Valencia, Spain  - Spanish bank notes contain the highest concentrations of cocaine in Europe, according to a study made public on Thursday.

Randomly selected Spanish euro notes contained traces of cocaine at an average concentration of 155 microgrammes, according to the study by Valencia University made public in the magazine Trends in Analytical Chemistry.

Cocaine was found not only on notes that had been in direct contact with the drug, but on nearly all notes in circulation, said Miguel de la Guardia, co-author of the study.

He attributed the phenomenon to cross-contamination between bank notes, as well as in money-counting machines in banks.

In the United States, which has the most contaminated bank notes in the world, dollar bills containing more than 1,300 microgrammes of cocaine have been registered.

Researchers attribute the contamination of the Spanish euro bills and the US dollars to the high cocaine consumption in the two countries.

Spain is regarded as the gateway of Latin American cocaine into Europe, with about 40 per cent of all European cocaine hauls made there in 2006. (dpa)