Abstract
Fulvic acids (FA) are one of the components of humic substances and play
an important role in the interaction with metallic species and,
consequently, the bioavailability, distribution and toxicity of metals.
However, only a few studies have investigated these FA properties in
specific environment, such as anthropogenic soils. Therefore, knowledge
about FA molecular composition as well as the FA-metal interaction is
essential to predict their behavior in the soil. For this reason, the
aim of this study was to investigate the molecular composition of FA
extracted from two sites in an anthropogenic soil (Terra Mulata), from
the Amazon region, as well as their interactions with Cu(II) ions as a
model. Results from C-13 NMR, infrared and elemental analysis showed
that these FA are composed mostly by alkyl structures and
oxygen-functional groups, e.g., hydroxyl, carbonyl and carboxyl. The
interaction with Cu(II) ions was evaluated by fluorescence quenching, in
which the FA showed both high quantity of complexing sites per gram of
carbon and good affinity to interact with the metal when compared with
other soil FA. The results showed that the complexation capacity was
highly correlated by the content of functional groups, while the binding
affinity was largely influenced by structural factors. In addition,
through the lifetime decay given by time-resolved fluorescence, it was
concluded that static quenching took place in FA and Cu(II) interaction
with the formation of a non-fluorescent ground-state complex. Therefore,
this fraction of soil organic matter will fully participate in
complexation reactions, thereby influencing the mobility and
bioavailability of metal in soils. Hence, the importance of the study,
and the role of FA in the environment, can be seen especially in the
Amazon, which is one of the most important biomes in the world.
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