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.
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.
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.
(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