The peer-reviewed study, the first to test for particles under 1 micrometer in length — or 1/70 the width of a human hair — found the liter bottles were loaded with an average of 240,000 plastic particles, according to the journal Proceedings of the National Academy of Sciences.

Previous studies only analyzed microplastics, which are between 1 and 5,000 micrometers in length.

Nanoplastics, however, pose potentially a greater health risk because they’re small enough to penetrate cells and enter the bloodstream, plus have the ability to impact organs, experts said.

They can also pass through the placenta in a pregnant woman and affect unborn babies.

“The investigation into the health impacts of nanoplastics is currently at a nascent stage, necessitating further research,” the study’s co-author Beizhan Yan, an environmental chemist at Columbia University, told The Post on Tuesday.

As part of the study, Yan and lead author Naixin Qian developed a new microscopy technique to identify nanoplastics — technology that hadn’t previously been advanced enough to confirm the tiny particles’ presence in bottled water.

The new tech was used to examine 25 different brands of 1-liter water bottles.

Though the researchers refused to specify which brands they tested, they found between 110,000 and 370,000 of these itty bitty plastic fragments in each of the liters — 90% of them nanoplastics, according to Bloomberg, which was a report to report on the study.

According to the Mayo Clinic, adult men should drink about 3.7 liters of water per day, while women should aim for 2.7 liters — an amount that subjects men and women to as many as 888,000 or 648,000, respectively, plastic particles per day should individuals choose to get their daily water intake entirely from water bottled in plastic containers.

“I would recommend the consumer to consider to switch to other options, such as tap water and reusable water bottles,” Yan said.

The co-authors told Bloomberg that their research on nanoplastics won’t stop at bottled water, and they have plans to investigate why tiny plastic particles appear in tap water and snow samples they plan on collecting from western Antarctica.

“We cannot definitively say that tap water is healthier,” Yan said.

“Tap water may contain other pollutants, such as heavy metals and black carbon, which may be less prevalent in bottled water. Checking your local water quality report would be a good idea.”

The researchers’ revelations come on the heels of last week’s Consumer Reports findings that potentially dangerous levels of plastic chemicals can be found in Cheerios, Coca-Cola, and Gerber cereals.

The non-profit advocacy group tested 85 food items sold at supermarkets and by fast food chains — finding some level of plastic chemicals in 84 of them.