Microbial pollution assessment in semi-exposed relics: A case study of the K9901 pit of the mausoleum of emperor Qin Shihuang

Abstract

Summer and autumn are peak tourist seasons, during which tourists congregate in semi-exposed site museums, heightening the possibility of damage both to the tourists and the exposed relics by airborne microorganisms. This study investigated the spatiotemporal distribution of microbial aerosols and the diversity of the microbial genera inside and outside the Emperor Qin Shihuang Mausoleum K9901 Pit. Furthermore, the risk of museum personnel exposure to microbial aerosols was also quantitatively assessed. The results showed that the bacterial aerosol concentrations were 3.5 and 2.5 times the WHO limits (500 CFU/m3) in summer and autumn, respectively. Similarly, the fungal aerosol concentrations in summer and autumn were, respectively, 0.9 and 4.3 times the ACGIH limits (500 CFU/m3). The percentages of bacterial and fungal aerosols in the museum with particle sizes smaller than 4.7 μm were as high as 80.2–89.5 % and 83.2 %–93.2 %, respectively. The count median diameter was at level V of the Anderson sampler (1.1–2.1 μm). The risk of these aerosols being inhaled by personnel and entering the lower respiratory tract was significant. The dominant microbial genera detected had conditional pathogenicity (e.g., Acinetobacter and Pseudomonas) and allergenicity (e.g., Aspergillus and Talaromyces). Regarding tourists, the potential exposure dose (PED) was higher for children than for adults and the elderly. Staff were exposed for longer periods and had 18 times the PED of tourists of the same age, which put them at greater risk. This study offers valuable insights for developing effective environmental optimization measures to protect site museums and public health.