In the context of
biology,
poisons are
substances that can cause disturbances to
organisms, usually by
chemical reaction or other
activity on the
molecular scale, when a sufficient quantity is
absorbed by an organism. Legally and in hazardous chemical
labelling,
poisons are especially toxic
substances; less toxic substances are labelled "harmful",
"irritant", or not labelled at all.
In
medicine (particularly veterinary) and
in
zoology, a poison is often distinguished
from a
toxin and a
venom.
Toxins are poisons produced via some biological function in nature,
and venoms are usually defined as biological toxins that are
injected by a bite or sting to cause their effect, while other
poisons are generally defined as substances which are absorbed
through epithelial linings such as the
skin or
gut.
Terminology
Some poisons are also
toxins, usually
referring to naturally produced substances, such as the
bacterial proteins that
cause
tetanus and
botulism. A distinction between the two terms is
not always observed, even among scientists.
Animal toxins that are delivered subcutaneously (e.g. by
sting or
bite) are also
called
venom. In normal
usage, a poisonous organism is one that is harmful to consume, but
a venomous organism uses poison to defend itself while still alive.
A single organism can be both venomous and poisonous.
The derivative forms "toxic" and "poisonous" are synonymous.
Within
chemistry and
physics, a poison is a substance that obstructs or
inhibits a reaction, for example by binding to a
catalyst. For an example, see
nuclear poison.
Paracelsus, the father of
toxicology, once wrote: "Everything is poison,
there is poison in everything. Only the dose makes a thing not a
poison." The phrase "poison" is often used colloquially to describe
any harmful substance, particularly
corrosive substances,
carcinogens,
mutagens,
teratogens and harmful
pollutants, and to exaggerate the dangers of
chemicals. The legal definition of "poison" is stricter. A medical
condition of poisoning can also be caused by substances that are
not legally required to carry the label "poison".
Uses of poison
Throughout human history, intentional application of poison has
been used as a method of
assassination,
murder,
suicide, and
execution. As a method of execution, poison has
been ingested, as the ancient Athenians did (see
Socrates), inhaled, as with
carbon monoxide or
hydrogen cyanide (see
gas chamber), or injected (see
lethal injection). Many languages describe
lethal injection with their corresponding words for "poison shot".
Poison's
lethal effect can be combined with its allegedly magical powers; an example is the Chinese
gu poison. Poison was also
employed in
gunpowder warfare. For
example, the 14th century Chinese text of the
Huo Long
Jing written by
Jiao Yu outlined the
use of a poisonous gunpowder mixture to fill
cast iron grenade
bombs.
On the whole, however, poisons are usually not used for their
toxicity, but may be used for their other properties. The property
of toxicity itself has limited non-lethal applications: mainly for
controlling pests and weeds, cleaning and maintenance, and for
preserving building materials and food stuffs. Where possible,
specific agents which are less poisonous to humans have come to be
preferred, but exceptions such as
phosphine continue in use.
Most poisonous materials still in use are used for their chemical
or physical properties other than being poisonous. Many
over-the-counter medications, such as
aspirin and
Tylenol, are
quite toxic if ingested in sufficiently large quantities.
Alcohol is also toxic if too
much is ingested in a short enough time. In laboratory
environments, where specific chemical properties are often
required, the most effective, easiest, safest, or cheapest option
for use in a
chemical synthesis
may be a poisonous material. If a toxic substance possesses these
properties more exactly than a non-toxic one, the toxic substance
is superior.
Chromic acid is an example
of such a "simple to use" reagent, but reactivity, in particular,
is important.
Hydrogen fluoride
(HF), for example, is both poisonous and extremely corrosive.
However, it has a high
affinity
(
free energy) for
silicon, which is exploited by using HF to
etch glass or to manufacture
silicon semiconductor chips.
On the other hand, certain medical treatments actually make
deliberate use of the toxicity of certain substances.
Antibiotics (originally harvested from organisms
but now artificially produced in laboratories) are highly
disruptive to the biochemistry of micro-organisms while having
almost no direct effect upon humans. Similarly, the drugs used in
chemotherapy are quite toxic; the
reason chemotheraputic drugs have far more severe side effects than
antibiotics is that their toxicity is not as narrowly tailored.
Their benefit arises from the fact that they are—hopefully—more
toxic to cancerous cells than normal ones. Such substances could be
classified as poisons under the categories defined above, as they
are generally artificial in nature, but are not generally discussed
as such.
Biological poisoning
Acute poisoning is exposure to a poison on one occasion or during a
short period of time. Symptoms develop in close relation to the
exposure. Absorption of a poison is necessary for systemic
poisoning. In contrast, substances that destroy tissue but do not
absorb, such as
lye, are classified as
corrosives rather than poisons.
Chronic poisoning is long-term repeated or continuous exposure to a
poison where symptoms do not occur immediately or after each
exposure. The patient gradually becomes ill, or becomes ill after a
long latent period. Chronic poisoning most commonly occurs
following exposure to poisons that
bioaccumulate such as
mercury and
lead.
Contact or absorption of poisons can cause rapid death or
impairment. Agents that act on the
nervous system can paralyze in seconds or
less, and include both biologically derived
neurotoxins and so-called
nerve gases, which may be synthesized for
warfare or industry.
Inhaled or ingested
cyanide, used as a
method of
execution in
gas chambers, almost instantly starves the body
of energy by
inhibiting the
enzymes in
mitochondria that make
ATP. Intravenous injection of an
unnaturally high concentration of
potassium chloride, such as in the
execution of prisoners in parts of the United States, quickly stops
the
heart by eliminating the
cell potential necessary for
muscle contraction.
Most biocides, including
pesticides, are
created to act as poisons to
target
organisms, although acute or less observable chronic poisoning
can also occur in non-target organism, including the
humans who apply the biocides and other
beneficial organisms. For example, the
herbicide
2,4-D imitates the action of a plant
hormone, to the effect that the lethal toxicity is specific to
plants. Indeed, 2,4-D is not a poison, but classified as "harmful"
(EU).
Many substances regarded as poisons are toxic only indirectly, by
toxication. An example is "wood alcohol"
or
methanol, which is not poisonous itself,
but is chemically converted to toxic
formaldehyde and
formic
acid in the
liver. Many
drug molecules are made toxic in the liver, and
the genetic variability of certain liver
enzymes makes the toxicity of many compounds differ
between individuals.
The study of the symptoms, mechanisms, treatment and diagnosis of
biological poisoning is known as
toxicology.
Exposure to radioactive substances can produce
radiation poisoning, an unrelated
phenomenon.
Poisoning management
- Poison Control Centers
(reachable at 1-800-222-1222 in the US worldwide) provide immediate, free, and expert
treatment advice and assistance over the telephone in case of
suspected exposure to poisons or toxic substances.
Initial management
Decontamination
- If the toxin was recently ingested, absorption of the substance
may be able to be decreased through gastric decontamination. This
may be achieved using activated
charcoal, gastric lavage,
whole bowel irrigation, or
nasogastric aspiration.
Routine use of emetics (syrup of
Ipecac), cathartics or laxatives are
no longer recommended.
- Activated charcoal is the
treatment of choice to prevent absorption of the poison. It is
usually administered when the patient is in the emergency room or
by a trained emergency healthcare provider such as a Paramedic or
EMT. However, charcoal is ineffective against metals such as sodium, potassium, and lithium, and
alcohols and glycols; it is also not recommended for ingestion of
corrosive chemicals such as acids and alkalis.
- Whole bowel irrigation
cleanses the bowel, this is achieved by giving the patient large
amounts of a polyethylene glycol
solution. The osmotically balanced polyethylene glycol solution is
not absorbed into the body, having the effect of flushing out the
entire gastrointestinal
tract. Its major uses are following ingestion of sustained
release drugs, toxins that are not absorbed by activated charcoal
(i.e. lithium, iron),
and for the removal of ingested packets of drugs (body packing/smuggling).
- Gastric lavage, commonly known as
a stomach pump, is the insertion of a tube into the stomach,
followed by administration of water or saline down the tube. The
liquid is then removed along with the contents of the stomach.
Lavage has been used for many years as a common treatment for
poisoned patients. However, a recent review of the procedure in
poisonings suggests no benefit. It is still sometimes used if it
can be performed within 1 h of ingestion and the exposure is
potentially life threatening.
- Nasogastric aspiration
involves the placement of a tube via the nose down into the
stomach, the stomach contents are then removed via suction. This
procedure is mainly used for liquid ingestions where activated
charcoal is ineffective, e.g. ethylene glycol poisoning.
- Emesis (i.e. induced by ipecac) is no
longer recommended in poisoning situations.
- Cathartics were postulated to decrease
absorption by increasing the expulsion of the poison from the
gastrointestinal tract. There
are two types of cathartics used in poisoned patients; saline
cathartics (sodium sulfate, magnesium citrate, magnesium sulfate) and saccharide
cathartics (sorbitol). They do not appear
to improve patient outcome and are no longer recommended.
Antidotes
Some poisons have specific
antidotes:
Enhanced excretion
Further treatment
- In the majority of poisonings the mainstay of management is
providing supportive care for the patient, i.e. treating the
symptoms rather than the poison.
Epidemiology
[[Image:Poisonings world map - DALY - WHO2004.svg|thumb|
Disability-adjusted life year
for poisonings per 100,000 inhabitants in 2004.
]]
See also
References
- Kautilya suggests
employing means such as seduction, secret use of weapons, poison
etc. S.D. Chamola, Kautilya Arthshastra and the Science of
Management: Relevance for the Contemporary Society, p. 40.
ISBN 8178711265.
- Kautilya urged detailed precautions against
assassination—tasters for food, elaborate ways to detect poison.
"Moderate Machiavelli? Contrasting The Prince with the Arthashastra
of Kautilya". Critical Horizons, vol. 3, no. 2 (September
2002). Brill Academic Publishers. ISSN 1440-9917 (Print) 1568-5160
(Online). DOI: 10.1163/156851602760586671.
- Needham, Joseph (1986). Science and Civilization in China:
Volume 5, Part 7. Taipei: Caves Books, Ltd. Page 180.
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