It’s approximately 7:45 in the morning. You retrieve a conveniently packaged coffee from your local establishment, cradle the warm vessel in your hands, savor a sip, and commence your journey to the office.
For the majority of us, this disposable cup appears innocuous—simply a practical conduit for caffeine. However, if the cup is fabricated from plastic or features an internal plastic coating, there exists a substantial probability that it is releasing an immense quantity of minute plastic particles directly into your beverage.
Within Australia alone, an astonishing 1.45 billion disposable hot drink receptacles are consumed annually, complemented by approximately 890 million plastic lids. On a global scale, this figure escalates to an estimated 500 billion cups each year.
In recent scientific inquiry, which I helped author and was published in the Journal of Hazardous Materials: Plastics, we meticulously investigated the behavior of these cups when subjected to elevated temperatures.
The principal takeaway is unequivocal: thermal energy acts as a significant catalyst for microplastic liberation, and the composition of your cup is of far greater consequence than one might initially assume.
What Constitutes Microplastics?
Microplastics are defined as plastic fragments that range in size from approximately one micrometer to five millimeters—essentially, from a particle of dust to the dimensions of a sesame seed.
These can originate from the degradation of larger plastic items or be directly emitted from products during their ordinary lifecycle. These minuscule particles ultimately permeate our environment, our food sources, and consequently, our own biological systems.
Currently, definitive evidence is lacking regarding the extent to which these microplastics persist within the human body. Research in this domain is exceptionally susceptible to contamination, and accurately quantifying the presence of such infinitesimal particles in human tissues presents considerable challenges.
Furthermore, scientists are continuously endeavoring to comprehend the potential long-term implications of microplastics for human health. While more extensive investigation is critically important, it is prudent in the interim to maintain awareness of potential microplastic sources encountered in our daily routines.
The Significance of Temperature
My colleagues and I initiated our investigation by conducting a meta-analysis—a statistical aggregation of existing scholarly work—examining data procured from thirty rigorously peer-reviewed studies.
We scrutinized the behavior of prevalent plastics, such as polyethylene and polypropylene, under a variety of environmental conditions. A single variable emerged as overwhelmingly dominant: temperature.
As the thermal energy of the liquid contained within a vessel escalates, so too does the emission of microplastics generally increase. Within the studies we analyzed, reported releases spanned from a few hundred particles to upwards of eight million particles per liter, contingent upon the material composition and the specific research methodology employed.
Intriguingly, the duration of “soaking” — the period a beverage remains in its cup — did not consistently correlate with increased release. This observation suggests that prolonged storage of our drink in a plastic container is less impactful than the initial temperature of the liquid upon contact with the plastic.
An Examination of 400 Coffee Cups
To ascertain the real-world manifestation of these phenomena, we procured four hundred coffee cups representing two principal categories from the vicinity of Brisbane: those entirely constructed from polyethylene and those featuring a plastic-lined paper composition, which visually resemble paper but incorporate an internal thin polymer coating.
These were subjected to testing at both 5°C (representative of iced coffee temperatures) and 60°C (typical for hot coffee). While both types exhibited microplastic shedding, the findings illuminated two predominant patterns.
Firstly, the material composition proved to be a critical factor. The paper cups with their plastic linings demonstrably released fewer microplastics than the wholly plastic cups at both tested temperatures.
Secondly, thermal energy instigates a substantial release. In the instance of cups made entirely of plastic, transitioning from chilled to hot liquid resulted in an approximate 33% increase in microplastic liberation. Should an individual consume 300 milliliters of coffee from a polyethylene cup daily, they could potentially ingest 363,000 microplastic particles annually.
But what specifically accounts for the profound influence of heat?
Employing high-resolution imaging techniques, we meticulously examined the interior surfaces of these cups and discovered that the all-plastic variants possessed significantly more irregular textures—characterized by numerous “peaks and valleys”—in contrast to the plastic-lined paper cups.
This rougher surface topography facilitates the detachment of particles. Elevated temperatures exacerbate this process by inducing plastic softening and leading to expansion and contraction cycles, which generate further surface irregularities that ultimately disintegrate into our beverages.
Mitigating Potential Risks
There is no imperative need to relinquish our daily takeaway beverage ritual; however, we can strategically modify our approach to effectively manage the associated risks.
For hot beverages, the most advantageous choice involves utilizing a reusable container fashioned from stainless steel, ceramic, or glass, as these materials are incapable of shedding microplastics. If the use of a disposable cup is unavoidable, our research indicates that plastic-lined paper cups generally release fewer particles than their all-plastic counterparts, although neither option is entirely devoid of microplastics.
Lastly, given that thermal energy is the primary trigger for plastic release, it is advisable to refrain from pouring boiling liquids directly into plastic-lined receptacles. Communicating to the barista to prepare our coffee at a slightly lower temperature before it enters the cup can diminish the mechanical stress on the plastic lining and consequently reduce overall exposure.
By cultivating a deeper understanding of the interplay between temperature and material selection, we are empowered to develop superior product designs and make more informed choices concerning our daily caffeine consumption.
The author expresses gratitude for the contributions of Professor Chengrong Chen to the development of this article.
