Bottled water contains up to 100 times more pieces of plastic than was previously estimated, scientists said. 

The average liter of bottled water contains around 240,000 detectable plastic fragments, researchers wrote in a study published Monday in the journal Proceedings of the National Academy of Sciences. They were able to find microscopic pieces of plastic, called nanoplastics, by probing samples with lasers that were tuned to make specific molecules resonate.

How much plastic is in bottled water?

Scientists have known for years that there's plastic in water. A 2018 study detected an average of around 300 particles of plastic per liter of water. 

At the time, they were measuring microplastics — small plastic pieces less than five millimeters long. 

In the latest study, researchers examined nanoplastics, which are particles less than 1 micrometer. For reference, the diameter of a human hair is about 70 micrometers.

With the new capacities to study nanoplastics, scientists found that the amount of plastic fragments in bottled water is about 10 to 100 times more than was previously discovered. 

How did the scientists find the plastic?

Researchers at Columbia University and Rutgers University tested three popular brands of bottled water sold in the U.S. They did not specify the brands tested in the study. 

Study co-author Wei Min, a biophysicist at Columbia, was one of the inventors of the laser method used to test the samples. Researchers probed the samples for seven common types of plastics before using a data-driven algorithm to interpret the results.

"It is one thing to detect, but another to know what you are detecting," Min said in a press release.

The researchers found 110,000 to 370,000 particles in each liter, according to the study. About 90% of the particles were nanoplastics, while the rest were microplastics. 

In response to the study, the International Bottled Water Association noted that there "currently is both a lack of standardized (measuring) methods and no scientific consensus on the potential health impacts of nano- and microplastic particles. Therefore, media reports about these particles in drinking water do nothing more than unnecessarily scare consumers."

What does this mean for your health?

People are exposed to microplastics when they breathe, drink and eat, according to health officials. The human body naturally flushes most microplastics, but some extremely small particles can remain in our systems.

The study's researchers said that "nanoplastics are believed to be more toxic since their smaller size renders them much more amenable, compared to microplastics, to enter the human body."

Researchers are unsure just how dangerous microscopic pieces of plastics are for people. The World Health Organization in 2019 said that the potential hazards associated with microplastics come in three forms: from the particles themselves, chemicals that make them up and "microorganisms that may attach and colonize on microplastics, known as biofilms."

At the time, WHO technical officer Jennifer de France said the organization was not alarmed. 

"With the data that we have, we can say that we believe the risk to be low, but at the same time, we can't rule out conclusively that there might never be a risk in the future," de France said in 2019.

Bottled water products in the U.S. are regulated by the Food and Drug Administration. Regulations require the water to go through filters that remove particles larger than one micron— .00004 inches —in size.

"From source to finished product, a multi-barrier approach helps prevent possible harmful contamination to the finished product as well as storage, production, and transportation equipment," the International Bottled Water Association said in a statement. "Many of the steps in a multi-barrier system are effective in safeguarding bottled water from microbiological and other contamination."

Aliza Chasan

Aliza Chasan is a digital producer at 60 Minutes and CBSNews.com. She has previously written for outlets including PIX11 News, The New York Daily News, Inside Edition and DNAinfo. Aliza covers trending news, often focusing on crime and politics.

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