Concomitant releases of various engineered nanoparticles (NPs) into the environment have resulted in concerns regarding their combined toxicity to aquatic organisms. It is however, still elusive to distinguish the contribution to toxicity of components in NP mixtures. In the present study, we quantitatively evaluated the relative contribution of NPs in their particulate form (NP_(particle)) and of dissolved ions released from NPs (NP_(ion)) to the combined toxicity of binary mixtures of ZnO NPs and graphene oxide nanoplatelets (GO NPs) to three aquatic organisms of different trophic levels, including an alga species (Scenedesmus obliquus), a cladoceran species (Daphnia magna), and a freshwater fish larva (Danio rerio). Our results revealed that the effects of ZnO NPs and GO NPs were additive to S. obliquus and D. magna but antagonistic to D. rerio. The relative contribution to toxicity (RCT) of the mixture components to S. obliquus decreased in the order of RCT_{GO NP(particle)} > RCT_{ZnO NP(particle)} > RCT_{ZnO NP(ion)}, while the RCT of the mixture components to D. magna and D. rerio decreased in the order of RCT_{ZnO NP(particle)} > RCT_{GO NP(particle)} > RCT_{ZnO NP(ion)}. This finding also implies that the suspended particles rather than the dissolved Zn-ions dictated the combined toxicity of binary mixtures of ZnO NPs and GO NPs to the aquatic organisms of different trophic level. The alleviation of the contribution to toxicity of the ionic form of ZnO NPs was caused by the adsorption of the dissolved ions on GO NPs. Furthermore, the ZnO NP_(particle) and GO NP_(particle) displayed a different contribution to the observed mixture toxicity, dependent on the trophic level of the aquatic organisms tested. The difference of the contributions between the two particulate forms was mainly associated with differences in the intracellular accumulation of reactive oxygen species. Our findings highlight the important role of particles in the ecological impact of multi-nanomaterial systems.

中文翻译：

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氧化锌和氧化石墨烯纳米颗粒混合物对不同营养水平的水生生物的毒性：颗粒优于溶解离子

各种工程化的纳米颗粒（NPs）伴随释放到环境中，引起了人们对它们对水生生物的综合毒性的担忧。然而，仍然难以区分NP混合物中组分对毒性的贡献。在本研究中，我们定量评估了NPs的颗粒形式（NP _（粒子））和NPs释放的溶解离子（NP _（ion））对ZnO NPs和氧化石墨烯纳米二元混合物的联合毒性的相对贡献。（GO NPs）对三种不同营养水平的水生生物，包括藻类（Scendesmus obliquus），锁骨类（Daphnia magna）和淡水鱼幼虫（Danio rerio））。我们的结果表明，ZnO NPs和GO NPs的作用对斜链球菌和大麦球藻有累加作用，但对里氏梭菌有拮抗作用。到毒性（相对贡献RCT混合物组分到的）斜生栅藻在的顺序减小RCT _{GO NP（颗粒）} >  RCT_{的ZnO NP（颗粒）}  >  RCT_{的ZnO NP（离子）}，而RCT混合物组分的至D. magna和D. rerio按RCT _{ZnO NP（颗粒）}  >  RCT _{GO NP（颗粒）}  > 的顺序减少RCT _{ZnO NP（离子）}。该发现还暗示，悬浮颗粒而不是溶解的Zn离子决定了ZnO NP和GO NP的二元混合物对不同营养水平的水生生物的综合毒性。ZnO NPs离子形式对毒性的贡献的减轻是由于溶解的离子在GO NPs上的吸附所致。此外，ZnO NP _（颗粒）和GO NP _（颗粒）对所观察到的混合物毒性显示出不同的贡献，这取决于所测试的水生生物的营养水平。两种颗粒形式之间的贡献差异主要与活性氧物种在细胞内积累的差异有关。我们的发现突出了颗粒在多纳米材料系统的生态影响中的重要作用。