EXPERT REACTION: Contaminated Australian honey

In response to the recent widespread media coverage of an international scientific study (Griffin et al. 2015) that found Australian honeys contained naturally-occurring pyrrolizidine alkaloids (PAs), and in support of the media statement from the Australian Honey Bee Industry Council (AHBIC) on 21 Jan 2016:

• There is no evidence that consumption of Australian honeys causes human harm. In fact numerous other recent scientific studies have demonstrated likely health benefits associated with Australian honey, including antibiotic activity, anti-fungal activity, prebiotic activity and inhibitory activity against viruses such as influenza. Far from being considered a carcinogen, honey is even sometimes used to help manage side-effects of cancer treatments.
• A soon-to-be-published report from the Rural Industries Research & Development Council will show that in terms of chemical contamination, Australian honey is some of the cleanest and purest in the world.
• The naturally-occurring substance (PA) detected in Australian honeys in the study by Griffin et al. (2015) is introduced into the honey when bees forage on flowers of noxious introduced weeds such as Paterson’s Curse.
•  All Australian honey samples tested by Griffin et al. (2015) were produced before 2012, some even before 2008. Since then the proportion of bees foraging on Paterson’s Curse in Australia has dropped significantly as efforts to control this noxious introduced weed have become more and more successful. By late 2015 it has been estimated that less than 0.001% of the commercial Australian honey crop involved nectar or pollen from Paterson’s Curse.
• 70-80% of Australian/NSW honey is produced by bees foraging on native flowering plants such as eucalypts. Eucalypts do not produce PAs.
• All of this adds even more weight to why Australian beekeepers need better access to good native floral resources.
• Honey in NSW is produced in compliance with Australian standards and recommendations.
• The Australian and international standards for food PA content are currently under review by experts. It should be noted that according to Griffin et al. (2015) even most European-produced honeys don’t meet the current European guidelines for PA content

Pyrrolizidine alkaloids are a class of more than 300 chemicals with similar structure, most commonly occurring in plants of the Senecio, Crotalaria, Heliotropium and Echium genera. These alkaloids occur in about 3% of flowering plants worldwide and are known to produce liver toxicity when consumed in sufficient quantity. The potency of the individual alkaloids varies and depends on their structure.

Several of these pyrrolizidine alkaloid containing plants occur in Australian pastures and occasionally poison grazing horses, cattle and sheep, or pigs and poultry fed grain contaminated with their seeds. Repeated consumption of small amounts of plant by livestock can cause liver damage, weight loss and potentially death. The majority of such plants are native species, but some are introduced species.

Pattersons Curse or Salvation Jane (Echium plantagineum) is an escaped garden plant introduced into Australia in the 1850s and now prevalent in pastures across the southern states of Australia (Figure 1). Pastures in other states are also affected by other pyrrolizidine alkaloid containing plants such as Fireweeds (Senecio) and Crotalaria species, which cause similar liver toxicity in livestock.

Pyrrolizidine alkaloid poisonings in humans are rare but have occurred from the consumption of herbal treatments containing such alkaloids (eg Comfrey tea) and from cereal crops infected with seeds. Low level pyrrolizidine alkaloid contamination of honey occurs through transfer of pollen from flowers of the culprit plants.

Pyrrolizidine alkaloids (PAs) are naturally occurring compounds found in Patterson's curse and in more than 600 plants that grow across most of the worlds pasture lands. Complete avoidance of PAs is therefore not possible.   During the summer months and particularly where other plants are water stressed, Patterson's curse may be the dominant flowering plant available for bee keepers to use for honey production. PAs are known to be liver toxins in humans at high intakes and some have been shown to be carcinogenic in rodents in studies where the animals are administered the compound for their entire lifetime.

In humans liver, or other, cancer has not been associated with high level PA exposure even where outbreaks of PA induced liver toxicity has been of sufficient severity to cause multiple deaths due to liver failure. Such outbreaks have only been reported in communities consuming relatively large quantities of PA containing seeds as contaminants in their grain and where protein intake has been low, impairing normal liver detoxification mechanisms. 

Consumers would be wise to avoid honey produced solely or predominantly from Patterson's curse, which is generally only available from specialist outlets or farmers markets, and honey producers have previously been advised to blend such honey with that produced from other flowering plants to keep levels as low as possible.  There is unlikely to be a significant human health risk from consuming normal amounts of Australian honey. Those consuming high levels of honey may wish to seek honey produced from other plants.

Plants often use toxic chemicals to stop animals eating them. One class of toxic chemicals are the pyrrolizidine alkaloids, which can cause liver and lung damage. Long term consumption of pyrrolizidine alkaloids may increase the risk of cancer. Pyrrolizidine alkaloids are present in plants ranging from comfrey to Patterson’s curse (Salvation Jane), and small amounts of pyrrolizidine alkaloids may be found in salads, herbal medicines, and honey. In many parts of Australia Patterson’s curse /Salvation Jane is a significant source of nectar for foraging bees.

This honey can have high levels of pyrrolizidine alkaloids, and must be diluted with honey from other sources to reduce the levels. The recent report shows that Australian honey has on average 4 times more pyrrolizidine alkaloids than European honeys. European guidelines are more stringent than Australian guidelines, mostly due to a more conservative estimate of cancer risk. While pyrrolizidine alkaloids are able to produce cancer in rats, evidence for cancer in humans is indirect. However, for most Australian honeys the risk is low.

For a 70 Kg person consuming the average amount of honey (around 3 grams per day, roughly three teaspoons) consumption of most of the Australian honeys would be safe at both European and Australian guidelines. There were a few exceptions, and these are of concern. However, people who are high consumers of honey are at much greater risk, and several honeys exceed both current Australian and European guidelines when consumed at levels seen in 5% of the Australian population. While for the average consumer the risk is low, further investigation will be needed to understand the risk to more vulnerable groups.

Industry is aware of the issue and has taken steps to mitigate it.

To say that Australian honey is the most contaminated in the world is an exaggeration and it depends on the contaminant. As Australia does not have the Varroa mite and a number of other pests and diseases, we use less chemicals to manage our bees; we also try to minimise exposure to pesticides.