CULTURABLE AND TOTAL FUNGI IN DUST ACCUMULATED IN AIR DUCTS IN SINGLE-FAMILY HOUSES

Fungal spore content in dust accumulated in air ducts was investigated in 24 mechanically ventilated single-family houses of which 15 had al so a central air heating system. Dust was collected from the ducts sim ultaneously with cleaning of the ventilation systems. Besides spore co ncentrations and flora of culturable fungi, total fungal spore concent rations were determined in dust samples by the aqueous two-phase techn ique and spore counting with epifluorescence microscopy. Culturable sp ore concentrations in the dust varied from 10(4) to 10(7) CFU/g and to tal spore concentrations from 10(7) to 10(8) spores/g. Total spore con centrations in the duct dust were significantly higher in the air heat ed houses than in the other mechanically ventilated houses. The differ ence resulted mainly from a higher proportion of recirculation air and a higher age of the air heated houses. Cladosporium, Penicillium, Asp ergillus and yeasts consisted of >90% of fungal flora in the dust. Alt hough total spore concentrations were at the same level both in the ex haust and in the supply ducts in both types of house, culturable funga l spore concentrations were slightly higher in the exhaust ducts than in the supply ducts. The proportion of culturable spores was <5% of to tal spores in dust accumulated in the ducts. (C) Indoor Air (1997).