Passive release of fungal spores from synthetic solid waste surfaces

Passive release of fungal spores can occur from various natural and anthropogenic sources leading to significant concentrations in ambient air with potential effect on health and climate. The estimation of fungal spore release is a critical parameter necessary for the realistic assessment of health risk using dispersion models and in global climate modeling. This paper presents results from experiments conducted to seek a better understanding of the process of passive fungal spore due to wind. Laboratory studies were conducted to measure emission fluxes of a test fungal species (Penicillium chrysogenum) grown on two test surfaces (aluminum foil and cardboard) in a flux chamber in response to air flow. Spore growth on the aluminum foil correlated with the amount of nutrient, while for cardboard, fungal growth was observed just with the presence of water without any external nutrients. The released spores were collected using a commercially available impinger (Biosampler®) and quantified using fluorescence microscopy. Spore flux correlated positively with the number of spores on the surface and with air velocity above a threshold velocity. Fungal spore flux decreased on continuous exposure to air. Microscopic inspection of the surface revealed that the normally upright hyphae bearing the fungal spores collapsed after exposure to air thus suggesting that the decrease in flux was due to a decrease in the aerodynamic drag on the spores. Fungal hyphae also collapsed when there was depletion of nutrients for spore growth leading to reduction in flux. A preliminary mathematical model that estimates spore flux based on the energy transfer between the air and the fungal spores and the energy required to remove the spores is presented. A characteristic energy parameter for aerosolisation was obtained from the model fit. Using this parameter, the model predicted experimental fluxes under various conditions reasonably well.