Kroll Alexandra, Behra Renata, Kaegi Ralf, Sigg Laura
Environmental Toxicology, Swiss Federal Institute of Aquatic Science and Technology (Eawag), Dübendorf, Switzerland.
Environmental Toxicology, Swiss Federal Institute of Aquatic Science and Technology (Eawag), Dübendorf, Switzerland; Institute of Biogeochemistry and Pollutant Dynamics IBP, Swiss Federal Institute of Technology in Zurich (ETHZ), Zurich, Switzerland.
PLoS One. 2014 Oct 21;9(10):e110709. doi: 10.1371/journal.pone.0110709. eCollection 2014.
Streams are potential receiving compartments for engineered nanoparticles (NP). In streams, NP may remain dispersed or settle to the benthic compartment. Both dispersed and settling NP can accumulate in benthic biofilms called periphyton that are essential to stream ecosystems. Periphytic organisms excrete extracellular polymeric substances (EPS) that interact with any material reaching the biofilms. To understand the interaction of NP with periphyton it is therefore crucial to study the interaction of NP with EPS. We investigated the influence of EPS on the physicochemical properties of selected NP (CeO2, Ag) under controlled conditions at pH 6, 7.6, 8.6 and light or dark exposure. We extracted EPS from five different periphyton communities, characterized the extracts, and exposed CeO2 and carbonate-stabilized Ag NP (0.5 and 5 mg/L, both 25 nm primary particle size) and AgNO3 to EPS (10 mg/L) over two weeks. We measured NP size distribution, shape, primary particle size, surface plasmon resonance, and dissolution. All EPS extracts were composed of biopolymers, building blocks of humic substances, low molecular weight (Mr) acids, and small amphiphilic or neutral compounds in varying concentrations. CeO2 NP were stabilized by EPS independent of pH and light/dark while dissolution increased over time in the dark at pH 6. EPS induced a size increase in Ag NP in the light with decreasing pH and the formation of metallic Ag NP from AgNO3 at the same conditions via EPS-enhanced photoreduction. NP transformation and formation were slower in the extract with the lowest biopolymer and low Mr acid concentrations. Periphytic EPS in combination with naturally varying pH and light/dark conditions influence the properties of the Ag and CeO2 NP tested and thus the exposure conditions within biofilms. Our results indicate that periphytic organisms may be exposed to a constantly changing mixture of engineered and naturally formed Ag NP and Ag+.
溪流是工程纳米颗粒（NP）潜在的接纳区域。在溪流中，纳米颗粒可能保持分散状态或沉降到底栖区域。分散和沉降的纳米颗粒都可能在称为周丛生物的底栖生物膜中积累，而周丛生物对溪流生态系统至关重要。周丛生物会分泌细胞外聚合物（EPS），这些聚合物会与任何到达生物膜的物质相互作用。因此，要了解纳米颗粒与周丛生物的相互作用，研究纳米颗粒与EPS的相互作用至关重要。我们在pH值为6、7.6、8.6且有光照或黑暗条件的受控环境下，研究了EPS对选定纳米颗粒（CeO2、Ag）物理化学性质的影响。我们从五个不同的周丛生物群落中提取了EPS，对提取物进行了表征，并在两周内将CeO2和碳酸盐稳定的Ag纳米颗粒（0.5和5 mg/L，初级粒径均为25 nm）以及AgNO3暴露于EPS（10 mg/L）中。我们测量了纳米颗粒的尺寸分布、形状、初级粒径、表面等离子体共振和溶解情况。所有EPS提取物均由生物聚合物、腐殖质的组成部分、低分子量（Mr）酸以及不同浓度的小两亲性或中性化合物组成。CeO2纳米颗粒在不考虑pH值和光照/黑暗条件的情况下都能被EPS稳定，而在pH值为6的黑暗环境中，溶解会随时间增加。在光照条件下，随着pH值降低，EPS会使Ag纳米颗粒尺寸增大，并且在相同条件下通过EPS增强的光还原作用，AgNO3会形成金属Ag纳米颗粒。在生物聚合物和低Mr酸浓度最低的提取物中，纳米颗粒的转化和形成速度较慢。周丛生物的EPS与自然变化的pH值和光照/黑暗条件共同影响了所测试的Ag和CeO2纳米颗粒的性质，进而影响了生物膜内的暴露条件。我们的结果表明，周丛生物可能会接触到不断变化的工程化和自然形成的Ag纳米颗粒及Ag+的混合物。
