Scientists have identified surprisingly high levels of a little-known silicone pollutant in the atmosphere, raising new questions about its potential risks to human health and the climate. This chemical, known as methylsiloxane, is commonly used in cosmetics, industrial products, transportation goods, and household products. Researchers have found these compounds in a wide range of environments, from large cities to rural villages and forests.
The study was led by researchers from Utrecht University and the University of Groningen and was published in the journal. atmospheric chemistry and physics.
Hidden silicon pollution discovered around the world
Contaminants such as PFAS and microplastics are already known to be widespread in the environment. However, methylsiloxane, a type of water-repellent silicone compound commonly used as a lubricant, has received less attention.
Scientists have long believed that the methylsiloxanes found in the air come primarily from evaporation from personal care products and industrial materials. But more recently, researchers have discovered that ships and automobiles emit another form of methylsiloxane, made up of much larger molecules that don’t easily evaporate.
New research shows these larger methylsiloxanes are not restricted to high-traffic areas. Scientists have detected these substances in urban, coastal, rural, and forest environments, suggesting that these chemicals are widespread in the atmosphere.
“Our results also suggest that atmospheric methylsiloxane concentrations are much higher than expected,” says Rupert Holzinger, associate professor at Utrecht University, who co-supervised the study.
According to the researchers, these polymeric methylsiloxanes account for 2 to 4.3 percent of the total mass of organic aerosols in the atmosphere, making them one of the most abundant synthetic compounds found in airborne particles. By comparison, atmospheric concentrations of PFAS are typically more than 1,000 times lower.
How engine oil releases methylsiloxane
Methylsiloxane added to lubricants is intended to aid in lubrication rather than combustion. However, when an engine is operating, moving parts such as the piston require constant lubrication, and it is inevitable that small amounts of engine oil will enter the combustion chamber.
Methylsiloxane is highly heat resistant and does not completely decompose during combustion, so some of it can withstand the high temperatures inside the engine and is released into the atmosphere through the exhaust gas.
highest level in the city
The highest concentrations were measured in urban areas. Samples taken in Brazil’s São Paulo metropolitan area reached concentrations of 98 nanograms per cubic meter. The lowest concentrations occurred in forest areas such as Lugsterskis, Lithuania, where concentrations were measured at 0.9 nanograms per cubic meter.
The researchers also collected air samples in Kabau, 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, allowing researchers to obtain data from a variety of climates, hemispheres, and economic regions that include both developed and emerging countries.
Potential health and climate impacts
Methylsiloxane appears to be almost ubiquitous in the air, so people are likely inhaling it on a continuous basis, the researchers said. Scientists still don’t know what effects this exposure may have on long-term health.
“However, we estimate that the daily inhaled dose of methylsiloxane may exceed that of other synthetic compounds such as PFAS and micro- and nanoplastics,” Holzinger says. “We therefore emphasize the urgent need to assess these health effects.”
Researchers also warn that these chemicals can affect climate and atmospheric processes. Methylsiloxanes can change the properties of aerosols, which play an important role in cloud formation and climate behavior.
For example, compounds can change the surface tension of an aerosol and affect how clouds form. It can also interfere with ice nucleation, a key step in the atmospheric cloud process.
Relationship between automobile exhaust gas and pollution sources
The study found that more than half of the large molecular weight methylsiloxane particles detected were likely derived from traffic emissions. Researchers believe the source is related to lubricants such as engine oil.
Scientists reached this conclusion after discovering that methylsiloxane diffuses into the atmosphere in a similar way to long-chain hydrocarbons commonly found in engine oil. Matching dispersion patterns strongly suggest that they come from the same source.
Interestingly, long-chain hydrocarbons were significantly reduced and diluted as they moved through the atmosphere. However, methylsiloxane remained much more stable. Even after long-distance transport, large amounts of the material remained in the atmosphere.
According to the researchers, this stability means the compound is likely to be able to travel long distances through the air.
