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.

中文翻译：

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雌激素作用增强的意外原因：低聚物在水中防腐剂对羟基苯甲酸乙酯的光降解中。

水中新出现的有机污染物（EOC）的广泛发生已明确地与对人类健康的不利影响相关联，因此对公众健康构成了重大风险。特别是在天然水甚至废水处理厂中EOC的光降解过程中，经常会观察到毒性的增加。然而，关于雌激素活性，尚未认识到增加毒性和形成机理的罪魁祸首。在这项研究中，通过将实验室实验与量子化学计算相结合，在防腐剂对羟基苯甲酸乙酯（EP）的光降解过程中，使用酵母双杂交报告基因检测法研究了人类雌激素活性的诱导作用，并鉴定了有毒产物和形成机理。结果表明，雌激素作用的增加是由光化学生成的低聚物而不是预期的OH加合物诱导的。最大的雌激素活性对应于低聚物的主要形成，而OH-加合物小于12％。发现两种光化学产生的低聚物有助于雌激素活性，这是由激发的三态态分子的裂解和随后的自由基自由基反应产生的。计算毒理学结果表明，增加的雌激素活性归因于低聚物[4-羟基-间苯二甲酸1-乙基酯3-（4-羟基-苯基）]，其EC50低于母体EP。相反，OH加成物比母体EP表现出更高的EC50值，同时仍具有雌激素活性。因此，