Comparative characterization of humic substances extracted from freshwater and peat of different apparent molecular sizes

Abstract

This paper compares the structural characteristics of aquatic humic substances (AHS) with humic substances from peat (HSP) through different analytical techniques, including elemental analysis, solid state ¹³C cross polarization/magic-angle-spinning nuclear magnetic resonance spectroscopy (¹³C CP-MAS NMR), ultraviolet/visible (UV/Vis) spectroscopy and Fourier transform infrared (FTIR) spectroscopy and total organic carbon (TOC). The AHS were extracted from water collected in a tributary of the Itapanhaú River (Bertioga/SP) using XAD 8 resin, and the HSP were extracted from peat collected in the Mogi Guaçu River bank (Luis Antonio/SP) with a KOH solution. After dialysis, both AHS and HSP extracts were filtered in membrane of 0.45 µm pore size (Fraction F1: < 0.45 µm) and fractioned by ultrafiltration in different apparent molecular sizes (AMS) (F2: 100 kDa-0.45 μm; F3: 30 kDa-100 kDa and F4: < 30 kDa). The extracts with the lowest AMS (F3 and F4) showed a higher number of aliphatic carbons than aromatic carbons, a higher concentration of groups containing oxygen and a higher percentage of fulvic acids (FA) than humic acids (HA) for both AHS and HSP. However, the AHS presented higher FA than HA content in relation to the HSP and distinct structural properties.