Hourly variations and inhalable exposure levels of airborne fungal spores in greenhouse work environment

Background and objectives: U.S. greenhouse operations accounts for approximately 2 million jobs and $148 billion in output. Enclosed spaces, high temperature/humidity, mold growth in potting materials, and plants can increase mold exposure among workers. The objectives of this study were to assess hourly exposure levels and inhalable exposure levels of fungal spores in three greenhouse farms.

Methods: The air samples were collected continuously for two days using the Burkard Volumetric Spore Trap. Five stationary inhalable aerosol samples were collected using Button Inhalable Aerosol Samplers during a work shift from the corners and the center of each greenhouse. Control samples were collected from nearby outdoor locations using Button Samplers. The tapes of Burkard spore trap was mounted using gelvatol and scanned under a high resolution light microscope. The filters of Button Samplers were extracted into 5 mL of pyrogen-free water containing 0.05% Tween 80, filtered again through a MCE filter, which was cleared by acetone vapor and directly analyzed for total fungal spores by microscopy. Activities of workers during work hours were recorded and the relationship between hourly spore concentrations and activities were analyzed.

Results: Overall, the concentrations of fungal spores varied widely, mostly between 10¹ and 10⁴ spores/m³ and highest spore contributing genera were Aspergillus/Penicillium. Levels of outdoor spore concentration were significantly lower than greenhouse workplaces. Hourly spore concentration peaks were observed after watering of plants.

Conclusions: Workers in greenhouses are exposed to elevated levels of airborne fungal spores and watering of plants can significantly increase workers’ spore exposure levels.