Damp Indoor Spaces and Health (2004) / Chapter Skim
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3 Exposure Assessment
3 Exposure Assessment
Pages 90-124
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From page 90... ...
However, the specific roles of infectious and noninfectious microorganisms and their components in diseases related to indoor environments are poorly understood. The lack of knowledge regarding the role of microorganisms in the development and exacerbation of those diseases is due largely to the lack of valid quantitative exposure-assessment methods and knowledge of which specific microbial agents may primarily account for the presumed health effects.
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From page 91... ...
Microbial exposure assessment in the indoor environment is therefore associated with large uncertainties, which potentially result in large measurement errors and biased exposure–response relationships. This chapter focuses on exposure assessment of microorganisms and microbial agents that occur in damp indoor environments.
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From page 92... ...
The deposition of spores is confirmed by their detection in dust samples taken from a broad array of indoor surfaces, including surfaces that are too dry to support fungal growth. 2Deposition on surfaces will cause 5-µm-aerodynamic-diameter particles to be removed from indoor air at a rate equivalent to 1.5–5 air changes per hour of ventilation (Thatcher et al., 2001)
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From page 93... ...
A better understanding of the process would enable a better assessment of exposures and might elucidate better means of reducing them. The significance of exposures to fungi in normal indoor environments through dermal contact and ingestion is also not well understood.
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From page 94... ...
The primary determinant of deposition of airborne particles is the aerodynamic particle diameter (dae)
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From page 95... ...
severely limit the potential to measure all agents of interest. Settled Dust vs Airborne Measurements Indoor exposure assessment may use air or surface sampling or both.
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From page 96... ...
However, airborne concentrations of specific agents are generally low in the residential indoor environment, and for many laboratory-based methods analytic sensitivity is not sufficient, so short-term airborne sampling is impossible for most agents. "Aggressive air sampling" has been suggested to overcome the problem of low indoor-air concentrations under "routine" conditions (IOM, 1993; Rylander, 1999; Rylander et al., 1992)
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From page 97... ...
Viable microorganisms in the air can be identified with great sensitivity, provided that one is able to capture them alive and select a medium that can support their growth so that they can be measured under normal circumstances with methods for airborne sampling. However, sampling of viable microorganisms in the air with culture techniques will provide at best a "snapshot" of current exposure, given the high variability of microbial concentrations, the episodic nature of emissions from some microbial agents, and the relatively short sampling time allowed for this method.
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From page 98... ...
Settled-dust sampling (which is reviewed in Macher, 2001a,b) may be the best option because microbial agents in house dust appear to be relatively stable over long periods, and current concentrations may be a reasonable proxy for past exposures, assuming that the subjects have not moved homes or substantially changed the home conditions.
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From page 99... ...
Endotoxin concentrations in house dust in 20 homes in the United States measured repeatedly during a period of 12 months were significantly correlated (r = 0.76 for bed dust and 0.40 for bedroom-floor dust) ; this suggests average to good reproducibility for this measure (Park et al., 2000)
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From page 100... ...
Little is known about spatial variation -- that is, variation in concentrations between sampling locations at the same site, such as, in the case of surface sampling, on the same floor or bed. For example, studies have shown that house dust mite and cat allergen distribution is highly variable in settled dust (Hirsch et al., 1998; Loan et al., 2003)
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From page 101... ...
Culture-Based Methods Exposure to microorganisms in the indoor environment can be studied by counting culturable propagules in settled-dust samples. Alternatively, airborne exposure can be studied with various devices for microbial bioaerosol sampling (these are reviewed at length by Eduard and Heederik, 1998)
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From page 102... ...
Traditionally used culture methods to assess concentrations of culturable microorganisms in indoor air or settled dust have proved to be of little use for quantitative exposure assessment. They usually provide qualitative, rather than quantitative, information that can be important in risk assessment in that not all fungal and bacterial species pose the same hazard.
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From page 103... ...
Little or no experience is available with the more recently developed and more advanced nonculture based methods (scanning electron and epifluorescence microscopy, and flow cytometry, for example) in the nonindustrial indoor environment so the usefulness of these methods in indoor risk assessment is unknown.
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From page 104... ...
ASSESSING BIOALLERGENS Antibody-based immunoassays, particularly ELISA, are widely used for the measurement of aeroallergens and allergens in settled dust in buildings. To date, the house dust mite allergens Der p 1, Der f 1, and Der p/f 2 have been most widely investigated, and the methods have been well described (Platts-Mills and Chapman, 1987; Platts-Mills and de Weck, 1989; Price et al., 1990)
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From page 105... ...
However, there is considerable variation in how the questions are framed. In some studies, the dampness indicator is limited to recent experience, such as "presence of damp stains or mold growth on indoor surfaces in last 2 years" (Brunekreef, 1992)
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From page 106... ...
Mold growth in last 2 years Dales et al., 1991 Mold sites -- number of sites with visible mold or mildew in last year Moisture -- appearance of wet or damp spots excluding basement in last year Flooding -- appearance of flooding, water damage, or leaks in basement in last year Dampness/mold -- any one of above variables positive Dales and Miller, By self-report: 1999 1) Ever have mold or mildew on any surface inside present home?
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From page 107... ...
Jaakkola et al., 2002 By self-report: Presence of visible mold and/or mold odor in workplace? Jedrychowski and By self-report: Flak, 1998 Presence of dampness or molds on walls: 0 = no moisture stains or mold growth 1 = only small moisture stains (up to 1 m2 )
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From page 108... ...
The presence and severity of visible mold growth on each wall were graded subjectively on a four
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From page 109... ...
A few studies involving children and school indoor environments suggested that the correlation between IgG and mold exposure is poor (Immonen et al., 2002; Taskinen et al., 2002)
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From page 110... ...
Bacteria Relatively few studies have reported concentrations of bacteria in indoor air. The problems of accurate exposure assessment discussed for fungi also apply to measurements of airborne bacteria.
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From page 111... ...
Endotoxins Endotoxin concentrations measured within particular nonindustrial indoor spaces vary widely, from a few to several thousand endotoxin units6 (EU) per milligram of house dust (Table 3-4)
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From page 112... ...
TABLE 3-4 Overview of Epidemiologic Studies Indicating Adverse or Protective Effects on Respiratory Health Related to Indoor Endotoxin Exposure Reference Population N Michel et al., 1991 Adult asthma patients 28 Michel et al., 1996 Adult asthma (40) and rhinitis (29)
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From page 113... ...
Only a few studies have focused on airborne concentrations in the indoor environment.
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From page 114... ...
, reference material from the literature can seldom be used. Thus, to draw valid conclusions, it is important in each study to include measurements in indoor environments of subjects without symptoms.
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From page 115... ...
FINDINGS, RESEARCH NEEDS, AND RECOMMENDATIONS Based on the review of the papers, reports and other information presented in this chapter, the committee has reached the following findings and recommendations, and has identified the following research needs regarding exposure assessment for damp indoor environments. • The evaluation of exposure characterization results should, whenever possible, be based on: -- Comparison of exposure data with background concentrations or, better, a comparison of exposures between symptomatic and nonsymptomatic subjects.
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From page 116... ...
1997. American Thoracic Society Workshop, Achieving Healthy Indoor Air.
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From page 117... ...
-glucans, and culturable fungi in repeated sampling of house dust. Indoor Air 11:171–178.
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From page 118... ...
-glucan in house dust and the relation with home characteristics: a pilot study in 25 German houses. Indoor Air 8:255–263.
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From page 119... ...
2002. Occurrence of toxigenic Aspergillus versicolor isolates and sterigmatocystin in carpet dust from damp indoor environments.
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From page 120... ...
1997. Residential indoor airborne microbial populations in the United Arab Emirates.
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From page 121... ...
1997. The use of ergosterol to measure exposure to fungal propagules in indoor air.
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From page 122... ...
1999. Indoor air-related effects and airborne (1→3)
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From page 123... ...
Indoor Air 10:13–18. Szponar B, Larsson L
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From page 124... ...
1998. Indoor environmental risk factors and childhood asthma: a case-control study in a subtropical area.
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