Environmental factors influencing fungal growth on gypsum boards and their structural biodeterioration: A university campus case study

Abstract

The new era in the design of modern healthy buildings necessitates multidisciplinary research efforts that link principles of engineering and material sciences with those of building biology, in order to better comprehend and apply underlying interactions among design criteria. As part of this effort, there have been an array of studies in relation to the effects of building characteristics on indoor microbiota and their propensity to cause health issues. Despite the abundance of scientific inquiries, limited studies have been dedicated to concomitantly link these effects to the deterioration of 'structural integrity' in the building materials. This study focuses on the observed biodeteriorative capabilities of indoor fungi upon the ubiquitous gypsum board material as a function of building age and room functionality within a university campus. We observed that the fungal growth significantly affected the physical (weight loss) and mechanical (tensile strength) properties of moisture-exposed gypsum board samples; in some cases, tensile strength and weight decreased by more than 80%. Such intertwined associations between the biodeterioration of building material properties due to viable indoor fungi, and as a function of building characteristics, would suggest a critical need towards multi-criteria design and optimization of next-generation healthy buildings. Next to structural integrity measures, with a better understanding of what factors and environmental conditions trigger fungal growth in built environment materials, we can also optimize the design of indoor living spaces, cleaning strategies, as well as emergency management measures during probable events such as flooding or water damage.

Fig 1. Indoor factors.

The relationship between indoor factors of (a) age of building, (b) type of room, and (c) type of flooring, influencing % fungal growth coverage range (1–5) and fungal diversity (# of genera) on gypsum board samples across 51 sampled rooms on campus. Control samples had no fungal growth. Capital letters between boxplots indicate significant differences in % growth coverage and fungal diversity between the factors using GzLM and Dunn-Bonferroni post hoc tests (p<0.05).

Fig 2. Correlating factors.

Visualization of a high correlation between (A) % growth coverage and diversity (# of genera) for the average of all 51 rooms sampled with p<0.01 and R² = 0.932. Each data point represents multiple rooms as displayed with numbers by each point. A high correlation between (B) relative weight loss (%) and ultimate tensile stress (MPa) was observed for the average of all 21 gypsum board samples tested with p<0.01 and R² = 0.984.

Fig 3. Principal component analysis (PCA) plot.

PCA with the random variables of temperature, humidity, dustiness, and occupancy level and the controlled variables of (A) age of building and (B) type of room for the 51 rooms sampled. Axes are the principal component, PC1, and PC2, with loading values.

Fig 4. The fungal taxa present in rooms of the sampled buildings.

No significant differences in fungal diversity were observed for the type of room and type of flooring. Significant differences in frequency of rooms were observed for each genus for the age of building, using chi-square test (p<0.05).

Fig 5. Biodeterioration assessment.

(A) The relative weight loss (n = 35) over a one-week time period, and (B) ultimate tensile stress (n = 31) of gypsum board samples with varying ranges of % growth coverage of fungi (1–5). Dry control samples were not exposed to water or dust, while wet control samples were only exposed to water. Error bars indicate standard deviation. Columns with different capital letters for (A) indicate significant differences in relative weight loss using ANOVA and Tamhane's post hoc tests (F_6,35 = 9810.2, p<0.05), and for (B) significant differences in tensile stress using ANOVA and Tamhane's post hoc tests (F_6,31 = 396.3, p<0.05).

Fig 6. SEM micrographs of gypsum board samples.

SEM of (A) the control pieces which were UV sterilized and not exposed to dust and high humidity conditions, and (B) the gypsum board pieces post tensile testing upon 4 weeks of exposure to dust and high humidity conditions.