Microbial secondary metabolites in indoor environments

Abstract

Background: Secondary metabolites produced by fungi and bacteria are part of a complex exposure situation in damp buildings and may contribute to adverse health outcomes in residents. Aims: To assess the occurrence of fungal and bacterial secondary metabolites in school buildings in relation to moisture damage and dampness and to explore their relevance in respiratory health. Methods: Settled dust samples (N=1390) were collected from schools in Spain, The Netherlands and Finland. School buildings were categorized as either 'index' or 'reference' based on observations of moisture damage, dampness and visible mould. Dust samples were analyzed for the presence of a wide variety of microbial secondary metabolites (>190) using mass-spectrometry based methods. Respiratory health questionnaire data from 645 teachers were used to explore associations of crude sum of concentrations of metabolites in dust versus respiratory symptoms. Results: Microbial secondary metabolites were detected in 55% of settled dust samples. 30 different metabolites were detected, with up to 10 compounds measurable from a single dust sample. We observed both, geographical and seasonal differences in indoor metabolite patterns. Higher numbers of metabolites at elevated levels were detected in index compared to reference school buildings, however, only few statistically significant differences were seen for the occurrence of individual compounds. Preliminary, crude analyses indicated a significant, dose-response association of microbial toxins in dust with nasal symptoms in teachers in Finland. Conclusions: Microbial secondary metabolites are common findings in school buildings. Moisture damage and dampness seem to somewhat increase levels of a number of those compounds, but it is evident that their indoor occurrence is also affected by outdoor sources. Associations of microbial toxin load in dust with respiratory symptoms in Finnish teachers will be further explored.