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Scientists discover a mysterious silicone pollutant that may be everywhere

Scientists have discovered a surprisingly abundant airborne silicone pollutant that may pose hidden risks to both human health and the climate.

Date:

May 13, 2026

Source:

Utrecht University, Faculty of Science

Summary:

Researchers have uncovered unexpectedly high levels of silicone-based pollutants called methylsiloxanes floating through the atmosphere across cities, rural regions, and even forests. Much of the pollution appears to come from vehicle emissions, likely linked to engine oil additives that survive combustion and escape into the air. Scientists say humans may inhale more of these compounds daily than other notorious pollutants like PFAS or microplastics.

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A hidden class of silicone pollutants from products like engine oils and cosmetics may be filling the atmosphere at far higher levels than expected. Credit: Shutterstock

Scientists have identified surprisingly high levels of a little-known silicone pollutant in the atmosphere, raising new questions about possible risks to human health and the climate. The chemicals, known as methylsiloxanes, are commonly used in cosmetics, industrial products, transportation, and household items. Researchers found these compounds across a wide range of environments, from major cities to rural villages and forests.

The study was led by researchers from Utrecht University and the University of Groningen and published in the journal Atmospheric Chemistry and Physics.

Hidden Silicone Pollution Found Worldwide

Pollutants such as PFAS and microplastics are already known for their widespread presence in the environment. But methylsiloxanes, a class of water-repelling silicone compounds often used as lubricants, have received far less attention.

For years, scientists believed the methylsiloxanes detected in the atmosphere mainly came from evaporation from personal care products and industrial materials. More recently, however, researchers discovered that ships and motor vehicles release a different form of methylsiloxanes made up of much larger molecules that do not easily evaporate.

The new research shows these larger methylsiloxanes are not limited to traffic-heavy locations. Scientists detected them in urban, coastal, rural, and forest environments, suggesting the chemicals are widespread in the atmosphere.

"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.

According to the researchers, these large molecular methylsiloxanes account for between 2 and 4.3 percent of the total mass of organic aerosols in the atmosphere, making them among the most abundant synthetic compounds detected in airborne particles. By comparison, atmospheric concentrations of PFAS are typically more than a thousand times lower.

> How Engine Oil Releases Methylsiloxanes

Methylsiloxanes added to lubricants are intended to assist with lubrication rather than combustion. However, during engine operation, moving parts such as pistons require constant lubrication, making it unavoidable that small amounts of engine oil enter the combustion chamber.

Because methylsiloxanes are highly heat resistant and do not fully break down during combustion, some survive the intense temperatures inside engines and are released into the atmosphere through exhaust gases.

Highest Levels Found in Cities

The highest concentrations were measured in urban regions. Samples collected in the São Paolo metropolitan area in Brazil reached 98 nanograms per cubic meter. The lowest levels appeared in forest locations, including Rugsteliskis, Lithuania, where concentrations measured 0.9 nanograms per cubic meter.

Researchers also collected air samples in Cabauw, a small rural village in the Netherlands, where concentrations reached 2 nanograms per cubic meter.

The measurements came from sites in the Netherlands, Lithuania, and Brazil, giving researchers data from different climates, hemispheres, and economic regions, including both developed and emerging economies.

Possible Health and Climate Effects

Because methylsiloxanes appear to be present almost everywhere in the atmosphere, researchers say people are likely inhaling them continuously. Scientists still do not know what long-term health effects this exposure could have.

"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."

Researchers also warn that the chemicals could influence climate and atmospheric processes. Methylsiloxanes can change the properties of aerosols, which play an important role in clou