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Pollution of the Arctic Ocean by potentially toxic elements (PTEs) is a current environmental problem. Humic acids (HAs) play an important role in the regulation of PTE mobility in soil and water. The permafrost thaw releases ancient organic matter (OM) with a specific molecular composition into the Arctic watersheds. This could affect the mobility of PTEs in the region. In our study, we isolated HAs from two types of permafrost deposits: the Yedoma ice complex, which contains pristine buried OM, and the alas formed in the course of multiple thaw–refreezing cycles with the most altered OM. We also used peat from the non-permafrost region as the recent environmental endmember for the evolution of Arctic OM. The HAs were characterized using 13C NMR and elemental analysis. Adsorption experiments were conducted to assess the affinity of HAs for binding Cu2+ and Ni2+. It was found that Yedoma HAs were enriched with aliphatic and N-containing structures as compared to the much more aromatic and oxidized alas and peat HAs. The adsorption experiments have revealed that the peat and alas HAs have a higher affinity for binding both ions as compared to the Yedoma HAs. The obtained data suggest that a substantial release of the OM from the Yedoma deposits due to a rapid thaw of the permafrost might increase the mobility of PTEs and their toxicity in the Arctic Ocean because of much lesser "neutralization potential". [ABSTRACT FROM AUTHOR]

The objective of this work was to study sorption of dissolved organic matter (DOM) onto Bondesil PPL and Bond Elut PPL sorbents with particular attention to impact of sorption loading on molecular composition of the DOM isolated with a use of solid phase extraction (SPE). It was shown that the batch sorption isotherms were best fitted with the Langmuir model, the sorption constants were 8.6·103 L·kgOC−1 and 10.7·103 L·kgOC−1 for Bond Elut PPL and Bondesil PPL, respectively. Breakthrough curves were satisfactorily fitted by a logistic equation; the maximum sorbent loading was 13% (wt. dissolved organic carbon) for both sorbents. The relationship between loading values and optical descriptors of the DOM at the column exit showed preferential sorption of low molecular weight aromatic DOM components in the range of low loading values (up to 4%), the similar trends were observed for size exclusion chromatography (SEC) measurements. Much lesser impact of loading onto molecular composition was observed within the range from 4 to 8% dissolved organic carbon (DOC). Given high recovery values (70–85%) in this loading range, it can be recommended as preferential for conducting DOM isolation from natural waters using SPE PPL-modified sorbents. [ABSTRACT FROM AUTHOR]

Redox moieties, which are present in the molecular backbone of humic substances (HS), govern their antioxidant properties. We hypothesized that a directed modification of the humic backbone via incorporation of redox moieties with known redox properties might provide an efficient tool for tuning up antioxidant properties of HS. In this work, hydroquinonoid and hydronaphthoquinonoid centres were used, which possess very different redox characteristics. They were incorporated into the structure of coal (leonardite) humic acids CHA) and peat fulvic acids (PFA). For this goal, an oxidative copolymerization of phenols was used. The latter was induced via oxidation of hydroquinones and hydroxynapjtaquinones with a use of Fenton's reagent. The structure of the obtained products was characterized using NMR and FTIR spectroscopy. H/D labelling coupled to FT ICR mass spectrometry analysis was applied for identification of the reaction products as a tool for surmising on reaction mechanism. It was shown that covalent -C-C- bond were formed between the incorporated redox centers and aromatic core of HS. The parent humic acids and their naphthoquinonoid derivatives have demonstrated high accepting capacity. At the same time, fulvic acids and their hydroquinonoid derivatives have possessed both high donor and high antioxidant capacities. The kinetic studies have demonstrated that both humic acids and their derivatives showed much slower kinetics of antioxidant reactions as compared to fulvic acids. The obtained results show, firstly, substantial difference in redox and antioxidant properties of the humic and fulvic acids, and, secondly, they can serve as an experimental evidence that directed chemical modification of humic substances can be used to tune and control antioxidant properties of natural HS. [ABSTRACT FROM AUTHOR]