Crime: Cocaine rubs off on US banknotes

Anyone who uses dollar bills in the United States is almost certainly tainted by Colombia's most famous export. Cocaine is now so widespread that it has contaminated almost every banknote in the US, according to FBI forensic chemists in Washington DC.

Their laboratory tests can now detect a few nanograms (thousandths of millionths of grams) of cocaine on a dollar bill. And they blame automatic counting machines in banks for spreading the white powder around.

New Scientist magazine reports that a rolled bill used to sniff cocaine can have a thousandth of a gram of the drug left on it. In a counting machine, the rapid riffling spreads cocaine dust on to moving parts, contaminating all the other bills. After a few machine-sortings, that first bill can have contaminated half a million other bills.

Although the amount of cocaine on each note is small, lawyers defending pushers and dealers, may now be able to argue that the discovery of cocaine on their clients' cash proves nothing. Finding cocaine on their hands is meaningless as they could claim it rubbed off from "ordinary money". Even the skills of the sniffer dogs have been called into question. In 1994 the 9th US Court of Appeals ruled that police officers could not seize suspected drugs money or raid premises just because a sniffer dog had indicated it was tainted. However, further tests indicated that the dogs were unable to detect cocaine at the levels found on money in general circulation and would only respond if there was a significant amount of narcotic odour so there are unlikely to be any false alarms.