Background concentrations of molds in house dust. Determination of mold concentrations in dwellings without known mold infestations in three parts of Germany

Mold concentrations of house dust samples from dwellings reportedly free from mold infestations were analysed to obtain background values. Samples from carpet floors were taken from 80 dwellings in three parts of Germany in winter and summer. Samples were analysed with the cultivation method (using suspension). This resulted in the detection of 35 mold species or genera. Concentrations of the genera Alternaria, Cladosporium, Fusarium and yeast increased in summer. In contrast concentrations of Aspergillus and Penicillium in the summer samples were nearly equal to those in the winter samples. The majority of the various molds were only found in a number of samples too small for a reliable comparison of the winter and summer findings to be made. The results were compared with findings of other authors. The authors propose the concentrations of the 95th percentile of each species (when representing over 10,000 KBE/g of dust) as background values, while a threefold higher value is regarded as an indication of mold presence. An exception should be made for the concentrations of molds which increase sharply in the outdoor air in summer. Because of the difficulty in estimating the outdoor influence, no evaluation proposals can be given for these species for the summer season.