Seitz Frank, Lüderwald Simon, Rosenfeldt Ricki R, Schulz Ralf, Bundschuh Mirco
Institute for Environmental Sciences, University of Koblenz-Landau, Landau Germany.
Institute for Environmental Sciences, University of Koblenz-Landau, Landau Germany; Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
PLoS One. 2015 May 1;10(5):e0126021. doi: 10.1371/journal.pone.0126021. eCollection 2015.
During their aquatic life cycle, nanoparticles are subject to environmentally driven surface modifications (e.g. agglomeration or coating) associated with aging. Although the ecotoxicological potential of nanoparticles might be affected by these processes, only limited information about the potential impact of aging is available. In this context, the present study investigated acute (96 h) and chronic (21 d) implications of systematically aged titanium dioxide nanoparticles (nTiO2; ~90 nm) on the standard test species Daphnia magna by following the respective test guidelines. The nTiO2 were aged for 0, 1, 3 and 6 d in media with varying ionic strengths (Milli-Q water: approx. 0.00 mmol/L and ASTM: 9.25 mmol/L) in the presence or absence of natural organic matter (NOM). Irrespective of the other parameters, aging in Milli-Q did not change the acute toxicity relative to an unaged control. In contrast, 6 d aged nTiO2 in ASTM without NOM caused a fourfold decreased acute toxicity. Relative to the 0 d aged particles, nTiO2 aged for 1 and 3 d in ASTM with NOM, which is the most environmentally-relevant setup used here, significantly increased acute toxicity (by approximately 30%), while a toxicity reduction (60%) was observed for 6 d aged nTiO2. Comparable patterns were observed during the chronic experiments. A likely explanation for this phenomenon is that the aging of nTiO2 increases the particle size at the start of the experiment or the time of the water exchange from <100 nm to approximately 500 nm, which is the optimal size range to be taken up by filter feeding D. magna. If subjected to further agglomeration, larger nTiO2 particles, however, cannot be retained by the daphnids' filter apparatus ultimately reducing their ecotoxicological potential. This non-linear pattern of increasing and decreasing nTiO2 related toxicity over the aging duration, highlights the knowledge gap regarding the underlying mechanisms and processes. This understanding seems, however, fundamental to predict the risks of nanoparticles in the field.
在纳米颗粒的水生生命周期中，它们会受到与老化相关的环境驱动的表面改性（例如团聚或包覆）影响。尽管纳米颗粒的生态毒理学潜力可能会受到这些过程的影响，但关于老化潜在影响的信息却十分有限。在此背景下，本研究依据相应的测试指南，调查了系统老化的二氧化钛纳米颗粒（nTiO2；约90纳米）对标准测试物种大型溞的急性（96小时）和慢性（21天）影响。nTiO2在不同离子强度的介质（超纯水：约0.00毫摩尔/升和美国材料与试验协会标准海水：9.25毫摩尔/升）中，在有或没有天然有机物（NOM）存在的情况下分别老化0、1、3和6天。无论其他参数如何，在超纯水中老化相对于未老化对照而言，并未改变急性毒性。相比之下，在没有NOM的美国材料与试验协会标准海水中老化6天的nTiO2导致急性毒性降低了四倍。相对于老化0天的颗粒，在含有NOM的美国材料与试验协会标准海水中老化1天和3天的nTiO2（这是此处使用的最接近环境实际情况的设置）显著增加了急性毒性（约30%），而老化6天的nTiO2则观察到毒性降低（60%）。在慢性实验中也观察到了类似的模式。对此现象的一个可能解释是，nTiO2的老化在实验开始时或换水时增加了颗粒尺寸，从小于100纳米增加到约500纳米，这是滤食性大型溞摄取的最佳尺寸范围。然而，如果进一步团聚，更大的nTiO2颗粒最终无法被大型溞的滤食器官保留，从而降低其生态毒理学潜力。这种nTiO2相关毒性随老化时间先增加后降低的非线性模式，凸显了关于潜在机制和过程的知识空白。然而，这种理解对于预测纳米颗粒在实际环境中的风险似乎至关重要。
