A new analysis of some of the world’s most popular bottled water brands found that more than 90 percent contained tiny pieces of plastic. In response to this finding, the World Health Organization (WHO) is launching a project to review the potential health risks of plastic in drinking water.

This finding was uncovered by scientists at the State University of New York in Fredonia and was commissioned by journalism project Orb Media.

According to The Guardian, the scientists analyzed over 250 bottles of water “from 19 locations in nine countries across 11 different brands” and found an average of 325 plastic particles for every liter of water. The study also reported that out of the 259 bottles that were tested, only 17 were free of plastics.

The brands tested in this Orb Media study were Aqua, Aquafina, Bisleri, Dasani, Epura, Evian, Gerolsteiner, Minalba, Nestlé Pure Life, San Pellegrino and Wahaha.

Polypropylene was the most common type of plastic fragment that was found. This type of plastic is used to make everything from bottle caps to medical equipment.

In another study commissioned by Story of Stuff, 19 bottled water brands in the United States were examined. This study, although unrelated to the Orb Media project, also concluded that plastic fragments were pervasive.

Plastic microfibers enter the water in a variety of ways. They can easily become airborne, so it is possible that they enter the water both inside and outside the factory.

A WHO spokesperson reported to The Guardian that they are unaware of any impacts that the plastic microfibers could have on human health, but plan to launch a comprehensive risk assessment.