Leader of the expedition, Robert Hoffman says climber must behave more responsibly (0'19")

The Everest Environmental Expedition, a private team consisting mainly of American climbers, has collected more than 1.2 tonnes of rubbish this week as part of a major effort to clean up the world's highest mountain.

Total amount of waste: more than 16 metric tonnes

Most of the waste was picked up from the peak's base camp, around 500 km to the east of the Nepalese capital Kathmandu. It took a helicopter to lift the rubbish and transport it to Kathmandu airport.

Empty tins, batteries, ropes and used oxygen cylinders, over 16 metric tonnes of plastic, broken ladders and even medicine bottles are thought to have been dumped since 1952, when the first attempt was made to reach the peak.

This is not the first clean-up operation on Everest but it is the biggest so far. Most of the rubbish will be exported to the United States for recycling.

Call for responsible behaviour

Environmentalists say climbers must start behaving more responsibly.

Most of the waste will be recycled in the US

Nepal and Tibet are opening up to tourism but the onslaught of visitors has brought problems.

Of particular concern to the clean-up team is the fact that in the freezing temperatures human excrement never breaks down.

"Climbers have to set up toilets to collect the waste. That has to be done by every team. They can no longer just leave human waste all over the place to flow around and contaminate large areas," says Robert Hoffman, the leader of the Environmental Expedition.

There are also huge piles of rubbish buried under Everest's glaciers. The glaciers become rivers flowing through the Himalayan kingdom and on into India and Bangladesh.

The environmentalists say that can lead to the contamination of the whole region's river water.