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近年来,天然和人工合成激素的不断排放严重影响了生态和环境健康[1-3],这引起了研究学者的关注[4-5]. 其中天然雌激素17β-雌二醇(E2)是一种广泛用于人类内分泌疾病治疗的天然雌激素[6],是天然水体中雌激素活性的主要贡献者[7]. E2已被检出于多种天然水体,如夏季在来自日本109条河流的256个样品中检出率为86.72%,平均浓度2.1 ng·L−1[8];德国的一些饮用水水样中E2的平均检出浓度为0.7 ng·L−1[9];此外E2在阿肯色州西北部的地下水体中也被检测到,浓度范围为6—66 ng·L−1[10]. 有文献报道E2在低浓度甚至环境浓度下足以干扰内分泌系统的功能,损害水生生物和人类健康,如对鱼性别产生诱导的最低可见效应浓度为10 ng·L−1[11],雌性虹鳟鱼中E2诱导卵黄蛋白原的阈值浓度为4.7 ng·L−1和7.9 ng·L−1[12]. E2等污染物在天然水体中的自然衰减途径主要有物理、化学和生物过程,如蒸发、稀释、水解、吸附、光降解和生物降解等,其中光降解和生物降解是污染物自然衰减的两个重要过程[13],对污染物的转化和归趋有着极其重要的影响.
光解分为直接光解和间接光解,前者是污染物可以有效地吸收光子从而发生光解,且污染物直接光解的量子产率越高,光化学活性越高;后者是水体中存在的光敏剂会产生活性氧物种(ROS)或将能量转移至污染物,从而导致污染物发生光解[14]. 据报道,E2可直接吸收290—320 nm范围内的太阳光而发生直接光降解,且水质成分,如腐殖酸,Mn(Ⅲ)和溶解性黑碳等,可明显促进E2的光降解[4, 15-16]. 生物转化主要是通过酶来降解这些污染物[17],其中过氧化物酶(POD)广泛存在于天然环境[18],且活性相当高,如在芬兰Mekkojärvi湖表层水中活性范围为73.6—272.9 nmol·L−1·h−1[19];在德国湖泊中浓度可达到0.06—4.71 mmol·L−1·h–1[20]. 有文献报道,辣根过氧化物酶(HRP)、木质素过氧化物酶以及大豆过氧化物酶等POD可通过氧化偶联反应有效去除三氯生、E2和乙酰氨基酚等多种污染物,且主要底物为酚类污染物[21-23]. 在自然水体中,光降解和酶促反应通常同时发生,且已有研究学者关注光降解和酶转化的复杂过程. 如HRP可利用腐殖质光解产生的H2O2进行氧化偶联反应去除E2,同时,腐殖质生成ROS促进E2的光降解[24],但是HRP在无腐殖质存在的条件下是否可直接影响E2的光转化尚不清楚,因此有必要进行这方面的研究.
本文通过降解动力学、活性氧物种鉴定、光酶结合产物鉴定以及常见水质成分比较等实验系统地研究了HRP对E2光解的影响机制,对光酶协同转化过程有更深的理解,为E2的环境归趋和酶处理技术在水处理方面的应用提供参考数据.
过氧化物酶对水中17β-雌二醇光降解的影响机制
The effect mechanism of peroxidase on the photodegradation of 17β-estradiol in water
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摘要: 过氧化物酶广泛存在于天然水体,在外加过氧化氢(H2O2)的条件下可有效地降解水体中的有机污染物.17β-雌二醇(E2)是水体中常见的雌激素,低浓度下仍具有极强的内分泌干扰效应,过氧化物酶可通过利用腐殖质产生的H2O2从而影响腐殖质介导的E2的光化学过程,但其是否可直接影响E2的光转化尚不清楚.本文系统地研究了辣根过氧化物酶(HRP)对E2光降解过程的影响.研究发现有活性的HRP可显著促进E2的光化学转化,且促进作用随着活性的增大而增强.活性氧猝灭实验结果表明E2自敏化产生的活性物种可激活HRP,从而促进了E2在光照条件下的酶降解,且E2在HRP溶液中的光解产物实验进一步证实了这一过程.HRP对E2酶降解的效率高于常见水质成分Suwannnee River Humic Acid(SRHA)和Fe3+的促进效率,弱于
${\rm{NO}}_3^{-} $ 引起的促进效率,表明HRP对污染物在天然水体中的环境归趋的影响是值得关注的.本文为深入认识雌激素的环境归趋提供科学数据,并为酶处理技术在水处理方面的应用带来巨大前景.Abstract: Peroxidase is widely widespread in aqueous environment, it can effectively degrade organic pollutants in the presence of hydrogen peroxide (H2O2). 17β-estradiol (E2), as a common estrogen, exhibits strong endocrine disrupting effect even at relatively low concentration. It is well known that peroxidase can affect humus induced photochemical process of E2 via the interaction with H2O2, while whether peroxidase can directly interact with E2 still remains unclear. In this study, the impact of horseradish peroxidase (HRP) on photochemical transformation of E2 was systematically evaluated. Our results revealed that active HRP could significantly promote the photodegradation of E2, and the promotion effect increased with the augment of enzyme activity. Self-sensitization of E2 was proposed to activate HRP, leading to the formation of a series of reactive oxygen species (ROS), which in turn oxidized E2. Such mechanisms were further verified by ROS quenching experiments and photoproducts identification. In addition, the promotion effect of HRP was found to be more pronounced than water components Suwannnee River Humic Acid (SRHA) and Fe3+, while less effective than nitrate, indicating that the involvement of HRP in the environmental fate of pollutants in natural water is noteworthy. The present study would provide scientific data for better understanding of the environmental fate of estrogen and bring great prospects for the application of enzyme treatment technology in water treatment.-
Key words:
- horseradish peroxidase /
- 17β-estradiol /
- enzyme degradation /
- photodegradation /
- water components
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表 1 E2在不同反应溶液中的假一级动力学速率常数(kobs)和直接光解、其他降解预测贡献率
Table 1. Observed pseudo-first-order rate constants (kobs) and predicted contributions from direct photolysis and other degradation of E2 in different water solutions.
溶液Solution kobs/d−1 Sλ kdp/d−1 kother/d−1 DP/% Other/% E2 0.456 1.00 0.456 — 100 — E2+SRHA 0.911 0.784 0.358 0.553 40 60 E2+ ${\rm{NO}}_3^{-} $ 2.37 0.995 0.454 1.916 19 81 E2+ HRP 1.383 1 0.456 0.927 33 67 E2 + Fe3+ 0.717 0.926 0.422 0.295 59 41 -
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