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纳米氧化锌(nZnO)作为一种应用广泛的纳米材料,全球年产量达3.15—3.40万吨,预计8%—20%被排入水环境中[1]. nZnO是一种带电型可溶性纳米颗粒,其颗粒态及离子态均可对水生生物产生不利影响[2]. 由于实际水环境的复杂性,纳米材料的环境行为与生物效应会受其他带电共存物的影响. 带负电的污染物如纳米二氧化钛[3]、多溴二苯醚[4]、十二烷基硫酸钠[5]可通过改变带正电荷的nZnO的ζ-电位,干扰nZnO与其他物质之间的相互作用从而减弱其生物毒性. 而带负电荷的污染物如nCu[6]可通过促进带负电荷的nZnO的Zn2+的溶出及生物积累,增强nZnO的生物毒性. 目前大部分研究集中于相反电性共存物与nZnO之间的生物毒性[7]及其对nZnO溶出行为的影响[8],对于相同电性或不带电的共存物对nZnO的影响还有待研究.
表面活性剂因具有优良的清洁和增溶性能被广泛应用于浮选剂和洗涤剂等产品中. 作为纳米材料生产使用过程中的助剂之一,表面活性剂是最有可能在水环境中与纳米材料接触的带电荷污染物之一[9]. 前期研究发现,带正电荷的十六烷基三甲基氯化铵(CTAC)可吸附在带负电荷的nZnO表面,改变其与带负电荷的藻细胞间的静电力作用,抑制nZnO的溶出,使nZnO主要以颗粒态吸附在细胞表面[10]. 为此,本研究以水生生态系统中常见的初级生产者小球藻作为受试生物,探究了3种不同电荷表面活性剂,阳离子型的CTAC、阴离子型的十二烷基苯磺酸钠(SDBS)、非离子型的聚乙二醇辛基苯基醚(TX-100)存在下nZnO对小球藻毒性效应及细胞分布的影响机制,以期为评价纳米颗粒在不同电荷水环境中的生物效应提供理论依据.
不同电荷表面活性剂影响下纳米氧化锌对小球藻的毒性效应与细胞分布
The toxic effect and cell distribution of nano-zinc oxide on Chlorella vulgaris under the presence of different-charged surfactants
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摘要: 水环境中的带电物质可改变可溶性纳米颗粒的理化性质和累积分布,从而影响纳米颗粒对水生生物的毒性效应. 本文探究了3种不同电荷表面活性剂,阳离子型的十六烷基三甲基氯化铵(CTAC)、阴离子型的十二烷基苯磺酸钠(SDBS)、非离子型的聚乙二醇辛基苯基醚(TX-100)存在下纳米氧化锌(nZnO)对小球藻(Chlorella vulgaris)的毒性效应,探明了3种表面活性剂对nZnO性质(电位粒径、Zn2+溶出等)及Zn元素细胞分布的影响. 结果表明,带有不同电荷的表面活性剂与nZnO复合具有不同的联合毒性效应及机制. 阳离子型CTAC促进nZnO的团聚并抑制Zn2+的溶出,增强nZnO与藻细胞间的静电相互作用,使细胞表面吸附的颗粒态nZnO增加,其联合毒性表现为拮抗作用;阴离子型SDBS促进nZnO的分散和Zn2+的溶出,增强nZnO与藻细胞间的静电排斥,使细胞内Zn2+含量增加,其联合毒性表现为协同作用;非离子型TX-100对Zn2+的细胞分布无显著影响,可能是通过空间位阻作用减少nZnO颗粒与细胞接触,使细胞内颗粒态nZnO降低,其联合毒性表现为拮抗作用. 研究结果为更准确、真实地评价纳米颗粒在含有不同电荷物质的水环境中的生态风险提供了理论依据.Abstract: The charged species in aqueous environments can alter the physicochemical properties, accumulation, and distribution of solubel nanoparticles, thereby affecting their toxicity on aquatic life. This study investigated the toxicity of zinc oxide nanoparticles (nZnO) on Chlorella vulgaris (C. vulgaris) under the stress of three different-charged surfactants, including the cationic surfactant cetyltrimethyl ammonium chloride (CTAC), anionic surfactant sodium dodecyl benzene sulfonate (SDBS), and nonionic surfactant octyl phenoxy polyethoxyethanol (TX-100). Meanwhile, we determined the effect of these surfactants on the properties of nZnO (potential, particle size, dissolution of Zn2+, etc.) and the intracellular distribution of Zn. Results showed that nZnO presented different combined toxicities and mechanisms after interacting with different-charged surfactants. Cationic CTAC promoted the agglomeration of nZnO but inhibited the dissolution of Zn2+. Moreover, CTAC enhanced the electrostatic attraction between nZnO and the algal cells, reducing the accumulation of nZnO in cells. This indicated an antagonistic effect of nZnO and CTAC on algal growth. In contract, a synergistic effect of anionic SDBS and nZnO was comfirmed because SDBS promoted the dispersion and dissolution of nZnO, and increased intracellular accumulation of Zn2+. Furthermore, nonionic TX-100 exhibited no significant effect on the cell distribution of Zn2+ and decreased intracellular accumulation of granular nZnO due to the steric hindrance. Thus the combined toxicity of nZnO and TX-100 on C. vulgaris exhibited an antagonistic effect. These results will provide more accurate and authentic evidence of the biological effects of nanoparticles in aqueous environments with different charged species.
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表 1 nZnO/不同电荷表面活性剂复合体系对小球藻的联合毒性评价
Table 1. Joint toxicity evaluation of nZnO/surfactant with different charges on Chlorella vulgaris
实验组
The experimental group评价方法
Evaluation method评价参数
Evaluation parameters评价结果
Evaluation resultsnZnO+0.2 mg·L–1 CTAC
(阳离子型Cationic)毒性单位法 M>M0(3.22>1.41) 拮抗作用 相加指数法 AI<0(AI= –2.23) 相似性参数法 0<λ<1(λ= 0.28) 混合毒性指数法 MTI<0(MTI= –2.35) nZnO+20 mg·L–1 SDBS
(阴离子型Anionic)毒性单位法 M<1(M= 0.97) 协同作用 相加指数法 AI>0(AI= 0.03) 相似性参数法 λ>1(λ= 1.05) 混合毒性指数法 MTI>1(MTI= 1.05) nZnO+100 mg·L–1 TX-100(非离子型Nonionic) 毒性单位法 M>M0(5.56>1.14) 拮抗作用 相加指数法 AI<0(AI= –4.56) 相似性参数法 0<λ<1(λ= 0.71) 混合毒性指数法 MTI<0(MTI= –11.62) 表 2 不同试验组生物量、积累量、投加量和溶出量间的相关性分析
Table 2. Correlation analysis among different test groups' biomass, accumulation, dosage, and dissolution
生物量
BiomassZn元素积累量
Accumulation of ZnZn2+积累量
Accumulation of Zn2+Zn2+投加量
Dosage of Zn2+Zn2+溶出量
Dissolution of Zn2+生物量 1 –0.538 –0.916** –0.946** –0.593* Zn元素积累量 1 0.813** 0.669* Zn2+积累量 1 0.979** 0.852** Zn2+投加量 1 Zn2+溶出量 1 注:*P<0.05, **P<0.01. -
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