What really puzzles is me is why they thought to do this study in the first place. And we're already told that Spain is the most contaminating country, but how about some follow-ups: which country's snorters are using the lowest denominations? Highest? Who's snorting the best coke? Is there a correlation between denomination and coke quality?
As recounted to me, in the context of a routine (drug related) criminal trial in the US, where the prosecution put on evidence of similarly tained currency, the defense put on evidence that an absurdly high percentage of US $ bills are tained. Maybe currency in general circulates more than we think and often ends up in the hands of cocaine users? Unfortunately I don't remember the details of the evidence/study.
Why I took time out of the work day to quickly search this I don't know, but here's a cite (for US money):
Jones v. United States Drug Enforcement Admin., 819 F. Supp. 698
Relevant passage:
As the Drug Enforcement Administration's own chemists reported in the memorandum of the results of their experiments (admitted at trial in this case), currency in general circulation in this country is contaminated with traces of narcotics..... See $ 53,082 in U.S. Currency, cited above, slip op. at 9, n.5 (quoting Dirty Money, United States Banker, October 1989, at 10, which discussed a study by Lee Hearn, Chief Toxicologist for Florida Dade County Medical Examiner's Office, in which he found that 97% of the bills from around the country tested positively for cocaine, and noting that clean bills are contaminated in banks when they come in contact with contaminated ones)
This is pretty scary if you start thinking about anthrax.