Assessment of health-related exposure limits for bioaerosols – a systematic review of human studies and experimental animal studies

Introduction: Studies suggest adverse health effects following exposure to bioaerosols in the environment and at the workplace. However, there is still a lack of health-related exposure limits. Objectives: The aim of the project was to derive health-related exposure limits for bioaerosols by analysis of (a) human studies and (b) animal studies regarding inhalation experiments in separate reviews in collaboration with a bioaerosol expert network. Methods: Two systematic reviews of studies including data on exposure and health effects in the same manuscript were carried out in Medline (Pubmed). Exposure limits should be derived by the experts according established approaches in regulatory toxicology. Results: Different search strategies were developed and resulted in n=1,565 human studies, n=138 animal studies following fungal exposure and n=163 animal studies following bacterial exposure. Subsequently, abstracts were screened using defined exclusion criteria. After full-text screening n=20 human studies were selected all related to occupational exposures. The screening of experimental animal studies resulted in four fungal studies and one bacterial study. Data on health effects and exposure was extracted using standardized extraction sheets. The studies were evaluated in collaboration with the experts. None of the human studies provided suitable dose-response relationships for derivation of exposure limits. The main reasons were: lack of studies with valid dose-response data; diversity of employed measuring methods for microorganisms and bioaerosol-emitting facilities; heterogeneity of health effects; insufficient exposure assessment. The experimental animal studies are currently under evaluation. Conclusions: Our results revealed that despite the documented health effects derivation of exposure limits for bioaerosols based on to date available human studies remain a matter of rough estimation. The analysis of experimental animal studies is in progress.