Geneva, Aug. 22 -- The World Health Organization says the levels of microplastics in drinking water don't appear to be risky, but that research has been spotty and more is needed into their effects on the environment and health.

Microplastics are created when man-made materials break down into tiny particles smaller than about 5 millimeters (roughly one-fifth of an inch), although there is no strict scientific definition.

In a report published Wednesday, the U.N. health agency said the minuscule plastics are "ubiquitous in the environment" and have been found in drinking water, including both tap and bottled, most likely as the result of treatment and distribution systems.

"But just because we're ingesting them doesn't mean we have a r...