Australian honeys are the most contaminated in the world with natural poisons linked to chronic disease including cancer, according to international researchers.
Pregnant and breastfeeding women in particular should be wary, experts say, with unborn and breastfed infants at higher risk of organ damage from such toxins.
The news affects varieties of honey sold by many leading brands and widely available on supermarket shelves. While the products do meet more relaxed Australian food safety standards, all but five Australian honeys tested had more contaminants than the European Food Safety Authority would consider safe or tolerable, the research published in the Food Additives and Contaminants scientific journal shows. 
The Australian Food Code bans the use of poisonous weeds such as Paterson's curse (also known as Salvation Jane) and Fireweed in human food. Their flowers are laced with chemicals called pyrrolizidine alkaloids that are considered the most common cause of poisoning in humans and livestock worldwide.
But Food Standards Australia and New Zealand (FSANZ) permits honey to be sourced from restricted plants, as long as it is blended with other honey to dilute it.
"Removing source plants is not feasible for many areas where apiaries are kept," a FSANZ spokesperson said. "Contaminants should be kept as low as achievable, therefore blending is the most practical way of reducing the levels of pyrrolizidine alkaloids."
In   October, German researchers from the Federal Institute for Risk Assessment found that even low-level exposure to these chemicals can cause gene mutations linked to chronic lung disease and cancers (such as leukaemia and breast cancer).
Australian toxicologist Dr John Edgar, a United Nations registered expert on this issue, said dietary exposure to these poisons could be a significant cause of cancer.
"Reducing the contamination in foods such as honey, teas, salads, flour, dairy and herbal products could result in a significant reduction in cancer cases worldwide," he told Fairfax Media.
Writing in the Australian Medical Journal last year, Dr Edgar called for better monitoring of such poisons and for consumers to be better informed when buying food.
FSANZ's level of safe intake for pyrrolizidine alkaloids is set  much higher than its European counterparts, who are more concerned with the potential cancer-causing effects.
The European tolerable intake is 0.007 micrograms per kilogram of body weight, per day. The Australian intake is 1 microgram per kilogram of body weight, per day.
The blending approach used in Australia is out of step with other world health authorities such as the European Food Safety Authority, the UK Committee on Toxicology and the German Institute for Risk Assessment who direct against the dilution of contaminated food. The latter has criticised the Australian approach as "counterproductive".
The result is that nearly every Australian honey was contaminated according to Irish researchers, who analysed the level of pyrrolizidine alkaloids in supermarket honeys here and in Europe.
Varieties such as Australian organic, floral blend, rainforest and blue borage had the highest levels of pyrrolizidine alkaloids, according to the researchers from various science organisations such as the Irish Agriculture and Food Development Authority and the Mass Spectrometry Research Centre. 
The report comes as the World Health Organisation develops a code of practice to reduce the amount of such contamination in food and stockfeed.
WHO has already identified pyrrolizidine alkaloids, which have been found in high levels in foods such as herbal teas and some herbal medicines, as a serious human health threat.
FSANZ recently acknowledged international research that suggested its daily tolerable intake limits "should be reduced".
A spokesperson said it had sent an expert to the WHO committee in Rome last year and would wait for new international food safety limits before reconsidering its current approach to pyrrolizidine alkaloids.
"FSANZ has not yet determined whether the tolerable intake set in [the year] 2000 is still appropriate, taking into account the subsequent information on the toxicities of different pyrrolizidine alkaloids," she said.
"We are aware of the reports on [pyrrolizidine alkaloids] in Australian and New Zealand honey."
She said FSANZ had not yet reviewed the German paper on the cancer-causing effects of pyrrolizidine alkaloids on cells.
"However, we note that caution is required in extrapolating from in vitro results to the risk in humans."
The Australian Honeybee Industry Association said the Irish report exaggerated the likelihood of toxicity by assuming larger honey consumption and lower body weight than is normal in Australia.
It said the amount of honey produced from agricultural weed has declined dramatically over the last decade because of modern farming techniques.
"Industry is fully aware of the problem with Paterson's curse honey and alkaloid content," a spokesperson said. "This honey is not produced in commercial quantities in Australia."
"There is not one single case documented of human health being unfavourably affected as a consequence of the consumption of honey containing very low levels of alkaloids." 
"Australian consumers of Australian honey have nothing to fear and they should continue to enjoy our great Australian honeys."