Silver nanoparticles (AgNPs) can gradually accumulate in algae to exert their toxicity; however, there is little knowledge about their bioaccumulation dynamics. For the first time, this study reports the effect of surface charge of AgNPs on their bioaccumulation dynamics in freshwater algae (Chlorella vulgaris) using biodynamic modeling. Polyethylene-coated AgNPs (PEI-AgNPs) and citrate-coated AgNPs (Cit-AgNPs) were selected as positively and negatively charged AgNPs, i.e., P-AgNPs and N-AgNPs, respectively. Their uptake and elimination dynamics were investigated at a concentration of 50% inhibition of growth rate values (EC50) and 10% inhibition of growth rate values (EC10). The one-component model can generally well simulate the algal uptake and elimination kinetics of N-AgNPs but not of P-AgNPs. At both concentrations, the uptake rate constants (ku) for P-AgNPs were ∼20 times higher than that for N-AgNPs. The parameters of biphasic elimination kinetics revealed that P-AgNPs were eliminated faster than N-AgNPs during depuration compared to in subsequent processes. Compared with N-AgNPs, extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and dark-field imaging revealed that P-AgNPs can be rapidly absorbed on the algal cell surface membrane owing to their remarkably lower energy barrier between algal cells, resulting in a faster adsorption/uptake process and aggregation of algal cells. Our results clearly demonstrate that the AgNPs exhibited surface charge-dependent bioaccumulation dynamics in algal cells. Thus, AgNP surface charge primarily influences the AgNP accumulation dynamics in algal cells.

中文翻译：

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纳米银在淡水藻中的表面电荷依赖性生物累积动力学。

银纳米颗粒（AgNPs）可以逐渐在藻类中积累，发挥其毒性。然而，关于它们的生物积累动态的知识很少。这项研究首次使用生物动力学模型报道了AgNPs的表面电荷对其在淡水藻类（Chlorella vulgaris）中生物蓄积动力学的影响。选择聚乙烯涂层的AgNPs（PEI-AgNPs）和柠檬酸盐涂层的AgNPs（Cit-AgNPs）作为带正电荷和负电荷的AgNPs，分别是P-AgNPs和N-AgNPs。在50％的增长率抑制值（EC50）和10％的增长率抑制值（EC10）浓度下研究了它们的吸收和消除动力学。单组分模型通常可以很好地模拟N-AgNPs的藻类吸收和消除动力学，而不能模拟P-AgNPs。在两种浓度下 P-AgNPs的吸收速率常数（ku）比N-AgNPs高约20倍。双相消除动力学的参数表明，与后续过程相比，纯化过程中P-AgNP的清除速度快于N-AgNP。与N-AgNPs相比，扩展的Derjaguin-Landau-Verwey-Overbeek理论（DLVO）和暗场成像显示，由于P-AgNPs明显降低了藻类细胞之间的能垒，因此它们可以在藻类细胞表面膜上快速吸收，从而以更快的吸附/摄取过程和藻类细胞的聚集。我们的结果清楚地表明，AgNPs在藻类细胞中表现出依赖表面电荷的生物蓄积动力学。因此，AgNP表面电荷主要影响藻类细胞中AgNP的累积动力学。双相消除动力学的参数表明，与后续过程相比，纯化过程中P-AgNP的清除速度快于N-AgNP。与N-AgNPs相比，扩展的Derjaguin-Landau-Verwey-Overbeek理论（DLVO）和暗场成像显示，由于P-AgNPs明显降低了藻类细胞之间的能垒，因此它们可以在藻类细胞表面膜上快速吸收，从而以更快的吸附/摄取过程和藻类细胞的聚集。我们的结果清楚地表明，AgNPs在藻类细胞中表现出依赖表面电荷的生物蓄积动力学。因此，AgNP表面电荷主要影响藻类细胞中AgNP的累积动力学。双相消除动力学的参数表明，与后续过程相比，纯化过程中P-AgNP的清除速度快于N-AgNP。与N-AgNPs相比，扩展的Derjaguin-Landau-Verwey-Overbeek理论（DLVO）和暗场成像显示，由于P-AgNPs在藻类细胞之间的能量垒极低，因此它们可以被藻类细胞表面膜迅速吸收，从而以更快的吸附/摄取过程和藻类细胞的聚集。我们的结果清楚地表明，AgNPs在藻类细胞中表现出依赖表面电荷的生物蓄积动力学。因此，AgNP表面电荷主要影响藻类细胞中AgNP的累积动力学。