Public concern about air pollution has traditionally focused on chemical pollutants such as vehicle exhaust and industrial emissions found in particulate matter (PM2.5). However, researchers at the Hong Kong Polytechnic University (PolyU) have discovered that seemingly insignificant microbial components present in the air, such as bacteria, fungi, viruses and cell debris, pose a long-overlooked health hazard. The study revealed that bacterial endotoxins can cause an inflammatory response in the human respiratory system in almost 20% of cases, despite accounting for less than one millionth of the total mass of PM2.5. The researchers also detected drug-resistant bacteria in urban air, further raising public health concerns.
The PolyU research team, consisting of Assistant Professor JIN Ling from the Department of Civil and Environmental Engineering and the School of Health Technology and Information Studies, Professor Polly LEUNG from the School of Health Technology and Information Studies, and co-supervising doctoral student Ms. Jinyan YU, conducted a systematic analysis of microbial components in PM2.5. This study showed that the microbial component of PM2.5 is primarily bacteria. Of these, structural components of bacterial cell walls known as endotoxins account for less than 0.0001% of the total mass of PM2.5, but cause up to 17% of the inflammatory response. Its toxicity-to-mass contribution is the highest of all known PM2.5 components. In other words, to effectively reduce health risks from air pollution, the key may not be to reduce the overall mass of PM2.5, but rather to precisely target and control these highly toxic trace components. The research results were published in an academic journal environmental science and technology.
Professor Jin Lin said, “Traditional air quality management has primarily focused on reducing overall PM2.5 levels. However, as global air cleanliness efforts reduce major pollution sources such as industrial and vehicle emissions, 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 protect public health.”
In addition to the health risks posed by bacteria, Professor Jin Ling is also concerned about the threat posed by airborne fungi. In another study published in Environmental science and technology letterProfessor Jin and Dr. Franklin Cho, from the School of Health Technology and Information Sciences, and their co-supervisors, postdoctoral researcher Dr. Chunlan Huang and doctoral student Tian Chen, analyzed Candida species commonly found in respirable airborne particulate matter (PM10) in urban areas and investigated how they are transported, transmitted, and subsequently cause infections in the community.
Candida species are classified as priority pathogens by the World Health Organization, and their potential health risks have attracted global attention. The research team identified multidrug-resistant Candida parapsilosis in the urban air and revealed a close genetic relationship with clinical strains from infected individuals. This suggests that the general population may be exposed to drug-resistant bacteria through daily breathing and skin contact with the air. The study also revealed that Candida species are seasonally prevalent in the ambient air of urban areas and widely distributed in anthropogenic environments such as sewage treatment plants, healthcare settings, and ventilation systems of residential buildings. In particular, Candida parapsilosis exhibits very strong environmental and drug resistance, making it a major pathogenic fungal threat in urban air.
Professor Jin said: “The prevalence of antifungal-resistant bacteria in both environmental and clinical settings and the growing number of at-risk populations around the world highlight that antifungal resistance is an important global environmental health issue. Going forward, the research team will identify urban-specific fungal reservoirs, investigate conditions that promote drug resistance, model airborne transmission routes, and provide the scientific basis for developing more effective public health strategies.”
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Hong Kong Polytechnic University
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DOI: 10.1021/acs.est.5c07255
