Quinone groups in DOM can promote microbes to degrade heavy metals (Reijonen et al., 2016) and organic pollutants (Guha et al., 2001). Many studies have shown that the fast degradation of pollutants in natural waters can usually be attributed to the accelerating effects of dissolved organic matter (DOM). Therefore, it is speculated that some active substances in natural aquatic environments enhance the biodegradation of SEs. According to previous studies in our laboratory, even when SEs are continuously discharged into surface water from STPs, their accumulation is not very obvious (Huang et al., 2013). SEs have been reported to have a biodegradation half-life of 20–40 days under aerobic conditions (Clouzot et al., 2008), and longer could be expected under anaerobic conditions (Ying et al., 2003). However, it has been shown that SE biodegradation by heterotrophic bacteria is very slow. Thus, the fate and behavior of SEs in natural water environments have generated extensive concern.Īmong the various fates of environmental SEs, biodegradation has been identified as one of the predominant removal mechanisms from both natural water and sediment. Although those compounds are normally found in water at only ng per litre levels, field and laboratory studies have demonstrated that they can still alter normal hormone functions and the physiological status of wildlife (Liu et al., 2011, Liu et al., 2012, Huang et al., 2015). Their incomplete removal in sewage treatment plants (STPs) and indeed direct discharge have led to their being widely detected in aquatic environments (Huang et al., 2014). Natural and synthetic steroid estrogens (SEs) such as estrone (E1), 17β-estradiol (E2), estriol (E3) and 17α-ethynylestradiol (EE2) have been recognized as potential endocrine disruptors (Huang et al., 2013). These results provide a more comprehensive understanding of microbial degradation of steroid estrogens in anaerobic environments and confirm DOM as an important terminal electron acceptor in pollutant transformation. The natural DOM contained more aromatic compounds, demonstrating their greater electron-accepting capacity and generally more effective support for microorganism growth and E2 oxidation than Aldrich humic acid (HA). Natural DOM containing lake humic acid (LHA) and lake fulvic acid (LFA) had a very important accelerating effect on the degradation of E2, the action mechanism of which was consistent with that defined using DOM models. However, further increase had an inhibiting effect. Compared with other DOM models, AQS best stimulated E2 biodegradation and the mediating effect was improved as the AQS concentration increased from 0 to 0.5 mM. Quinone-reducing bacteria can use the quinone structure of DOM components as a terminal electron acceptor coupling with microbial growth to promote biodegradation. The optimum reduction conditions were found to be in the dark under anaerobic conditions at pH 8.0 and 30 ☌. The influence of temperature, pH, dissolved oxygen and light illumination on the reduction efficiency of anthraquinone-2-disulfonate (AQS) was investigated using 17β-estradiol (E2) as the target species. Steroid estrogen in natural waters may be biodegraded by quinone-reducing bacteria, dissolved organic matter (DOM) may serve as a terminal electron acceptor in this process.
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