House dust in seven Danish offices

Floor dust from Danish offices was collected and analyzed. The dust was to be used in an exposure experiment. The dust was analyzed to show the composition of the dust which can be a source of airborne dust indoors. About 11 kg of dust from vacuum cleaner bags from seven Danish office buildings with about 1047 occupants (12 751 m 2) was processed according to a standardized procedure yielding 5.5 kg of processed bulk dust. The bulk dust contained 130.000–160.000 CFU g −1 microorganisms and 71.000–90.000 CFU g −1 microfungi. The content of culturable microfungi was 65–123 CFU 30 g −1 dust. The content of endotoxins ranged from 5.06–7.24 EU g −1 (1.45 ng g −1 to 1.01 ng g −1). Allergens (ng g −1) were from 147–159 (Mite), 395–746 (dog) and 103–330 (cat). The macro molecular organic compounds (the MOD-content) varied from 7.8–9.8 mg g −1. The threshold of release of histamine from basophil leukocytes provoked by the bulk dust was between 0.3 and 1.0 mg ml −1. The water content was 2% (WGT) and the organic fraction 33%. 6.5–5.9% (dry) was water soluble. The fiber content was less than 0.2–1.5% (WGT) and the desorbable VOCs was 176–319 μg g −1. Most of the VOC were aldehydes. However, softeners for plastic (DBP and DEHP) were present. The chemical composition includes human and animal skin fragments, paper fibers, glass wool, wood and textilefibers and inorganic and metal particles. The sizes ranged from 0.001–1 mm and the average specific density was 1.0 g m −3. The bulk dust was resuspended and injected into an exposure chamber. The airborne dust was sampled and analyzed to illustrate the exposures that can result from sedimented dirt and dust. The airborne dust resulting from the bulk dust reached concentrations ranging from 0.26–0.75 mg m −3 in average contained 300–170 CFU m −3. The organic fraction was from 55–70% and the water content about 2.5% (WGT). The content of the dust was compared to the similar results reported in the literature and its toxic potency is estimated to be relatively low. The storage of the bulk dust during the experiment had little effect on the specific biological and chemical composition.