WASHINGTON - You may be carrying a whiff of cocaine in your wallet, purse or pocket if you have US bank notes.

In what researchers describe as the largest, most comprehensive analysis to date of cocaine contamination in bank notes, scientists are reporting that cocaine is present in up to 90 percent of US bank notes.

The scientists found traces of cocaine in 95 percent of the bank notes analysed from Washington D.C. alone.

Scientists tested bank notes from more than 30 cities in five countries, including the US, Canada, Brazil, China, and Japan, and found “alarming” evidence of cocaine use in many areas.

The US and Canada had the highest levels, with an average contamination rate of between 85 and 90 percent, while China and Japan had the lowest, between 12 and 20 percent contamination.

The study is the first report about cocaine contamination in Chinese and Japanese currencies.

Scientists have known for years that paper money can become contaminated with cocaine during drug deals and directly through drug use such as snorting cocaine through rolled bills.

Contamination can spread to bank notes not involved in the illicit drug culture because bills are processed in banks’ currency-counting machines.

“To my surprise, we’re finding more and more cocaine in bank notes,” said study leader Yuegang Zuo, of the University of Massachusetts in Dartmouth.

Zuo says that the high percentage of contaminated US currency observed in the current study represents nearly a 20 percent jump in comparison to a similar study he conducted two years ago. That earlier study indicated that 67 percent of bills in the US contained traces of cocaine.

“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,” Zuo said.

Such studies are useful, he noted, because the data can help law enforcement agencies and forensic specialists identify patterns of drug use in a community.

These findings were presented at the 238th National Meeting of the American Chemical Society.