If you handled cash in London around the year 2000, there was a 99% chance your banknotes were contaminated with cocaine. When researchers tested 5,000 notes supplied by the Bank of England's facility in Essex, only 1% came back clean.

This wasn't a one-off finding. A 1999 study examined 500 notes from London and found just four notes without any cocaine traces whatsoever. Similar studies across the UK consistently showed contamination rates of 80% or higher nationwide.

How Does Money Get Contaminated?

The contamination happens in two ways. First, there's direct contamination when notes are rolled up and used to snort cocaine, or when they're handled during drug deals. But that accounts for only a small fraction of contaminated notes.

The real culprit is cross-contamination. When clean notes are stacked together with contaminated ones—which happens constantly in cash registers, ATMs, bank vaults, and wallets—microscopic cocaine particles transfer from one note to another. It's like a game of chemical tag that eventually touches nearly every note in circulation.

The research revealed that while most notes had low contamination levels from this secondary transfer, about 4% showed significantly higher levels, suggesting they'd been used directly in drug-related activities.

The Polymer Note Revolution

Between 2016 and 2020, the UK replaced its traditional paper notes with new polymer (plastic) ones. Scientists wondered: would the slippery plastic surface be harder to contaminate?

Recent studies comparing paper and polymer notes found something interesting. Both types do get contaminated and retain cocaine for extended periods. However, polymer notes don't hold onto cocaine particles as stubbornly as paper notes. The smooth plastic surface means:

Cocaine particulates transfer more easily from polymer notes to other surfaces
Paper notes retain larger amounts of cocaine after handling
Both types can stay contaminated long enough to transfer to multiple other notes

When Money Gets Too Dirty

There's actually an official threshold for drug contamination on UK banknotes. When notes exceed this level, they're pulled from circulation and destroyed. The Bank of England destroys over £15 million worth of banknotes annually because they're too contaminated to remain in circulation.

The contamination isn't just cocaine, either. Studies have found traces of methamphetamine, MDMA (ecstasy), and ketamine on banknotes as well, though cocaine remains the most prevalent.

Should You Worry?

Before you panic, the amounts detected are microscopic. The median contamination level found in studies is measured in nanograms (billionths of a gram). You'd need to handle an absurd number of banknotes for any pharmacological effect.

The findings are more useful for forensic scientists and public health researchers than they are cause for concern. Though you might want to wash your hands after handling cash—not because of the cocaine, but because money genuinely is one of the dirtiest objects we handle daily.

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