The samples were taken on the trekking routes close to the Khumbu Glacier, at Everest Base Camp, and high into the "Death Zone".Microplastics have been discovered in snow and stream water close to the summit of Mount Everest, according to new research.The polyester, acrylic, nylon and polypropylene fibres were present in samples collected on the mountain and in the valley below.Some were present in samples from the Balcony of Mount Everest which is 8,440m (27,690ft) above sea level - representing the highest recorded microplastics ever found on Earth.Dr Imogen Napper, the study's lead author, said: "Microplastics are generated by a range of sources and many aspects of our daily lives can lead to microplastics entering the environment."Over the past few years, we have found microplastics in samples collected all over the planet - from the Arctic to our rivers and the deep seas."With that in mind, finding microplastics near the summit of Mount Everest is a timely reminder that we need to do more to protect our environment."The study, published in the journal One Earth, was led by researchers from the University of Plymouth, working with colleagues from the UK, US and Nepal.Scientists say the materials found are increasingly being used to make high-performance outdoor clothing commonly used by climbers, as well as the tents and climbing ropes used in attempt to scale the mountain.As a result, they suggest the fibres could have fragmented from larger items during expeditions to reach the summit.But it is also possible the plastics could have been transported from lower altitudes by the extreme winds that regularly impact the mountain's higher slopes.The samples were collected in April and May 2019 as part of National Geographic and Rolex's Perpetual Planet Everest Expedition, then analysed in specialist facilities in Plymouth.They were taken along the trekking routes close to the Khumbu Glacier, in the snow at Everest Base Camp, and high into the Death Zone near the mountain's summit.The highest quantities - 79 microplastic fibres per litre of snow - were found at Base Camp, where expeditions are based for periods of up to 40 days.However, evidence was also found at Camps 1 and 2 on the climbing route, with 12 microplastic fibres per litre of snow recorded from the Balcony.There were lower quantities in streams leading down from the mountain to the Sagarmatha National Park, which scientists suggest could be due to the continuous flow of water created by the region's glaciers.