-
近年来,镉系量子点(quantum dots,QDs)因其优异的光响应性、带隙可调控和充足且较高的导带能位而被用于制造光催化剂、存储设备、显示器、发光二极管和化学传感器[1-2]。而镉系QDs的大规模商业应用大大增加了其释放到环境中的暴露风险,进而增大其进入污水处理厂的概率以及富集质量浓度。镉系 QDs也将随排水泄露到自然环境,最终危害微生物,藻类和动植物[3-4]。污水处理厂作为防止镉系 QDs进入自然环境的关键一环,明确其长期暴露对污水处理过程的影响至关重要。
活性污泥系统是污水处理厂实现污水净化的核心环节[5],大量研究发现,纳米颗粒(TiO2,ZnO,聚苯乙烯等)进入活性污泥后会通过物理化学吸附等作用从水相转移至污泥中富集[6-8],进而影响污泥絮凝体的结构和功能,造成出水水质恶化[9-11]。当纳米颗粒与微生物长期接触,微生物群落结构和代谢功能也将做出相应响应[12]。对于粒径更小(2~10 nm)、更易进入细胞的含镉量子点(CdSe、CdTe/CdS、CdSe/ZnS)[13],其在污泥内富集的环境风险可能更为突出。目前,尽管研究人员已经在关注镉系QDs的生物毒性研究,但目标生物(细胞、细菌、斑马鱼和少数藻类)和实验条件较为单一[14-15],其在复杂系统中的毒理效应尚不明确,镉系QDs对污水处理厂处理效能的影响和作用机制仍未可知。因此,有必要明确镉系QDs对污水处理厂出水水质、污泥絮体物化特性以及微生物群落结构的影响,从而为QDs的安全应用和排放提供理论依据。
本研究通过评估污水处理效果、污泥絮凝沉淀性能、胞外聚合物(extracellular polymeric substances,EPS)物化特征,微生物群落结构及其代谢功能对CdSe QDs长期胁迫的响应,全面揭示CdSe QDs对活性污泥的毒性效应及其内在机制,将为QDs的环境行为研究及其暴露风险评估提供理论支撑。
活性污泥对硒化镉量子点暴露的胁迫响应机制
The stress response mechanisms of activated sludge exposed to CdSe quantum dots
-
摘要: 为揭示硒化镉(CdSe)量子点(quantum dots, QDs)在复杂环境体系中的生物毒性效应,本研究以活性污泥为研究对象,探讨了CdSe QDs(0.1~10 mg·L−1)长期暴露对序批式活性污泥反应器运行效能、污泥性能以及微生物代谢作用的影响。结果表明,在实验质量浓度范围内,出水COD值和硝酸盐波动较大,而硝化作用影响较小,且低剂量CdSe QDs的存在加速了NH4+-N的降解,1 mg·L−1 CdSe QDs将平均氨氧化速率由2.2 mg·(L∙h)−1提高到3.3 mg·(L∙h)−1。尽管CdSe QDs会引起出水浊度略微增加,但污泥沉降性能始终维持稳定。CdSe QDs主要与污泥表面的C—O—C、C—O、C—C和磷酸基团结合,诱导胞外聚合物的酪氨酸类蛋白荧光淬灭。同时,微生物会通过分泌色氨酸类蛋白以缓解胁迫影响。此外,活性污泥的物种丰富度和多样性均受CdSe QDs的抑制,但低质量浓度CdSe QDs有利于Nitrospirae相对丰度的增加。PICRUSt2预测显示,微生物的新陈代谢和遗传信息处理相关的代谢通路均受到CdSe QDs的显著抑制,膜传输和信号传导的代谢通路丰度最终分别下降至32 552和7 876,导致反应器出水COD值随暴露剂量的增加而逐渐增大。因此,CdSe QDs通过改变微生物群落结构和功能影响活性污泥有机物的去除效果,但对硝化反应及污泥絮凝和沉淀性能并未表现出明显负面效果。Abstract: In order to reveal the biotoxicity of CdSe quantum dots (QDs) in complex environmental systems, activated sludge was taken as the research object to study the effects of long-term exposure to CdSe QDs (0.1~10 mg·L−1) on the operation efficiency, sludge performance and microbial metabolism in sequencing batch reactor (SBR). The results showed that COD and nitrate concentrations in effluent fluctuated greatly under the stress of CdSe QDs (0.1~10 mg·L−1), but nitrification performance was stable. Low dosed CdSe QDs accelerated degradation of NH4+-N, and 1 mg·L−1 CdSe QDs could increase average oxidation rate of NH4+-N from 2.2 to 3.3 mg·(L∙h)−1. Although CdSe QDs caused a slight increase in effluent turbidity, the sludge sedimentation maintained stable. CdSe QDs mainly bound to C—O—C, C—O, C—C and phosphate group on sludge surface, and caused the fluorescence quenching of tyrosine-like protein in extracellular polymeric substance. Meanwhile, microorganisms also secreted tryptophan-like proteins to alleviate stress. Besides, both abundance and diversity of microbes in activated sludge were inhibited by CdSe QDs, but low level CdSe QDs were conducive to abundance of Nitrospirae. The results predicted by PICRUSt found that the metabolic pathway for metabolism and genetic information processing was significantly inhibited by CdSe QDs, and the abundances of the metabolic pathway for membrane transport and signal transduction finally decreased to 32 552 and to 7 876, respectively. That might be the reason for the increase in effluent COD with the rise of exposure dosage. Therefore, CdSe QDs affected the organic matter removal by changing the structure and function of microbial community in activated sludge, but showed no obvious negative effects on nitrification, sludge settling and flocculation.
-
表 1 CdSe QDs胁迫下活性污泥微生物群落多样性指数
Table 1. Alpha diversity indexes of activated sludge exposed to CdSe QDs
CdSe QDs质量
浓度/( mg·L−1)序列数 OTUs Shannon Chao 1 ACE 覆盖率/
%0 65 288 1 720 7.07 1 720.0 1 739.5 99.9 0.1 43 101 881 7.46 882.1 951.3 99.7 1 40 025 805 6.74 805.9 881.3 99.7 10 32 356 700 6.69 701.1 801.7 99.6 -
[1] CAI Q Q, WU D, LI H K, et al. Versatile photoelectrochemical and electrochemiluminescence biosensor based on 3D CdSe QDs-DNA nanonetwork-SnO2 nanoflower coupled with DNA walker amplification for HIV detection[J]. Biosensors and Bioelectronics, 2021, 191: 113455. doi: 10.1016/j.bios.2021.113455 [2] ZHAO Z J, LIU Z L, ZHU Z X, et al. Ultrathin zinc selenide nanosheet-based intercalation hybrid coupled with CdSe quantum dots showing enhanced photocatalytic CO2 reduction[J]. Chinese Chemical Letters, 2021, 32(8): 2474-2478. doi: 10.1016/j.cclet.2021.01.004 [3] LIAN F, WANG C G, WANG C X, et al. Variety-dependent responses of rice plants with differential cadmium accumulating capacity to cadmium telluride quantum dots (CdTe QDs): Cadmium uptake, antioxidative enzyme activity, and gene expression[J]. Science of the Total Environment, 2019, 697: 134083. doi: 10.1016/j.scitotenv.2019.134083 [4] YU Z, HAO R, ZHANG L, et al. Effects of TiO2, SiO2, Ag and CdTe/CdS quantum dots nanoparticles on toxicity of cadmium towards Chlamydomonas reinhardtii[J]. Ecotoxicology and Environmental Safety, 2018, 156: 75-86. doi: 10.1016/j.ecoenv.2018.03.007 [5] LIU F, HU X M, ZHAO X, et al. Rapid nitrification process upgrade coupled with succession of the microbial community in a full-scale municipal wastewater treatment plant (WWTP)[J]. Bioresource Technology, 2018, 249: 1062-1065. doi: 10.1016/j.biortech.2017.10.076 [6] BRAR S K, VERMA M, TYAGI R D, et al. Engineered nanoparticles in wastewater and wastewater sludge-evidence and impacts[J]. Waste Management, 2010, 30(3): 504-520. doi: 10.1016/j.wasman.2009.10.012 [7] LI H X, XU S S, WANG S, et al. New insight into the effect of short-term exposure to polystyrene nanoparticles on activated sludge performance[J]. Journal of Water Process Engineering, 2020, 38:101559. [8] WEI L L, DING J, XUE M, et al. Adsorption mechanism of ZnO and CuO nanoparticles on two typical sludge EPS: Effect of nanoparticle diameter and fractional EPS polarity on binding[J]. Chemosphere, 2019, 214: 210-219. doi: 10.1016/j.chemosphere.2018.09.093 [9] 马娇, 曾天续, 宋珺, 等. 纳米单质铁对厌氧氨氧化脱氮性能的影响[J]. 中国环境科学, 2022, 42(6): 2619-2627. [10] 王树涛, 李素萍, 王未青, 等. ZnO纳米颗粒对SBR活性污泥活性的影响[J]. 中国环境科学, 2014, 34(10): 2575-2580. [11] 高静湉, 胡鹏, 蔡怡婷, 等. 纳米ZnO胁迫下SBBR污染物去除性能及微生物群落响应[J]. 中国环境科学, 2022, 42(8): 1-8. [12] YANG Y, QUENSEN J, MATHIEU J, et al. Pyrosequencing reveals higher impact of silver nanoparticles than Ag+ on the microbial community structure of activated sludge[J]. Water Research, 2014, 48: 317-325. doi: 10.1016/j.watres.2013.09.046 [13] HU L, ZHONG H, HE Z G. Toxicity evaluation of cadmium-containing quantum dots: A review of optimizing physicochemical properties to diminish toxicity[J]. Colloids and Surfaces B:Biointerfaces, 2021, 200: 111609. doi: 10.1016/j.colsurfb.2021.111609 [14] LU T, ZHANG Q, ZHANG Z Y, et al. Pollutant toxicology with respect to microalgae and cyanobacteria[J]. Journal of Environmental Sciences, 2021, 99: 175-186. doi: 10.1016/j.jes.2020.06.033 [15] ZHENG N Y, YAN J H, QIAN W, et al. Comparison of developmental toxicity of different surface modified CdSe/ZnS QDs in zebrafish embryos[J]. Journal of Environmental Sciences, 2021, 100: 240-249. doi: 10.1016/j.jes.2020.07.019 [16] YANG Y, YUAN Z, LIU X P, et al. Electrochemical biosensor for Ni2+ detection based on a DNAzyme-CdSe nanocomposite[J]. Biosensors and Bioelectronics, 2016, 77: 13-18. doi: 10.1016/j.bios.2015.09.014 [17] 曾湘梅, 李咏梅, 赵俊明. SBR工艺去除模拟城市污水中双酚A的研究[J]. 环境污染与防治, 2008, 30(10): 23-27. [18] 国家环境保护总局. 水和废水监测分析方法[M]. 4版. 北京: 中国环境科学出版社, 2002. [19] YIN C Q, MENG F G, CHEN G H. Spectroscopic characterization of extracellular polymeric substances from a mixed culture dominated by ammonia-oxidizing bacteria[J]. Water Research, 2015, 68: 740-749. doi: 10.1016/j.watres.2014.10.046 [20] DONG Q, LIU Y C, SHI H C, et al. Effects of graphite nanoparticles on nitrification in an activated sludge system[J]. Chemosphere, 2017, 182: 231-237. doi: 10.1016/j.chemosphere.2017.04.144 [21] GUO L K, YANG L, Ren Y X, et al. The response and anti-stress mechanisms of nitrifying sludge under long-term exposure to CdSe quantum dots[J]. Journal of Environmental Sciences, 2024, 135: 174-184. doi: 10.1016/j.jes.2022.11.016 [22] WANG C, LIU S Q, HOU J, et al. Effects of silver nanoparticles on coupled nitrification-denitrification in suspended sediments[J]. Journal of Hazardous Materials, 2020, 389: 122130. doi: 10.1016/j.jhazmat.2020.122130 [23] ZHANG H M, CAO J, TANG B P, et al. Effect of TiO2 nanoparticles on the structure and activity of catalase[J]. Chemico-Biological Interactions, 2014, 219: 168-174. doi: 10.1016/j.cbi.2014.06.005 [24] 高丽英, 汤兵, 梁玲燕, 等. 纳米磁粉协同解偶联剂作用下活性污泥性能的研究[J]. 环境科学, 2012, 33(8): 2766-2772. [25] ZHAO J F, LIU S X, LIU N, et al. Accelerated productions and physicochemical characterizations of different extracellular polymeric substances from Chlorella vulgaris with nano-ZnO[J]. Science of the Total Environment, 2019, 658: 582-589. doi: 10.1016/j.scitotenv.2018.12.019 [26] ZHANG S J, JIANG Y L, CHEN C S, et al. Ameliorating effects of extracellular polymeric substances excreted by Thalassiosira pseudonana on algal toxicity of CdSe quantum dots[J]. Aquatic Toxicology, 2013, 126: 214-223. doi: 10.1016/j.aquatox.2012.11.012 [27] 袁乙卜, 张建民, 陈希, 等. 大分子有机物作用下胞外聚合物对除磷污泥颗粒化的影响[J]. 环境工程学报, 2021, 15(4): 1321-1332. [28] 王远红, 张红波, 罗世田, 等. 胞外聚合物对水中Cd(Ⅱ)的吸附性能研究[J]. 环境工程学报, 2010, 4(10): 2185-2189. [29] 张国威, 黄建, 崔浩, 等. 活性污泥对Pb(Ⅱ)的吸附机理[J]. 环境工程学报, 2016, 10(7): 3707-3714. [30] ZHENG S M, ZHOU Q X, CHEN C H, et al. Role of extracellular polymeric substances on the behavior and toxicity of silver nanoparticles and ions to green algae Chlorella vulgaris[J]. Science of the Total Environment, 2019, 660: 1182-1190. doi: 10.1016/j.scitotenv.2019.01.067 [31] HAN F, WEI D, NGO H H, et al. Performance, microbial community and fluorescent characteristic of microbial products in a solid-phase denitrification biofilm reactor for WWTP effluent treatment[J]. Journal of Environmental Management, 2018, 227: 375-385. [32] WANG X L, ZHANG L, PENG Y Z, et al. Enhancing the digestion of waste activated sludge through nitrite addition: insight on mechanism through profiles of extracellular polymeric substances (EPS) and microbial communities[J]. Journal of Hazardous Materials, 2019, 369: 164-170. doi: 10.1016/j.jhazmat.2019.02.023 [33] 陈鑫童, 郝庆菊, 熊艳芳, 等. 铁矿石和生物炭添加对潜流人工湿地污水处理效果和温室气体排放及微生物群落的影响[J]. 环境科学, 2022, 43(3): 1492-1499. [34] SHARMA M, KHURANA H, SINGH D N, et al. The genus Sphingopyxis: Systematics, ecology, and bioremediation potential - A review[J]. Journal of Environmental Management, 2021, 280: 111744. doi: 10.1016/j.jenvman.2020.111744 [35] WANG Z Q, GAO J F, DAI H H, et al. Microplastics affect the ammonia oxidation performance of aerobic granular sludge and enrich the intracellular and extracellular antibiotic resistance genes[J]. Journal of Hazardous Materials, 2021, 409: 124981. doi: 10.1016/j.jhazmat.2020.124981 [36] WANG Q, ZHOU G Y, QIN Y X, et al. Sulfate removal performance and co-occurrence patterns of microbial community in constructed wetlands treating saline wastewater[J]. Journal of Water Process Engineering, 2021, 43: 102266. doi: 10.1016/j.jwpe.2021.102266 [37] MANNACHARAJU M, SOMASUNDARAM S, GANESAN S. Treatment of refractory organics in secondary biological treated post tanning wastewater using bacterial cell immobilized fluidized reactor[J]. Journal of Water Process Engineering, 2021, 43: 102213. doi: 10.1016/j.jwpe.2021.102213 [38] 张雪, 乔雪姣, 苏佳, 等. 垃圾渗滤液处理厂活性污泥微生物种群结构和功能分析[J]. 北京大学学报(自然科学版), 2021, 57(5): 927-937. [39] LIU N, TANG M. Toxicity of different types of quantum dots to mammalian cells in vitro: An update review[J]. Journal of Hazardous Materials, 2020, 399: 122606. doi: 10.1016/j.jhazmat.2020.122606