Fungi, mites/ticks, allergens, and endotoxins in different size fractions of house dust from long-term uninhabited houses and inhabited houses

Abstract

Considering the necessity of countermeasures against microbial contamination in long-term uninhabited houses after the Fukushima accident, fungi, mites/ticks, allergens, and endotoxins in house dust from long-term (6–7 years) uninhabited houses (N = 37) and inhabited houses (N = 17) were investigated. In addition, the particle size dependence of microbial concentrations was evaluated to know what sieving size is desirable for microbial hazard and exposure assessments in dust. No difference in particle size distribution was observed between the two types of houses. Fungal concentrations were much higher in the long-term uninhabited houses than those in the inhabited houses, with the values decreasing with increase in particle size. Aspergillus spp. was dominant in 78% of the long-term uninhabited houses but in only 31% of the inhabited houses. Mite concentrations were not different between long-term uninhabited and inhabited houses; in both, the highest mite concentrations were observed in 63–180 μm dust particles while the highest Der 1 and Der 2 concentrations were observed in 20–63 μm dust particles. In inhabited houses, Dermatophagoides were predominant, whereas they represented <50% of mite population in long-term uninhabited houses. Endotoxin concentrations were lower in inhabited houses than in long-term uninhabited houses. The endotoxin concentration in the long-term uninhabited houses increased with increasing particle size. In conclusion, residents should reduce fungal and mite concentrations through careful cleaning prior to occupancy. The dependence of microbial concentration on particle size varied with microbial species and location, confirming that sieving size deserves attention in microbial hazard and exposure assessment.