Invisible Silicone Pollutant: 1000x Worse Than PFAS

Scientists working in a laboratory with microscopes and test tubes

Every breath you take contains more of this invisible silicone pollutant from car engines than the infamous forever chemicals known as PFAS.

Story Snapshot

Researchers detected large molecular methylsiloxanes in air samples from urban, coastal, rural, and forest sites across the Netherlands, Lithuania, and Brazil.
These compounds make up 2 to 4.3 percent of organic aerosols, dwarfing PFAS concentrations by over 1,000 times.
Over half originate from vehicle emissions, likely engine oils that resist breakdown during combustion.
High stability allows long-distance travel, raising questions about universal human exposure.
Health and climate effects remain poorly understood, demanding urgent research.

Unexpected Detection of Widespread Silicone Pollutants

Researchers analyzed atmospheric aerosols using high-temperature thermal depolymerization, revealing large molecular methylsiloxanes previously undetectable by standard methods. Samples from diverse sites in three countries confirmed their presence everywhere, from São Paulo traffic tunnels to remote forests. This breakthrough exposed a pollutant hiding in plain sight, comprising a major fraction of airborne particles.

Rupert Holzinger, associate professor at Utrecht University, noted concentrations far exceed expectations. Unlike volatile methylsiloxanes studied before, these large molecules persist in particle form, evading typical breakdown. Their detection at desorption temperatures over 200 degrees Celsius pinpointed them as traffic-derived.

Vehicle Emissions as Primary Source

Over 50 percent of large molecular methylsiloxanes trace to traffic, matching patterns of long-chain hydrocarbons in engine oils. Emission factors averaged 1.16 milligrams per kilogram of fuel for light-duty vehicles and 1.53 for heavy-duty ones. Global annual emissions from vehicle aerosols range from 0.0035 to 0.0060 teragrams.

Ships also contribute, as prior studies detected similar compounds in marine emissions. These silicones survive combustion intact, unlike hydrocarbons that degrade quickly. Urban areas face highest loads, but rural dispersion shows no safe havens.

Engine lubricants, rich in polydimethylsiloxane, release these during use. Tunnel samples from São Paulo provided direct evidence in primary aerosol particles. This source dominance holds despite cosmetics and industrial uses of smaller siloxanes.

Concentrations Dwarf Known Pollutants

Large molecular methylsiloxanes account for 2 to 4.3 percent of total organic aerosol mass, far surpassing per- and polyfluoroalkyl substances (PFAS). PFAS levels sit more than three orders of magnitude lower. Humans inhale substantial amounts daily through omnipresent aerosols.

Stability enables long-range transport, persisting from urban hotspots to distant coasts. This ubiquity implies chronic exposure without historical baselines, as detection tech lagged until now.

Unresolved Health and Climate Risks

Potential health effects from inhaling particle-bound methylsiloxanes require toxicological assessment. No studies yet quantify risks like genotoxicity or long-term impacts, despite decades of silicone use. Epidemiological silence on mass events suggests low acute danger.

Climate concerns involve aerosol effects on clouds and ice formation, but lack modeling or data. Facts support presence and sources; alarmist claims falter without evidence. Further research into toxicity and global inventories will clarify true threats.