During a busy day, enjoying a cup of coffee can be a rare peaceful respite. However, a new study revealed a risk you may not have thought of linked to grabbing a hot beverage on the run.
Research recently published in the Journal of Hazardous Materials: Plastics indicated that some containers released microplastics more with increased temperatures. This release depended on the type of polymer.
“Daily ingestion of microplastics (MPs) is a growing public-health concern, partially linked to widespread use of single use of plastic cups and containers,” the researchers noted.
As of last year, other research indicated that average person already had around 7 grams worth of microplastics in their brain. For reference, that’s equal to around a spoonful. Audacy has reported that even some glass bottles have microplastics.
To better understand the roles of temperature, polymer, container (or cup) material, and soaking time when it comes to microplastics exposure, authors of the recent research conducted a meta-analysis of 237 observations from 30 peer-reviewed studies. They also conducted an experimental case study comparing microplastic release from polyethylene (PE) cups and PE-coated paper cups.
PE is a material often found in clear disposable cups used for cold drinks. Hot drink cups are often made from polystyrene foam or paper coated with a thin layer of PE. A previous study showed that those coated hot drink cups can be toxic to some aquatic organisms.
“The meta-analysis revealed that MP release from products made of PE, polyethylene terephthalate (PET), polypropylene (PP), and polystyrene (PS) significantly increased with temperature, though the extent varied significantly, depending on the type of polymer, ranging from hundreds to over eight million particles,” the study authors said.
Higher temperatures accelerate the degradation rate of plastics, they said. On a lighter note, they also found that PE-coated paper cups consistently released fewer MPs than PE plastic cups at both 41 degrees and 140 degrees.
“Specifically, MP release from PE cups increased by 32.7% when the temperature rose from 41 degrees to 140 degrees, a trend not observed in the PE-coated paper cups,” the researchers discovered. One reason why might be the higher peak-to-valley roughness on the surface of the cups, leading to less shedding of MPs, they explained.
Overall, the research indicated that cup design does have an impact on mitigating the release of microplastics.
“Collectively, the results from both the meta-analysis and case study highlight that temperature-induced physical degradation, especially in polymers with rougher surfaces or lower thermal stability, is a key driver of microplastic release, and that material design plays a critical role in mitigating this effect,” the researchers said. “These findings offer practical insights for reducing microplastic exposure through material selection and support future regulatory efforts aimed at safer consumer packaging.”
When it comes to popular coffee brands, Dunkin Donuts announced in 2020 that it would transition from using polystyrene foam cups to paper cups, though they did not specify if the new cups were lined. McDonald’s also announced a switch from foam to double-walled paper in 2021, though it also did not address whether the cups were lined with PE.
Last year, Starbucks announced that its iconic paper cups would switch from a plastic lining to a the silica-based Qwarzo coating in Europe. It said the new cups can be composted by customers at home.