DARTMOUTH, Mass. (9/8/09)--Nine out of 10 pieces of U.S. currency contain traces of cocaine, according to a new study by the American Chemical Society conducted at the University of Massachusetts-Dartmouth. Even bills not involved in drug deals can become contaminated during the automated bill counting process in financial institutions. The drug--a fine powder--adheres to the green ink on the bills--mostly $5, $10s, $20s and $50s--and spreads easily, according to the study. Scientists studied banknotes from nearly three dozen cities in five countries--the U.S., Canada, Brazil, Japan and China. The bills from the U.S. and Canada saw between 85% and 90% contamination. A similar study two years ago found the U.S. contamination rate at 67%. China and Japan had the cleanest bills, with 20% and 12% contamination, respectively. Banknotes from Washington, D.C., had the most contamination--95% had traces of the drug. Other cities with larger amounts of contaminated bills included Detroit, Boston, Baltimore, Miami, Orlando and Los Angeles. The amounts of cocaine are not enough to cause any health or drug-testing concerns, researchers said.