Lung deposition and retention measurements are now required by the newly revised OECD inhalation toxicity testing guidelines 412 and 413 when evaluating the clearance and biopersistence of poorly soluble nanomaterials, such as multi-walled carbon nanotubes (MWCNTs). However, evaluating the lung deposition concentration is challenging with certain nanomaterials, such as carbon-based and iron-based nanomaterials, as it is difficult to differentiate them from endogenous elements. Therefore, the current 28-day inhalation toxicity study investigated the lung retention kinetics of tangled MWCNTs. Male Sprague Dawley rats were exposed to MWCNTs at 0, 0.257, 1.439, and 4.253 mg/m3 for 28 days (6 h/day, 5 days/week, 4 weeks). Thereafter, the rats were sacrificed at day 1, 7, and 28 post-exposure and the pulmonary inflammatory response evaluated by analyzing the bronchoalveolar lavage fluid. Plus, the blood biochemistry, hematology, and histopathology of the lungs were also examined. The lung deposition and retention of MWCNTs were determined based on the elemental carbon content in the lungs after tissue digestion. The number of polymorphonuclear cells and LDH concentration were both found to be significantly higher with the medium and high concentrations (1.439 and 4.253 mg/m3) and dose dependent. The estimated retention half-life for the high concentration (4.253 mg/m3) was about 35 days. The results of this study indicate that tangled MWCNTs seem to have a relatively shorter retention half-life when compared to previous reports on rigid MWCNTs, and the no-observed adverse effect level (NOAEL) for the tested tangled MWCNTs was 0.257 mg/m3 in a previous rat 28-day subacute inhalation toxicity study.

中文翻译：

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为期28天的吸入毒性研究，评估了肺部沉积和缠结的多壁碳纳米管的保留。

现在，当评估难溶性纳米材料（例如多壁碳纳米管（MWCNT））的清除率和生物持久性时，新修订的OECD吸入毒性测试指南412和413现在需要进行肺部沉积和保留测量。但是，对于某些纳米材料，例如碳基和铁基纳米材料，评估肺部沉积浓度具有挑战性，因为很难将其与内源性元素区分开。因此，当前的28天吸入毒性研究研究了缠结的MWCNT的肺保留动力学。将雄性Sprague Dawley大鼠分别以0、0.257、1.439和4.253 mg / m3的MWCNT暴露28天（6小时/天，5天/周，4周）。此后，在第1、7天处死大鼠。和28暴露后，通过分析支气管肺泡灌洗液评估肺部炎症反应。另外，还检查了肺的血液生化，血液学和组织病理学。根据组织消化后肺中的碳元素含量确定MWCNT在肺中的沉积和保留。发现中，高浓度（1.439和4.253 mg / m3）且剂量依赖性的多形核细胞数量和LDH浓度均显着较高。高浓度（4.253 mg / m3）的估计保留半衰期约为35天。这项研究的结果表明，与以前关于刚性MWCNT的报道相比，缠结的MWCNT似乎具有相对较短的保留半衰期，