For people who have their coffee on the go, paper cups have become the preferred go-to choice. They’re lightweight, easy to handle, and cheap, but there’s a catch: they’re coated with plastic. This actually makes them non-recyclable and non-biodegradable (and is the reason why they don’t melt).

Now, researchers have found another reason to ditch them: they might be leaking plastic into your coffee.

Disposable paper cups are made of 90–95% paper, and the remaining 5–10% is a hydrophobic plastic film. Mostly, the interior layer is made of Polyethylene (PE). Studies have shown in the past that that harmful chemicals and substances can leach from paper into the food or drink meant for human consumption.

So far, concerns regarding leaching of microplastics from these food packaging materials have rarely been addressed or quantified by researchers. Microplastics have been identified in many food substances like salt, branded milk, fish and other seafood, and tea from teabags, with still unknown consequences for our health.

“Microplastics act as carriers for contaminants like ions, toxic heavy metals such as palladium, chromium and cadmium, as well as organic compounds that are hydrophobic,” said Sudha Goel, one of the authors of the study in a statement. “When ingested regularly over time, the health implications could be serious.”

With this in mind, Sudha and other researchers from the Indian Institute of Technology (ITT) decided to identify the types of plastic layers used in paper cups and evaluate the changes in their mechanical, physical, and chemical properties when they come in contact with hot liquid. They also quantified the microplastic load in the liquid.

The researchers poured hot water into the disposable paper cups and allowed it to sit for 15 minutes. The water was then analyzed for the presence of microplastics as well as additional ions that may have leached into the liquid from the paper cup. They also looked at the changes experienced in the properties of the plastic films of the cup.

They found that 25,000 micron-sized microplastic particles are released into 100 mL of hot liquid (85 to 90ºC) residing in the paper cups for 15 minutes. Thus, an average person drinking three regular cups of tea or coffee daily, in a paper cup, would be ingesting 75,000 tiny microplastic particles.

“This study shows that careful consideration needs to be done before the promotion of replacements for bio-hazardous products and environmental pollutants. We have been quick to replace plastics cups and glasses with disposable paper cups,” said IIT-Kharagpur director, Virendra Tewari, in a statement.

Still, the researchers acknowledge that the convenience of paper cups is such that it is hard to find a suitable replacement, especially in modern office settings where paper cups go with coffee-vending machines. Globally, some 264 billion paper cups were produced in 2019 for consuming food and beverages.

Still, potential solutions are coming in at all angles, from every corner of the world. Reusable cups from bamboo or other non-plastic materials are popping up more and more. Entrepreneurs have developed reusable cup rental systems, plant-based and biodegradable single-use cups, fiber-based cups and lids, compostable cups grown from mushrooms, and a gourd cup grown in 3D-printed molds. The solutions exist. They may require an extra bit of effort compared to paper cups, but they exist.

The study was published in the Journal of Hazardous Materials.