Public concern about air pollution has traditionally focused on chemical pollutants in fine particulate matter (PM2.5), such as vehicle exhaust and industrial emissions. However, recent research from The Hong Kong Polytechnic University (PolyU) shows that microbial components in the air — including bacteria, fungi, viruses and cellular debris — may also pose significant but overlooked health risks.
The study was led by Prof. Nathanael Jin Ling, Assistant Professor in the Department of Civil and Environmental Engineering and Department of Health Technology and Informatics. The research team carried out a systematic analysis of the microbial components of PM2.5 and found that bacteria make up the largest share. In particular, they identified endotoxin, a structural component of bacterial cell walls, as a major concern. Although endotoxin represents less than 0.0001% of the total mass of PM2.5, it can account for up to 17% of the inflammatory response in the human respiratory system. In other words, among all currently known PM2.5 components, endotoxin exhibits the highest toxicity and health impact relative to its mass.
The findings suggest that reducing the overall mass of PM2.5 alone may not be enough to lower the health risks of air pollution. Instead, more effective protection may depend on identifying and controlling trace components with very high toxicity, even when present at extremely low concentrations. The study was published in Environmental Science & Technology under the title “Disproportionately Higher Contribution of Endotoxin to PM2.5 Bioactivity than Its Mass Share Highlights the Need to Identify Low-Concentration, High-Potency Components”.
In a separate study, Prof. Jin’s team collaborated with researchers from overseas universities to investigate airborne Candida in urban air and assess its potential transmission routes and community infection risks. Candida species are classified by the World Health Organization as priority pathogens. The researchers detected multidrug-resistant Candida parapsilosis in urban air and found close genetic links between these airborne strains and clinical strains from infected patients. This suggests that people may unknowingly be exposed to drug-resistant fungi through everyday breathing or skin contact, thereby increasing the potential risk of community infection.
The study also showed that Candida species are seasonally common in urban air and widely distributed across various built environments, including wastewater treatment plants, healthcare settings and residential ventilation systems. Among the species studied, Candida parapsilosis showed particularly strong environmental resilience and drug resistance, making it a notable fungal threat in urban air. This study was published in Environmental Science & Technology Letters under the title “Public Health Implications of Airborne Candida: Viability, Drug Resistance, and Genetic Links to Clinical Strains”.
Prof. Jin is a member of several research units under PAIR, including the Research Institute for Future Food (RiFood), the Research Institute for Sustainable Urban Development (RISUD) and the Mental Health Research Centre (MHRC).
Read the full studies:
https://pubs.acs.org/doi/10.1021/acs.est.5c07255
https://pubs.acs.org/doi/10.1021/acs.estlett.5c00795
Press release:https://polyu.me/48CazTc
Online coverage:
Mirage - https://polyu.me/3QKCiuI
The National Tribune - https://polyu.me/4cJzdnm
Bastille Post - https://polyu.me/42EmA6X
EurekAlert - https://polyu.me/3OLPTBx
Head Topics - https://polyu.me/49nP8Wb
| Research Units | Research Institute for Future Food | Research Institute for Sustainable Urban Development | Mental Health Research Centre |
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