Characteristics of removal of waste-water marking pharmaceuticals with typical hydrophytes in the urban rivers
Graphical abstract
Introduction
Pharmaceuticals have been regarded as the emerging environmental micropollutants since the late 1990s (Daughton and Ternes, 1999), and increasingly gained public concerns. With the steady development of medical system, a large number of pharmaceuticals have been used in the hospitals, livestock productions and human daily life. The residues together with their metabolites are excreted mainly through urine. These compounds are continually introduced into the aquatic environment through various pathways, usually the discharge from the conventional wastewater treatment plants (WWTPs). Previous studies (Yan et al., 2014; Aymerich et al., 2016; Zhao et al., 2016) verified that numerous pharmaceuticals and their metabolites could not be totally removed in the conventional WWTPs, and would finally be released into the urban aquatic environment. In our previous study (Zhou et al., 2014), the wastewater-marking pharmaceuticals (WWMPs) were demonstrated that it could be regarded as the tracers of wastewater. WWMPs are referred to as those pharmaceuticals which are detected frequently in the urban aquatic environment, demonstrating the status and variation tendency of the polluted water and representing the aquatic environment safety problems caused by them. They have been found ubiquitously in the urban river and WWTPs in numerous countries (Beretta et al., 2014; Li, 2014; Mandaric et al., 2017; Pereira et al., 2017; Bean et al., 2018; Hanamoto et al., 2018). Some pharmaceuticals and their metabolites might cause harmful environmental issues even at low concentration levels (Donner et al., 2013; Zhu et al., 2013). Furthermore, some pharmaceuticals, such as carbamazepine (CBM) and clofibric acid (CLF), which are recalcitrant to hydrolysis, biodegradation and photodegradation would accumulate in the water phase and sediment (Fernandez-Fontaina et al., 2013; Zhang et al., 2013). Although most pharmaceuticals studied have short half-lives ranging from about 3.5 d to 30 d (Bu et al., 2016), they become pseudo persistent pollutants in urban aquatic environment because of wide and continual consumption. Hence, the potential environmental risk caused by pharmaceuticals and their metabolites in the urban river should not be neglected.
In addition to the increasing investigations on the occurrence and distribution of pharmaceuticals in the aquatic environment, some also purposed to focus on the transfer and transformation of pharmaceuticals (Fatta-Kassinos et al., 2011; Li, 2014). The persistence of pharmaceuticals in the urban aquatic environment is governed by hydrolysis, biodegradation, photodegradation and adsorption on suspended particulates and sediment. According to different physico-chemical properties of pharmaceuticals, the main degradation pathway and adsorption affinity of pharmaceuticals existed considerable distinctions. For example, some pharmaceuticals like azithromycin (AZM) and clarithromycin (CLM) are sensitive to biodegradation (Topp et al., 2016). However, propranolol (PCR) and diclofenac (DCF) are recalcitrant to biodegradation (Lin et al., 2010; Kruglova et al., 2014), but particularly sensitive to photodegradation (Yamamoto et al., 2009; Zhang et al., 2012). Triclosan (TCS) showed strong adsorption affinity in soils in previous papers (Xu et al., 2009; Yu et al., 2013). Besides, CBM was found with high persistence in the water phase due to its difficulty in biodegradation and photodegradation (Yamamoto et al., 2009; Zhang et al., 2013). For CLF, it is also recalcitrant to both biodegradation and photolysis (Zhang et al., 2013).
Constructed wetlands (CWs) have been used to remove pharmaceuticals from untreated and treated wastewaters and purify the water quality because of their low-cost in construction, operation and maintenance, well efficient removal, and environmental friendliness (Greenway, 2005; Verlicchi and Zambello, 2014). Aquatic plants can play an important role in CWs. Once pharmaceuticals are introduced into CWs, they will undergo a variety of removal mechanisms and procedures including hydrolysis, biodegradation, photodegradation, sorption and plant uptake (Li et al., 2014). Nuel et al. (2018) investigated the behavior of 86 pharmaceuticals in the full-scale surface flow treatment wetland with 5 target plants, i.e. white willow (Salix alba), yellow flag (Iris pseudacorus), soft rush (Juncus effusus), callitriche (Callitriche palustris) and sedge (Carex caryophyllea). Large variations of removal efficiencies were observed, and the SFTW removal ability was better in the summer than in the winter. The 5 plants showed their ability to uptake drugs from water and soil to the leaves in a species-specific manner. Vymazal et al. (2017) also surveyed the removal of 31 pharmaceuticals at four horizontal flow constructed wetlands in rural areas of the Czech Republic. Wide variations in removal efficiency among systems as well as among pharmaceuticals were found. The highest average removal was found for paracetamol (91%), caffeine (CAF) (84%) and furosemide (75%). The removal of metoprolol (48%), DCF (41%), warfarin (31%), ketoprofen (31%) and gabapentin (14%) was insufficient and did not exceed 50%. Therefore, the use of aquatic plants for treating different pharmaceuticals in urban rivers may have great potentials. However, this is an extended application field that requires further study as the circumstances are different from the CWs, and plants with different living ways can be adopted.
In this paper, 13 WWMPs were selected through an established screening system in our previous paper (Zhou et al., 2014). In addition, three kinds of hydrophytes including submerged aquatic plant Myriophyllum verticillatum L. (M. verticillatum), emergent aquatic plant Typha orientalis Presl (cattail) and floating aquatic plant Lemna minor L. (L. minor) were individually cultivated in a simulated urban river system, respectively. The whole investigation was conducted in 4 hydrophyte conditions, i.e. without plants, with submerged, emergent and floating aquatic plant conditions. Furthermore, mass balance calculation was also used to analyze the overall removal efficiencies of each pharmaceutical in the whole system. The objectives of this study were to investigate (1) the roles of submerged, emergent, floating aquatic plant in a simulated urban river system in WWMPs removal and water quality restoration; (2) the variations of the target WWMPs under different hydrophyte conditions in the water phase and sediment; (3) the plant uptakes of target WWMPs in a simulated urban river by aquatic plants with 3 living ways. To the best of our knowledge, this is the first investigation on the variations and fate of the pharmaceuticals in water phase, sediment and plant tissues under the actions of aquatic plants with 3 living ways in a simulated urban river system.
Section snippets
Chemicals and materials
Thirteen WWMPs selected in this study included antibiotics AZM, CLM, sulfathiazole (STZ), and trimethoprim (TMP); analgesic drugs ibuprofen (IBU), and PRC; anti-inflammatory drug DCF; beta-blockers atenolol (ATL), and propranolol (PNL); lipid regulator CLF; antiepileptic CBM; psychomotor stimulant caffeine (CAF); and broad spectrum antimicrobial TCS. Their reference standards (>98.5% purity) were purchased from Dr. Ehrenstorfer, Augsburg, Germany. The physicochemical properties of all target
Conventional water quality indicators under different hydrophyte conditions
The pH, DO, TN, NH3-N, TP and COD were measured in the circulating flume under 4 hydrophyte conditions. DO ranged from 2.1 to 2.8 mg/L without plants, and ranged from 2.9 to 4.2 mg/L under the planted conditions. The higher DO levels were measured under the planted conditions because of the oxygenic photosynthesis and metabolism of aquatic plants. The pH ranged from 7.1 to 7.5 during the whole tests.
The concentrations of TN, NH3-N, TP and COD under 4 hydrophyte conditions are shown in Fig. 2. The
Discussion
In general, the higher OREs of WWMPs under the planted conditions could be obtained. The variations and differences of 13 target WWMPs in water phase, sediment and plant tissues could be mainly attributed to the hydrolysis, biodegradation, photolysis, adsorption, desorption and plank uptake (Yamamoto et al., 2009; Acuna et al., 2015; Cui et al., 2015). Cui et al. (2015) reported that pharmaceuticals might be adsorbed through the roots into the aquatic plants, and then translocated to shoot
Conclusions
Aquatic plants can not only effectively absorb and utilize the nutrients (such as nitrogen and phosphorus) and organic matters, and played an important role in conventional water quality restoration, but also effectively remove the pharmaceuticals in the urban river system. Although the direct uptake by aquatic plants might not be a dominant pathway to the overall removal of WWMPs, the distinct higher removal efficiencies of most pharmaceuticals were found under the planted conditions, implying
Acknowledgements
This work was financially supported by the Natural Science Foundation of Shanghai, China (18ZR1426100), and the National Natural Science Foundation of China (NSFC; Grant No. 51279108).
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