Up to 90 percent of US paper money contains traces of cocaine, according to researchers in what is described as the largest, most comprehensive analysis to date of cocaine contamination in banknotes. The scientists found the most cocaine in large cities such as Baltimore, Boston, and Detroit. In fact, they found traces of cocaine in 95 percent of the banknotes analyzed from Washington DC alone. The new study suggests that cocaine abuse is still widespread and may be on the rise in some areas, and it could help raise public awareness about cocaine use and lead to greater emphasis on curbing its abuse, the researchers say. The scientists tested banknotes 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, they say. "To my surprise, we're finding more and more cocaine in banknotes," said study leader Yuegang Zuo, PhD, of the University of Massachusetts in Dartmouth. Zuo says that the high percentage of contaminated U.S. 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 U.S. 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 says. 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. In the study, Zuo and colleagues describe use of a modified form of a standard laboratory instrument termed a gas chromatograph-mass spectrometer. It allows a faster, simpler and more accurate measurement of cocaine contamination than other methods, without destroying the currency. The researchers used the method to analyze banknotes of several different denominations from the five countries surveyed. The scientists analyzed a total of 234 banknotes from the US and found that up to 90 percent of the banknotes contain traces of cocaine. Amounts ranged from .006 micrograms (several thousands of times smaller than a single grain of sand) to over 1,240 micrograms of cocaine per banknote (about 50 grains of sand). For comparison: A grain of sand weighs approximately 23 micrograms; there are one million micrograms in a gram and 28 grams in an ounce. The scientists collected U.S. banknotes from 17 U.S. cities and found that larger cities like Baltimore, Boston, and Detroit had among the highest average cocaine levels. Washington, D.C., ranked above the average, with 95 percent of the banknotes sampled contaminated with the drug. The lowest average cocaine levels in U.S. currency appeared in bills collected from Salt Lake City. Despite the high percentage of cocaine-contaminated banknotes, Zuo points out that the amount of cocaine found on most notes was so small that consumers should not have any health or legal concerns about handling paper money. "For the most part, you can't get high by sniffing a regular banknote, unless it was used directly in drug uptake or during a drug exchange," Zuo said. "It also won't affect your health and is unlikely interfere with blood and urine tests used for drug detection."