Plastic releases trillions of nanoparticles when exposed to hot water

Plastic surrounds us, whether it’s the grocery bags we use in the supermarket or household items like shampoo and detergent bottles. Plastics exist not only as large objects, but also as microscopic particles that are released from these large products. These microscopic plastics can end up in the environment, and they can be ingested into our bodies.

Now, researchers at the National Institute of Standards and Technology (NIST) have analyzed two widely used consumer products to better understand these microscopic plastics. They found that when plastic products are exposed to hot water, they release trillions of nanoparticles per liter into the water.

The National Institute of Standards and Technology (NIST) researchers published their findings in the scientific journal Environmental Science and Technology.

“The main takeaway here is that there are plastic particles everywhere we look. And there are a lot of them. Trillions per liter. We don’t know if they have bad health effects on humans or animals. Chemist Christopher Zangmeister said:

There are many different types of plastics, but they are all made of polymers, natural or man-made materials made up of large molecules bound together. Scientists have found microscopic particles of these large plastics in oceans and many other environments. Researchers classify them into two groups: micro and microplastics.

Microplastics are generally smaller than 5 millimeters in length and can be seen with the naked eye, while nanoplastics are smaller than one millionth of a meter (one micrometer) and most of them cannot be seen even with a standard microscope. Recent studies have shown that some consumer products that contain or interact with liquids, such as polypropylene (PP) baby bottles and nylon plastic tea bags, release these plastic particles into the surrounding water.

In their study, the NIST researchers looked at two types of commercial plastic products: food-grade nylon bags, such as baking liners — transparent plastic sheets placed in baking pans to create a non-stick surface that prevents moisture loss — and hot, single-use cups, such as coffee cups. The beverage cups they analyzed were covered with low-density polyethylene (LDPE), a soft flexible plastic film often used as a liner.

LDPE-lined beverage cups were exposed to water at 100 °C (212 °F) for 20 minutes.

To analyze the nanoparticles emitted by these plastic products, the researchers first needed to determine how they were detected. “Imagine having a glass of water in a generic cup of coffee. It could contain billions of particles, and we would need to figure out how to find these nanoplastics. It’s like finding a needle in a haystack,” Zangmeister said.

Therefore, he and his colleagues had to use a new approach. “We used a method of taking the water in the cup, spraying it in a fine mist, and drying the mist and whatever was left inside the solution,” Zangmeister said. Through this process, the nanoparticles are isolated from the rest of the solution.

This same technique was previously used to detect minute particles in the atmosphere. “So, we’re not reinventing the wheel but applying it in a new area,” Zangmeister said.

After the mist dried, the nanoparticles in it were sorted according to their size and charge. The researchers can then select a specific size, for example nanoparticles around 100 nanometers in size, and pass it to a particle counter. The nanoparticles were exposed to hot vapor of butanol, a type of alcohol, and then rapidly cooled. As the alcohol condenses, the particles swell from nanometer to micrometer in size, making them more detectable. This process is automated and powered by a computer program that counts the particles.

Researchers can also determine the chemical composition of nanoparticles by placing them on a surface and observing them with techniques known as electron microscopy, which takes high-resolution images of a sample using a beam of high-energy electrons, Fourier transform infrared spectroscopy, a technique that captures the infrared spectrum of a gas, solid or liquid.

All of these techniques used together provided a more complete picture of the nanoparticle size and composition.

In their analyzes and observations, the researchers found that the average size of the nanoparticles was between 30 nanometers and 80 nanometers, just over 200 nanometers. In addition, the concentration of nanoparticles released in hot food-grade nylon water was seven times higher than in single-use beverage cups.

“In the past decade, scientists have found plastics wherever we look in the environment. People have looked at the ice in Antarctica, the bottom of glacial lakes, and they have found microplastic particles larger than about 100 nanometers, which means they are not small enough to enter cell and causing physical problems.”

“Our study is different because these nanoparticles are so small and so large that they can get inside the cell, which can disrupt its function,” Zangmeister said, stressing that no one had identified it.

The US Food and Drug Administration (FDA) regulates plastics that come into contact with the food we eat or the water we drink. The agency has safety standards and measures in place to determine what is safe. FDA researchers perform rigorous testing on these plastics and measure how much plastic mass is lost when exposed to hot water. For example, the US Food and Drug Administration (FDA) has determined that food grade nylon (such as that used in tea bags) can safely lose up to 1% of its mass under high temperature conditions. In a NIST study using their new method, researchers found that one-tenth of a percent of the mass was lost, well below the current FDA limits for what is considered safe.

Zangmeister noted that there is no commonly used test to measure LDPE released into water from samples such as coffee cups, but there are tests for nylon plastic. The results of this study could aid efforts to develop such tests. Meanwhile, Zangmeister and his team analyzed additional products and consumables, such as fabrics, polyester cotton, plastic bags, and water stored in plastic tubes.

The results of this study, along with those from other types of material analyzed, will open up new avenues for research in this area going forward. Most studies on this topic have been written with the aim of educating fellow scientists. This paper will do both: educate scientists and conduct public outreach,” Zangmeister said.

Reference: Zangmeister CD, Radney JG, Benkstein KD, Kalanyan B. Commonly used single-use consumer plastic products release trillions of sub-100 nm nanoparticles per liter into water during normal use. Environ Sci Technol. Published online April 20, 2022. doi: 10.1021/acs.est.1c06768

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