Can the cocaine on dollars be used to track drug use?

More than 90 percent of U.S. currency is contaminated with cocaine, according to a study presented this week at the annual meeting of the American Chemical Society. The study’s lead author told reporters that the rate had been 67 percent two years ago and that the increase may be due to a rise in consumption of the drug spurred by the economic downturn. Can dirty money really be used to track cocaine use?

Yes—at least in Europe. National drug surveys, drug-confiscation statistics, and reported enrollment in rehabilitation programs provide a spotty picture of actual drug use, so scientists have tried to broaden their methods. In Nuremberg, Germany; Valencia, Spain; and Dublin, Ireland, projects are under way to correlate the rate of contamination of newly introduced euro bills with cocaine use statistics across Europe. (Cocaine is an especially good candidate for this type of study. The drug is often taken by snorting it through rolled-up bills, and its crystals happen to fit snugly between a bill’s fibers.) After collecting more than 13,000 notes in eight years, the German team found that the most contaminated euro bills come from Spain—which makes perfect sense, since that country serves as the gateway for South American cocaine imports and has the highest reported rate of cocaine use in Europe (PDF). (An estimated 3 percent of Spaniards use the drug, compared with 2.3 percent for the United States.) In contrast, Spain’s next-door neighbor Portugal has some of the least contaminated currency on the Continent—and one of the lowest rates of cocaine use by conventional estimates. This correlation could prove useful, since currency tests are cheaper and faster to conduct than national drug-use surveys.

Still, contaminated cash may not be much help when it comes to indentifying drug use trends over time in the United States. Surveys show that the rate of cocaine use here has declined or remained steady since 1993. But studies of U.S. cash dating back as far as 1989 have reported a growing degree of contamination. One problem is methodological: The U.S. studies have not been consistent with one another on what denomination of bills were used, how many were analyzed, and from what location they came. (Epidemiologists working in Europe caught a lucky break when a completely new, “clean” currency was introduced in 12 countries in 2002.* That gave them the opportunity to study fresh contamination with a discrete starting point and a fairly stable methodology.)