"martin" wrote in message
...
See
http://www.chm.bris.ac.uk/motm/ptq/ptq.htm

and
http://www.planorganic.com/news_july_02.htm
"Hill walking could give you cancer! Bracken (Pteridum aquilinium),
that common fern much admired by tourists, is very prominent
throughout the British Isles at this time of the year. It mainly
features on upland soils where it forms thick, hip-high cover beloved
by children for games of hide-and-seek - and adults, for a little
alfresco slap-and-tickle, perhaps!
During late July and August it matures, releasing billions of spores
which have a quite distinctive smell. These airborne microscopic
fellows are the problem. Experiments with rats and guinea pigs have
shown that the spores are carcinogenic.* It seems that bracken
contains chemicals related to benzene.
Farmers have always been aware of the dangers of the plant, especially
in its mature stage, and many animals are lost to it every year. One
estimate puts UK animal deaths to bracken at £8 million!
Milk from animals that have eaten the plant has also been linked to
human cancers in Costa Rica. The food-adventurous Japanese eat the
young shoots of bracken and it is suggested that this has a connection
to the fact that they have the highest rates of stomach cancer in the
world.
Some years ago, shepherds and farm workers in Britain were advised to
wear masks when they were working in or near bracken.
The spores also contaminate watercourses.
Bracken is increasingly becoming a pest in the UK where, Triffid-like,
it is advancing at the rate of 3% per year, mostly at the expense of
heather.
Methods to eliminate it, include spraying, cutting regularly (which
should wear out the plant in three seasons) and ploughing it up. This
is the option I chose when I wanted to clear a 20 year old growth of
bracken - some up to 6 foot high - here on my holding on Beara. I
ploughed up the huge mats of roots or rhizomes, about 25 tons per
acre, I estimated - allowed them to dry - it was a rare dry summer
here - then burned and spread the ashes. I had a wonderful crop of
potatoes from the 2 acres I cleared.
Every scrap of root however must be destroyed otherwise it will start
to propagate again.
* The Bracken Advisory Commission was set up six years ago and is
headed by Prof. Jim Taylor, emeritus professor of geography at the
Univ. of Wales, Aberyswyth."

Very fulsome response thanks Martin, but can we establish that the risks
refer to massive exposure, such as hill walking amongst densely populated
bracken and not the odd fern in the garden?

Patrick