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
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公眾過往對空氣污染的關注，主要集中於細懸浮粒子（PM2.5）中的化學污染物，例如車輛廢氣及工業排放。然而，香港理工大學（理大）最新研究顯示，空氣中的微生物物質，包括細菌、真菌、病毒及細胞碎片等，亦可能對人類健康構成長期被忽視、卻不容小覷的風險。
該研究由理大土木及環境工程學系以及醫療科技及資訊學系助理教授金靈領導。研究團隊對 PM2.5 中的微生物成分進行了系統性分析，發現細菌佔其中最大比例，當中尤以「內毒素」最值得關注。內毒素是細菌細胞壁的結構成分，雖然其質量只佔 PM2.5 總質量的不到 0.0001%，卻可引發高達 17% 的人體呼吸系統發炎反應。換言之，內毒素在目前所有已知 PM2.5 成分中，其毒性及對健康影響最高。
研究結果顯示，單純降低 PM2.5 的總質量，未必足以減低空氣污染帶來的健康風險。相反，更關鍵的是識別並控制那些濃度極低、但毒性極高的微量成分。相關研究已發表於《Environmental Science & Technology》，題目為「Disproportionately Higher Contribution of Endotoxin to PM2.5 Bioactivity than Its Mass Share Highlights the Need to Identify Low-Concentration, High-Potency Components」。
在另一項研究中，金教授的團隊與外地大學研究員合作，聚焦於城市空氣中的念珠菌，探討其潛在的傳播途徑及社區感染風險。念珠菌被世界衛生組織列為重點關注的病原體。研究人員在城市空氣中，檢測到具多重耐藥性的「近平滑念珠菌」（Candida parapsilosis），並發現這些空氣中的菌株與受感染病人身上的菌株，基因排列存在高度相似性。這顯示人們在日常呼吸或皮膚接觸過程中，可能無意間暴露於耐藥真菌之下，從而增加社區感染的潛在風險。
研究亦指出，念珠菌物種在城市空氣中具有季節性及普遍存在的特徵，並廣泛分布於多種人造環境之中，包括污水處理廠、醫療場所及住宅通風系統。在所研究的物種中，近平滑念珠菌表現出特別強的環境適應力和耐藥性，使其成為城市空氣中一項值得高度關注的真菌威脅。該研究以「Public Health Implications of Airborne Candida: Viability, Drug Resistance, and Genetic Links to Clinical Strains」為題，發表於《Environmental Science & Technology Letters》。
金教授為理大高等研究院轄下多個研究單位的成員，包括未來食品研究院、可持續城市發展研究院及精神健康研究中心。
閱讀研究全文：
https://pubs.acs.org/doi/10.1021/acs.est.5c07255
https://pubs.acs.org/doi/10.1021/acs.estlett.5c00795
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