EXPOSURE TO BIOAEROSOLS

Project leader: Aino Nevalainen, National Public Health Institute (KTL), Laboratory of Environmental Microbiology, P.O. Box 95, FIN-70701 Kuopio, Finland, tel. +358-17-201 342, e-mail: Aino.Nevalainen *ktl.fi
 
 

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TIIVISTELMÄ SUOMEKSI

Researchers:
National Public Health Institute (KTL):
Mika Toivola, tel. +358-17-201 369, Mika.Toivola@ktl.fi
Sari Alm, tel. +358-17-201 394, Sari.Alm@ktl.fi
Marjut Roponen, tel. +358-17-201 320, Marjut.Roponen@ktl.fi
Maija-Riitta Hirvonen, tel. +358-17-201 303, Maija-Riitta.Hirvonen@ktl.fi
Tuula Husman, tel. +358-17-201 325, Tuula.Husman@ktl.fi
Jari Koivisto, tel. +358-17-201 383, Jari Koivisto@ktl.fi

Tiina Reponen, University of Cincinnati, tel. +1-513-558-0571, Tiina.Reponen@uc.edu
Mikko Vahteristo, Orion-Pharma, Kuopio, tel. +358-10-4286 446, Mikko.Vahteristo@orionpharma.com
Sirpa Kolari, VTT Building and Transport, tel. +358-9-4564 836, Sirpa.Kolari@vtt.fi

Consortium: Moisture, mould and health
Financing SYTTY organisation: The Academy of Finland
Funding from SYTTY / Total funding of project (€): 193029 / 263163
Person-months of work funded by SYTTY / Total person-months of work: 76,5 / 109

KEY WORDS: bioaerosols, exposure assessment, indoor air, particles
 

EXTENDED ABSTRACT

1 Introduction

Moisture and mould problems of buildings are associated with respiratory symptoms and diseases. The association between the building damage and the adverse health effects is well known, but little is known about the mechanisms of the diseases and about the actual exposure causing these health effects. The exposure in damaged buildings has usually been characterized with many indirect methods. The indoor air measurements have shown that both the concentrations and the microflora of the bioaerosol in the indoor air of a damaged building differ from that of a normal building. However, the concentrations and the microflora of personal exposures of individuals living and working in normal and/or damaged buildings are not known. It seems that exposure phenomenon in the mould problem buildings should be better known in order to understand the causal relationships between the exposure and the adverse health effects, and to develop properly focused control measures.

The aim of this study was to compare the personal exposure to bioaerosols and particles with the exposure assessed by stationary samples in the main microenvironments, i.e., home and work place. The study design makes it possible to evaluate the variation of bioaerosol exposure within person and between persons and to find out the determinants of particle and bioaerosol exposures among a random sample of elementary school teachers. We are also studying whether the same inflammatory mediators which are detected in the nasal lavage fluid of exposed individuals, can be detected in vitro in the cell culture medium of macrophages after the exposure to particles, collected during the exposure period.

2 Methods

A short background questionnaire containing questions about the health and the indoor environment in the home and work place was sent in October 1998 to all 823 elementary school teachers of two Finnish cities. The response rate was 67 %. From these teachers, a random sample of 81 individuals were chosen for wintertime measurement period (November 98 - March 99, November - December 99) when the snow cover eliminates outdoor airborne microbes.

A 24-hour sample collection for bioaerosol and other particles was conducted using personal sampling and microenvironmental measurements in homes and an 8-hour sample collection in the working places. The sampling period was repeated two times with each individual. Standard operation procedures (SOP) were written and followed for all field procedures and laboratory analysis.

Bioaerosol and fine particle samples in both personal and stationary sites were collected onto a 25 mm PVC filter (0.8 :m pore size, Millipore, Bedford, MA, USA) with a button aerosol sampler (SKC, Eighty Four, PA, USA) with a flow rate of 4 l/min. The sampler has been desinged to follow the ACGIH/CEN/ISO inhalable convention curve. Personal exposure measurements were conducted with a BGI AFC 400S personal sampler pump (BGI Inc., Waltham, MA, USA) packed into aluminium case. The microenvironmental measurements were conducted with PQ100 pumps (BGI Inc., Waltham, MA, USA) equipped with a microprocessor-controlled timing and mass flow adjustment system.

The concentrations of collected particles were measured by weighing the filters with a microbalance (Mettler-Toledo AG, Greifensee, Switzerland) before and after the sampling. The reflectances of filters were measured with Black Smoke method according to the ISO protocol (1993) by a smokestain reflectometer (M43D, Diffusion Systems Limited, London U.K.). After these measurements the particles were extracted from the filter and the suspension was divided into two parts; one part for microbial analyses and the other for toxicological analyses. Viable microorganisms of filter were cultured on 2% malt-extract agar (M2), dichloran glycerol 18 agar (DG18) and tryptone-yeast-glucose agar media and the total number of biological particles were counted with an epifluorescence microscope (Olympus BH-2, Olympus Optical Co., Tokyo, Japan) after acridine orange staining.

Forty-one teachers were selected to a sub-study in which a nasal lavage fluid (NAL) sample was taken after the sampling period. The production of inflammatory mediators (nitrite, tumor necrosis factor alpha (TNFalpha), interleukin(IL)-1beta, IL-4, IL-6) was analysed in the NAL samples of the studied subjects as well as in the cell culture medium of mouse RAW264.7 macrophages, which were exposed to the combined extracts of personal, home and work filter samples. Also symptoms of preceding seven days were inquired.

At the end of each sampling period, the teachers filled in a questionnaire concerning the events of the previous 24 hours possibly affecting the exposure. After the both measurements, an extensive background questionnaire of health symptoms and home and work place characters was filled in. In both homes and work places, a technical investigation by a civil engineer for signs of moisture or mould damage was conducted according to a checklist developed in previous studies.

3 Results and discussion

This study was designed to give a novel approach for documentation of bioaerosol exposure, previously dominated by short time sampling of individual microenvironments. The main emphasis was on the personal exposures to bioaerosol measured by personal exposure samplers. To our knowledge, such total estimations of bioaerosol exposure have not previously been reported.

The study population consisted of a random sample of teachers and there were no statistically significant differences in characteristics between the exposure study sub-sample (n=81) and all the respondents of the short screening questionnaire (n=562). Also the age and gender distribution of the sample was representative to the teacher population in Finland.

Field blanks (6% of the total number of samples) were used to evaluate the possible contamination of samples during the field phase. The results showed systematic increase in the particle mass and total bacteria concentrations and a slight increase in some total fungi, viable fungi and bacteria concentrations. The reasons of these increases in blanks may be explained by contamination during sample handling or passive sedimentation of particles during the measurement period. Duplicate samples (8% of the total number of samples) were collected to investigate the repeatability of the methods. There were no significant differences in the results between the duplicate samples. The variations in total fungi and total bacteria duplicates, however, were high. The microbial results of the filter collection were close to detection limits, and longer sampling times would be needed to get better reliability.

Total fungi concentrations were the highest in work places and there was no correlation (Spearman's rank correlation, rSp<0.20) between personal exposures and microenvironmental concentrations. The viable fungi personal exposures were higher than the concentrations of home or work place samples. These findings indicate that the short time stationary measurements probably underestimate the actual personal exposure. This may partly explain the poor correlation between the measured fungal levels and health outcomes reported in many studies.

The most common fungal genera culturable on M2 medium in home, personal and work samples were Penicillium, Cladosporium, yeasts and non-sporing isolates. In addition to these genera, common on DG18 medium was also Verticillium. The number of detected fungal genera was highest in the personal samples. It seems that the individual may attend several microenvironments each of which has its own sources of fungi, while microenvironmental measurements capture only those genera present in that environment.

Total bacteria concentrations were highest in work places and there were only slight correlation between personal exposure and microenvironmental concentrations. Viable bacteria concentrations were significantly lower and varied less in home environment than in work places or personal exposures. Actinobacteria was detected in over 20 % of the home and personal samples and 8 % of the work place samples. There were some correlation (rSp=0.48-0.67) between the personal exposures and microenvironmental concentrations of viable bacteria.

The personal particle mass exposures were significantly higher than home and work place mass concentrations and they were only slightly correlated with home (rSp=0.3, p<0.001) or work place (rSp=0.3, p<0.001) concentrations. Personal activities can cause resuspension of coarse particles, which are mainly detected by button sampler used in this study. The absorption coefficients of personal and work place filters were on the same level and higher than that of filters collected at home. There was some correlation between the absorption coefficients of personal exposure filters (rSp=0.64, p<0.001) and the absorption coefficients of home (rSp=0.64, p<0.001) and work place (rSp=0.64, p<0.001) filters. Most of the schools located in near-by traffic areas which may explain the higher absorption coefficients of work place and personal exposure filters than home filters.

The total microbial mass concentration (fungi and bacteria) was below 1 % of the particle mass concentration. The viable microbial mass concentration accounts for only 0.001-0.003 % of  the particle mass concentration. The viable bacteria explained almost 10 % of the particle mass concentration variation in the work place and home samples while the viable fungi did not explain the variation at all.

Repeated measurements of particle mass concentrations and viable bacteria were slightly correlated (rSp>0.38) while there was no correlation between two repeated measurements of the concentrations of total fungi. However, the variation in bioaerosol measurements was higher than the variation in particle mass concentration and absorption coefficients of the filters.

Within-subject variations of all the cytokine measurements by NAL and filter samples were low, but the correlation between used methods in the individual level was poor. Filter samples with high concentrations of bacteria or fungi induced a significant increase in the production of TNFalpha, IL-1beta, IL-6 in the RAW264.7 macrophages, as compared to those with low concentration. Cytokine levels in the NAL samples of subjects with high microbial exposure were slightly increased compared to corresponding values of the subjects with low exposure. However, only the concentration of IL-4 approached statistical significance.

4 Conclusions

The results of this study indicate that personal exposure measurements of bioaerosols are feasible and add to the information obtained by stationary samplers. However, variation in the personal exposure and microenvironmental results of fungi and bacteria samples were high, which emphasises the importance of quality assurance (duplicates and field blanks) in the microbial field measurements.

Total personal exposures for particle mass, elementary carbon (absorption coefficient) and fungi were higher than the concentrations measured with stationary sampling at home or in work places. Instead, bacteria concentrations were highest in heavily populated work places. The concentrations of the all measured parameters were the lowest at homes, except viable fungi which were lowest in work places.

The variation in the repeated personal exposure and microenvironmental measurements of bioaerosols was larger than the variation in particle mass concentration and absorption coefficient measurements. Repeated bioaerosol measurements are needed to assess exposure of target population and microenvironmental  concentrations reliably.

Present results suggest that the cytokine measurements of both NAL and filter samples of one subject are not much varying and, in group level, discriminate between subjects with high and low microbial exposure. However, in the individual level, inflammatory changes in the upper airways induced by relatively low exposure are not necessarily detectable with NAL method, even though microbes present in the individual’s microenvironments have cytotoxic and inflammatory potential in immunological cells in vitro.
 

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