Is Ragwort a risk to human health?
Research has shown that the pyrrolizidine alkaloids that cause problems for grazing animals actually occur in 3% of all flowering plants(1).
Ragwort is not consumed as a food plant at all. Rare cases of Pyrrolizidine Alkaloid poisoning have been recorded outside the UK. However these are caused by the
consumption of herbal remedies from plants other than Ragwort over
long periods of time. Extrapolating from figures known from horses
and cattle a human being would have to eat possibly as much as a
stone (14lbs) in weight of the plant to reach a lethal dose.
Concern has been expressed in some quarters of the risk of handling
Ragwort. The concern being that the toxins could be absorbed through
the skin and poisoning occur. However, alkaloids which are absorbed through the skin are in the N-Oxide form having not passed through the digestive system(1) and are therefore non-toxic. These are excreted from the system within 24-48 hours (1)
The absorption levels are also not high. A study was done on Comfrey
a common herbal remedy that does contain pyrrolizidine alkaloids.
In this case two groups of rats were treated with Comfrey. One group
was fed the plant and the other had it applied to the skin. Tests
showed that amount of Pyrrolizidine Alkaloids absorbed through the
skin into the blood is from twenty to fifty times lower than that found if the
rats had been fed the plants.(1) This shows that firstly Pyrrolizidine
Alkaloids are not well absorbed through the skin and secondly even if they were the evidence is that
they are in a non-toxic form so there is no risk of poisoning in humans through casual
contact with Ragwort.
The website Ragwort myths and facts
is produced by horse owner Esther Hegt in conjunction with an international array of experts, including Dr Pieter Pelser,
who is a world authority on ragwort with a Phd specifically on the plant.
It has the following quote in an article co-authored by Dr Pelser :-
"Report on the Internet by Dr. Knottenbelt (Liverpool University). This veterinarian is quoted on the internet quite a lot, because he stated, during a debate in the House of Commons, that the toxic substance in ragwort can almost certainly be absorbed through the skin. In response to this we contacted Dr. Knottenbelt. Through an email he informed us that there is no scientific proof for his statements. He writes that he himself has suffered liver damage after manually removing ragwort plants. The results of this 'experiment' have not been published and, according to us, are not obtained through a good scientific trial.
Through our research about the sources of the reports on the danger of touching ragwort, we conclude that there is no substantial evidence that there is a health risk for people.
The amount of pyrrolizidine alkaloids that might be absorbed through the skin is very low and there is no proof that these alkaloids are being changed into a toxic form."
A standard text book on the pyrrolizidine alkaloids is Chemistry and Toxicology
of Pyrrolizidine Alkaloids. by Dr A. R Mattocks of
the Toxicology Unit of the UK's Medical Research Council Laboratories.
It runs to 393 pages and discusses these chemicals which are commonly found in 3% of the plants in the world. It contains an entire chapter on the effects on humans as some of the other plants can contaminate
food in less developed countries. It scarcely mentions ragwort at all
and what it does say does not imply any real danger to people.
Elsewhere in the book it mentions the research on absorption through the skin several times. This is a typical quote.
" Alkaloids... applied to the body externally are
absorbed through the skin, but at under 5% of the level ingested
orally (Brauchi et al) Moreover, these remain largely in the form of
N-oxides which are much less toxic than the corresponding basic PAs .Thus dermal absorption is unlikely to be harmful.
One point however to remember is that ragwort making contact with the skin may cause an allergic reaction called Compositae Dermatitis
. This is caused by Sesquiterpene Lactones which are commonly produced by plants of the daisy family.
For sensitive people this can cause problems but it is important to remember that these lactones do not cause the long term liver problems that the Pyrrolizidine alkaloids cause.(2)(3)
For worries about Ragwort contaminating meat. See Ragwort
and Meat in the Common Myths section.
Ragwort poisoning in Humans
There is also information on the legal aspects of ragwort at The Weeds Act 1959 and in the
Ragwort Control Act 2003.
Return to Ragwort Facts index
(1)Brauchli J., J. Luthy, U. Zweifel & C. Schlatter. 1982. Pyrrolizidine alkaloids from Symphytum officinale L. and their percutaneous absorption in rats. Experientia (Basel) 38: 1085-1087.
(2) Gordon, L. A. 1999. Compositae dermatitis. Australas. J. Dermatol. 40: 123-128.
(3) Warshaw, E. M. & K. A Zug. 1996. Sesquiterpene lactone allergy. Am. J. Contact. Dermat. 7: 1-23