A Fair Go investigation has revealed previously undetected levels of methamphetamine or P on banknotes.

All samples returned positive tests for the drug, with most above the Ministry of Health guideline for clean-up that applies to P labs.

One group of notes showed 100 per cent contamination.

That compares with a 2008 study that found methamphetamine on four out of 50 notes from ten US cities and a 2012 study that found the drug on 42 per cent of dollar bills in Birmingham, Alabama.

The continuing Fair Go investigation into the meth detection business collected 20 banknotes from four suburban Auckland shops – a supermarket, a dairy, a bakery and a takeaway bar - and sent them to an accredited laboratory with extensive experience in testing for methamphetamine.

All four note bundles tested positive for methamphetamine but not for precursors used to manufacture it, so the drug traces had likely come from contact with users rather than from a P lab.

Nonetheless, three of the bundles tested above the health guideline for remediation if those samples had been taken from a P lab site.

That guideline limit is 0.5 microgrammes per 100cm2 of wall or other surface. The note bundles showed levels from 0.4 to 0.8 microgrammes per 100cm2.

Fair Go commissioned further testing to drill into the results for individual notes.

Five of the $20 bills were checked and all five were positive for methamphetamine – the highest reading for a single note was 3 microgrammes of the drug. This would be the equivalent of nearly 1.5 microgrammes/100cm2 of surface, three times the MoH guideline for a lab cleanup.

The results have been validated by further testing at the laboratory and were reviewed by Massey University toxicologist Dr Nick Kim, who can understand they’re alarming but cautions people not to panic.

“I’d say people are justifiably concerned because of the way guidelines are commonly interpreted, or misinterpreted.”

Fair Go previously reported Dr Kim’s view that even at an exposure to meth residue of 20 times the guideline limit, health effects would only just be plausible for a toddler, so the traces on the notes pose no health risk.

“When you start looking at trace level, at forensic level for chemical residues, you start finding them because we have such great analytical instruments” says Dr Kim.