A new study found six out of ten ‘nicotine-free’ e-cigarette liquids in fact contained nicotine.

Analysis by the Telethon Kids Institute found the liquids purchased on-line and over-the-counter in Australia and were labelled ‘nicotine-free’ also showed signs of 2-chlorophenol – a chemical used in insecticides, herbicides and disinfectants.

The 2-chlorophenol may have come from residue of pesticides used on plants grown to make glycerine – a substance often used as an inactive filler to carry flavour and nicotine compounds.

The nicotine found in three of the samples was at levels comparable to those found in low-dose nicotine e-liquids, and lower levels in the other three samples in which it was present.

“We also found other things – by-products of animal or human bodily functions – which indicates the process of making the e-liquids might not be as clean as you might hope,” says Associate Professor Alexander Larcombe, Head of Respiratory and Environmental Health at Telethon Kids.

Associate Professor Larcombe said these ingredients were regarded as relatively benign for humans, however it is unclear how such chemicals may affect health when heated, aerosolised and inhaled during e-cigarette usage.

“Most of those sorts of things are food additives qualified as ‘safe to eat’, but the way e-cigarettes work is the liquid is heated to 200-250 degrees – and it’s unknown what that heating process does to the chemical composition of these ingredients, especially when it’s being breathed into the lungs,” he said.

Associate Professor Colin Mendelsohn from the University of New South Wales - who supports the use of electronic cigarettes as a harm reduction measure for tobacco smokers - says dosage is important.

“The harm depends on the level of the chemical and the toxicity of that chemical,” he told the ABC.

“Lots of studies have looked at the chemicals in vaping, and they're way below occupational health standards. I suspect these products would be down at that level.

“We know vaping is dramatically less harmful than smoking.

“I think nicotine liquids should be available for sale for smokers who are unable to quit, because the alternative for these people is to keep smoking — and two out of three will die from that.”