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2:11:20 
2026-04-20 
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Scientists have uncovered unexpectedly high levels of methylsiloxanes in the air worldwide, suggesting a hidden and widespread form of pollution.
Scientists have uncovered a largely overlooked form of air pollution hiding in plain sight. A new study finds that methylsiloxanes, silicone-based compounds used in everything from cosmetics to industrial lubricants, are far more widespread in the atmosphere than previously recognized.
Notably, their concentrations are much higher than expected, raising new questions about their role in human health and the environment. The research, led by Utrecht University and the University of Groningen , appears in Atmospheric Chemistry and Physics.
Synthetic pollutants such as PFAS and microplastics are known for their persistence, yet methylsiloxanes have received far less attention.
Scientists once believed their presence in the air mainly came from evaporation of ingredients in personal care and industrial products. More recent work, however, has shown that ships and vehicles release large amounts of a different form made up of bigger molecules that do not readily evaporate.
High concentrations
The new findings show that these larger methylsiloxanes are widespread in the atmosphere, not just near traffic sources but also in coastal, rural, and forested areas.
“The findings also suggest that concentrations of methylsiloxane in the atmosphere are much higher than expected,” says Rupert Holzinger, associate professor at Utrecht University who co-supervised the study
These compounds account for about 2 to 4.3 percent of the total mass of organic aerosols, making them among the most abundant synthetic substances in the air. By comparison, PFAS levels in the atmosphere are typically more than a thousand times lower.
Cities and forests
The highest concentrations were measured in urban regions, reaching 98 nanograms per cubic meter in São Paulo, Brazil. The lowest levels appeared in forested areas, with 0.9 nanograms per cubic meter recorded in Rugsteliskis, Lithuania. In Cabauw, a rural village in the Netherlands, concentrations were about 2 nanograms per cubic meter.
Samples were collected across the Netherlands, Lithuania, and Brazil, covering a range of climates, regions, and economic settings across both hemispheres.
Unknown health risks
Because methylsiloxanes are so widespread, people are likely inhaling them continuously. The health effects of this exposure are still unclear.
“However, we estimate that the daily inhalation dose of methylsiloxanes may exceed that of other synthetic compounds, such as PFAS and micro- and nanoplastics,” says Holzinger. “We therefore underscore the urgent need for the evaluation of these health impacts.”
Beyond human health, these compounds may also influence climate processes. They can change the physical properties of aerosols, which affects how these particles behave in the atmosphere. For example, methylsiloxanes may alter surface tension and influence cloud formation, and they could also interfere with ice formation in clouds.
Long-distance transport
More than half of the detected large molecular methylsiloxanes appear to come from traffic emissions, likely linked to lubricants such as engine oil. This conclusion is based on their similarity to long-chain hydrocarbons, which are common components of engine oil and show similar dispersion patterns.
Unlike those hydrocarbons, which break down more quickly as they spread through the atmosphere, methylsiloxanes remain largely intact. A significant portion persists in its large molecular form, suggesting these compounds are highly stable and capable of traveling long distances.
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