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 distribution data, then a cascade impactor such as the Andersen 6-stage sampler also should be used. For example, if an SAS-Compact sampler was the selected sampler for collection of culturable Escherichia coli, an Andersen 6-Stage sampler should be used to determine the particle size distribution at each location sampled. However, a membrane filter sampler is not appropriate for sampling culturable E. coli because the cells would desiccate and become either nonviable or viable but not culturable under these conditions [Jensen et al. 1992]. In another example, an impactor with a d50 of 4 µm should not be used to collect Aspergillus niger spores (dae 1-3 µm) because most spores would remain entrained in the air passing through the instrument. General guidelines for matching the appropriate sampler with the bioaerosol of interest are shown in Table II. The bioaerosol of interest categories include culturable bioaerosol sampling, and nonculturable and nonviable bioaerosol sampling. Subcategories include free bacteria (i.e., mostly single cells), free fungi (i.e., mostly single spores), and clumped bacteria and fungi with MMAD 4 µm. Culturable bioaerosol sampling instruments must minimize injury during the collection process and maintain the culturability of the collected microorganisms. Free bacteria and fungi are the bioaerosols of interest in some environmental investigations, and the sampler must collect these small aerosols [Wright et al. 1969; Lee et al. 1973]. Often, however, the bioaerosols will be clumps of microorganisms or microorganisms attached to another particle such as a skin scale or piece of lint. When using any culturable bioaerosol sampler, the investigator must select sampling time, considering estimated concentration, such that 30-100 colonies (up to 300 in some situations) develop per plate [Tortora et al. 1989]. The lower limit (30 colonies) is necessary to obtain sufficient statistical power for comparison purposes. However, when a clean room or other environment having extremely low levels of culturable bioaerosols is sampled, the lower limit of 30 colonies may not be achievable. In such a situation, a qualitative representation must be used without accommodation of statistical validity. The upper limit (100-300 colonies) is the maximum range in which one can easily count and differentiate colonies. When nonviable microorganisms are sampled or when culturability is not of concern, collection efficiency is the overriding concern. Table II is not an all inclusive listing of bioaerosol samplers. Investigators should take special note of the limitations listed at the bottom of the table.

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NIOSH Manual of Analytical Methods