Nine out of 10 dollar bills test positive for cocaine

Up to nine out of 10 American bank notes bear traces of cocaine, research has shown. In some large US cities evidence of "dirty money" is even stronger. Analysis of bank notes from Washington DC, home to Congress and the US Presidency, were the most contaminated, with 95 per cent of them carrying minute amounts of the Schedule II (Class A in Britain) drug.

The study was the biggest ever undertaken of cocaine contamination of bank notes. Paper money can pick up cocaine particles directly from users snorting the drug through rolled up bills, or from the handling of cash during drug deals. Contamination can spread when bills are stacked together or run through counting machines.

Scientists tested bank notes from more than 30 cities in the US, Canada, Brazil, China and Japan. They found "alarming" evidence of cocaine contamination in many areas. The US and Canada had the highest levels, with an average contamination rate of between 85 per cent and 90 per cent. China and Japan had the lowest rates of 20 per cent and 12 per cent.

Contamination of US currency was up 20 per cent on its level two years ago when the same scientists conducted a similar study. Dr Yuegang Zuo, from the University of Massachusetts in Dartmouth, who led the research, said: "To my surprise, we're finding more and more cocaine in banknotes. I'm not sure why we've seen this apparent increase, but it could be related to the economic downturn, with stressed people turning to cocaine." Larger US cities such as Baltimore, Boston and Detroit had the highest average cocaine levels.

The "cleanest' bills were collected from Salt Lake City, home of the Mormons. Dr Zuo presented the findings at the American Chemical Society's annual meeting in Washington.