Abundance and environmental health risk of airborne pathogenic fungi in residential environments surrounding rice mills

Abstract

Airborne fungi released from rice mill activities pose a critical but underrecognized health hazard in rural Southeast Asia, where agricultural and residential zones closely coexist. This study investigated the abundance, diversity, and potential health risks of airborne fungi in residential areas surrounding nine rice mills in Thailand. A cross-sectional field survey with a stratified spatial sampling design was conducted during the rice harvesting season (November–December 2022) across 81 sites, integrating concurrent measurements of PM<inf>10</inf>, PM<inf>2.5</inf>, CO<inf>2</inf>, and key environmental parameters (wind speed, light intensity, temperature, relative humidity) with culture-based fungal identification and a screening-level health risk assessment using the Hazard Quotient (HQ) approach. Fungal concentrations were strongly associated with elevated particulate matter (PM<inf>10</inf> and PM<inf>2.5</inf>) emitted from mills. Downwind areas showed significantly higher PM<inf>10</inf> and PM<inf>2.5</inf> concentrations, exceeding WHO and national standards, with fungal communities measurably altered up to 1000 m downwind. Multivariate analyses linked high pollutant levels with key pathogenic species, including Aspergillus niger, Rhizopus stolonifer, and Cladosporium herbarum. Furthermore, Ulocladium chartarum and Aspergillus fumigatus showed strong negative correlations with distance from mills, suggesting their potential as indicator species of rice mill-related fungal pollution. HQ values consistently exceeded the safety threshold (HQ > 1) for children and the elderly near high-capacity mills, indicating substantial non-carcinogenic risks. These findings provide critical evidence of the environmental health risks posed by rice mill emissions and underscore the urgent need for targeted mitigation strategies and the inclusion of fungal bioaerosols in air quality management frameworks to protect vulnerable communities.