Personal exposure to microbial aerosols

At present very little is known about total exposures to bioaerosols. Short-time stationary samples correlate poorly with the health effects and probably represent, at best, only surrogates of the true exposure, because during a single day, an individual will be exposed to different concentrations of bioaerosols in several environments. It is necessary to understand better this phenomenon if we are to pinpoint determinants and find associations between exposure and health effects. A random sample of 81 teachers was selected from 823 teachers working in two municipalities in Eastern Finland for the wintertime measurement period (1998 1999). Bioaerosol and other particles were collected on filters using personal sampling and microenvironmental measurements in homes and at work. Particle mass, black smoke, viable and total microorganisms were analysed from each filter. The 24-hour sampling period was repeated twice. Questionnaires of home and workplace characteristics and events during the sampling period were filled in after the measurements. The homes and working places were also inspected for visible signs of moisture by a civil engineer. The personal particle mass (57 g/m), total fungi (12200 spores/m) and viable fungi (33 cfu/m) mean concentrations were higher than home (17 g/m, 10800 spores/m and 30 cfu/m) or workplace (34 g/m, 12000 spores/m and 19 cfu/m) concentrations. Personal (1.10x10 1/m) and work (1.12x10 1/m) BS concentrations were higher than the home (0.67x10 1/m) concentration. Total and viable bacteria concentrations in workplace (145000 cells/m, 1090 cfu/m) were higher than the personal exposure (86400 cells/m, 715 cfu/m) or home concentrations (60600 cells/m, 338 cfu/m). Personal exposure mass concentrations were only moderately correlated with home or work concentrations (r=0.3, p<0.001) while black smoke concentration of personal and home/work filters showed better correlations (r=0.6-0.7, p<0.001). There was no correlation between personal and home/work fungal concentrations. Those samples with higher viable fungal concentrations also had a higher diversity of fungi than the samples with lower concentrations. The concentration ratio of viable fungi and bacteria counts to total counts of fungi and bacteria was close to 1:100. The estimated mass concentrations of total fungi and bacteria were less than 1% of the total particle mass concentration. Variation in the concentration of Penicillium explained between 25 up to 95 % of the variations of viable fungal concentration in personal exposure, home and workplace environment. There was an association between personal exposure and home concentration of viable fungi and between personal exposure and home and work concentrations of viable bacteria. However, the results also indicate that observation of a certain fungus in a main microenvironment does not necessarily coincide with findings from personal exposure samples. There were several determinants (such as behaviour, traffic or building factors) contributing to personal exposure and increasing home and workplace concentrations of particles and microbes. There were common determinants for both personal exposure and microenvironments such as teaching subjects, condensation on window, ventilation and traffic, which point to the presence of potential pollutant sources in these microenvironments. Personal exposure measurements of bioaerosols in indoor environments are feasible ways to assess the real exposure to bioaerosols. In addition to personal bioaerosol exposure, stationary sampling in main microenvironments is often needed to determine the extent to which the microenvironment influences the measurements of total exposure and to design cost effective strategies to reduce exposure and related health effects.