Plastic was identified in 93-percent of samples. Reverse osmosis filters and ion exchange system are more effective because they can remove smaller particles, Elbracht said.
"What the results don't show is where these plastic particles are coming from - but I would expect that most is coming from the processing and packing process, though some may be coming from the original water source in some cases".
Separately, scientists based at the State University of NY in Fredonia were commissioned by journalism project Orb Media to analyse the bottled water.
There is no evidence that microplastics can harm human health but the WHO said it wanted to assess the state of knowledge. National brands that were studied included Aquafina, Dasani, Evian, Nestlé Pure Life, and San Pellegrino.
Researchers tested 250 bottles of water from 11 different brands in Brazil, China, India, Indonesia, Kenya, Lebanon, Mexico, Thailand and the United States.
In order to test bottled water, a dye called Nile Red is infused into each bottle which then binds to the plastic. So, partly in response to Orb Media's research, the World Health Organization has now told the BBC it is launching its own review into the potential risks.
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A few bottles were found to have thousands of particles - the vast majority being the smaller ones that are "probably plastic" - but others from the same pack had virtually none. But it too acknowledged that micro-plastics "appear to be ubiquitous and therefore may be found at minute levels even in highly treated products".
Dr Tamer Abdelgawad, medical director at Advanced Care Oncology Centre in Dubai, said bottled water could be carcinogenic if misused or unsafely stored.
Orb consulted several toxicologists and microplastics experts throughout the entire process who also reviewed the findings. The company also pointed out that the Nile Red Dye technique is known to produce false positives.
Danone, which sells Evian and Aqua, told Orb it is "not in a position to comment as the testing methodology used is unclear. There is still limited data on the topic, and conclusions differ dramatically from one study to another".
The American Beverage Association, which represents numerous biggest brands across North America, including Nestle, Evian, Dasani and Aquafina, told Orb that "the science on microplastics and microfibres is nascent and an emerging field...."
Minalba told Orb that it abides by the Brazilian government's quality and security standards.