Project Title: “Water uptake in household dust varies by home”
Mentor: Karen Dannemiller, Civil, Environmental, and Geodic Engineering & College of Public Health
Abstract:
People spend 90% of their time indoors, where they can be exposed to a variety of harmful microorganisms found in household dust. Microbial growth in dust is impacted by water availability, meaning increased moisture in homes can increase harmful microbial growth. Previous research into water uptake by dust established a thermodynamic model that accounts for exponential growth of dust mass ratios and increased water activity levels as equilibrium relative humidity (ERH) is increased. However, only one sample location was used to test this model. The goal of this investigation was to apply this thermodynamic model to indoor dust from different locations to determine how location impacts water uptake and retention in dust. Triplicate 0.5 g samples of dust were collected from homes in Florida, Ohio, Texas, and California. Dust samples were incubated in glass chambers at 50 to 98% ERH in intervals of 10% over 1-day increments. The water activity and mass of dust were measured each day. Mass ratios were determined from the ratio of the mass at each ERH level to the mass at 50% ERH. The samples were then incubated using the same method from 98% to 50% ERH to investigate effects of hysteresis. Experimental results confirm the original thermodynamic model. As ERH was increased to 98%, water activity increased for all sites (p < 0.0001). The mass ratio of dust also increased as ERH increased (p < 0.0001) and resulted in an exponential curve for all sites. These results demonstrate that increasing relative humidity increases the water available to the dust. Ohio and Florida dust samples demonstrated the greatest possible effects of hysteresis, evidenced by the statistical significance of the separation between the mass ratios at 60% and 80% ERH confirmed by a Welch Two-Sample t-test (Ohio p=0.001, Florida p=0.04). Texas and California dust showed minimal effects of hysteresis (p>0.05). While all locations demonstrated an uptake in water with increasing ERH conditions, this hysteresis effect reveals that location may impact how dust retains water as ERH is decreased. Understanding how dust uptakes and retains water is important to reduce the impact of harmful microbial growth in homes.
Video Presentation: