Interactions of Zn(II) Ions with Humic Acids Isolated from Various Type of Soils. Effect of pH, Zn Concentrations and Humic Acids Chemical Properties

Abstract

The main aim of this study was the analysis of the interaction between humic acids (HAs) from different soils and Zn(II) ions at wide concentration ranges and at two different pHs, 5 and 7, by using fluorescence and FTIR spectroscopy, as well as potentiometric measurements. The presence of a few areas of HAs structures responsible for Zn(II) complexing was revealed. Complexation at α-sites (low humified structures of low-molecular weight and aromatic polycondensation) and β-sites (weakly humified structures) was stronger at pH 7 than 5. This trend was not observed for γ-sites (structures with linearly-condensed aromatic rings, unsaturated bonds and large molecular weight). The amount of metal complexed at pH5 and 7 by α and γ-structures increased with a decrease in humification and aromaticity of HAs, contrary to β-areas where complexation increased with increasing content of carboxylic groups. The stability of complexes was higher at pH 7 and was the highest for γ-structures. At pH 5, stability decreased with C/N increase for α-areas and -COOH content increase for β-sites; stability increased with humification decrease for γ-structures. The stability of complexes at α and β-areas at pH 7 decreased with a drop in HAs humification. FTIR spectra at pH 5 revealed that the most-humified HAs tended to cause bidentate bridging coordination, while in the case of the least-humified HAs, Zn caused bidentate bridging coordination at low Zn additions and bidentate chelation at the highest Zn concentrations. Low Zn doses at pH 7 caused formation of unidentate complexes while higher Zn doses caused bidentate bridging. Such processes were noticed for HAs characterized by high oxidation degree and high oxygen functional group content; where these were low, HAs displayed bidentate bridging or even bidentate chelation. To summarize, the above studies have showed significant impact of Zn concentration, pH and some properties of HAs on complexation reactions of humic acids with zinc.

The influence of weathering and soil organic matter on Zn isotopes in soils

“…Whereas solid organic matter decreases Zn solubility by sorbing Zn on to surface functional groups (Boguta and Sokolowska, 2016), the complexation of Zn with dissolved organic compounds increases Zn solubility and mobility (Weng et al, 2002;Houben and Sonnet, 2012). Soil organic matter turnover is an additional process which can affect Zn solubility as Zn released during litter decomposition may be leached into the soil or become sorbed by the organic matter of the soil surface (Scheid et al, 2009).…”

“…The pool of Zn associated with stable soil OC potentially constitutes a sink of Zn preserved in soils, which might also exist in organic-rich sediments. To date, most studies investigating the impact of SOM on Zn biogeochemical cycling have predominantly focused on the relative contribution of dissolved organic matter and bulk soil organic matter on Zn mobility (Sauvé et al, 2000;Fan et al, 2016;Boguta and Sokolowska, 2016). By contrast, the specific role of the stable pool of SOM on Zn biogeochemical cycling remains poorly understood.…”

Colloidal Mobilization and Fate of Trace Heavy Metals in Semi-Saturated Artificial Soil (OECD) Irrigated with Treated Wastewater

“…Obviously A 245 is an indirect measure of DOM and does not give information about the quality of organic matter and this is another reason for the observed data dispersion. As discussed below, molecular characterization of DOM, and in detail its structure, aggregation state, humification degree, molecular weight distribution, presence of metal chelating functional groups are all factors that influence the interaction with HMs [20,25]. From the observation of 3DEEM (Figure 4) it was clear that at the experimental time corresponding to the metal accumulation, the features of the organic substance in the leachate were significantly different from the background.…”

“…The displacement was attributable to the presence of higher conjugation in the aromatic system as well as to the presence of auxochromes functional groups. The increase in ex-em wavelengths was also associated with higher molecular weight distribution and "humic" character of the fluorophores [19,20]. Further information was obtained via the 1 H-NMR spectra of the leachates collected at days 6.5, 8.5, 9.5, plotted in Figure 5.…”

Nutrient acquisition and eucalyptus growth affected by humic acid sources and concentrations

“…However, since nutrient solution is a medium that is not highly buffered, the HA can form complexes with nutrients of lower availability, especially with metals, which would affect their acquisition by plants (PINHEIRO et al, 2010). The main factor that controls the bioavailability of the complexes formed between nutrients and HA is their chemical stability (BOGUTA; SOKOŁOWSKA, 2016;NUZZO et al, 2013). Tomasi et al (2014), in cucumber plants, verified an increase in acquisition of Fe combined with humic fractions extracted in water.…”