Scientists have found single-use paper cups widely used for takeaway coffee release millions of microplastic particles when exposed to hot liquid.

The warning comes after a University of Queensland research team looked at single-use cups lined with fossil-based polyethylene (PE) and the biodegradable alternative polylactic acid (PLA).

Both types of cups were found to release plastic particles, UQ’s Queensland Alliance for Environmental Health Sciences said.

However, the supposedly more environmentally friendly biodegradable PLA cups released 12 times more.

Research fellow Dr Elvis Okoffo said a cup made mostly of paper did not mean it was plastic-free, with many containing a thin plastic lining that provided water resistance and structural integrity. “Our results show that plastic-lined paper cups release substantial quantities of micro- and nanoscale plastic material when exposed to hot water,” he said.

“The PLA-lined cups released a total particle mass approximately 12-fold higher than PE-lined cups in our experiments.”

Researchers measured approximately 4.3 million nanoparticles per millilitre from PLA-lined cups, compared with 2.7 million particles per millilitre from PE-lined cups.

The nanoparticles are around a thousand times thinner than a human hair.

Dr Okoffo said the study contributed to growing evidence that new plastic products used for food storage and preparation represented a significant yet often overlooked source of human exposure.

“This does not mean that people should necessarily stop using paper cups, or that PLA is inherently unsafe,” he said.

“But the impact of plastic particles on human health is unclear and we know that the chemicals in plastic are not meant to be consumed.”

He said materials used in food-contact products needed to be evaluated not only for their environmental sustainability, but also for their particle releases during everyday use.

Dr Okoffo said consumers should be provided with information about the materials used to line paper cups and called for regulators to consider safety guidelines or product labels warnings.

“Policymakers and regulators could consider whether testing for micro and nanoplastic release should form part of the safety assessment of food-contact materials,” he said.

“By combining better product design, improved labelling, and public awareness, we can help limit the amount of plastic entering both our bodies and the environment.”