Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 55, Issue 11, Pages 7741-7751Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.est.1c01283
Keywords
dissolved organic matter; manganese oxide; ultrahigh resolution mass spectrometry
Categories
Funding
- National Science Foundation [DEB-2027284]
- National Science Foundation Division of Chemistry and Division of Materials Research [DMR-1644779]
- State of Florida
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The study found that manganese oxides can oxidize dissolved organic matter, but the selectivity for oxidation and oxidative alterations of compounds still need further investigation. Results showed that polycyclic aromatic hydrocarbons, polyphenols, and carbohydrates were more reactive to reduction, and oxidized species had higher molecular weights and hydrogen content.
Manganese (Mn) oxides can oxidize dissolved organic matter (DOM) and alter its chemical properties and microbial degradability, but the compound selectivity for oxidation and oxidative alterations remain to be determined. We applied ultrahigh mass spectrometry to catalog the macro-molecular composition of Suwannee River fulvic acid (SRFA) before and after oxidation by a Mn oxide (delta-MnO2) at pH 4 or 6. Polycyclic aromatic hydrocarbons, polyphenols, and carbohydrates were more reactive in reducing delta-MnO2 than highly unsaturated and phenolic (HuPh) compounds and aliphatics, but highly abundant HuPh contributed the most (similar to 50%) to the overall reduction of delta-MnO2. On average, oxidized species had higher molecular weights, aromaticity, carbon unsaturation degree, nominal oxidation state of carbon, and oxygen and nitrogen contents but were lower in hydrogen content compared to unoxidized species. The oxidation decreased these molecular indices and oxygen and nitrogen contents but increased the hydrogen content, with stronger changes at the lower pH. This DOM oxidation on polar mineral surfaces was more selective but shared similar selectivity rules to adsorption. The abiotic oxidation resembles microbial oxidative degradation of organic matter, and Mn oxide-oxidizable carbon may be a useful index for detection and identification of labile organic carbon.
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