More than 90 percent of bottled water contained tiny particles of plastic, according to a disturbing new study that’s prompted the World Health Organization to launch a probe into potential health risks.

The study tested 259 bottles from 11 brands, including Aquafina, Evian, Dasani, Nestle Pure Life and San Pelligrino, purchased from 19 locations in nine countries.

Experts used a red dye called Nile Red which absorbs to the surface of plastics, making them easier to see under infrared light.

Ninety-three percent of the bottles showed “some sign” of microplastic contamination, with an average of 10 plastic particles per liter of water larger than .1 millimeter and an average of 325 plastic particles per liter of tinier pieces.

Microplastics are pieces of plastic less than five millimeters long.

Some brands contained more particles than other – Nestle Pure Life had 930 microplastics per liter and Gerolsteiner had 807 microplastics per liter. San Pelligrino and Minalba had the lowest level of contamination, with 30 and 63.

Some of the larger pieces were identified as polypropylene, common plastic found in bottle caps. Other plastics were found to be polystyrene, nylon and polyethylene terephthalate.

Of the 259 bottles tested, 17 had no particles.

The testing was conducted at SUNY Fredonia in conjunction with nonprofit journalism organization Orb Media.

“When you’re drink bottled water, you are ingesting plastic. Our study verifies that,” said Sherri Mason, a professor and microplastics researcher who conducted the study at Fredonia. “Are you excreting that plastic? Probably, possibly. The body is a very warm environment and that allows the leaching of these chemicals. What are the effects that those are having? Those are questions that we’re still investigating.”

Though the health risks of plastic contaminates in bottled water aren’t exactly clear, Orb Media says 90 percent of microplastic particles pass through the body without a problem. But the remaining 10 percent can become trapped in the intestinal wall or travel though the body’s lympathic system.

Smaller pieces measuring 20 microns, or .02 millimeters, can enter the bloodstream before becoming lodged in the kidney and liver, Orb said, citing UN’s Food and Agriculture Organization.

Larger particles the size of 110 microns, or .11 millimeters, can pass through the body’s hepatic portal vein, which carries blood from the intestines, gall bladder, pancreas and spleen to the liver.

Many water brands included in the study said they’ve conducted their own tests that show far fewer microplastics in their bottles.