Substâncias húmicas aquáticas do rio Negro-AM: impacto da variação da sua composição na labilidade de íons metálicos e em seu efeito redutor de toxicidade aguda.

Abstract

This aim of this work is to investigate the metal complexation behavior of Aquatic Humic Substances (SHA) against the variations in the proportions of their majority fractions Humic Acid (HA) and Fulvic Acid (FA), pointing out the difficulties of differentiation and ways to minimize these difficulties. Therefore, samples of the Rio Negro SHA collected in August 2016 and in March, June, September and December 2012 were characterized. The characterization of their chemical components was made using the Elemental Analysis techniques, 13C Nuclear Magnetic Resonance, Fourier Transform Infrared Spectroscopy, Visible Ultraviolet Spectroscopy and Inductively Coupled Plasma Atomic Emission Spectrometry. Liability studies of Cu, Fe, Al, Mg, Mn and Zn metals in the different samples were made using the Tangential Flow Ultrafiltration (UF-TG) system and Cu2+ ions as exchanger ion. A new method of calculating the order of lability of the different metals has been suggested. The new calculation proposal was used in the results obtained by UF-TG in studies with SHA and its fractions AH and AF. Using the proposed method, it was possible to differentiate and order the lability of the metal ions present in the AH and AF fractions with that of the metal ions present in the SHA. The efficiency and impact of batch dialysis purification on the concentration of orginally complexed metal ions in SHA, AH and AF extracts were also studied. The results showed that seven batches of dialysis are required to reduce excess Na ions from the extraction of SHA and its fractions, and that K ions, originally complexed in SHA and its fractions, are lost during the dialysis process. These results reinforce the importance of estimating the loss of metal ions during the purification process, thus avoiding erroneous statements, for example in studies of metal ion exchange and determination of stability constants. The influence of the complexing character of SHA metal ions and its fractions was also observed in acute copper ion toxicity assays in Artemia Salina sp. In these tests, it was found that increasing the AH fraction in the SHA structure tends to improve its toxicity-reducing effect.