Abstract
In this study, the extraction and characterization of aquatic humic substances (AHS) from two blackwater rivers in the Amazon basin was carried out in order to assess the seasonal effects in the AHS structure. In addition, an investigation of the complexing capacities (CC) of the structures containing the metal ions CdII, NiII and PbII was also done. The characterization (of the AHS) was done using UV-Vis, molecular fluorescence, and infrared spectroscopy. AHS from the Negro River showed more aromatic characteristics in its structures and molecular weight, than the AHS from the Caru River. The AHS studied presented a seasonal pattern characterized by higher humification levels during the rainy season. For all the metals, the AHS complexing capacity was higher for the Negro River. The highest complexing capacities were observed for the NiII assays, which were 0.56 and 0.12 µmol NiII mg-1 dissolved organic carbon (DOC), for AHS RN and AHS RC-II, respectively. We concluded that the transport, bioavailability, and toxicity, of these metal species should be higher for Caru River.
Highlights
In the aquatic environments, the organic matter (OM) can stem from autochthonous and allochthonous sources, being formed by simple and defined, or complex structures, with different reactivity within the functions of its chemical characteristics, microbiological and photochemical processes by which the precursor material had been alterated.[1,2,3] An important fraction of OM is present in a humified form
For aquatic humic substances (AHS) from the Carú River, the sample extracted during the dry season (RC-I) had Fmax at λexc/λem = 300/426 nm and AHS RC-II, the sample extracted during the rainy season, had Fmax at λexc/λem = 310/420 nm
The lower values H/C atomic ratio indicate the presence of more humificated material and they were correlated to higher HIX indexes, for the AHS the results were 1.17, 1.01 and 1.02, for RN, RC-I and RC-II, respectively, similar results as observed for fulvic fraction extracted from other blackwaters.[29,33,37]
Summary
The organic matter (OM) can stem from autochthonous and allochthonous sources, being formed by simple and defined, or complex structures, with different reactivity within the functions of its chemical characteristics, microbiological and photochemical processes by which the precursor material had been alterated.[1,2,3] An important fraction of OM is present in a humified form (humic substances, HS). Studies[12,13,20,21,22] were conducted to characterize, and to assess, the complexing capacity (CC) of aquatic humic substances (AHS) with metal species, in the rivers of the Amazon basin.
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