Hot food may cause plastic containers to release much more microplastics, according to a new review of studies that offers practical ways to reduce exposure to the potentially toxic particles.

And hot coffee in plastic cups release upto tens of thousands more microplastic particles than cold coffee, scientists also found.

A growing body of studies warns that the daily ingestion of microplastics poses potential health risks, ranging from hormone imbalance, diabetes, respiratory and reproductive problems, as well as increased odds of several types of cancers.

The inadvertent ingestion of these particles, ranging in size from a thousandth of a millimetre to five millimetres, is tied to the widespread use of single-use plastic cups and containers, researchers say.

Estimates suggest that as many as 500 billion single-use plastic cups are used every year globally.

However, the roles of the type of polymer material used to make the containers, as well as food temperature and soaking time in the release of microplastics, remain poorly understood.

The research can “offer practical insights for reducing microplastic exposure”, scientists say.

Disposable coffee cup pictured in Manchester, England (Getty Images)

In the latest study, scientists assessed 30 published studies, alongside an experimental case study to compare microplastic release from polyethylene (PE) cups and PE-coated paper cups under varying temperatures.

The findings reveal that the number of microplastic particles released from products made of PE, polyethene terephthalate (PET), polypropylene (PP), and polystyrene (PS) “significantly increased with temperature”.

Depending on the material used, hot food may cause the release of microplastics, “ranging from hundreds to over eight million particles per litre, depending on the material and study design”, according to the study published in the Journal of Hazardous Materials: Plastics.

Scientists also assessed about 400 coffee cups and found that PE-coated paper cups released fewer microplastic particles than PE plastic cups at temperatures of about 5C (iced coffee temperature) and 60C (hot coffee temperature).

“Specifically, microplastic release from PE cups increased by 32.7 per cent when the temperature rose from 5C to 60C,” researchers wrote, adding that the trend was not observed in the PE-coated paper cups.

“As the temperature of the liquid inside a container increases, the release of microplastics generally increases too,” study author Xiangyu Liu writes in The Conversation, adding that heat is a “primary driver of microplastic release”.

Advanced microscopic analysis revealed that PE cups had a higher surface roughness that may account for greater microplastic shedding.

The study confirms that temperature-induced degradation of polymers with rougher surfaces is a key driver of microplastic release.

“For the all-plastic cups, switching from cold to hot water increased the microplastic release by about 33 per cent,” Dr Liu says.

“If someone drinks 300 millilitres of coffee in a cup made of polyethylene per day, they could ingest 363,000 pieces of microplastic particles every year,” he says.

The findings can provide practical insights for reducing microplastic exposure and can support future regulatory efforts for safer consumer packaging, scientists say.