The compounds can accumulate in living things, it is claimed.

Levels of the chemicals in Lochnagar were almost ten times higher than in other high mountain lakes.

These concentrations are not known to be hazardous, but it is feared they may pass up the food chain to humans.

The World Wildlife Fund (WWF) says the compounds are resistant to degradation and can accumulate in living things.

Fish are at the top of the food chain so these persistent chemicals build up in their organs Dr Richard Dixon, WWF Scotland

"Fish are at the top of the food chain so these persistent chemicals build up in their organs. Humans are a top predator too so the only long-term solution is to phase out these chemicals entirely," said Dr Richard Dixon, Head of Policy at WWF Scotland.

Prevailing winds

All the lakes are situated far from local sources of pollution, so it seems likely that the contamination is being carried through the air, WWF claims, often from hundreds of kilometres away.

"These PBDEs will have arrived as dust washed out of the air by rain and snow. Once in the lake water they would have entered the food chain, eventually reaching the trout and anyone who has been eating them," Dr Dixon explained.

Joan Grimalt of the Consejo Superior de Investigaciones Cientificas in Barcelona, Spain, and his colleagues from Spain and Norway sampled fish in 12 high mountain lakes, including 11 in Europe and one in Greenland.

They found fish in all lakes examined were found to be contaminated with the chemicals.

The researchers believe the experience with another group of chemicals, polychlorobiphenyls (PCBs) might foreshadow the situation with PBDEs, because the latter group have been more recently introduced into the environment.

When they are released, PCBs evaporate and travel on winds to cold countries where they then condense out. This is known as "global distillation", and it has caused PCBs to accumulate in ecosystems in the Arctic circle.

They have been blamed by some researchers for harmful effects seen in some Arctic animals.

"The information already available on PCB studies could be taken as an early warning of their likely environmental fate," the researchers write in Environmental Science and Technology

In other studies fish samples taken from lowland rivers and lakes have shown even higher contamination by PBDEs.

Lochnagar sits at an altitude of 785 metres (2,575 feet) in the centre of Balmoral Forest.