hgino, and Hgorg in the water samples were, respectively: sampling 1 (< 0.01 - 15.71), sampling 2 (< 0.01 - 7.65), sampling 3 (< 0.01 - 3.58), sampling 4 (< 0.01 - 1.40), sampling 5 (< 0.01 - 0.36) and sampling 6 (< 0.01 - 0.89). In general, only water and sediment samples showed HgT concentrations above the permitted level, with excesses of 2 (sediment) to 80 (water) the maximum legal value. Throughout the sampling period, 50% of the water samples had HgT concentrations higher than those permitted by law. In the water samples, Hgorg was the majority species. However, national legislation only recommends limit values for HgT with values of 0.2 μg L-1 (water) and 0.3 μg g -1 (sediment). About the bivalve samples of the species Mytella charruana (native species) and Mytilopsis sallie (invasive species), all the HgT concentrations were below the legislated values, with concentrations ranges equal to 0.01 - 0.35 and < 0.01 - 0.07 μg g-1, respectively, in dry mass. The initial results indicate that the average value of HgT levels in the blood of the CELMM fishermen (n = 20) was 4.68 ± 1.39 μg L-1; in contrast, for the control group (n = 20), it was 2.06 ± 0.63 μg L-1, which means that 25% of the fishermen had values higher than those recommended by the EPA. For the urine samples from these two groups, values of 0.447 ± 0.19 μg L-1 (fishermen) and 0.147 ± 0.03 μg L-1 (control group) were obtained, although the concentrations were below the limits of current legislation7 . However, the level of HgT was around 3 higher with the fishermen. Finally, the monitoring of Hg in different samples can help understand the dynamics of the ecosystem and assist in implementing public policies aimed at making beneficial decisions for society.