By Rebecca Morelle
Science reporter, BBC News, York
Measurements of drug contamination on UK banknotes are being used to link cash to crime, scientists say.
Almost every UK banknote is tainted, the research says
Almost every UK banknote in circulation is tinged with drugs such as cocaine and heroin, the research finds.
But the residue levels are on average the same throughout the UK - even if the note hails from an area where drug use is rife.
The findings are now being used to link money that has an unusually high drug contamination to drug crime.
We are pretty much talking about all bank notes being contaminated with cocaine
The Bristol-based scientists analysed tens of thousands of banknotes from general circulation to work out the average drug profile of the UK's banknotes.
Karl Ebejer, from Mass Spec Analytical, who worked on the study, said: "We are pretty much talking about all banknotes being contaminated with cocaine; one in 20 are contaminated with heroin or cannabis; and on average less than half are contaminated with ecstasy and amphetamines.
"We are talking traces - these are amounts we cannot see or feel, these are amounts that require sensitive instrumentation to detect. They are in the order of nanograms (billionths of a gram)."
Rich and poor
The scientists have now investigated whether the drug contamination of a note differs across the UK.
They looked at £10 and £20 notes taken from eight different locations: Oxford, Folkestone, Grangemouth, Cardiff, Troon, Dunfermline, Burntisland and Pontyclun.
These were chosen to represent places that were urban, rural, rich, poor, ports of entry and those that had high and low crime rates, to see if any of these factors had an influence on the amount of drug residues found.
Gavin Lloyd, from Bristol University who carried out the experiment, said: "We found that none of the factors were significant, the contamination was exactly the same."
The scientists say their work will be key for some UK court cases.
When money is seized in a drugs or smuggling case, sometimes analysis finds an unusually high level of drug contamination in a large number of notes.
Karl Ebejer, who frequently acts as an expert witness in courts, said: "In court, the defence might say that is because you got it from 'drugsville', everyone does drugs there, of course, the money is contaminated."
But now, Dr Ebejer said, the new work is being used in court to show that this is not the case and that drug activity may be a more likely cause.
Dr Ebejer stressed that research had already been used as evidence in some cases.
The researchers believe note contamination is caused by drug use but also as notes brush up against each other in cash sorting machines or AGMs.
Even a brand new note is likely to have some drug contamination from the sorting process that took place as the banknotes were counted, the researchers said.