'In one 1985 study done by the U.S. Drug Enforcement Administration on the money machines in a U.S. Federal Reserve district bank, random samples of $50 and $100 bills revealed that a third to a half of all the currency tested bore traces of cocaine.'
Cocaine Contamination of United States Paper Currency
Jonathan Oyler, William D. Darwin, and Edward J. Cone
The exchange of illicit cocaine for money by drug dealers is an everyday occurrence in cities in the United States. There is ample opportunity during the exchange, storage, and use of cocaine for paper currency to become contaminated. Because currency is exchanged frequently, it is likely that contaminated currency would be found in common use. We examined ten single dollar bills from several cities in the United States for the presence of cocaine. Individual bills were extracted with methanol (10 mL). Cocaine was purified from the methanol extract by solid-phase extraction (SPE). The SPE extract was analyzed by gas chromatography–mass spectrometry (GC–MS). Standard curves were constructed with new, uncirculated currency. Cocaine was identified qualitatively by full scan and quantitated by selected ion monitoring. Cocaine was present in 79% of the currency samples analyzed in amounts above 0.1 µg and in 54% of the currency in amounts above 1.0 µg. Contamination was widespread and was found in currency from all sites examined. Cocaine amounts were highly variable and ranged from nanogram to milligram amounts. The highest amount of cocaine detected on a single one-dollar bill was 1327 µg. These results indicated that cocaine contamination of currency is widespread throughout the United States and is likely to be primarily a result of cross-contamination from other contaminated currency and from contaminated money-counting machines.
Journal of Analytical Toxicology, Volume 20, Number 4, July/August 1996, pp. 213-216.
And there's more!
'Other drugs detected on dollar bills include methylphenidate (Ritalin, figure 2) and procaine. Procaine is a local anesthetic used by drug dealers as a cocaine adulterant. Substances commonly detected on US bills include nicotine, diethyltoluamide (DEET bug repellent), sunscreen, dioctylphthalate (plasticizer), triethanolamine (from cosmetics) and glycerol and other polyols.'