The common habit of grabbing a takeaway coffee might seem harmless, but new research reveals that your favorite morning brew could be silently exposing you to thousands of microplastic particles. And this is the part most people miss—particularly how temperature and material choice influence the release of microplastics into your drink. If you're someone who relies on disposable coffee cups daily, it's a controversy worth exploring, especially considering potential health implications.
Picture this: it's 7:45 am, and you stroll into your local café to pick up a warm cup of coffee. You wrap your hands around the cozy container, take that familiar sip, and head out the door toward work. For many, this routine is perfectly normal, a quick fix for waking up. But underneath this simple gesture lies a hidden concern: if your cup is made of plastic or coated with a thin plastic lining, there’s a significant chance it’s shedding countless tiny plastic fragments – microplastics – directly into your beverage.
In Australia alone, the numbers are staggering: over 1.45 billion single-use hot beverage cups are used yearly, complemented by about 890 million plastic lids. Globally, that figure skyrockets to approximately 500 billion cups annually. It's an enormous volume, highlighting just how pervasive this daily habit is worldwide.
Related: Expert Uncovers 5 Unexpected Sources of Microplastics in Our Daily Food
In a recent study that I coauthored and was published in the Journal of Hazardous Materials: Plastics, we investigated how these cups behave when exposed to heat. The key takeaway? Heat significantly accelerates the release of microplastics, and the type of material used for the cup plays a critical role.
What exactly are microplastics?
Microplastics are tiny plastic particles ranging from about 1 micrometre (a millionth of a meter) to 5 millimetres (roughly the size of a sesame seed). They originate from larger plastic items breaking down or can be released directly from products during everyday use. These microscopic pieces eventually infiltrate our environment, our food, and—possibly—our bodies.
However, current research leaves us with many questions. There's no definitive proof yet about how much microplastic remains in human tissues, partly because collecting such precise data is incredibly challenging. Contamination during testing and the minuscule size of these particles make accurate assessments tricky. Additionally, scientists are still unraveling what potential health effects microplastics could have over the long term. While the full picture remains incomplete, raising awareness about potential sources—like our beloved coffee cups—is crucial.
Why does heat matter?
Our team conducted a comprehensive analysis of existing scientific studies—called a meta-analysis—reviewing data from 30 peer-reviewed reports on plastic behavior under different conditions. We focused on plastics like polyethylene and polypropylene, common materials in disposable cups.
The strongest factor influencing microplastic release? Temperature. As liquids get hotter, the amount of microplastics shed from these plastics increases notably. Our review showed that in some studies, the number of particles released ranged from a few hundred to over 8 million per litre, depending on the specifics.
Surprisingly, 'soaking time'—how long the drink stays in the cup—did not consistently affect particle release. This suggests that the initial temperature of the liquid at the time it contacts the plastic is more important than how long it’s left there. Essentially, hot liquids cause more microplastic particles to break off immediately, rather than over time.
Testing real-world coffee cups
To explore this further, we analyzed 400 coffee cups from Brisbane—both polyethylene cups and paper cups lined with plastic inside. We tested them with beverages at 5°C (iced coffee temperature) and 60°C (hot coffee temperature). Both types released microplastics, but the results highlighted two key points:
- Material choice significantly impacts microplastic release. The paper cups with plastic linings released fewer particles than fully plastic cups at both temperatures.
- Heat boosts microplastic shedding. For all-plastic cups, transferring from cold to hot increased microplastic release by approximately one-third.
If someone drinks 300 millilitres of coffee daily in a polyethylene cup, they might ingest around 363,000 microplastic particles per year—that’s a staggering amount!
Why does heat cause so much more damage?
Using advanced imaging techniques, we examined the inner surfaces of these cups and discovered that plastic-only cups had rougher, more irregular surfaces dotted with peaks and valleys. This textured surface makes it easier for microplastic particles to break free. When heated, the plastic softens, expands, and contracts repeatedly, causing these irregularities to form and eventually fragment, shedding tiny particles into your drink.
Managing the risks
While it’s understandable that many of us rely on disposable cups, there are practical ways to reduce our exposure to microplastics. The most effective approach for hot drinks is to switch to reusable cups made of stainless steel, ceramic, or glass—materials that do not shed microplastics at all. If you must opt for disposable options, choosing paper cups with plastic lining (rather than plain plastic cups) can slightly lower the amount of microplastics released, although they are not entirely free from the risk.
Most importantly, avoid pouring boiling liquids directly into plastic-lined cups. Asking your barista to serve coffee at a slightly cooler temperature can significantly decrease the stress on the plastic lining, further reducing microplastic shedding.
By understanding how temperature influences plastic breakdown and how different materials behave, we can make smarter choices. These decisions not only affect our health but can also inspire safer product designs in the future.
The author acknowledges Professor Chengrong Chen for his valuable contribution to this research.
Xiangyu Liu, Research Fellow, School of Environment and Science & Australian Rivers Institute, Griffith University
This article is a republication from The Conversation, licensed under Creative Commons. Read the original piece here.
