Synergy mechanisms of algal extracellular organic matter and manganese oxides in 17α-ethinylestradiol photochemical degradation

Abstract

17α-ethinylestradiol (EE2) is a persistent endocrine-disrupting chemical that threatens aquatic ecosystems. Algal extracellular organic matter (EOM), widespread manganese oxides (MnO_x) and their photochemical interactions can drive the natural degradation of EE2. However, these processes can be regulated by the unique surrounding conditions in eutrophic plateau lakes, including elevated levels of dissolved organic carbon, high pH, and abundant anions. Here, we investigated the enhancement of EE2 photodegradation mediated by EOM and MnO_x, with emphasis on the effects of above unique surrounding conditions. Results showed that higher EOM concentrations proceed faster EE2 photodegradation rate by providing sufficient binding sites and more superoxide radicals for Mn(III) generation. In contrast, elevated pH inhibited EE2 degradation due to pH-dependent surface modifications of MnO_x, which suppressed Mn(III) formation. Nitrate can enhance EE2 photodegradation without influencing Mn(III) generation. Product identification and density functional theory calculations suggest that EE2 degradation proceeds via free radical attack and Mn(III/IV)-mediated electron transfer, producing both small oxidized products and oligomers such as dimers and trimers. This study clarifies the environmental drivers of organic micropollutants’ degradation in eutrophic lakes, highlighting the environmental significance of surrounding conditions.

Graphical abstract

Keywords

17α-ethinylestradiol degradation / Algal extracellular organic matter / Manganese oxide / Reactive Mn(III) / Photochemistry

Highlight

	● EOM-mediated MnO x reduction generates Mn(III), which enhances EE2 photodegradation.
	● EOM levels, pH, DO, and anions unique in eutrophic waters regulate EE2 degradation.
	● EOM components and MnO x surface properties changed significantly after reaction.
	● EE2 degrades through radical attack and electron transfer involving Mn(III/IV).

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