The World Health Organization on Thursday announced it will review the potential risks of plastic in drinking water after an analysis of popular bottled-water brands revealed that more than 90% contained tiny pieces of plastic, The Guardian reported.

An analysis of 259 bottles across 11 brands and 19 locations in nine countries, including India, found an average of 325 plastic particles for every litre of water being sold, non-profit collective Orb Media revealed. Scientists at the State University of New York in Fredonia had commissioned them to conduct the study.

“Sizes [of the plastic] ranged from the width of a human hair down to the size of a red blood cell,” Orb Media reported. “Some bottles had thousands. A few effectively had no plastic at all.” One bottle of Nestlé Pure Life had a concentration of more than 10,000 particles per litre.

Polypropylene was the most common type of plastic fragment found. The other plastic debris that were found are nylon and polyethylene terephthalate, which is used to make bottle caps. Apart from India, the bottles analysed were bought in from the United States, China, Brazil, Indonesia, Mexico, Lebanon, Kenya and Thailand. Some of the bottled-water brands that were studied include Aqua, Aquafina, Bisleri, Dasani, Epura and Evian.

“In this study, 65% of the particles we found were actually fragments and not fibers,” microplastic researcher Sherri Mason, who led the study, told AFP. “I think it is coming through the process of bottling the water. I think that most of the plastic that we are seeing is coming from the bottle itself, it is coming from the cap, it is coming from the industrial process of bottling the water.”

A person who drinks a litre of bottled water a day might be consuming tens of thousands of microplastic particles each year, Orb Media’s findings suggested. “How this might affect your health, and that of your family, is still something of a mystery,” the collective said.