Microplastics have been found in Rocky Mountain rainwater 

Scientists have found tiny plastic particles in rainwater samples taken from the Rocky Mountains.

Their discovery, set out in a new US Geological Survey (USGS) study titled It is Raining Plastic, adds to growing evidence that microplastics are polluting some of the remotest places on Earth, from the deep ocean to mountaintops.

The study’s lead author Gregory Wetherbee, a USGS research chemist, told The Guardian he had been collecting rainwater samples in Colorado to study nitrogen pollution.

To his surprise, when he analyzed the samples under a microscope he found more than 90% of them contained multicoloured plastic fibres, as well as tiny beads and shards.

The samples came from eight sites along Colorado’s Front Range, varying from urban areas around Denver and Boulder to a spot 3,159 metres above sea level in the Rocky Mountain National Park.

The USGS scientists aren’t certain how the bits of plastic got into Colorado’s rainwater, but they called for better methods for measuring microplastics and their potential effects on plant and animal life.

Microplastics are everywhere

Microplastics – defined as less than 5 millimetres long – have been found in marine ecosystems, waste and fresh water, the air, food and in the stomachs of animals and people.

Scientists estimate the average American may be eating 50,000 tiny plastic particles a year, and inhaling around the same amount again, although the potential health effects of this are not yet clearly understood. The World Health Organization has called for more research into their impact, while noting that they don't appear to post a health risk at current levels.

Some microplastics are released directly into the environment as tiny particles: for example, microfibres from clothing, fragments from car tyres and microbeads in facial scrubs. Others originate from the breakdown of larger plastic items, such as bags and bottles.

Earlier this year, researchers discovered microplastics in a remote area of the French Pyrenees mountain range. Though unable to pinpoint the source of the contamination, the study showed the particles may have travelled over a distance of up to 95 km.

As well as being found in remote parts of the Pyrenees and the Rockies, microplastics are turning up in other areas considered to be pristine wilderness, such as in Arctic sea ice and even in the Mariana Trench, 7,000 metres below the surface of the Pacific Ocean.