Tests on major brands of bottled water have found that all of them contained tiny particles of plastic. In the largest investigation of its kind, 250 bottles in different countries were examined. Research led by journalism organisation Orb Media discovered an average of 10 plastic particles per liter, each larger than the width of a human hair.

Presently, there is no evidence that ingesting very small pieces of plastic is harmful, but understanding the potential implications is an active area of science. The plastic have been discovered in seafood, beer, sea salt and air in the past. The screening for plastic involved adding a dye called Nile Red to each bottle, a technique recently developed by British scientists for the rapid detection of plastic in seawater.

Previous studies have established how the dye sticks to free-floating pieces of plastic and makes them fluoresce under certain wavelengths of light. Researchers filtered their dyed samples and then counted every piece larger than 100 microns-roughly the diameter of a human hair.
Some of these particles- large enough to be handled individually were analysed by infrared spectroscopy, confirmed as plastic and further identified as particular types of polymer.

Particles smaller than 100 microns and down to a size of 6.5 microns were much more numerous (an average of 314 per litre) and were counted using a technique developed in astronomy for totalling the number of stars in the night sky. The particles below 100 microns had not been identified as plastic, opening a bottle may shed particles inside.
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