Top 10 Most Dangerous Fruits and Vegetables in the World
Rhubarb (Rheum rhabarbarum) is a species of plant in the family Polygonaceae.
They are herbaceous perennials growing from short, thick rhizomes. They have
large leaves that are somewhat triangular, with long fleshy petioles. They have
small flowers grouped in large compound leafy greenish-white to rose-red
In culinary use, fresh raw petioles (leaf stalks) are crisp (similar to celery)
with a strong, tart taste. Most commonly, the plant's leaf stalks are cooked
with sugar and used in pies and other desserts. A number of varieties have been
domesticated for human consumption, most of which are recognised as Rheum x hybridum by the Royal Horticultural Society.
Rhubarb is usually considered to be a vegetable; however, in the United States,
a New York court decided in 1947 that since it was used in the United States as
a fruit, it was to be counted as a fruit for the purposes of regulations and
duties. A side effect was a reduction on imported rhubarb tariffs, as tariffs
were higher for vegetables than fruits. Rhubarb also contains glycosides
especially rhein, glucorhein and emodin which impart cathartic and laxative
activities to it. It is hence useful as a cathartic in case of constipation.
Rhubarb leaves contain poisonous substances, including oxalic acid which is a
nephrotoxic and corrosive acid that is present in many plants. The LD50 (median
lethal dose) for pure oxalic acid in rats is about 375 mg/kg body weight, or
about 25 grams for a 65 kg (~140 lb) human. (Other sources give a much higher
oral LDLo (lowest published lethal dose) of 600 mg/kg.) While the oxalic acid
content of rhubarb leaves can vary, a typical value is about 0.5%, so a rather
unlikely 5 kg of the extremely sour leaves would have to be consumed to reach an
LD50 of oxalic acid. Cooking the leaves with soda can make them more poisonous
by producing soluble oxalates. However, the leaves are believed to also contain
an additional, unidentified toxin, which might be an anthraquinone glycoside
(also known as senna glycosides).
In the petioles, the amount of oxalic acid is much lower, only about 2-2.5% of
the total acidity, which is dominated by malic acid. This means the raw stalks
may not be hazardous, although the tart taste of raw stalks is so strong as to
be unpalatable to many.
Rhubarb is a relative of buckwheat and has an earthy, sour flavor. Rhubarb
thrives in cold climates and originated in Western China, Tibet, Mongolia,
Siberia and neighboring areas. The traditional role was medicinal-the dried root
was a popular remedy for a wide range of illnesses. Its primary function was to
induce vomiting, although rhubarb is also a
mild astringent. This medicinal role caused the price of the dried root to rise.
In 1542, rhubarb sold for ten times the price of cinnamon in France and in 1657
rhubarb sold for over twice the price of opium in England (Schneider, 2001).
Beginning in the eighteenth century, rhubarb began to be consumed in foods,
primarily drinks and meat stews.
Botanically speaking, rhubarb is considered a vegetable, but it's most often
treated as a fruit ¬ó though it's rarely eaten raw. Just like fresh cranberries,
rhubarb is almost unbearably tart on its own and needs the sweetness of sugar,
honey, or fruit juice added to it to balance out the acidity. Rhubarb's nickname
is the "pie plant" because that is the
primary use for this vegetable.
Rhubarb was introduced to the United States at the end of the eighteenth
century. Today most rhubarb is frozen for commercial and institutional use; only
about a quarter of the crop is sold fresh.
Rhubarb has been used in Chinese traditional medicine for a long time. its side
effects should be minimal for usual doses and dosage design. However, the side
effects could be serious if you have cancer or vascular issues. It is unclear if
rhubarb is anti-cancer or carcinogenic. There are reports that it may cause
cancer; there are also reports that its ingredients have anti-cancer activities.
Its effect on vascular system is also unclear. A few reports indicated its
vasodilutory effects, while some showed its muscle contraction effects. It may
also enhance blod clotting.
The side effects for eating its leave can be fatal. The leaves are poisonous
because they contain oxalate. This toxin, plus another unknown toxin also found
in the leaves, has been reported to cause poisoning when large quantities of raw
or cooked leaves are ingested. Some ingredients of rhubarb were also found to be
Oxalates are contained in all parts of rhubarb plants, especially in the green
leaves. There is some evidence that anthraquinone glycosides are also present
and may be partly responsible. It is not clear as to the exact source of
poisoning from rhubarb, possibly a result of both compounds. The stalks contain
low levels of oxalates, so this does not cause problems.
During World War I rhubarb leaves were recommended as a substitute for other
veggies that the war made unavailable. Apparently there were cases of acute
poisoning and even some deaths. Some animals, including goats and swine, have
also been poisoned by ingesting the leaves.
The biodynamic (toxicity) mechanism by which oxalic acid works is somewhat
different from organic poisons and is more analogous to heavy metal poisoning.
Organic poisons often work through at the biochemical level, e.g. cyanide by
interfering with respiration at the cellular level, strychnine by screwing up
inter-synaptic transmission. There are many molecular substances in foods which
offer no nutritional benefit, and must be processed and excreted. Oxalic acid,
for example, is excreted in the urine, and its crystals are commonly found in
microscopic urinalysis. Too much oxalic acid in the urine will result in kidney
or bladder stones. Calcium combines with oxalic acid to form the less soluble
salt, calcium oxalate, which is also found in kidney stones. Plant leaves,
especially rhubarb, cabbage, spinach, and beet tops, contain oxalic acid. Oxalic
acid is also found in potatoes and peas. Vitamin C is metabolized to oxalic
acid; it contributes to over-saturation of the urine with crystals and possibly
to stone formation.
Oxalic acid is a strong acid of the composition HOOC-COOH, which crystallizes as
the ortho-acid (HO)3 CC (OH)3 . It is sometimes also called "ethane diacid". It
occurs naturally in some vegetables (like rhubarb). The can also be produced by
heating sodium formate and treating the resulting oxides with sulfuric acid. It
can also be obtained by the action of nitric acid on sugar, or of strong
alkali's on sawdust. The product is normally traded as colorless crystals with a
melting point of 101.5?C, and can be dissolved in water or alcohol. Oxalic acid
reduces iron compounds, and is therefore used in metal polishes, stain removers,
and writing inks. When it absorbs oxygen, it is converted to the volatile carbon
dioxide and to water, and it is used as a bleaching agent, in detergents, and as
a mordant in dyeing processes.
rom an MSDS (Material Safety Data Sheet) for Oxalic acid, LD50 (LD50 is the
Median Lethal Dose, which is the dose of a drug or chemical predicted to produce
a lethal effect in 50 percent of the subjects to whom the dose is given) in rats
is 375 mg/kg. So for a person about 145 pounds (65.7 kg) that's about 25 grams
of pure oxalic acid required to cause death. Rhubarb leaves are probably around
0.5% oxalic acid, so that you would need to eat quite a large serving of leaves,
like 5 kg (11 lbs), to get that 24 grams of oxalic acid. Note that it will only
require a fraction of that to cause sickness.
Symptoms of Oxalic Acid Poisoning
On the body body as a whole one might experience weakness, burning in the mouth,
death from cardiovascular collapse; on the respiratory system - difficulty
breathing; on the eyes, ears, nose, and throat - burning in the throat; one the
gastrointestinal system - abdominal pain, nausea, vomiting, diarrhea; and on the
nervous system - Convulsions, coma.
Precautions for rhubarb gardening
Trim leaves from stalk immediately.
Don't use stalks from frost bitten plants.
Wash the stalks well.
Children should be taught to eat only the rhubarb stalks, preferably
Special Precautions & Warnings:
Pregnancy and breast-feeding: Rhubarb is possibly unsafe when used in amounts
greater than those found in foods.
Diarrhea or constipation: Rhubarb can make diarrhea or constipation
worse, depending on the preparation used.
Gastrointestinal (GI) conditions: Donít take rhubarb if you have a bowel
obstruction; appendicitis; unexplained stomach pain; or inflammatory conditions
of the intestines including Crohn's disease, colitis, and irritable bowel
Kidney disease: There is a chemical in rhubarb that might harm the
kidneys. In fact, a supplement that contained rhubarb has been linked to one
report of kidney failure. If you already have kidney disease, donít risk making
it worse by taking rhubarb.
Kidney stones: Rhubarb contains a chemical that the body can convert into kidney
stones. If you have ever had kidney stones, donít take rhubarb.
Dated 06 June 2013