Interação entre a matéria orgânica natural, o cobre e microorganismos heterotróficos: implicações na dinâmica do metal e sua disponibilização para a biota aquática
Abstract
The increasing eutrophication and contamination of aquatic ecosystems motivates the
study of interactions between natural dissolved organic matter (DOM), metals and the biota.
Metals are mainly released into the environment by industrial processes, whereas organic
materials through municipal sewage sludge. The association of these two processes and its
effect on the environment poses unknown risks to aquatic communities. The support capacity of
aquatic systems is related to its ability to associate with dissolved elements. In this study, the
complexation capacity of Monjolinho Reservoir (eutrophic), from which the test organisms
were obtained, was evaluated. The results showed that two copper-complexing sites were
present, what contributes to the low free copper ion concentration in such environment. It is
known that natural DOM is formed by humic like and recently produced organic compounds.
Suwannee River natural organic matter was used throughout this investigation as models of
humic substance DOM (commercial standard), whereas as model substance of recently
produced organic material, cyanobacteria (Anabaena spiroides) exopolysaccharides were used.
Considering that the environmental fate and chemical speciation of copper are dominated by
natural DOM and that heterotrophic bacteria processes are responsible for nutrient regeneration,
carbon transfer and energy, it was also investigated the influence of the interaction DOM-Cuorganisms
on copper dynamic and bioavailability. The results showed that the natural bacteria
population was copper resistant, tolerating up to 10-6 M total copper concentration. The
degradation of DOM by heterotrophic bacteria, detected by fluorescence spectroscopy, revealed
that after Cu-complexed DOM degradation, the metal was liberated into the environment,
causing toxicity and bioaccumulation in the microbial food chain. Nevertheless, this was less
pronounced when the organic materials were exopolysaccharides. In general, the results showed
that copper complexed to natural DOM or exopolysaccharides was less toxic to the organisms
than free copper ions. The present results are a contribution to aquatic ecosystems management
and to the knowledge of copper speciation, availability and interaction with aquatic organisms,
as it relates to dissolved organic materials in aquatic ecosystems.