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A large volume of historical archives was extensively damaged by flood water, following Typhoon Hagibis in Fukushima, Japan, in October 2019. They were rescued from the stricken area within a week, however, the prolonged exposure of paper documents to water caused severe biodegradation by fungal growth. To disinfect fungi, the paper documents were exposed to gamma radiations emitted by a source of Cobalt 60 by the industrial irradiation service. The wet paper documents were mainly contaminated with hydrophilic and cellulolytic fungi, including Trichoderma, Stachybotrys, and Fusarium; no fungi grew after irradiation. These results indicated that the average absorbed dosage from 13.1 kGy to 16.1 kGy were sufficient to disinfect paper documents heavily contaminated with fungi. In the present study, we demonstrated the successful practical use of irradiation in fungi-damaged paper documents using a commercial gamma-irradiation facility.

A total of 75 locations in 26 houses were examined for fungal contamination. Sixteen genera from 68 locations were detected. Cladosporium was the dominant contaminant. A high frequency of contamination was seen to involve Cladosporium, of which C. sphaerospermum and C. cladosporioides were detected most frequently at rates of 63.6% and 14.6%, respectively.

The growth of four fungal species (four isolates) from bathrooms was examined under various environmental conditions. These fungi were found several times in bathrooms and washing machines, but not in other indoor environments such as house dust or windows. The four species (Ramichloridium strelitziae, Cyphellophora laciniata, Phoma fimeti, and Exophiala sp.) were identified using DNA and morphological analyses. These bathroom fungi were able to consume surfactants, soap and shampoo, but were unable to grow well in high-temperature or dry conditions. Soap and shampoo seem to affect fungal flora in the bathroom.

Cladosporium contaminants on materials and utensils that come into contact with food were morphologically investigated. The most common contaminants, C. cladosporioides and C. sphaerospermum, were detected on the samples. The morphological changes of the Cladosporium species were investigated by using stereoscopic, optical light, fluorescent, and scanning electron microscopes. Microscopically the Cladosporium contaminants were observed as aggregated dark brown spots, strongly pigmented, irregularly swollen, and in long chains. Using fluorescent microscopy, the Cladosporium mycelia were clearly stained with fluorescein diacetate as viable cells, but the old cells were mostly non-viable, as shown by staining with propidium iodide. The dynamics of the morphological changes showed that the penetrating mycelia were closely attached to the surface of the materials and utensils under investigation. These results provide information about the significance of Cladosporium contamination on materials and utensils in contact with food and may contribute to the control of fungal contamination.