Fungal spores are a significant component of bioaerosols found in the air, and they have important implications for human health, agriculture, and climate. In developing countries like India, where open dumping of municipal solid waste is common, these open waste dumpsites serve as significant breeding grounds for fungal growth, leading to the subsequent release of spores. Realistic prediction of the spore emission flux from such waste sites is a critical input to models that are used to understand and assess their potential impacts on human health, agriculture, and climate. The overall objective of this study was to investigate the fungal growth and passive spore release from different food substrates to refine the developed mathematical model for understanding passive spore release from solid waste surfaces.
Experiments were conducted in a laboratory scale flux chamber to measure the fungal growth and spore release from representative exposed cut fruit and vegetable substrates. The aerosolised spores were measured using an optical particle sizer. Significantly higher surface spore densities were observed for the fungi on the food substrates as compared to that on the synthetic media. The spore flux was high initially and then decreased on continued exposure to air. The spore emission flux trends that are observed with the different substrates were found to be similar. A mathematical model was applied to the experimental data, and the observed flux trends were explained in terms of the model parameters. The second segment of this study focussed on fungal communities associated with the fruits and vegetables. Two pathways of fungal contamination of spores were identified in the food substrates that can lead to further growth – a) inherent fungal spores b) deposition of spores from ambient air. Experiments were conducted to observe the relative importance of these two pathways of contamination. DNA extraction and Next Generation Sequencing (NGS) techniques were employed to obtain species-level information. The analysis of the data revealed that both pathways of contamination were generally equally important. However, certain species exhibited preferences for specific substrates and displayed selective growth. In the third segment of this work, the effect of relative humidity in air on passive release of spores was studied. Preliminary investigations indicated an increase in spore flux with reduced air humidity, with a rapid change in spore flux. To verify if rapid drying under lower relative humidity was causing greater spores release, experiments were conducted using a quartz crystal microbalance with dissipation (QCM-D). The analysis of mass transfer of water to and from the spores indicated that the bulk of the transfer occurred within a minute of exposure to any relative humidity. This confirms that hypothesis that the passive spore release is affected by moisture transfer. The effect of the ambient RH was explained using the mathematical model, with the changes in the energy parameter, E.
In summary, this study provides valuable insights into the emission of fungal spores from food substrates commonly found in municipal solid waste. It emphasizes the significance of moisture dynamics in influencing passive spore release, shedding light on the complexities of fungal spore dispersion and its implications for human health, agriculture, and climate.