Common Plastic Items Shed Trillions of Nanoparticles When Exposed to Hot Water

When you drink hot tea or coffee from a plastic cup, you could be swallowing trillions of bits of plastic so small that 1,000 of them could fit on a human hair.

That’s one concerning finding from a study published in the journal Environmental Science and Technology this month, which tested how many nanoplastics—plastic bits smaller than 0.001 millimeters in size—are released when exposed to water. 

“[T]he most important finding has been the measurement of particles below 100 nm [nanometers] in water from things that people use in their everyday lives,” study co-author and National Institute of Standards and Technology (NIST) chemist Christopher Zangmeister told Treehugger in an email.  

In Hot Water 

The NIST-based study team wanted to see what would happen if everyday plastic items were exposed to water at increasing temperatures. While the study authors actually tested several plastics—and found that all of them released nanoplastics—they chose to focus the study on two types: food-grade nylon bags and coffee cups lined with low-density polyethylene. Food grade nylon is frequently used in the food industry for both wrapping and cooking food, while coffee cups are “ubiquitous,” Zangmeister explains. 

They exposed the materials to water at increasing temperatures and found that they released more nanoplastics as the water warmed. 

"The number of particles released into water increase[s] rapidly with water temperature up until about 100 degrees Fahrenheit (40 degrees Celsius) and then it levels off,” Zangmeister said. “So, water temperatures between 100 degrees Fahrenheit up to boiling point water released the same number of particles in water.” 

A typical cup of coffee is served at between 160 and 185 degrees Fahrenheit, definitely hot enough to expose the average caffeine addict. And they could potentially be swallowing quite a lot. In hot water, the average coffee cup released more than a billion nanoplastic particles per milliliter. 

“For reference, a small coffee cup is about 300 milliliters,” Zangmeister says. “So, that could lead to exposure to trillions of particles per cup.” 

The types of nylon bags used in slow cookers released 10 times more nanoplastics than the coffee cups, meaning they could be an even greater source of exposure. 

Microplastics and Nanoplastics 

How much of a problem is this? The truth is that scientists don’t yet know, but the size of the particles does make them potentially hazardous. 

“It’s believed that particles this small can make their way into cells, which may impact cellular function,” Zangmeister says. “But we don’t know that yet.” 

The concern over nanoplastics builds on the growing worry over the slightly larger microplastics–plastics less than 5 millimeters in size. 

“I think there is more interest in the release of plastics into water because we’re just starting to really understand that they’re everywhere we look,” Zangmeister tells Treehugger. “Microplastics in the Arctic, soils from deep lakes, the water on Capitol hill. So, it really makes you ask the question of how they get there, their sources, and how small do they get.” 

There is a growing body of research attempting to understand the spread and impact of nanoplastics as well. A recent study published in Environmental Research found them embedded in the ice in both the North and South poles, while a study published in iForest—Biogeosciences and Forestry this month discovered they could enter a tree through its roots. Another pair of studies published in Chemosphere and the Journal of Hazardous Materials found micro-and nano-tire particles were ending up in estuary and freshwater ecosystems respectively and harming some of the organisms that lived there. 

“The presence of adverse effects in M. beryllina [Inland Silverside] and A. bahia [mysid shrimp] indicate that even at current environmental levels of tire-related pollution, which are expected to continue to increase, aquatic ecosystems may be experiencing negative impacts,” the authors of the Chemosphere study conclude. 

Zangmeister says that more research needs to be done to understand the impact of nanoplastics both on human health and the environment. It isn’t clear how long they would remain in water or whether they would clump together over time. What is clear from his research is that plastics do continue to break down even past the microplastic level. 

“As particles get smaller, more of their surface is exposed to the environment and more chemical reactions can occur to the exposed surface, leading to more pathways for these materials to breakdown into the environment,” he says. 

Nanoplastics Are Difficult to Study

One of the reasons that nanoplastics are such a mystery is that they are difficult to study in water. 

“Looking for nanoplastics in water is much harder than microplastics,” Zangmeister says. “If a microplastic is a tree, a nanoplastic is a leaf. So, we have to come up with new ways to isolate, detect, and characterize them.” 

The challenge of detecting the tiny particles in water is one of the reasons that Zangmeister and his team chose to focus on nanoplastics instead of microplastics, and the novel method they developed is another important finding from the study. 

The NIST explains how the process works:

1. Spray the water contained within the plastic cup into a mist.
2. Allow the mist to dry, leaving the nanoplastics behind.
3. Sort the nanoplastics by charge and size. 

Zangmeister tells NIST that a similar process is used to detect small particles in the atmosphere, but his team adapted it to water. 

He now plans to continue the research by looking at particles released into water from other materials and working to further understand what happens to these particles chemically. But he didn’t develop a new method to aid his efforts alone. 

“I also hope that other groups will use our technique to also investigate other materials,” he tells Treehugger.