The Dustfall Collector - a Simple Way to Measure Exposure to Microorganisms

A new developed dustfall collector has been investigated which collects airborne dust by sedimentation. The dustfall collector was placed at least 1.5 m above the floor. It was made of cardboard and the collecting surface was covered with aluminium foil; a chicken wire covered the box. After 140 days the dust was collected using the VacuMark sampler. Bioaerosols were sampled three times during a school day with one week intervals using IOM samplers. Airborne total particulate mater (TPM) was sampled on closed faced Millipore cassettes. Floor dust was sampled at the end of a school day using an HVS-3-sampler. Dust collected by the three sampling methods was weighed and analysed for culturable fungi. Comparing the levels of culturable fungi of airborne dust or collected from the dustfall collector in mechanically ventilated classrooms indicates an association between the two ways of measuring the exposure to culturable fungi. INDEX TERMS Schools, Fungi, Exposure assessment, Dustfall collector, Bioaerosols, Floor dust, TPM INTRODUCTION Many epidemiological studies have stated a relationship between mould/moisture and health outcomes but no dose response have been established yet (Bornehag et al, 2001). The reason for that could be that exposure assessment is not good enough (Husman, 1996). For quantification of exposure personal exposure measurements or stationary measurements of airborne dust usually have to be used. These measurement may be poor predictors of long term avarage exposures because bioaerosol levels vary widely due to e.g. the activity level and degree of ventilation see e.g. (Würtz et al, 1999). Some researchers have used floor dust as a surrogate for exposure measurements because this dust is considered to be less influenced by indoor activities and ventilation and therefore represents more of a long term pattern than air sampling (Wickman et al, 1992) and some analysis require bigger amounts of dust than possible to get using air sampling. Using floor dust is not without problems. It is not known how well the dust reflects the exposure, the age of the dust is often not known and the mass and concentration of e.g. of microorganisms may vary depending of the level of dust and dirt from the outside environments. Usually only one floor dust sample is taken from each site but studies of the reproducibility shows that the content of fungi may vary from one period to each other (Verhoeff et al, 1994). The purpose of this study was to investigate if a new sampling method (the dustfall collector) could overcome these problems. The dustfall collector collects dust by sedimentation from the air during long sampling periods e.g. 5 months or more. 1 Contact author: [email protected] Proceedings: Indoor Air 2002