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The advent of high‐throughput sequencing methods allowed researchers to fully characterize microbial community in environmental samples, which is crucial to better understand their health effects upon exposures. In our study, we investigated bacterial and fungal community in indoor and outdoor air of nine classrooms in three elementary schools in Seoul, Korea. The extracted bacterial 16S rRNA gene and fungal ITS regions were sequenced, and their taxa were identified. Quantitative polymerase chain reaction for total bacteria DNA was also performed. The bacterial community was richer in outdoor air than classroom air, whereas fungal diversity was similar indoors and outdoors. Bacteria such as Enhydrobacter, Micrococcus, and Staphylococcus that are generally found in human skin, mucous membrane, and intestine were found in great abundance. For fungi, Cladosporium, Clitocybe, and Daedaleopsis were the most abundant genera in classroom air and mostly related to outdoor plants. Bacterial community composition in classroom air was similar among all classrooms but differed from that in outdoor air. However, indoor and outdoor fungal community compositions were similar for the same school but different among schools. Our study indicated the main source of airborne bacteria in classrooms was likely human occupants; however, classroom airborne fungi most likely originated from outdoors.

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This study investigated the toxicity of Cu (1, 10, 15, and 25 mol%) loaded TiO 2 and pure TiO 2 nanometersized photocatalysts during the development of zebrafish embryogenesis. The hatch rate decreased in the Cu x TiO y nanoparticles exposed groups (10, 20 ppt) compared to pure TiO 2 nano-particles (10, 20 ppt) exposed or control groups. These Cu x TiO y and TiO 2 nanoparticles led to developing mutated embryos with abnormal notochord formation, no tail, damaged eyes and abnormal heart development. Exposure to Cu x TiO y and pure TiO 2 nanoparticles led to glutathione increase, catalase activity increase, GST increase and GSR increase than control. Penetration of the Cu x TiO y and pure TiO 2 nanoparticles to the embryo was also tested. It was observed that Cu x TiO y and pure TiO 2 nanoparticles penetrated into cells. Moreover Cu x TiO y penetrated into the skin, nerve and yolk sac epithelium cells on the zebrafish larvae as aggregated particles, which may induce the direct interaction between nanoparticles and cell to cause adverse biological responses. As a result, the Cu-loaded TiO 2 nanoparticles had the toxicity of zebrafish embryo and larvae in the water environment.