Especiação de metais pesados em sedimentos aquáticos de um reservatório costeiro no Nordeste do Brasil

Abstract

Metals such as Cd, Cr, Cu, Ni, Pb and Zn have the potential to cause toxic effects and have several human sources such as domestic and industrial sewage, agrochemicals and emissions from vehicles powered by petroleum derivatives. The choice of method for extracting these metals from different matrices (e.g. water, soil, plant) can vary according to the desired objective. Single-step extraction methods can be used in plant metal availability analyzes and are more aimed at extracting the total bioavailable phase. Sequential extraction procedures are among the most commonly used methods to obtain information on the speciation of trace metals in contaminated soils and sediments. Our general objective was to evaluate the relationship between the results of ecotoxicological tests and trace metals removed (leached) from different chemical phases (exchangeable, reducible, oxidizable and residual) in the bottom sediments of Extremoz Lake, in Rio Grande do Norte, Brazil. The two specific objectives were: to evaluate, by different extraction methods (ME – Mehlich-1 and SEP – Sequential Extraction Procedure), the availability of heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) in aquatic sediments of the Extremoz Lake; to evaluate the influence of heavy metals released from different bioavailable chemical fractions in sediments on the survival of the amphipod Hyalella azteca. The results showed that the extraction performed by SEP, when compared to ME, showed greater efficiency in removing the metals Cd, Cr, Cu and Zn according to the averages obtained and, among these elements, only Cd did not have significant correlations with the survival of H. azteca. The results of the SEP extraction indicated that the bioavailable chemical fractions may reflect the interactive effect of metals in the mixtures on the survival of the test organism. Even though they do not point to toxic effects in the short term, the bioaccumulation of metals such as Cd, Cr, Cu, Ni, Pb and Zn may have future consequences. Works like this one enable a perception of the constant degradation of aquatic environments due to anthropogenic influence, highlighting the importance of deepening more detailed studies related to the physical and chemical characteristics of water reservoirs in urban environments.