Public concern about air pollution has traditionally centred on chemical pollutants such as vehicle exhaust and industrial emissions found in fine particulate matter (PM2.5). However, researchers at The Hong Kong Polytechnic University (PolyU) have discovered that seemingly insignificant microbial components in the air, including bacteria, fungi, viruses and cellular debris, pose a long-overlooked health hazard. The research revealed that, although accounting for less than one-millionth of the total mass of PM2.5, bacterial endotoxins can trigger inflammatory responses in the human respiratory system in nearly 20% of cases. The research team also detected drug-resistant fungi in urban air, raising further public health concerns.
A PolyU research team comprising Prof. JIN Ling, Assistant Professor of the Department of Civil and Environmental Engineering and the Department of Health Technology and Informatics, Prof. Polly LEUNG, Professor of the Department of Health Technology and Informatics, and their jointly supervised PhD student, Ms Jinyan YU, conducted a systematic analysis of the microbial components in PM2.5. The study showed that the microbial constituents of PM2.5 are predominantly bacteria. Among them, a structural component of bacterial cell walls known as endotoxin accounts for less than 0.0001% of the total mass of PM2.5, yet triggers up to 17% of inflammatory response. Its toxicity-to-mass contribution ratio is the highest of all known PM2.5 components. In other words, to effectively reduce the health risks posed by air pollution, the key may not lie in lowering the overall PM2.5 mass, but in precisely targeting and controlling these highly toxic trace components. The findings have been published in the academic journal Environmental Science & Technology.
Prof. Jin Ling noted, "Traditional air quality management has largely focused on reducing the overall PM2.5 level. However, as major pollution sources such as industrial and vehicular emissions decline due to global clean-air initiatives, previously overlooked microbial pollutants will play an increasingly important role in future public health risk management. Accurately identifying these toxic components and their sources will help safeguard public health."
In addition to the health risks posed by bacteria, Prof. Jin Ling is also concerned about the threat posed by airborne fungi. In another study published in Environmental Science & Technology Letters, Prof. Jin, Dr Franklin CHOW, Research Assistant Professor of the Department of Health Technology and Informatics, and their jointly supervised Postdoctoral Fellow Dr Chunlan FAN and PhD student Mr Tian CHEN, analysed Candida species commonly found in respirable suspended particulates (PM10) in urban areas, exploring how they are carried and transmitted and then cause infections in the community.
Candida species are classified by the World Health Organization as priority pathogens and their potential health risks have drawn global attention. The research team identified multidrug-resistant Candida parapsilosis in urban air and revealed its close genetic links to clinical strains from infected individuals. This suggests that the general public may be exposed to drug-resistant fungi through everyday breathing or skin contact with the air. The research also revealed that Candida species are seasonally prevalent in urban ambient air and widely distributed in anthropogenic settings such as wastewater treatment facilities, healthcare environments and ventilation systems in residential buildings. Notably, Candida parapsilosis showed exceptionally strong environmental resilience and drug resistance, making it a major pathogenic fungal threat in urban air.
Prof. Jin said, "The spread of drug-resistant fungi in both environmental and clinical settings, alongside a growing at-risk population worldwide, highlights antifungal resistance as a critical global environmental health issue. Moving forward, the team will identify urban-specific fungal reservoirs and investigate conditions that promote drug resistance and model airborne transmission pathways, providing a scientific basis for developing more effective public health strategies."
