Roles of Natural Phenolic Compounds in Polycyclic Aromatic Hydrocarbons Abiotic Attenuation at Soil–Air Interfaces through Oxidative Coupling Reactions

Abstract

Little information is available on the roles of natural phenolic compounds in polycyclic aromatic hydrocarbons (PAHs) attenuation at dry soil–air interfaces. The purpose of this study was to determine the roles of model phenolic constituents of soil organic matter (SOM) on the abiotic attenuation of PAHs. The phenolic compounds can significantly change the attenuation rates of PAHs, among which hydroquinone was the most effective in promoting anthracene and benzo[a]anthracene attenuation. Product identification and sequential extraction experiments revealed hydroquinone enhanced the formation of oxidative coupling products and promoted the incorporation of PAHs into humic analogues, thereby reducing potential risks to humans and ecosystems. Electron paramagnetic resonance spectroscopy analyses showed both PAHs and phenolic compounds could donate electrons to Lewis acid sites of soil minerals, resulting in the generation of persistent free radicals (PFRs). PFRs could promote the generation of ·OH to enhance PAH oxidation and could cross-couple with PAHs, resulting in high-molecular-weight oxidative coupling products. This study revealed for the first time the reaction mechanism between PAHs and phenolic components of SOM under relatively dry conditions and provided new insights into promoting PAHs detoxification in soils but also a potential strategy to increase the organic carbon sequestration.

Molecular Weights of Dissolved Organic Matter Significantly Affect Photoaging of Microplastics

“…Significant four characteristic peaks of intensity 1:2:2:1 and three characteristic signals of intensity 1:1:1 were detected in the system where PSMPs were coincubated with FA <1kDa and HA <1kDa under UV illumination, which were stronger other MW DOM (Figure S10). In simulated sewage treatment processes (40−48 μm bulk white PSMPs) and natural vitamin C-induced processes (1 μm globular white PSMPs), similar signals can be observed, but with a weaker overall intensity, 16,45 possibly predicting a higher environmental activity and ROS-generating capacity of lower MW DOM. In addition, Fe 2+ was not detected within the detection limit of phenanthroline-UV spectrophotometry in different MW DOM, which directly refuted our earlier hypothesis and confirmed that signals in the EPR were not derived from the Fenton reaction.…”

“…In addition, Fe 2+ was not detected within the detection limit of phenanthroline-UV spectrophotometry in different MW DOM, which directly refuted our earlier hypothesis and confirmed that signals in the EPR were not derived from the Fenton reaction. It has been suggested that even without UV irradiation, soil organic matter or biochar with condensed structures rich in phenol and quinone moieties are able to transfer electrons to oxidants (O 2 ), , resulting in the formation of some resonance-stabilized radicals, such as cyclopentadienyls, and phenoxyls that further induce continuous ROS production through redox cycling, ultimately oxidizing and even mineralizing organic pollutants. These mechanisms enabled the generation of ROS from DOM containing various chromophores (e.g., phenolic and quinone moieties) in dark reactions with PSMPs.…”

Natural Attenuation of 2,4-Dichlorophenol in Fe-Rich Soil during Redox Oscillations: Anoxic–Oxic Coupling Mechanism

“…The cross-coupling process is common in the solid surface according to previous study . In this study, the 2-CP molecule was liable to be sorbed on the soil surface due to its lipophilicity (partition coefficient, log P = 2.18). , Afterward, the solid surface might result in the formation of 2-CP radical, which in turn interacted with soil substances to generate the cross-coupling product. , Besides, product analysis also showed the cross-coupling product of 2,4-DCP (Figure S6b,c), which might be because 2,4-DCP tends to accumulate on the soil solid (log P = 2.99) and has an aromatic structure. Thus, the cross-coupling process could be responsible for the similar transformation efficiency (14.1–17.1%) of alternating and control systems in the presence of 1,10-phenanthroline.…”

“…56 In this study, the 2-CP molecule was liable to be sorbed on the soil surface due to its lipophilicity (partition coefficient, log P = 2.18). 17,18 Afterward, the solid surface might result in the formation of 2-CP radical, which in turn interacted with soil substances to generate the cross-coupling product. 18,57 Besides, product analysis also showed the cross-coupling product of 2,4-DCP (Figure S6b,c), which might be because 2,4-DCP tends to accumulate on the soil solid (log P = 2.99) and has an aromatic structure.…”

“…Ong et al revealed that Fe­(II) porphyrins was capable of rapidly reducing nitro compounds . However, Cervini-Silva and Hofstetter found that the chlorinated aliphatic compounds and 2-acetyl nitrobenzene can be reduced by phyllosilicate structural Fe­(II). , Additionally, Fe­(II) might induce the adsorbed contaminants (e.g., polycyclic aromatic hydrocarbons) to form polycyclic aromatic radical cations, and the radical could react with other radicals or substances in the soil via cross-coupling reactions. − Although the reduction process of organic contaminants by Fe-containing compounds has been extensively reported, the existing forms of Fe­(II) are diverse in a complexed soil system. Therefore, the dominant active Fe­(II) as well as the corresponding reduction mechanism remain to be further explored.…”