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Occurrence of Aspergillus fumigatus during composting of sewage sludge
Abstract:
Aspergillus fumigatus, a medically important fungal opportunist and respiratory allergen, was isolated from woodchips and sewage sludge used in the production of compost at the U.S. Department of Agriculture's composting research facility in Beltsville, Md. It was also regularly isolated as a dominant fungus during forced aeration composting and after 30 days in an unaerated stationary curing pile; in both cases, the fungus was found in pile zones with temperatures less than 60 degrees C. Compost stored outdoors in stationary unaerated piles from 1 to 4 months after screening out of woodchips contained easily detectable amounts of A. fumigatus in the exterior pile zones (0- to 25-cm depths). Semiquantitative studies of the airspora at the composting site revealed that A. fumigatus constituted 75% of the total viable mycoflora captured. At locations 320 m to 8 km from the compost site, the fungus constituted only 2% of the total viable mycoflora in the air. Of 21 samples of commercially available potting soil, one had levels of A. fumigatus nearly equivalent to those of 1-month-old storage compost; 15 others had lower but detectable levels.
Insights
Aspergillus fumigatus, a common mold, thrives in compost piles, posing potential respiratory risks. This fungus was frequently detected in compost, even in commercially available potting soil.
Area of Science:
- Environmental microbiology
- Mycology
- Public health
Background:
- Aspergillus fumigatus is a significant fungal pathogen and allergen.
- Composting processes can create environments where fungi proliferate.
Purpose of the Study:
- To investigate the presence and prevalence of Aspergillus fumigatus in compost produced at a USDA facility.
- To assess the potential for airborne dispersal of A. fumigatus from compost sites.
Main Methods:
- Isolation and identification of Aspergillus fumigatus from compost materials (woodchips, sewage sludge).
- Monitoring fungal populations in different composting stages (forced aeration, stationary curing).
- Air sampling to quantify A. fumigatus levels at varying distances from the compost site.
- Analysis of commercially available potting soil for A. fumigatus contamination.
Main Results:
- Aspergillus fumigatus was frequently isolated from compost materials and during various composting stages, particularly in cooler zones (<60°C).
- High concentrations of A. fumigatus were found in the air surrounding the composting site (75% of viable mycoflora), decreasing significantly with distance.
- Detectable levels of A. fumigatus were present in a majority of tested commercial potting soils.
Conclusions:
- Compost production environments are significant sources of Aspergillus fumigatus.
- Airborne dispersal from compost sites can lead to widespread environmental contamination.
- The presence of A. fumigatus in potting soil indicates a potential exposure route for the general public.
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