Fungal levels in houses in the Fukushima Daiichi Nuclear Power Plant evacuation zone after the Great East Japan Earthquake

ABSTRACT

Residences located within 20 km of the damaged Fukushima Daiichi Nuclear Power Plant were evacuated shortly after the Great East Japan Earthquake. The levels of airborne and surface fungi were measured in six houses in the evacuation zone in August 2012 and February 2013. Airborne fungal levels in all of the houses in the summer were higher than the environmental standard levels for residential houses published in Architectural Institute of Japan (>1000 colony-forming units [CFU]/m³). In two houses whose residents rarely returned to visit, fungal levels were extremely high (>52,000 CFU/m³). Although fungal levels in the winter were much lower than those in the summer, they were still higher than environmental standard levels in several houses. Indoor fungal levels were significantly inversely related to the frequency with which residents returned, but they were not correlated with the air exchange rates, temperature, humidity, or radiation levels. Cladosporium spp. and Penicillium spp. were detected in every house. Aspergillus section Circumdati (Aspergillus ochraceus group) was also detected in several houses. These fungi produced ochratoxin A and ochratoxin B, which have nephrotoxic and carcinogenic potential. The present study suggests that further monitoring of fungal levels is necessary in houses in the Fukushima Daiichi Nuclear Power Plant evacuation zone, and that some houses may require fungal disinfection.

Implications: The results suggest that residents’ health could be at risk owing to the high levels of airborne fungi and toxic fungi Aspergillus section Circumdati. Therefore, monitoring and decontamination/disinfection of fungi are strongly recommended before residents are allowed to return permanently to their homes. In addition, returning to home with a certain frequency and adequate ventilation are necessary during similar situations, e.g., when residents cannot stay in their homes for a long period, because fungal levels in houses in the Fukushima Daiichi Nuclear Power Plant evacuation zone were inversely correlated with the frequency with which residents returned to visit their houses.

Introduction

In March 11, 2011, the Great East Japan Earthquake and subsequent tsunami devastated the northeastern coast of Japan and damaged the Fukushima Daiichi Nuclear Power Plant (Tokyo Electric Power Co., Inc. [TEPCO], 2012). On March 12, 2011, based on the emergency situation at the plant, 77,000 residents were evacuated from 10 towns and villages that are located within 20 km of the power plant (Ministry of Economy, Trade and Industry [METI], 2011a). Although the evacuees of Minamisoma City, which is located within 20 km of the power plant, were restricted to enter the restricted area, they once were allowed to return to their houses for 2–5 hr after April 23, 2011 (METI, 2011b). They were allowed to return to their houses in the daytime after April 26, 2012, but they are restricted from staying overnight (METI, 2012). Some evacuees frequently return to repair and clean their houses, whereas others rarely return because of radiation concerns.

Previous studies reported increased fungal levels in flooded areas after Hurricane Katrina (Solomon et al., 2006; Rao et al., 2007; Schwab et al., 2007). Lung and respiratory diseases were also increased in these areas after Hurricane Katrina (Alderman et al., 2012). In the tsunami-flooded areas of the Great East Japan Earthquake, indoor fungal levels are predicted to be high. In addition, fungi are predicted to grow easily in residences in the evacuation zone of the Great East Japan Earthquake because of potentially high indoor humidity resulting from low ventilation and because food and waste were left behind at the time of the evacuation.

We have continuously investigated indoor environment of temporary houses in devastated areas after the Great East Japan Earthquake (Shinohara et al., 2013, 2014). During the survey, we interviewed evacuees, which revealed that some residents want to return to live in their own house someday after lowering of the regional radioactive levels and lifting of evacuation zones, although they do not return home now to avoid the radiation exposure. If the indoor fungal levels are high in the houses that are abandoned for long years, there might be a risk of health damage from the indoor fungi.

Therefore, it is critical to measure fungal levels in houses in the evacuation zone. In the present study, airborne and surface fungal levels were measured in five houses, which differed based on the frequency with which residents returned, and in a tsunami-flooded house in August 2012 and February 2013 in the evacuation zone. Multivariate analysis of various factors was performed to determine which, if any, factors influenced house fungal levels. The results of our study reveal which residences are predicted to have high fungal levels and will likely require decontamination measures before residents are allowed to return permanently.

Materials and methods

Survey area and period

Houses in Minamisoma City, located in the coastal area of Fukushima Prefecture (Figure 1), were selected for survey. The area has a marine climate, with average temperatures and rainfall levels of 2.0 °C and 41.4 mm in the winter (January and February) and 23.0 °C and 174.7 mm in the summer (July and August), respectively (1981–2010; Figure 1; Japan Meteorological Agency [JMA], 2012). Approximately one-third of Minamisoma City is located within 20 km of the Fukushima Daiichi Nuclear Power Plant.

Figure 1. Map of houses surveyed in the present study and Fukushima Daiichi Nuclear Power Plant. ♦ shows the houses surveyed in the present study. ● shows Fukushima Daiichi Nuclear Power Plant.

Indoor and outdoor airborne fungal levels, surface fungal levels on the floor of residences, air exchange rates, temperature, humidity, and radiation levels were measured between the hours of 9:00 a.m. and 6:00 p.m. on August 30–31, 2012 (i.e., summer), and on February 13–14, 2013 (i.e., winter).

Local weather conditions on the days of the surveys were as follows: occasionally sunny (temperature, 29.6 ± 1.1 °C; rainfall, 0 mm; wind, 2.7 ± 1.1 m/sec [northeast–southeast]) in the summer and occasionally sunny (temperature, 6.3 ± 1.5 °C; rainfall, 0 mm; wind, 3.9 ± 2.7 m/sec [northwest–southeast]) in the winter. Local weather conditions during 2 weeks before the survey were sunny and cloudy (average temperature, 25.9 °C; total rainfall, 0 mm) in summer and sunny, cloudy, and occasionally light rain (average temperature, 3.1 °C; total rainfall, 7 mm [maximum rain fall 1 mm/hr]) in winter.

Characteristics of target houses

Houses in the evacuation zone (approximately 15 km from the Fukushima Daiichi nuclear plant) were selected for the present study. Most of residents who evacuated from their own old houses lived in houses that were far from their old houses. Therefore, we asked the city government to recruit subjects whose houses were located in the evacuate area and possible to be lived in again (not completely destroyed). Among city employees, residents of five houses (houses A–E) satisfied the requirement. Additionally, we measured a house (house F) that was tsunami-flooded. Houses A and E were located in mountainside, houses B, C, and D were located in city area, and house F was located in coastal area. House A was located right across the street from house E. Every house was a wooden detached house. House E was 2 years old, whereas the other houses were more than 10 years old.

The frequencies with which residents returned were different among five houses. The occupants of house A did not return after the earthquake, whereas the occupants of houses B, C, D, and E returned once, once a month, once or twice a month, and once a week, respectively, after restrictions were lifted on April 26, 2012. Since the first floor of house F was completely damaged by the tsunami (Figure S1), sampling was conducted on the second floor. Although more samples were wanted to add to the survey, not enough volunteer residents could gather in the evacuation zone. There were signs of forced entry of rats and mice in most houses except house E.

Indoor and outdoor airborne fungal levels

Indoor airborne fungal levels were sampled at five locations in the living room of residences, and outdoor airborne fungal levels were sampled at one location adjacent to the house. Samples were collected onto DG18 agar (Dichloran 18% glycerol agar) plates at a height of 1.5 m using air sampler (SAS Super 100; Bioscience International, Rockville, MD), with a volume of 50 L (flow rate: 100 L/min; sampling period: 0.5 min). Collected fungi were cultured at 25 °C for 7 days for subsequent counting. Isolates were identified on the basis of their colony and microscopic characteristics after subculturing on potato dextrose agar (PDA), malt extract agar (MEA), and Czapek yeast extract agar (CYA) plates (Klich, 2002; Samson et al., 2004). The detection limit for indoor airborne fungal levels was 4 colony-forming units [CFU]/m³ both in the summer and winter.

Surface fungal levels

Surface fungi on the floor, kitchen sink, and windows of residences were sampled at two to three accessible locations (10 cm × 10 cm) in the kitchen. Floor of houses A, B, C, D, E, and F were polyvinyl chloride (PVC), tatami, wooden, wooden, wooden/tatami, and carpet. Two samplers, a sterilizing monitoring kit (PF-2002; Eiken Chemical Co., Ltd., Tokyo, Japan), which is rayon swab with phosphate-buffered saline (PBS), and sterilizing stamp (TF-4000; Eiken Chemical), which is made of dry polyethylene foam, were used. Sampled fungi were cultured on DG18 agar plates for counting and on PDA, MEA, and CYA agar plates for characterization and identification. The detection limit for surface fungal levels was 100 CFU/100 cm² in both the summer and winter.

Ochratoxins produced by Aspergillus section Circumdati detected in air

Aspergillus section Circumdati includes species that can produce carcinogenic ochratoxins (Frisvad et al., 2004). Section Circumdati isolates were analyzed for ochratoxin A and ochratoxin B (OTA and OTB, hereafter). For examination of ochratoxins production, a 50-mL Erlenmeyer flask to which 5 g of barley grains, 4 mL of tap water, and 1 mL of 1% peptone water had been added was autoclaved. The grains were inoculated with section Circumdati to be incubated at 20 °C for 10 days. After the incubation, 20 mL of ethyl acetate was added to the culture and the ochratoxins were extracted; 1 mL of the extracted solution was dried up at 40 °C, and the resulting solid was dissolved in 1.5 mL of ethanol.

The extract was diluted 13-fold with 50% methanol in a graduated test tube. Preliminary measurements were taken with a high-performance liquid chromatography (HPLC) system (Hewlett Packard 1090 HPLC DAD, 1046 FLD; Palo Alto, CA) with a diode array detector and a fluorescent detector in tandem. Samples with high concentrations were diluted with 20% methanol as required for measurements with liquid chromatography–tandem mass spectrometry (LC/MS/MS) (Waters Alliance 2695 HPLC [Milford, MA], Applied BioSystems API 3000 [Thermo Fisher Scientific Inc., Waltham, MA]). The column used for the measurement of OTA and OTB was an Inertsil ODS-3V (GL Sciences, Tokyo, Japan; 5 μm, 2.1 mm inner diameter [I.D.] × 150 mm), which was gradient-eluted with acetonitrile and 5 mM ammonium acetate buffer.

For toxin detection, OTA and OTB were ionized using electrospray ionization (ESI) in negative ion mode with OTA measured at precursor ion m/z 402.1 and product ion m/z 357.9 and 166.9 and OTB at precursor ion m/z 368.1 and product ion m/z 324.0 and 280.0. The limits of quantification for OTA and OTB were 0.011 and 0.003 mg/L, respectively.

Air exchange rates

After sampling for fungi, air exchange rates in the houses were measured by the carbon dioxide (CO₂) decay method, which is appropriate for obtaining short-term air exchange rates in unoccupied houses. CO₂ gas, either from cylinders or dry ice, was released into every room of each house, and the indoor air was mixed using a fan until the CO₂ concentration equilibrated at several locations in every room. The indoor CO₂ concentration was monitored at two locations in the living room at a height of 1.5 m for 2 hr using a CO₂ monitor (Telaire7001; Onset Computer Co., Bourne, MA). The outdoor CO₂ concentration was also measured for 15 min, before and after measurement of indoor CO₂ concentration.

The air exchange rate was obtained by fitting the difference in the indoor and outdoor CO₂ concentrations with an exponential function. Before the survey, the instruments were properly calibrated with accurate IAQ monitor (model 2211; Kanomax Japan, Inc., Osaka, Japan) with zero and span reference gases.

Temperature and humidity

The indoor temperature and humidity were monitored in the living room of residences every 2 min during the duration of the survey (approximately 3 hr), and at a distance of more than 10 cm from the wall, using thermohygrometers (Ondotori TR-72Ui; T&D Corporation, Tokyo, Japan).

Radiation levels

In and around houses A–E, radiation levels were measured at five indoor and outdoor locations at a height of 1.5 m using a Geiger-Müller tube (radiation monitor RADEX RD 1503; Quarta-Rad, Moscow, Russia).

Results

Airborne fungi

The average ± SD (N = 5) indoor airborne fungal levels in houses A–F was >52,000, >52,000, 7200 ± 1300, 3200 ± 650, 1100 ± 190, and 7500 ± 1400 CFU/m³ in the summer and 4100 ± 2500, 9000 ± 3400, 580 ± 520, 260 ± 86, 250 ± 81, and 4000 ± 1500 CFU/m³ in the winter, respectively (Figure 2). The indoor airborne fungal levels were significantly inversely related to the frequency with which residents returned (Jonkheere-Terpstra test, P = 0.00 [summer], P = 0.01 [winter]).

Figure 2. Indoor and outdoor airborne fungal levels in houses in the evacuation zone determined in the summer (a) and winter (b).

The outdoor airborne fungal levels in houses A–F were 1500, 4800, 2220, 1800, 1500 and 10,000 CFU/m³ in the summer and 40, 650, 200, 420, 40, and 4400 CFU/m³ in the winter, respectively (Figure 2). The indoor-outdoor (I/O) ratios were >35, >11, 3.3, 1.8, 0.72, and 0.73 for houses A–F in the summer and 103, 14, 2.9, 0.62, 6.2, and 0.92 in the winter, respectively.

The abundance ratios of fungal species in houses A–F are shown in Figure 3. Alternaria spp., Aspergillus spp., Cladosporium spp., and Penicillium spp. were detected in every house in the summer. Similarly, Aspergillus section Restricti, Cladosporium, Penicillium, and Wallemia sebi were detected in every house in the winter. The I/O ratios of these fungi were high in houses A and B. Section Circumdati, which has potential to produce nephro-toxic and carcinogenic ochratoxins, was detected only indoors in four of the surveyed houses in the summer and in two of the surveyed houses in the winter.

Figure 3. Abundance ratios of indoor and outdoor airborne fungal levels in houses in the evacuation zone determined in the summer (a) and winter (b).

Surface fungi

The surface fungal levels and the abundance ratios of fungal species are shown in Figures 4 and 5, respectively. The airborne and surface fungal levels in houses A and B were higher than those in houses C, D, and E. The surface fungal levels on the floor were higher than those on the kitchen sink in all houses. Cladosporium spp., Penicillium spp., and section Circumdati were detected in several places in the summer. In the winter, yeast was detected on every floor, although not in the air.

Figure 4. Surface fungal levels at three indoor locations in houses in the evacuation zone determined in the summer (a) and winter (b).

Figure 5. Abundance ratios of surface fungal levels at two indoor locations in houses in the evacuation zone determined in the summer (a) and winter (b).

Air exchange rates

The air exchange rates of houses A–E were 1.4/hr, 1.3/hr, 0.6/hr, 0.2/hr, and 1.1/hr in the summer and 2.1/hr, 0.4/hr, 0.2/hr. 0.3/hr, and 0.9/hr in the winter, respectively. The air exchange rate of house F was 6.4/hr in the summer but was not measured in the winter. In house E, a ventilation fan was kept on continuously during the survey in both the summer and winter. The indoor airborne fungal levels were not related to air exchange rates (Pearson test: P = 0.83).

Production of ochratoxins by Aspergillus section Circumdati detected in air

Table 1 shows the amounts of OTA and OTB that the tested section Circumdati strains produced with barley. Seven of the nine strains of section Circumdati produced OTA and OTB. The amounts of OTA and OTB production were 0–4100 and 0–1000 µg/g, respectively.

Table 1. Ochratoxin productivity of Aspergillus section Circumdati isolates from air in the summer.

Strain	OTA (µg/g)^a	OTB (µg/g)^a	Origin
FCG979	4100	1000	House A, living room
FCG980	86	13	House A, living room
FCG981	1200	330	House A, living room
FCG984	N.D.^b	N.D.	House B, living room
FCG985	900	13	House B, living room
FCG982	1400	19	House C, living room
FCG983	670	23	House C, living room
FCG986	430	41	House F, living room
FCG987	N.D.	N.D.	House F, living room

^aOchratoxin (OTA) μg per gram barley as a substrate.

^bN.D. = not detected. The limits of quantification for OTA and OTB were 33 and 9 µg/g, respectively.

Temperature and humidity

The average indoor temperatures of houses A–F were 32, 32, 33, 32, 35, and 32 °C in the summer and 11, 10, 8.0, 9.6, 12, and 13 °C in the winter, respectively. The average indoor relative humidity levels in houses A–F were 70%, 68%, 64%, 64%, 57%, and 66% in the summer and 47%, 52%, 52%, 47%, 46%, and 50% in the winter, respectively.

Radiation levels

The indoor and outdoor radiation levels in and around mountainside houses A and E (average: 1.5 ± 0.41 μSv/hr) were higher than those in city-area houses B, C, and D (average: 0.34 ± 0.11 μSv/hr) (Table S1). The I/O ratios of radiation levels ranged between 0.41 and 0.78 in the summer and between 0.48 and 0.83 in the winter.

Discussion

According to standard AIJES-A00-2013 (Architectural Institute of Japan [AIJ], 2013) of the Architectural Institute of Japan, the indoor airborne fungal levels in Japan should be maintained under 1000 CFU/m³, or the I/O ratio should be under 2 in cases where the fungal levels exceed 1000 CFU/m³. The European Collaboration Action (ECA) has also categorized airborne fungal levels exceeding 1000 CFU/m³ as “high” and those exceeding 10,000 CFU/m³ as “very high” (ECA, 1993). The total indoor airborne fungal levels in the houses surveyed in this study were 1100 to >52,000 and 250 to 9000 CFU/m³ in the summer and winter, respectively. The indoor airborne fungal levels in every house in the summer and houses A, B, and F in the winter exceeded 1000 CFU/m³. The average indoor airborne fungal levels of typical Japanese houses, counted using DG18 cultures, have been found to be <13 to 3750 CFU/m³, with a geometric mean (GM) of 138 CFU/m³ (Takahashi, 1997) and 0 to 3370 CFU/m³, with a GM of 248 CFU/m³ (Saijo et al., 2011). Compared with these levels, the indoor fungal levels in houses in the evacuation zone were higher. The I/O ratio was greater than 10 for houses A and B in both the summer and winter, and approximately 3 for house C. These ratios exceeded the standard AIJES-A00-2013, indicating dissemination of many fungal species in these houses.

Indoor fungal levels in summer were higher than those in winter as well in the previous study (Mentese et al., 2012). Although the variation in mold activity and growing could depend on the environmental conditions between days (LeBouf et al., 2012), the climate of both seasons was sunny and the rainfall amounts were quite low in 2 weeks before both of the survey durations in the present study. Therefore, the fungal levels measured in the present study could be representative for each season.

Indoor airborne fungal levels were inversely related to the frequency with which residents returned to their houses. This is likely because when residents returned, the doors and windows were opened, leading to air exchange, and the floors were vacuumed, although they did not make a strong effort to remove fungi. These actions likely reduced the indoor humidity and resulted in a cleaner environment, decreasing the levels of indoor fungi. The houses should be cleaned and/or renovated prior to the residents’ return to their homes, and the fungal concentration should be checked before inhabiting the houses.

In water-damaged houses after Hurricane Katrina, indoor airborne fungal levels were only 3700 CFU/m³ in mildly damaged houses and 67,000 CFU/m³ in moderately and heavily damaged houses (Rao et al., 2007). The I/O ratio of fungi in these houses was 7.1 (Rao et al., 2007). In the present study, the indoor airborne fungal levels in the tsunami-flooded house F were 7500 and 4000 CFU/m³ in the summer and winter, respectively, and the I/O ratios were 0.73 and 0.92 in the summer and winter, respectively. The low I/O ratios in house F likely occurred because the first floor was completely destroyed (i.e., the first floor had no doors and windows; Figure S1), permitting constant air exchange between the indoor and outdoor environments (air exchange rate: 6.4/hr). In addition, the outdoor airborne fungal levels were high (10,000 and 4400 CFU/m³ in the summer and winter, respectively). In a previous report, the outdoor airborne fungal levels increased with proximity to a rubble yard (National Institute for Environmental Studies [NIES], 2013). Refuse, including building materials and furniture, which were carried by the tsunami to the area around house F and left neglected for more than 2 yr, likely contributed to the spread and growth of fungi in this area.

In surface fungi, yeast was detected in most houses at high levels, differently from airborne fungi. It is possible that this was owing to the neglected food.

Cladosporium spp., Aspergillus spp., and Penicillium spp. were the dominant airborne fungi in the present study (the abundance ratios of airborne levels were 38%, 26%, and 21% in the summer and 8.5%, 48%, and 14% in the winter, respectively), which is consistent with the results of previous studies (Takahashi, 1997; Saijo et al., 2011). It is notable that section Circumdati was detected in the indoor environment in the present study. Section Circumdati, such as A. westerdijkiae, A. steynii, or A. ochraceus, can produce ochratoxins, which are nephrotoxic and carcinogenic (International Agency for Research on Cancer [IARC], 1993; Hussein and Brasel, 2001; Frisvad et al., 2004). Although these fungi have been of concern as a foodborne pathogen (Duarte et al., 2010; Canel et al., 2013), they are rarely a cause for concern as an airborne pathogen. The qualitative and quantitative frequencies of Aspergillus ochraceus were previously found to be 5.0% and 0.9% in water-damaged buildings in Denmark (Andersen et al., 2011). In typical Japanese houses, Aspergillus ochraceus constitutes only 0.3% or 0.6% of the total fungi population as detected using DG18 or PDA cultures (Takahashi, 1997), respectively, and indoor airborne levels are not high (<1 CFU/m³). In the present study, section Circumdati was isolated in houses A, B, C, and F in the summer and in houses A and B in the winter. In particular, airborne levels were quite high in houses A and B (1900 and 1200 CFU/m³) in the summer compared with the previous studies. Because not every strain of Circumdati produces ochratoxin, we checked the ochratoxin production capacity of the strain of Circumdati sampled in the present study. The results show that the section Circumdati isolates that could produce OTA and OTB were detected in the air in the summer. Previous studies similarly have shown that the OTA production rate of section Circumdati isolated from Japanese indoor air is comparatively high, and that OTA production of strains in barley often reaches 1000 µg/g (Hashimoto et al., 2012). In the present study, the ochratoxin production by the highly toxic strain reached 4000 µg/g. It is not clear how ochratoxins contained in airborne fungal spores are related to effects on the human body; however, damage to human health by mycotoxins contained in fungal spores was previously observed for Stachybotrys chartrum in a flood disaster in Ohio, USA. Mycotoxins produced by inhaled S. chartrum were suggested to be a likely cause of pulmonary hemorrhage in infants (Centers for Disease Control and Prevention [CDC], 1997). In the present study, airborne section Circumdati was likely present because evacuees left behind food in their houses for more than 2 yr and feral animals scavenged some of them, which might have permitted the propagation of section Circumdati in the indoor environment. In addition, in houses A and B, section Circumdati was detected on the floor as surface fungi, suggesting another potential source of the airborne fungi. The floors in these two houses were made of vinyl chloride, whereas the floors in the other houses were made of wood. The nature of the material used for the floors could be associated with the growth of section Circumdati because Aspergillus ochraceus was previously reported to be associated with concrete but not wallpaper in water-damaged houses (Andersen et al., 2011).

In areas where radiation levels were not quite high, residents may be permitted to return permanently in the near future. In such situation, some residents might decide to return to live in their own house. Although the results in the present study suggested that frequency of return to home was associated with the indoor fungal levels, sample size was insufficient. A larger survey is required before reinhabiting of residences in the area. In addition, if the indoor fungal levels will be high, including section Circumdati in their houses that have been abandoned for long years, occupants’ health will be of concern. Therefore, monitoring and resolution of indoor fungal problems in each house will be required before living.

Conclusion

Although the results of the present study were preliminary and representative of only a small sample size, indoor airborne fungal levels were found to be high in houses in the evacuation zone of the Fukushima Daiichi Nuclear Power Plant. Because airborne fungal levels were inversely correlated with the frequency with which residents returned, frequent visits and improved ventilation are important to keep indoor airborne fungal levels low. Toxic fungi, such as Aspergillus section Circumdati, were found at high levels in these houses.

Continued progress in radiation decontamination will eventually permit residents to return permanently to their homes. Based on the results of the present study, monitoring and decontamination/disinfection of fungi are strongly recommended before residents are allowed to return permanently. In addition, a larger survey is warranted to better determine the degree of fungal pollution in houses in the evacuation zone.

Acknowledgment

The authors express their gratitude to the Minamisoma city government, Mayor Katsunobu Sakurai, and the staff of the Minamisoma government for their cooperation. They would also like to thank Dr. Yoshiki Onji for advice on analysis of ochratoxins.

Funding

This project was conducted as a part of the project “Development of new mildew-proofing and insect deterrent technology for renovation of tsunami-flooded houses in the Great East Japan Earthquake,” which was funded by the Maeda Engineering Foundation (April 2012 to March 2013).

Supplemental data

Supplemental data for this article can be accessed on the publisher’s website.

Additional information

Funding

This project was conducted as a part of the project “Development of new mildew-proofing and insect deterrent technology for renovation of tsunami-flooded houses in the Great East Japan Earthquake,” which was funded by the Maeda Engineering Foundation (April 2012 to March 2013).

Notes on contributors

Naohide Shinohara

Naohide Shinohara is a senior researcher at the Research Institute of Science for Safety and Sustainability (RISS), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan.

Masahiro Tokumura

Masahiro Tokumura is a research assistant professor at Graduate School of Nutritional and Environmental Science, the University of Shizuoka, Shizuoka, Japan.

Kazuhiro Hashimoto

Kazuhiro Hashimoto and Yuji Kawakami are researchers at the Laboratory of Integrated Pest Management, FCG Research Institute Inc., Tokyo, Japan.

Katsuyoshi Asano

Katsuyoshi Asano is a researcher at the Nara Prefectural Landscape and Environment Center, Nara, Japan.

Yuji Kawakami

Kazuhiro Hashimoto and Yuji Kawakami are researchers at the Laboratory of Integrated Pest Management, FCG Research Institute Inc., Tokyo, Japan.