The report, led by Orb Media, a US-based non-profit, revealed widespread contamination with plastic debris including polypropylene, nylon, and polyethylene terephthalate (PET).
‘A person who drinks a litre of bottled water a day might be consuming tens of thousands of microplastic particles each year.’
Plastic was identified in 93 per cent of the samples. Particle concentration ranged from zero to more than 10,000 in a single bottle.
On average, plastic particles in the 100 micron (0.10mm) size range -- known as microplastics -- were found at an average rate of 10.4 plastic particles per litre.
Even smaller particles were more common, averaging about 325 per litre.
Bottles of water from the same brand contained a wide range of plastic contamination, with particles as small as 6.5 microns.
This variability is "similar to what is seen when we sample open bodies of water" for microplastic pollution
, said Sherri Mason, leading microplastics researcher from the State University of New York at Fredonia.
Valued at $147 billion per year, bottled water is marketed the fastest-growing beverage market in the world.
However, the researchers are not yet sure about the extent and consequences of it on human health, the report said.
Including India, the samples came from 19 locations in nine countries in five continents besides Brazil, China, Indonesia, Kenya, Lebanon, Mexico, Thailand, and the US.
To test the invisible plastic in bottled water, the team used a special dye, an infrared laser and a blue light.
Under a laminar airflow hood that sucks dust and airborne particles up and away, each bottle was infused with a dye called Nile Red that binds to plastic polymer. The dyed water was then poured through a glass fibre filter.
When viewed through a microscope, under the blue beam of the crime light, with the aid of orange goggles, the residue from each bottle glowed with the flame-coloured fluorescence of sometimes thousands of particles.
The study identified particles between 100 microns and 6.5 microns.