Grantee Research Project Results
Final Report: Impacts of Weatherization on Microbial Ecology and Human Health
EPA Grant Number: R835757Title: Impacts of Weatherization on Microbial Ecology and Human Health
Investigators: Brown, G Z , Johnson-Shelton, Deborah , Green, Jessica , Den Wymelemberg, Kevin Van
Institution: University of Oregon , Oregon Research Institute
EPA Project Officer: Chung, Serena
Project Period: August 1, 2015 through April 30, 2017 (Extended to April 30, 2018)
Project Amount: $993,557
RFA: Indoor Air and Climate Change (2014) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Climate Change , Air
Objective:
Our goal was to investigate relationships between ventilation strategies, indoor air quality, occupant behavior, and microbial ecology in pre- and post-weatherized residential homes, and their respective effects on qualitative human health.
Summary/Accomplishments (Outputs/Outcomes):
We studied residential single-family homes built before 1994 in Oregon’s two ASHRAE climate zones (4C-marine and 5B-dry high desert) during winter and summer seasons. The homes were located primarily in Portland and Bend and included a group undergoing weatherization (treatment homes) and group that was not (comparison homes). We collected from households recruited and served through Weatherization Assistance Programs (WAPs) and those recruited through our for-profit partner agency (non-WAP). Two one-week long home visits were used before and after weatherization to collect microbial, air quality and environmental, and architectural inventory data. Resident health and behavior surveys were administered during the 2 home visits and a third timepoint approximately 1 year after the first. Bacterial and fungal microbial communities were collected inside and out by bioaerosol settling dishes, were time-integrated, and were analyzed by high-throughput DNA sequencing. Air quality and environmental data was collected inside and out, was time-resolved, and included radon, carbon dioxide, carbon monoxide, formaldehyde, total volatile organic compounds, ozone, particulates, temperature, relative humidity, air velocity, wind direction and velocity, and solar radiation.
Weatherization and Health
We did not find significant health effects of weatherization between the larger treatment and comparison groups in the study. However, we did find differences between WAP and non-WAP households. Baseline characteristics of both groups were also significantly different. WAP households reported significantly lower income, educational attainment, and had a larger proportion of single headed households. WAP and non-WAP treatment groups also reported statistically significant baseline differences on health indicators. WAP households had lower scores on a satisfaction with life scale, physical functioning, greater limitations due to physical health, and lower general health scores. At baseline, treatment and comparison households exhibited similar cleaning practices, window opening behaviors, and home conditions. Among WAP and non-WAP treatment homes, a larger proportion of WAP participants reported their home feeling damp/musty. WAP treatment homes reported cleaning their homes more frequently compared to non-WAP treatment homes. A smaller proportion of WAP treatment homes reported their home feeling too warm.
Results of weatherization analyses indicated positive changes in limitations in activities due to physical health among WAP treatment homes. That is, the association between weatherization and reduced reported physical limitations was statistically significant only for WAP homes. We also found that weatherization was associated with a decrease in the odds of reporting asthma among WAP treatment homes. This negative association was statistically significant in both cross-sectional and longitudinal models.
We analyzed possible changes in home operation behaviors post-weatherization. We thought that if the weatherization was associated with changes in occupant behaviors, such as frequency of cleaning and/or opening windows, these behavioral changes may mediate or mitigate the potential impact of weatherization on occupant health. We also considered self-reported comfort of the home and home conditions change with weatherization. Accounted for socio-demographic characteristics and seasonality as described above, our results indicated that weatherization had no statistically significant relation to home-related behaviors, measures of dampness and moldiness, pest problems, and pet presence at home. However, weatherization appeared to increase thermal comfort at home. We also found that reports of air leaks and home feeling drafty declined in both WAP and non-WAP homes post-weatherization. The process differences between WAPs and non-WAPs make the mechanisms of health improvement unclear but our findings support weatherization as a policy to improve health (and presumably lower healthcare costs) as well as reducing energy consumption for low-income households.
Weatherization and Effect of the Home on the Microbial Community Indoors
Weatherization had no significant effect on the richness (number of taxa) or diversity (when those taxa are equally abundant) of bacteria or fungi in settled dust. Moreover, weatherization did not alter the composition of bacterial or fungal communities, or the dissimilarity of the bacterial community indoors to the bacterial community outdoors - a measure of in/out connectivity. Housing cohort, indicating the weatherization recruitment program that each home participated in, however, did have some effects on bacterial communities indoors. Homes participating in a weatherization assistance program (WAP) exhibited less variability between their indoor bacterial communities than other cohorts at both the pre- and post-weatherization timepoints, when controlling for sample collection month.
Older homes had significantly more bacterial taxa present, but age of the home had no effect on fungal richness indoors. Home age explained 16% of variation in the indoor bacterial community. Visually, there appears to be a significant shift in the taxa which discriminate the microbial community in older homes from that of younger homes in the early 1970s. This may reflect changing dominant construction techniques and materials or building code standards.
Weatherization has been questioned recently as potentially having a negative impact on indoor occupant health outcomes and shifting indoor microbial communities. Our findings suggest that weatherization does not have an impact on indoor microbial communities or negative human health outcomes. However, there are many other residential building types with different strengths of these and other drivers. Additional studies might investigate microbes other than bacteria and fungi, such as viruses; climate zones more comprehensively; homes other than older site-built, wood-framed ones, and types other than single family detached housing in urban settings; why microbial communities vary by building age and whether these reasons have implications for how residences should be constructed; and whether our findings hold for homes with visible microbial growth or moisture damage.
Relationships Between Microbes and Behavior That May Bear on Health
In many microbial ecosystems, particularly in host-associated ones, richness and diversity are associated with health states. It is unknown whether a rich or depauperate indoor microbiome has any relation to human health. The goal of this project was to associate indoor microbial communities with asthma, allergies, or overall health status, and has brought us closer to answering health questions concerning microbial diversity in the built environment. Our findings suggest that occupant behavior and therefore education could play a mediating role in creating indoor microbial communities to promote health. Seasonal patterns of window operation behavior impact indoor microbes. While natural ventilation reduces energy consumption and carbon emissions and so mitigates harm to society, filtered mechanical ventilation can provide valuable improvements in air quality to residents during periods of poor outdoor air quality. The answer to this apparent conflict may lie in the inclusion of microbial ecology as an air quality metric in defining appropriate applications for natural and mechanical ventilation. On the other hand, lifestyle choices such as pets, plants, and indoor composting may prove useful, even during periods when outdoor conditions prevent opening of windows and doors.
Figure 1, Temperature synchrony of indoor air with outdoor air, modulated by window operation
Window operation drove an indoor-outdoor connection which could be quantified as temperature synchrony, and exhibited a clear seasonal trend of window operation behavior (Figure 1). Indeed, the primary driver of microbial communities in the Portland homes sampled was window operation. Homes which self-reported using windows more often (i.e. 12 hours or more per day over the month prior to sampling) exhibited greater taxonomic richness, diversity, and hosted microbial communities which were more similar to those found in outdoor air.
Bacterial richness did not significantly correlate with self-reported health measures or collective health scales, nor with homeowner reports of whether a home exacerbated their asthma or allergy symptoms. There was a significant association of Risk Avoidance on the indoor bacterial community; being risk avoidant correlated with increased dissimilarity between indoor and outdoor bacterial communities but this was not because Risk Avoidant individuals used their windows less. As there are not clear interactions between bacteria indoors and health measures, it is more likely that health measures are indicative of behavioral patterns which may affect the indoor microbiome in indirect ways. For example, window use was correlated with physical mobility, emotional wellbeing, and satisfaction with life.
Pets, indoor plants, and an indoor compost receptacle all increased the bacterial richness found indoors. However, each source contributed to the community differently. Categorically, indoor-based pet ownership (typically dog or cat) made the bacterial community in homes less similar to each other (not shown), although this was driven by a shift in the community associated with dog homes but not with cat homes, while plants did not make home dust more similar to each other but compost significantly did (Figure 2).
Figure 2, Ordination of indoor home dust samples colored by the presence of A) pets, B) living plants indoors, and C) an indoor receptacle for compost. Circles show the 95% confidence intervals.
The change in total bacterial community similarity was reflected in the profile of the discriminatory taxa which were associated with having, or not having, pets, plants, and compost. Pet ownership was able to be classified based on the bacterial community with 75% accuracy (Figure 3), 87.5% accuracy when predicting whether or not a home had a dog, and 57.7% in predicting whether a cat was present. Pet ownership resulted in an added bacterial signature, the top 20 most important taxa of which are visualized by relative abundance below. Similarly, having indoor living plants could be classified with 70.2% accuracy, and having an indoor compost receptacle with 63.1% accuracy. Unlike with pets, the lack of indoor plants was characterized as having more discriminant taxa, which may reflect that different plant species and soil types host different microbial communities. On the other hand, having an indoor compost receptacle or not had different discriminant taxa, indicating that food decomposition might select for a particular bacterial signature, possibly driven by a similarity in the types of food waste commonly composted.
Figure 3, Discriminant bacterial taxa for homes which owned an indoor-based pet
Pet ownership had no significant effect on how similar indoor bacterial communities were to those out-of-doors, indicating that pets may not track in a significant amount of outdoor microorganisms, or their dispersal may be restricted to floor or other direct contact surfaces. The number of reported occupants of the home also had no significant effect on the indoor/outdoor connection. However, having plants or compost indoors made the indoor bacterial community more similar to the outdoor bacterial community. Distance to the nearest park was also an indicator of having a stronger indoor-outdoor connection, regardless of window usage.
Journal Articles:
No journal articles submitted with this report: View all 17 publications for this projectSupplemental Keywords:
Weatherization, microbial ecology, air quality, health, behavior, low-income weatherization assistance program, bacteria, fungiRelevant Websites:
Project recruitment website Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.