Unexpected culprit of increased estrogenic effects: Oligomers in the photodegradation of preservative ethylparaben in water. (1st June 2020)

• Record Type: Journal Article
• Authors: Gao, Yanpeng; Niu, Xiaolin; Qin, Yaxin; Guo, Teng; Ji, Yuemeng; Li, Guiying; An, Taicheng
• Is Part Of: Water research. Volume 176(2020)
• Publication Date: 2020-06-01
• Subjects: Parabens -- Photochemical transformation -- Degradation mechanism -- Estrogenic effect -- Theoretical calculation; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2020.115745
• Languages: English
• ISSNs: 0043-1354

Abstract

Abstract: Widespread occurrence of emerging organic contaminants (EOCs) in water have been explicitly associated with adverse effects on human health, therefore representing a major risk to public health. Especially the increased toxicity is frequently observed during the photodegradation of EOCs in natural water, and even wastewater treatment plants. However, the culprit of increased toxicity and formation mechanism has yet to be recognized regarding the estrogenic activity. In this study, by combining laboratory experiments with quantum chemical calculations, the induction of human estrogenic activity was investigated using the yeast two-hybrid reporter assay during the photodegradation of preservatives ethylparaben (EP), along with identification of toxic products and formation mechanisms. Results showed that the increase in estrogenic effect was induced by photochemically generated oligomers, rather than the expected OH-adduct. The maximum estrogenic activity corresponded to the major formation of oligomers, while OH-adducts were less than 12%. Two photochemically generated oligomers were found to contribute to estrogenic activity, produced from the cleavage of excited triplet state molecules and subsequent radical-radical reactions. Computational toxicology results showed that the increased estrogenic activity was attributed to oligomer [4-Hydroxy-isophthalic acid 1-ethyl ester 3-(4-hydroxy-phenyl)] and its EC50 was lower than that of the parent EP. In contrast, OH-adducts exhibited higher EC50 values than the parent EP, while still possessing estrogenic activity. Therefore, more attention should be paid to these photodegradation products of EOCs, including OH-adducts. Graphical abstract: Image 1 Highlights: The estrogenic activity increased during ethyl-paraben photochemical transformation. Hydroxylated product was not responsible for the increase of estrogenic activity. The EC50 of hydroxylated product 3-EP-OH is first reported as 2.32 × 10 −4 M. Photo-oligomers were the potential reason why the increased estrogenic effect. Excited triplet state was the main RS during ethyl-paraben phototransformation.