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How much harm do plants actually cause?

Accidental Plant Poisoning

It cannot be said often enough that the number of serious incidents of accidental plant poisoning is extremely small but finding evidence to justify that statement is made more difficult because, in an odd way, the truth of it makes evidence hard to provide.

Because it is such a small problem, there is no point in expending resources to monitor it in any detail. Unlike, say, motor vehicle accidents or tourism numbers, there are no annual reports into plant poisoning.

But, there is one detailed study that, though now 15 years old, offers an indication of the plants that do cause the very few incidents that occur.

The Experience of One Country

Evidence of the limited harm caused by plants comes from a 1996 paper  by Jaspersen-Schib et al and published by the Swiss Journal of Medicine entitled ‘Serious plant poisonings in Switzerland 1966-1994. Case analysis from the Swiss Toxicology Information Center’ (STIC)  

The researchers looked at 24,950 cases of contact with or ingestion of toxic plant material reported to the STIC. Severe plant poisonings occurred in only 152 cases (0.6% of the total) and sufficient details were available for 135 cases to be analysed. These cases involved 112 adults and 23 children and included 5 adult deaths.  

[It would be wrong to assume that a country as small as Switzerland and with its particular geography could be typical of the whole world but it does seem to be broadly similar to the USA where, in 2008, of 63,362 'reported poisonings' only 67 (0.1% of the total) produced a ‘major’ outcome with a further 1,252 (2.0%) having ‘moderate’ effects. The 63,362 number is calls to US Poison Control Centres and many of these may have been simply seeking information. This doesn't stop some people claiming that this is the number of actual poisonings and labelling these plants as 'wicked' as a result.]

In terms of number of cases, within the 135, there were eleven plants resulting in more than one case. These were;  

• Atropa belladonna, deadly nightshade, (42 cases)
• Heracleum mantegazzianum, giant hogweed, (18)
• Datura stramonium, jimsonweed, (17)
• Dieffenbachia, dumb cane, (11)
• Colchicum autumnale, naked ladies,(10 including 2 deaths)
• Veratrum album, sneezewort, (8)
• Aconitum napellus, monkshood, (4)
• Aesculus hippocastanum, horse chestnut, (3)
• Hyoscyamus niger, black henbane, (3)
• Oenanthe crocata, hemlock water dropwort, (2 including 1 death)
• Taxus baccata, yew, (2 including 1 death)  

The fifth fatal case was the result of the only reported incident of poisoning by Narcissus pseudonarcissus. This is the only case of fatal daffodil poisoning I have heard of and it resulted from inhalation of plant material which would, of course, have avoided the gastrointestinal upset that is usually found with daffodil ingestion and usually limits the effects of the toxins.  

Other plants involved in a single serious poisoning during the 29 years studied were Arum maculatum (cuckoopint), Asarum europaeum (wild ginger), Chrysanthemum vulgare (common tansy), Cyclamen persicum (cyclamen), Datura sauveolens (angels’ trumpet), Glycyrrhiza glabra (liquorice), Laburnum anagyroides (laburnum), Lycopodium (clubmoss), Nerium oleander (oleander), Senecio vulgaris (groundsel) and Vicia faba (broad bean).  

That the most common (albeit extremely rare) cause of serious poisoning, deadly nightshade, did not result in any fatalities suggests that its danger if often over-stated. That giant hogweed ranks second as a cause of serious harm is an answer to those who say that concern about Heracleum mantegazzianum is overblown and that there are many more dangerous plants around.