Abstract

BackgroundMicrobes can grow in indoor environments if moisture is available, and we need an improved understanding of how this growth contributes to emissions of microbial volatile organic compounds (mVOCs). The goal of this study was to measure how moisture levels, building material type, collection site, and microbial species composition impact microbial growth and emissions of mVOCs. We subjected two common building materials, drywall, and carpet, to treatments with varying moisture availability and measured microbial communities and mVOC emissions.ResultsFungal growth occurred in samples at >75% equilibrium relative humidity (ERH) for carpet with dust and >85% ERH for inoculated painted drywall. In addition to incubated relative humidity level, dust sample collection site (adonis p=0.001) and material type (drywall, carpet, adonis p=0.001) drove fungal and bacterial species composition. Increased relative humidity was associated with decreased microbial species diversity in samples of carpet with dust (adonis p= 0.005). Abundant volatile organic compounds (VOCs) that accounted for >1% emissions were likely released from building materials and the dust itself. However, certain mVOCs were associated with microbial growth from carpet with dust such as C10H16H+ (monoterpenes) and C2H6SH+ (dimethyl sulfide and ethanethiol). CO2 production from samples of carpet with dust at 95% ERH averaged 5.92 mg hr-1 kg-1, while the average for carpet without dust at 95% ERH was 2.55 mg hr-1 kg-1.ConclusionMicrobial growth and mVOC emissions occur at lower relative humidity in carpet and floor dust compared to drywall, which has important implications for human exposure. Even under elevated relative humidity conditions, the VOC emissions profile is dominated by non-microbial VOCs, although potential mVOCs may dominate odor production.5qHJBwjppp9jyb9CEJTu9oVideo

Highlights

  • Microbes can grow in indoor environments if moisture is available, and we need an improved understanding of how this growth contributes to emissions of microbial volatile organic compounds

  • Determination of relative humidity level required to support growth Fungal growth was measured in carpet samples with CA dust and painted drywall inoculated in CA home 1 at different RH levels

  • The fungal species composition of carpet with CA dust were statistically associated with three distinct groups based on relative humidity condition: Low equilibrium relative humidity (ERH) = 50%, 65% and 70%, Medium ERH = 75%, 80% and 85% and High ERH = 95% (R2=0.18, p=0.001)(Fig. 3, Figure S2 & S3)

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Summary

Introduction

Microbes can grow in indoor environments if moisture is available, and we need an improved understanding of how this growth contributes to emissions of microbial volatile organic compounds (mVOCs). Microbial growth and moldy odors in indoor environments are associated with harmful human health effects [2,3,4,5] such as the development of asthma, wheezing and reduced lung function [6,7,8,9]. The agent(s) may be a component of microorganisms or the microbial volatile organic compounds (mVOCs) microorganisms release as part of the primary and secondary metabolic processes [11, 12]. The relative humidity of indoor air does not stay constant and varies with outdoor humidity, occupant density, indoor activities, the air exchange rate, and moisture buffering materials inside [16, 17]

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