Nanoplastics become more harmful after being outdoors

When cutlery, insulation, packaging and other items made of polystyrene plastic break down, they can form nanoplastics up to 100 times thinner than the average human hair — small enough to be inhaled into the lungs.

For the first time, researchers have begun to understand how these plastics are affected by time and weather when they degrade outdoors, and what those changes mean for human health.

A study by an environmental health expert with the Texas A&M University School of Public Health, along with others at Texas A&M, found that environmental weathering doesn’t just break plastics down; it can actually make them more harmful.

“Our data show that even low levels of aged polystyrene nanoplastics can trigger oxidative stress and inflammation in bronchial cells, raising important concerns for respiratory health,” said Natalie Johnson, who also chairs Texas A&M’s interdisciplinary program in toxicology.

She added that hundreds of common items can turn into nanoplastics, and these microscopic particles have been found in soil, wastewater, rivers and oceans around the world.

For their study, the researchers used lab-grown human airway cells to compare how fresh and air-aged polystyrene particles affect human lung cells at the air-blood interface in the alveolar sacs, closely mimicking real breathing conditions.

Their three main takeaways are that environmental exposure:

• Changes nanoplastics’ surface chemistry.
• Changes nanoplastics’ shape.
• Makes nanoplastics more harmful to the lungs.

Changes to nanoplastics’ surface chemistry and shape

First, the researchers found that when lung cells were exposed to environmentally aged nanoparticles, the cells reacted more strongly than when they were exposed to fresh particles. As the particles aged in the air, the amount of oxygen on their surfaces increased — especially when exposed to certain chemicals — changing how they interacted with lung cells.

“For example, both gene activity and protein levels in the cells were much higher when exposed to particles that were aged for about 16 or 21 days, compared to fresh ones,” said toxicology graduate student Olivia Lampe, who led the study’s lung cell toxicity assessment.

She added that this aligns with other studies showing that air exposure can create new chemical groups on polystyrene, potentially making the particles stickier when they come into contact with lung cells and increasing their harmful effects.

Second, being outdoors also changed the shape of the nanoparticles over time.

“Their surfaces also became rougher, with more cracks, and the ratio of oxygen to carbon increased, making them more likely to trigger inflammation and stress in lung cells,” said atmospheric sciences graduate student Alan Dodero.

Increased harmfulness to lungs

The bottom line is that when polystyrene nanoplastics age in the environment, their surfaces and chemical properties change in ways that caused more oxidative stress and inflammation in lung cells than fresh, unaged particles.

“This is likely due to three environmental factors: physical fragmentation resulting from wave action, weathering or road traffic; photodegradation from exposure to sunlight; and chemical degradation due to exposure to chemicals in soil or water,” said Yue Zhang with Texas A&M’s Department of Atmospheric Sciences and interdisciplinary faculty of toxicology.

After being exposed to aged nanoplastic particles, the lung cells showed clear signs of inflammation and stress. Key genes linked to inflammation — interleukin-8 and tumor necrosis factor alpha — were much more active at six and 48 hours after exposure.

Levels of another inflammatory marker, interleukin-6, also increased, confirming that the cells were reacting with inflammation. In addition, heme oxygenase-1, a gene related to oxidative stress, became more active six hours after exposure.

“Our findings show that when we test how inhaling these plastics affects human health, we need to consider how they are changed by aging in the environment, which better reflects what we actually encounter in the real world,” Johnson said, adding that future studies should focus on how other plastic particles — like nylon and polyethylene — are affected by being outdoors.

The research was supported by the Texas A&M Center for Environmental Health Research, the Innovation X grant from Texas A&M, and the U.S. National Science Foundation Division of Atmospheric and Geospace Sciences and was published in Chemical Research in Toxicology,

Others involved in the study were Texas A&M toxicology graduate students Sahir Gagan and Sining Niu.