Indoor air particles and bioaerosols before and after renovation of moisture-damaged buildings: The effect on biological activity and microbial flora

Abstract

Many building-related health problems coincide with moisture damage and mold growth within a building. Their elimination is assumed to improve indoor air quality. The aim of this study was to follow the success of remediation in two individual buildings by analyzing the microbial flora and immunotoxicological activity of filter samples. We compare results from samples collected from indoor air in the moisture-damaged buildings before and after renovation and results from matched reference buildings and outdoor air. The microbial characteristics of the samples were studied by analyzing ergosterol content and determining the composition of fungal flora with quantitative polymerase chain reaction (QPCR). In addition, the concentrations of particles were monitored with optical particle counter (OPC). The immunotoxicological activity of collected particle samples was tested by exposing mouse macrophages (RAW264.7) for 24 h to particle suspension extracted from the filters, and measuring the viability of the exposed cells (MTT-test) and production of inflammatory mediators (nitric oxide, IL-6 and TNFα) in cell culture medium by enzyme-linked immunoassay (ELISA). The results show that for Location 1 the renovation decreased the immunotoxicological activity of the particles collected from damaged building, whereas no difference was detected in the corresponding samples collected from the reference building. Interestingly, only slight differences were seen in the concentration of fungi. In the Location 2, a decrease was seen in the concentration of fungi after the renovation, whereas no effect on the immunotoxicological responses was detected. In this case, the immunotoxicological responses to the indoor air samples were almost identical to those caused by the samples from outdoor air. This indicates that the effects of remediation on the indoor air quality may not necessarily be readily measurable either with microbial or toxicological parameters. This may be associated with different spectrum of harmful agents in different mold and moisture-damaged buildings.

Introduction

Failure to provide good indoor air quality often manifests itself as complaints and reports of adverse health effects among the occupants. Many of the building-related health problems coincide with moisture damage and mold growth within the building. This has been shown as increased prevalence of respiratory and other symptoms in damp indoor environments. A decrease in both prevalence of symptoms and concentrations of microbes has been demonstrated after a thorough renovation of mold damage (Sudakin 1998; Ahman et al., 2000; Meklin et al., 2005).

In addition to overcrowding of workspace and lack of office cleanliness, the reported work-related symptoms have been correlated, e.g. with number of fungi in dust from office chairs (Park et al., 2006). Airborne culturable fungal concentrations are not, however, always higher than normal even in case of evident observations of dampness and mold (Hyvärinen et al., 1993). The reasons for this are not well known, but may be explained by the fact that growing fungi are not constantly releasing spores into their environment. In some studies, airborne concentrations of fungi have been linked to upper respiratory symptoms in spite of the low levels of fungi (Chao et al., 2003). The extent of the exposure to fungi may, however, be higher than estimated based on the number of airborne culturable spores, since only a fraction of environmental microbial material is culturable, and since the small airborne fragments of fungi may contribute to the exposure (Górny et al., 2002; Green et al., 2006). Nevertheless, studies have shown that reported symptoms can be attributed to allergenic reaction towards fungal components only in a small subgroup of workers (Husman, 1996; Menzies et al., 1998).

Dust and consequently indoor air contains physiologically reactive agents originating from outdoor air and various sources indoors including microbes. In addition to microbial cells, spores and metabolites such as mycotoxins, also fragments and structural components such as polysaccharides, endotoxins and (1→3)-β-d-glucans are present (Rao et al., 2005). Part of the dust particles are airborne and small enough to be inhaled all the way to alveolar level of the lungs, where the macrophages make their effort to destroy the foreign agents. As a result, the production of inflammatory mediators and amount of activated cells in the airways are increased, leading to local inflammatory reaction (Sibille and Marchandise, 1993). If this inflammatory reaction is excessive or sustained for too long, it may damage the surrounding tissues and lead to the unspecific symptoms typical for occupants staying in buildings with mold contamination.

The markers mediating inflammatory reaction include nitric oxide (NO) and cytokines such as tumor necrosis factor (TNF)α and interleukin (IL)-6. A study of teachers working in a moisture- and mold-damaged school building showed, that levels of these inflammatory markers in nasal lavage fluid were higher compared to control group, and decreased significantly during absence from the moldy environment (Hirvonen et al., 1999). The same inflammatory markers have been measured from cell cultures and mouse model in experimental studies on the immunotoxic potential of moldy house microbes (Huttunen 2003; Jussila 2003). The potential of organic dust to induce production of inflammatory mediators in cell culture systems has also been utilized to compare different indoor environments (Allermann and Poulsen, 2000), but there are no studies available about immunotoxic properties of airborne particles collected in intervention studies.

Thorough repairs of mold- and moisture-damaged buildings have been shown to decrease the frequency of reported symptoms among the occupants and also the counts of viable airborne fungi (Meklin et al., 2005). However, the usually low concentrations of viable fungi in office-type environments do not necessarily reflect the presence of various harmful agents in the indoor air (Salonen et al., 2007). Therefore, we monitored the overall biological activity of the particle material when evaluating the effect of renovation on quality of indoor air.

The aim of this study was to follow the success of repairs in two locations by characterizing the changes in indoor air quality with analyses of airborne particles collected before and after renovation. In addition to particle counts, the immunotoxicological activity and microbiological characteristics of the collected filter samples were determined. Samples taken before and after renovations were also compared with samples collected from reference buildings and outdoors.