August 18, 2009

Drugs on Your Paper Money

After the American Century

In the past two days a story has been widely repeated on the Internet about cocaine on dollar bills. The gist of it, as reported on Danish national radio was that 95% of the dollar bills circulating in Washington DC have been used to sniff cocaine. Or that was the impression given. While I admit that this would help explain the erratic behaviour of Congressmen, I thought the science behind the story might be interesting.

As seems to typically be the case with Danish journalism, this story was made as sensational as possible without looking into the matter very far. A few minutes on the Internet cleared up the story somewhat. The research on which this story was based has been done by several people employed at the University of Massachusetts branch campus at Dartmouth. They gave a paper at the American Chemical Society's annual meeting in Washington. As reported in Science News, "of the 234 banknotes sampled from 17 U.S. cities, those with the heaviest cocaine residues – as much as 1,240 micrograms per bill – tended to come from relatively big cities with serious drug problems. Cities like Baltimore, Boston, Detroit and Los Angeles."

Note the numbers here. They looked at 234 dollar bills from 17 cities, or on average slightly less than 14 from each city. That sounds like a small sample. It also turns out that just one tainted bill passing through a bank counting machine will contaminate the equipment and many bills that pass through the equipment afterwards. The American chemists had very sensitive measurements, and could detect an amount of cocaine as small as 1/1000 of a grain of sand. Some bills had 100,000 times as much. In short, a few "dirty bills" could contaminate a very large number of others.

Then there were the international comparisons. According to the story, in Brazil 80% of the banknotes had traces of cocaine, while China had only 20% (22 of 112 bills examined). Japan's currency was the cleanest, only two of twelve having traces of the drug. But are all currencies equally liable to retain cocaine? They are not. The Argonne National Laboratory found that the British pound, for example, is made of fibers less abrasive and more tightly woven than those in American greenbacks, with the result that little adheres to them. I always knew the Brits were uptight in many areas, but this was new to me.

All in all, then, we should not conclude that 90% of Americans are snorting cocaine through their declining currency. Take the report with a grain of, er, salt.