Stand-alone portable air purifiers (APs) have become an increasingly popular method of controlling individual inhalation exposure. Exposure to bacterial endotoxins has a causative role in respiratory inhalation health. Here, we studied the changes in endotoxin levels in indoor air before and after purification by a portable AP equipped with HEPA (high-efficiency particulate air) filters. An increase in endotoxins was observed when a previously used AP was turned on to clean the air. Replacing the HEPA filters in the AP helped to mitigate the increase in endotoxins of larger sizes but not endotoxins of smaller sizes. Consequently, the use of APs could lead to increased endotoxin deposition in airways, especially in the alveolar region. The endotoxin concentrations on the HEPA filters were well correlated with the free DNA concentrations on the HEPA filters. This correlation indicates that the disrupted bacteria, which released free DNA, could also release endotoxins, thus making HEPA filters a source of indoor airborne endotoxins. Our results illustrate a potential endotoxin inhalation risk associated with HEPA-APs as an air cleaning strategy and highlight the importance of composition-specific air cleaning while reducing the particle number/mass.

独立便携式空气净化器（AP）已成为控制个人吸入暴露的一种越来越流行的方法。接触细菌内毒素在呼吸吸入健康中具有致病作用。在这里，我们研究了通过配备HEPA（高效微粒空气）过滤器的便携式AP净化前后室内空气中内毒素水平的变化。当打开以前使用的AP清洁空气时，观察到内毒素增加。在AP中更换HEPA过滤器有助于减轻较大尺寸内毒素的增加，但不能减轻较小尺寸内毒素的增加。因此，使用AP可能会导致内毒素在气道中的沉积增加，尤其是在肺泡区域。HEPA过滤器上的内毒素浓度与HEPA过滤器上的游离DNA浓度密切相关。这种相关性表明，释放出游离DNA的被破坏的细菌也可能释放内毒素，从而使HEPA过滤器成为室内空气传播的内毒素的来源。我们的研究结果表明，作为空气净化策略，与HEPA-AP相关的潜在内毒素吸入风险，并着重说明了特定成分的空气净化在减少颗粒数量/质量的同时的重要性。