The poison garden

I’ve just got back from a week’s holiday in Northumbria. It’s a region I haven’t visited previously I’ve never got past Newcastle before. It’s a very beautiful area with a fantastic coastline and lots of historic monuments to visit.

One of the places I visited during my trip was Alnwick Castle and Gardens. The gardens were redesigned only 10 years ago by Jacques and Peter Wirtz and provide a contemporary take on the traditional stately home estate.

One part of the gardens I found particularly interesting was the “Poison Garden“.  This contains a collection of  “poisonous” plants locked away behind a gate and which can only be accessed when accompanied by a guide. The collection included opium poppies, cannabis and the coca plant, for which the Alnwick Garden Trust had to obtain a special licence. However, most of the plants on display could be found in the countryside or domestic gardens. They included some obvious harmful weeds such as nettle and giant hogweed, well-known poisonous plants such as, belladonna and wormwood, but also decorative plants such as laburnum, willow and even some foodstuffs, including rhubarb.

The message that came across during the tour is one that occupational hygienists should be familiar with – everything is poisonous if we absorb enough of it and that even plants we consider harmful have their beneficial uses.

The opium poppy produces the highly addictive and harmful drugs opium and heroin, but it’s also used to produce morphine which is used to relieve severe pain. Of course morphine is addictive and uncontrolled doses are lethal (and the infamous G.P.  Harold Shipman used it to murder his patients) – a clear case of the dose “differentiating a remedy from a poison” .

Opium poppies

Laburnum have attractive yellow flowers and pea-like pods and are very popular garden trees. However all parts of this plant, – the roots, bark, wood, leaves, flower-buds, petals, and seedpods – are toxic, containing cytisine. There are hospital admissions every year, normally where children have eaten the pea-like seeds from the tree. But the tree is probably planted in hundreds of thousands of gardens around the country and very few of them cause harm – this can only occur if someone ingests the toxin.

I don’t know how popular rhubarb is these days, but I certainly enjoy this tart fruit. Yet here it was planted up in the poison garden.  The part of the plant we eat is the stalk. The leaves, however, contain  oxalic acid in the form of oxalates and anthraquinone alkaloids. Contrary to popular belief, it’s the latter, rather than the former that are the cause of harmful effects when the leaves are eaten.

Its risk that matters – the likelihood of the harm occurring –  and even the most toxic substance can’t cause harm in practice if it isn’t absorbed. So we can have laburnum trees in our gardens and grow and eat rhubarb providing we don’t ingest those parts of the plant containing the toxins. Even if we do, death doesn’t necessarily result – the effects we experience depend on how much we absorb. Similarly highly toxic chemicals can be used in the workplace without anyone being adversely affected if exposure is adequately controlled.

As Paracelsus noted many years ago

“All substances are poisons ; there is none which is not a poison. The right dose differentiates a poison from a remedy”

The poison garden at Alnwick is a good illustration of this.

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