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In the context of biology, poisons are substances that can cause injury, illness, or death to organisms, usually by chemical reaction or other activity on the molecular scale.
In medicine (particularly veterinary) and in zoology, a poison is often distinguished from a venom. Venoms are usually defined as biologic toxins that are injected to cause their effect, while poisons are generally defined as toxins 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.
Lay use
The phrase "poison" is often used colloquially to describe other categories of substances:
Warning symbols
Poisons have been known to be symbolized by the skull and crossbones (shown beside), although since this attracts children (being linked to pirates) it is gradually being replaced by Mr. Yuk in the United States. In the United Kingdom and some parts of Europe, irritant poisons are symbolised by a large "X" on an orange background.
Uses of poison
Deliberate application of poison has throughout the ages been used as method of assassination, murder, suicide and execution. As a method of execution, the poison can be administered as ingested, as the ancient Athenians did (see Socrates), breathed, such as carbon monoxide or hydrogen cyanide (see gas chamber) or intravenously (see lethal injection). Many non-English languages describe lethal injection with their corresponding words for "poison shot".
Biological poisoning
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 as used as method of execution on US gas chambers almost instantly starves the body of energy by poisoning mitochondria and the synthesis of 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. Such rapid reactions are often called acute poisoning.
Most (but not all) pesticides are created to act as poisons to target organisms, although acute or less observable chronic poisoning can also occur to non-target organism, including the humans who apply the pesticides and other beneficial organisms.
A poison may also act slowly. This is known as chronic poisoning and is most common for poisons that bioaccumulate. Examples of these types of poisons are mercury and lead.
Many substances regarded as poisons are toxic only indirectly. An example is "wood alcohol" or methanol, which is not poisonous itself, but is chemically converted to toxic formaldehyde 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 one individual and the next.
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 in children
Background
- Poisoning is the fourth most common cause of accidents in children.
- Children less than 5 years of age and adolescent are prone to poisoning.
- Accidental ingestions are most common in children less than 5 years old.
- Adolescent ingestions are more typically a result of suicidal attempts or experimentation with illicit drugs.
- 90% of all poisonings occur at home, the most common site being the kitchen and the bathroom.
- Accidental poisonings occur most frequently when routines are disrupted, for example moving and vacations.
- Child safety caps have helped decrease the number of poisonings; however they are not 100% effective and should not give a false sense of security.
- All potential poisons should be properly labeled, stored out of reach of children, and locked.
- Medications should not be taken in front of small children.
- Parents should receive anticipatory guidance regarding poisonings and should have the number for Poison Control.
- If the poisoning occurs at home, Poison control should be called first!
- If the poison is an inhalant, remove the patient from the area.
- If the poisoning is affecting the skin, remove the clothing and wash the skin thoroughly unless a dry powder is the cause of the poisoning.
- If the patient has swallowed the poison, induce vomiting if appropriate and take the patient to the hospital.
- If the poison is in the eye, flush the eye thoroughly.
- When caring for poisoning in the emergency room center doctors will focus on the ABC's, airway, breathing, and circulation.
- Reviewing the patient's history and performing a pertinent, focused physical examination is a must.
Management
- Treat the patient for shock, burns, and pain
- If a narcotic is suspected, give naloxone
- The goal is to prevent absorption. This may be done using emesis in the first 4 hours, gastric lavage, activated charcoal, cathartics, and diuresis. Ipecac is no longer recommended.
- Indications for gastric lavage include coma or impending coma, seizures, or a depressed gag reflex. Gastric lavage is most effective within 1 h of ingestion, and the largest possible orogastric tube should be used. Gastric lavage should be done only in older children.
- Activated charcoal has no real contraindications and is the treatment of choice to prevent absorption of the poisoning when the patient is in the emergency room. However charcoal is ineffective against cyanides, metals, Na, K, Cl, acids, and bases.
- Cathartics decrease absorption by increasing the rate of excretion.
- Magnesium sulfate should not be used if the patient has renal failure.
- Diuresis may be done using hemodialysis, hemoperfusion, and peritoneal dialysis.
- Exchange transfusion should only be performed if the patient is unresponsive to appropriate care.
Types of poisons
The majority of this section is sorted by ICD-10 code, which classifies poisons based upon the nature of the poison itself. However, it is also possible to classify poisons based upon the effect the poison has (for example, "Metabolic poisons" such as Antimycin, Malonate, and 2,4-Dinitrophenol act by adversely disrupting the normal metabolism of an organism.)
(T38) Poisoning by hormones and their synthetic substitutes and antagonists, not elsewhere classified
Neurotoxins interfere with nervous system functions and often lead to near-instant paralysis followed by rapid death. They include most spider and snake venoms, as well as many modern chemical weapons. One class of toxins of interest to neurochemical researchers are the various cone snail toxins known as conotoxins.
Anticholinesterases (T44.0)
Acetylcholine antagonists
Cell membrane disrupters
Others
- Nicotine - not strictly a neurotoxin, but capable in large doses of causing heart attack
(T50) Poisoning by diuretics and other unspecified drugs, medicaments and biological substances
(T51-T65) Toxic effects of substances chiefly nonmedicinal as to source
(T54) Toxic effect of corrosive substances
Corrosives mechanically damage biological systems on contact. Both the sensation and injury caused by contact with a corrosive resembles a burn injury.
- Acids and bases, corrosives
- Various light metal oxides, hydroxides, superoxides
- Bleach, some pool chemicals, other hypochlorates (acidic and oxydizing effect)
- Hydrofluoric acid
Acids (T54.2)
Strong inorganic acids, such as concentrated sulfuric acid, nitric acid or hydrochloric acid, destroy any biological tissue with which they come in contact within seconds.
Bases (T54.3)
Strong inorganic bases, such as lye, gradually dissolve skin on contact but can cause serious damage to eyes or mucous membranes much more rapidly. Ammonia is a far weaker base than lye, but has the distinction of being a gas and thus may more easily come into contact with the sensitive mucous membranes of the respiratory system. Quicklime, which has household uses, is a particularly common cause of poisoning. Some of the light metals, if handled carelessly, can not only cause thermal burns, but also produce very strongly basic solutions in sweat.
(T56) Toxic effect of metals
A common trait shared by heavy metals is the chronic nature of their toxicity (a notable exception would be bismuth, which is considered entirely non-toxic). Low levels of heavy metal salts ingested over time accumulate in the body until toxic levels are reached.
Heavy metals are generally far more toxic when ingested in the form of soluble salts than in elemental form. For example, metallic mercury passes through the human digestive tract without interaction and is commonly used in dental fillings—even though mercury salts and inhaled mercury vapor are highly toxic.
Examples:
(T57) Toxic effect of other inorganic substances
Reducing agents
- (T57.1) The most notable substance in this class is phosphorus.
Oxidizers
Poisons of this class are generally not very harmful to higher life forms such as humans (for whom the outer layer of cells are more or less disposable), but lethal to microorganisms such as bacteria. Typical examples are ozone and chlorine (T59.4), either of which is added to nearly every municipal water supply in order to kill any harmful microorganisms present.
All halogens are strong oxidizing agents, fluorine (T59.5) being the strongest of all.
- See also: Free radical
(T61) Toxic effect of noxious substances eaten as seafood
(T62) Toxic effect of other noxious substances eaten as food
(T64) Toxic effect of aflatoxin and other mycotoxin food contaminants
(T65) Toxic effect of other and unspecified substances
- (T65.0) Cyanide is a metabolic poison that bonds with an enzyme involved in ATP production.
See also
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