The influence of seasonalness on the structural characteristics of aquatic humic substances extracted from Negro River (Amazon State) waters: interactions with Hg(II)

Luciana C De Oliveira,André H Rosa,Julio C Rocha,Ézio Sargentini Jr,Wilson T L Da Silva,Marcelo L Simões,Ladislau Martin-Neto,Ricardo L Serudo

doi:10.1590/s0103-50532007000400028

Abstract

In this work, humic substances were extracted from water samples collected monthly from the Negro River basin in the Amazon state (Brazil) to study their properties in the Amazonian environment and interactions with the mercury ion considering the influence of seasonalness in this formation. The C/H, C/N and C/O atomic ratio parameters, functional groups, concentration of semiquinone-type free radicals, pH, pluviometric and fluviometric indices, and mercury concentrations were interpreted using hierarchical cluster analysis (HCA) and principal component analysis (PCA). The statistical analyses showed that when the pluviometric index was greater and the fluviometric index was smaller, the degree of humification of aquatic substances was greater. The following decreasing order of the degree of humification of the AHS collected monthly was established: Nov/02 to Feb/03 > Mar/02 to May/02 > Jun/02 to Oct/02. The greatest concentrations of mercury were detected in more humidified samples. These results suggest that due to inter and/or intra-molecular rearrangements, the degree of humification of aquatic humic substances is related to its affinity for Hg(II) ions.

Highlights

Fresh water streams have an important function in the global carbon cycle in that they conduct organic matter (OM) of terrestrial origin and transfer it to theVol 18, No 4, 2007 function in the Amazonian ecosystem
The solutions containing the aquatic humic substances (AHS) samples were heated for two hours to 70 °C and they were left to rest for twelve hours
Comparing the C/N atomic ratios with those found in literature (Table 3), there is an inference of a lesser degree of humification of the AHS samples utilized in this study, and comparable to values obtained for OM extracted from samples taken from the Amazon River having particle sizes between 0.1 and 63 μm.[41]

Summary

Introduction

Fresh water streams have an important function in the global carbon cycle in that they conduct organic matter (OM) of terrestrial origin and transfer it to theVol 18, No 4, 2007 function in the Amazonian ecosystem. Leenheer[36] and Ertel et al.[37] verified structural similarities of AHS in comparison with HS from soil samples from the central-Amazonian-basin region indicating that the AHS from black-water rivers are originally from podzol-type soils. An increase in the hydrogen content indicates a greater number of aliphatic carbons (CH2) than aromatic carbons (C=C).[39] The values of the H/C atomic ratios for samples of AHS vary between 1.17 and 1.33 (Table 2).

Results

Conclusion