Influence of seasons and sampling strategy on assessment of bioaerosols in sewage treatment plants in Switzerland

Ann Occup Hyg. 2005 Jul;49(5):393-400. doi: 10.1093/annhyg/meh108. Epub 2005 Feb 9.


An assessment of sewage workers' exposure to airborne cultivable bacteria, fungi and inhaled endotoxins was performed at 11 sewage treatment plants. We sampled the enclosed and unenclosed treatment areas in each plant and evaluated the influence of seasons (summer and winter) on bioaerosol levels. We also measured personal exposure to endotoxins of workers during special operation where a higher risk of bioaerosol inhalation was assumed. Results show that only fungi are present in significantly higher concentrations in summer than in winter (2331 +/- 858 versus 329 +/- 95 CFU m(-3)). We also found that there are significantly more bacteria in the enclosed area, near the particle grids for incoming water, than in the unenclosed area near the aeration basins (9455 +/- 2661 versus 2435 +/- 985 CFU m(-3) in summer and 11 081 +/- 2299 versus 2002 +/- 839 CFU m(-3) in winter). All bioaerosols were frequently above the recommended values of occupational exposure. Workers carrying out special tasks such as cleaning tanks were exposed to very high levels of endotoxins (up to 500 EU m(-3)) compared to routine work. The species composition and concentration of airborne Gram-negative bacteria were also studied. A broad spectrum of different species within the Pseudomonadaceae and the Enterobacteriaceae families were predominant in nearly all plants investigated.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aerosols
  • Air Microbiology*
  • Air Pollutants, Occupational / analysis
  • Endotoxins / analysis
  • Environmental Exposure / analysis*
  • Environmental Monitoring / methods*
  • Fungi
  • Gram-Negative Bacteria
  • Humans
  • Inhalation Exposure / analysis
  • Occupational Exposure / analysis
  • Seasons*
  • Sewage / microbiology*
  • Statistics, Nonparametric
  • Switzerland
  • Waste Disposal, Fluid*


  • Aerosols
  • Air Pollutants, Occupational
  • Endotoxins
  • Sewage