Bacterial endotoxins are high-potency, low-mass drivers of PM鈧�.鈧� toxicity, sampling study reveals
Sanjukta Mondal
contributing writer
Sadie Harley
scientific editor
Robert Egan
associate editor
Endotoxin, a toxic chemical found in bacteria, makes up only 0.0001% of PM2.5 fine particles but packs a serious punch when it comes to its bioactivity.
According to by researchers from The Hong Kong Polytechnic University, endotoxin drives 0.1鈥�17% of the inflammatory responses triggered by these airborne particles, with its toxicity contribution being three to five orders of magnitude higher than its mass contribution.
The findings are published in Environmental Science & Technology.
Air pollution is now the world's leading environmental health threat, linked to more than three million premature deaths every year. One of the key culprits is PM2.5, which refers to airborne particles smaller than 2.5 micrometers, small enough to slip deep into the lungs and even seep into the bloodstream.
Scientists have long been focusing on PM2.5 because evidence consistently links it to respiratory illnesses, such as asthma, chronic obstructive pulmonary disease, and airway inflammation. Studies suggest that the damage caused by PM2.5 could be due to oxidative stress and the triggering of immune responses in the lungs following exposure.
PM2.5 is a complex atmospheric cocktail of natural and anthropogenic particles containing biological, inorganic, and organic constituents.
For decades, researchers have extensively studied the impact of chemicals鈥攊ncluding transition metals, polycyclic aromatic hydrocarbons, and industrial smoke鈥攑roduced by human activities. These components, however, contribute to less than half of the respiratory damage inflicted by PM2.5, leaving roughly 60% of its impact still unexplained.
Researchers of this study conducted daily 24-hour PM2.5 sampling for a year across an urban and coastal area of Hong Kong. To assess inflammatory responses, the researchers exposed human bronchial epithelial cells to PM2.5 and measured the release of interleukin-8 (IL-8)鈥攁 small protein, called a cytokine, that is released by the immune system鈥� as a marker of inflammation.
Endotoxin concentrations were measured using the Limulus Amebocyte Lysate (LAL) assay, then researchers used DNA sequencing and source tracking to identify the Gram-negative bacteria they came from. Finally, they applied mixture-toxicity modeling to estimate how much these endotoxins contributed to the overall harmful effects of PM2.5 exposure.
They found that despite making up only a minuscule fraction of the total PM2.5 mixture, it drove about 0.1 to 17% of the IL-8 release triggered by PM2.5.
Among all reported PM2.5 components, endotoxin demonstrated the highest toxicity-to-mass contribution ratio, 10,000:1 to 100,000:1, establishing its extreme biological potency. These findings show that less is indeed more.
The researchers note that this study brings to light the importance of identifying highly toxic components present in low concentrations and tracing their sources. Pinpointing these toxicity drivers can help us design cost-effective strategies in which even modest reductions in PM2.5 mass could yield substantial decreases in overall toxicity.
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More information: Jinyan Yu et al, Disproportionately Higher Contribution of Endotoxin to PM2.5 Bioactivity than Its Mass Share Highlights the Need to Identify Low-Concentration, High-Potency Components, Environmental Science & Technology (2025).
Journal information: Environmental Science & Technology
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