Toxicity is the degree to which a substance is able to damage an exposed organism In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole. An organism may either be unicellular (single-celled) or be composed of, as in humans, many trillions of cells grouped into. Toxicity can refer to the effect on a whole organism, such as an animal Animals are a major group of mostly multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and independently. All animals are also, bacterium The bacteria ( [bækˈtɪəriə] ; singular: bacterium)[α] are a large group of single-celled, prokaryote microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals. Bacteria are ubiquitous in every habitat on Earth, growing in soil, acidic hot springs, radioactive waste,, or plant Plants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants, bryophytes, ferns and fern allies. As of 2004,, as well as the effect on a substructure of the organism, such as a cell The cell is the functional basic unit of life. It was discovered by Robert Hooke and is the functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. Some organisms, such as most bacteria, are unicellular . Other organisms, such as humans, (cytotoxicity Cytotoxicity is the quality of being toxic to cells. Examples of toxic agents are a chemical substance, an immune cell or some types of venom) or an organ (organotoxicity), such as the liver The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion. The liver is necessary for survival; there is currently no way to compensate for the absence of liver function (hepatotoxicity The liver plays a central role in transforming and clearing chemicals and is susceptible to the toxicity from these agents. Certain medicinal agents, when taken in overdoses and sometimes even when introduced within therapeutic ranges, may injure the organ. Other chemical agents, such as those used in laboratories and industries, natural chemicals). By extension, the word may be metaphorically A metaphor is an analogy between two objects or ideas; the analogy is conveyed by the use of a metaphorical word in place of some other word. For example: "Her eyes were glistening jewels" used to describe toxic effects on larger and more complex groups, such as the family unit or society at large.

A central concept of toxicology Toxicology is the study of the adverse effects of chemicals on living organisms. It is the study of symptoms, mechanisms, treatments and detection of poisoning, especially the poisoning of people is that effects are dose A dose is a quantity of something that may impact an organism biologically; the greater the quantity, the larger the dose. In nutrition, the term is usually applied to how much of a specific nutrient is in a person's diet or in a particular food, meal, or dietary supplement. In medicine, the term is usually applied to the quantity of a drug or-dependent; even water can lead to water intoxication Water intoxication is a potentially fatal disturbance in brain functions that results when the normal balance of electrolytes in the body is pushed outside of safe limits by over-consumption of water. Normal, healthy (physically, nutritionally and mentally) individuals have little reason to worry about accidentally consuming too much water. Nearly when taken in large enough doses, whereas for even a very toxic substance such as snake Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with many more joints than their lizard ancestors, venom Venom is any of a variety of toxins used by certain types of animals. Generally, venom is injected by such means as a bite or a sting there is a dose below which there is no detectable toxic effect.

Types of toxicity

There are generally three types of toxic entities; chemical, biological and physical:

• Chemicals In chemistry, a chemical substance is a material with a specific chemical composition include inorganic Traditionally, inorganic compounds are considered to be of a mineral, not biological origin. Complementarily, most organic compounds are traditionally viewed as being of biological origin. Over the past century, the precise classification of inorganic vs organic compounds has become less important to scientists, primarily because the majority of substances such as lead Lead is a main-group element with symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed to air. Lead has a shiny chrome-silver luster when it is melted into a, mercury Mercury , also quicksilver (/ˈkwɪksɪlvər/) or hydrargyrum (/haɪˈdrɑrdʒɨrəm/ hye-DRAR-ji-rəm), is a chemical element with the symbol Hg (Latinized Greek: hydrargyrum, from "hydr-" meaning watery or runny and "argyros" meaning silver) and atomic number 80. A heavy, silvery d-block metal, mercury is one of six chemical, asbestos Asbestos is a set of six naturally occurring silicate minerals exploited commercially for their desirable physical properties. They all have in common their asbestiform habit, long, (1:20) thin fibrous crystals. The inhalation of asbestos fibers can cause serious illnesses, including malignant lung cancer, mesothelioma (a formerly rare cancer, hydrofluoric acid Hydrofluoric acid is a solution of hydrogen fluoride in water. While it is extremely corrosive and difficult to handle, it is technically a weak acid. Hydrogen fluoride, often in the aqueous form as hydrofluoric acid, is a valued source of fluorine, being the precursor to numerous pharmaceuticals such as fluoxetine (Prozac), diverse polymers such, and chlorine Chlorine (pronounced /ˈklɔəriːn/ KLOR-een, from the Greek word 'χλωρóς' , is the chemical element with atomic number 17 and symbol Cl. It is a halogen, found in the periodic table in group 17 (formerly VII, VIIa, or VIIb). As the chloride ion, which is part of common salt and other compounds, it is abundant in nature and necessary to gas, organic compounds An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered inorganic. The distinction between "organic" and " such as methyl alcohol Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with formula C , most medications, and poisons from living things.
• Biological toxic entities include those bacteria and viruses that are able to induce disease in living organisms. Biological toxicity can be complicated to measure because the "threshold dose" may be a single organism. Theoretically one virus A virus is a small infectious agent that can replicate only inside the living cells of organisms. Most viruses are too small to be seen directly with a light microscope. Viruses infect all types of organisms, from animals and plants to bacteria and archaea. Since the initial discovery of tobacco mosaic virus by Martinus Beijerinck in 1898, about 5,, bacterium or worm The term worm refers to an obsolete taxon used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, and stems from the Old Norse word for sea serpent. Currently it is used to describe many different distantly-related animals which have a long cylindrical body and no legs can reproduce to cause a serious infection An infection is the detrimental colonization of a host organism by a foreign species. In an infection, the infecting organism seeks to utilize the host's resources to multiply, usually at the expense of the host. The infecting organism, or pathogen, interferes with the normal functioning of the host and can lead to chronic wounds, gangrene, loss. However, in a host with an intact immune system An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own healthy cells and tissues in order to function the inherent toxicity of the organism is balanced by the host's ability to fight back; the effective toxicity is then a combination of both parts of the relationship. A similar situation is also present with other types of toxic agents A biological agent is a bacterium, virus, prion, fungus, or biological toxin that can be used in bioterrorism or biological warfare. More than 1200 different kinds of biological agents have been described and studied to date. Applying a slightly broader definition, some eukaryotes and their associated toxins can be considered as biological agents.
• Physically toxic entities include things not usually thought of under the heading of "toxic" by many people:^{[citation needed]} direct blows, concussion, sound and vibration Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes is used to be synonymous with "oscillation.&, heat and cold, non-ionizing electromagnetic radiation Electromagnetic radiation is a phenomenon that takes the form of self-propagating waves in a vacuum or in matter. It comprises electric and magnetic field components, which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. Electromagnetic radiation is classified into several types according to such as infrared and visible light, and ionizing radiation Ionizing radiation consists of subatomic particles or electromagnetic waves that are energetic enough to detach electrons from atoms or molecules, ionizing them. The occurrence of ionization depends on the energy of the impinging individual particles or waves, and not on their number. An intense flood of particles or waves will not cause such as X-rays X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3 × 1016 Hz to 3 × 1019 Hz) and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma rays. In many and alpha Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus; hence, it can be written as He2+ or 42He2+. They have a net spin of zero, and normally a total energy of about 5 MeV. They are a highly ionizing form of particle radiation, and have low penetration, beta Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay. They are designated by the Greek letter beta . There are two forms of beta, and gamma Gamma radiation also known as gamma rays is electromagnetic radiation of high frequency (very short wavelength). They are produced by sub-atomic particle interactions such as electron-positron annihilation, neutral pion decay, radioactive decay, fusion, fission or inverse Compton scattering in astrophysical processes. Gamma rays typically have radiation.

Toxicity can be measured by its effects on the target (organism, organ, tissue or cell). Because individuals typically have different levels of response to the same dose of a toxin, a population-level measure of toxicity is often used which relates the probabilities of an outcome for a given individual in a population. One such measure is the LD₅₀ In toxicology, the median lethal dose, LD50 , LC50 (Lethal Concentration, 50%) or LCt50 (Lethal Concentration & Time) of a toxic substance or radiation is the dose required to kill half the members of a tested population after a specified test duration. LD50 figures are frequently used as a general indicator of a substance's acute toxicity. When such data does not exist, estimates are made by comparison to known similar toxic things, or to similar exposures in similar organisms. Then "safety factors Factor of safety can mean either the fraction of structural capability over that required, or a multiplier applied to the maximum expected load (force, torque, bending moment or a combination) to which a component or assembly will be subjected. The two senses of the term are completely different in that the first is a measure of the reliability of" are added to account for uncertainties in data and evaluation processes. For example, if a dose of toxin is safe for a laboratory rat, one might assume that one tenth that dose would be safe for a human, allowing a safety factor of 10 to allow for interspecies differences between two mammals; if the data are from fish, one might use a factor of 100 to account for the greater difference between two chordate classes (fish and mammals). Similarly, an extra protection factor may be used for individuals believed to be more susceptible to toxic effects such as in pregnancy or with certain diseases. Or, a newly synthesized and previously unstudied chemical that is believed to be very similar in effect to another compound could be assigned an additional protection factor of 10 to account for possible differences in effects that are probably much smaller. Obviously, this approach is very approximate; but such protection factors are deliberately very conservative and the method has been found to be useful in a wide variety of applications.

Assessing all aspects of the toxicity of cancer-causing agents involves additional issues, since it is not certain if there is a minimal effective dose for carcinogens, or whether the risk is just too small to see. In addition, it is possible that a single cell transformed into a cancer cell is all it takes to develop the full effect (the "one hit" theory).

It is more difficult to assess the toxicity of chemical mixtures than of single, pure chemicals because each component display its own toxicity and components may interact to produce enhanced or diminished effects. Common mixtures include gasoline Gasoline or petrol is a petroleum-derived liquid mixture which is primarily used as a fuel in internal combustion engines. It is also used as a solvent, mainly known for its ability to dilute paints, cigarette smoke Tobacco smoking is the practice where tobacco is burned and the vapors either tasted or inhaled. The practice began as early as 5000–3000 BC. Many civilizations burnt incense during religious rituals, which was later adopted for pleasure or as a social tool. Tobacco was introduced to the Old World in the late 1500s where it followed common trade, and industrial waste Industrial waste is a type of waste produced by industrial activity, such as that of factories, mills and mines. It has existed since the outset of the industrial revolution. Even more complex are situations with more than one type of toxic entity, such as the discharge from a malfunctioning sewage treatment plant, with both chemical and biological agents.

Global classifications of toxicity

For substances to be regulated and handled appropriately they must be properly classified and labelled. Classification is determined by approved testing measures or calculations and have determined cut off levels set by governments and scientists. While currently many countries have different regulations regarding the types of tests, amounts of tests and cut off levels, the implementation of Global Harmonization will begin unifying these countries as early as 2008.^[1][2]

Global Classification looks at three areas: Physical Hazards (explosions and pyrotechnics),^[3] Health Hazards^[4] and Environmental Hazards.^[5]

Health hazards

The types of toxicities where substances may cause lethality to the entire body, lethality to specific organs, major/minor damage, or cause cancer. It should be noted that these are globally accepted definitions of what toxicity is.^[4] Anything falling outside of the definition cannot be classified as that type of toxicant.

Acute toxicity

Acute toxicity looks at lethal effects following oral, dermal or inhalation exposure. It is split into five categories of severity where Category 1 requires the least amount of exposure to be lethal and Category 5 requires the most exposure to be lethal. The table below shows the upper limits for each category.

Note: The undefined values are expected to be roughly equivalent to the category 5 values for oral and dermal administration.^{[citation needed]}

Other methods of exposure and severity

Skin corrosion and irritation are determined though a skin patch test analysis. This examines the severity of the damage done; when it is incurred and how long it remains; whether it is reversible and how many test subjects were affected.

Skin corrosion from a substance must penetrate through the epidermis into the dermis within four hours of application and must not reverse the damage within 14 days. Skin irritation shows damage less severe than corrosion if: the damage occurs within 72 hours of application; or for three consecutive days after application within a 14 day period; or causes inflammation which lasts for 14 days in two test subjects. Mild skin irritation minor damage (less severe than irritation) within 72 hours of application or for three consecutive days after application.

Serious eye Eyes are organs that detect light, and convert it to electro-chemical impulses in neurons. The simplest photoreceptors connect light to movement . In higher organisms complex neural pathways exist that connect the eye, via the optic nerve to the visual cortex and other areas of the brain. Complex optical systems with resolving power have come in damage involves tissue damage or decay of vision which does not fully reverse in 21 days. Eye irritation involves changes to the eye which do fully reverse within 21 days.

Other categories of toxicity

• Respiratory sensitizers cause breathing hypersensitivity when the substance is inhaled.
• A substance which is a skin sensitizer causes an allergic response An allergic response is a hypersensitive immune reaction to a substance that normally is harmless or would not cause an immune response in everyone. An allergic response may cause harmful symptoms such as itching or inflammation or tissue injury from a dermal application.
• Carcinogens A carcinogen is any substance, radionuclide or radiation, that is an agent directly involved in the exacerbation of cancer or in the increase of its propagation. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive substances are considered carcinogens, but their carcinogenic induce cancer, or increase the likelihood of cancer occurring.
• Reproductively toxic substances cause adverse effects in either sexual function or fertility Fertility is the natural capability of giving life. As a measure, "fertility rate" is the number of children born per couple, person or population. Fertility differs from fecundity, which is defined as the potential for reproduction . Infertility is a deficient fertility to either a parent or the offspring.
• Specific-target organ toxins damage only specific organs.
• Aspiration hazards are solids or liquids which can cause damage through inhalation.

Environmental hazards

Environmental hazards tend to focus on degradability, bioaccumulation and aquatic toxicity.^[5]

Aquatic toxicity

Aquatic toxicity testing submerges key indicator species of fish or crustacea to certain concentrations of a substance in their environment to determine the lethality level. Fish are exposed for 96 hours while crustacea are exposed for 48 hours. While GHS does not define toxicity past 100 mg/l, the EPA currently lists aquatic toxicity as “practically non-toxic” in concentrations greater than 100 ppm.^[6]

Note: A category 4 is established for chronic exposure, but simply contains any toxic substance which is mostly insoluble, or has no data for acute toxicity.

Factors influencing toxicity

Toxicity of a substance can be affected by many different factors, such as the pathway of administration (whether the toxin is applied to the skin, ingested, inhaled, injected), the time of exposure (a brief encounter or long term), the number of exposures (a single dose or multiple doses over time), the physical form of the toxin (solid, liquid, gas), the genetic makeup of an individual, an individual's overall health, and many others. Several of the terms used to describe these factors have been included here.

acute exposure

a single exposure to a toxic substance which may result in severe biological harm or death; acute exposures are usually characterized as lasting no longer than a day.

chronic exposure

continuous exposure to a toxin over an extended period of time, often measured in months or years; it can cause irreversible side effects.

Etymology

"Toxic" and similar words came from Greek Greek , an independent branch of the Indo-European family of languages, is the language of the Greeks. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. In its ancient form, it is the language of classical ancient Greek literature and the New Testament of τοξον = "bow (weapon) The technique of using a bow is called archery. Someone who makes bows is known as a bowyer, and one who makes arrows is a fletcher" via "poisoned arrow Arrow poisons are used to poison arrow heads or darts for the purposes of hunting. They have been used by hunter-gatherer peoples worldwide and are still in use in areas of South America, Africa and Asia", which came to be used for "poison 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 labeling, poisons are especially toxic substances; less toxic substances are labeled "" in scientific language, as the usual Classical Greek word ('ιον) for "poison" would transcribe as "io-", which is not distinctive enough. In some biological names In biology, binomial nomenclature is the formal system of naming species. The system is called binominal nomenclature , binary nomenclature (particularly in botanical circles), or the binomial classification system. The essence of it is that each species name is in (modern scientific) Latin and has two parts, so that it is popularly known as the &, "toxo-" still means "bow", as in Toxodon = "bow-toothed" from the shape.

See also

• Agency for Toxic Substances and Disease Registry (ATSDR)
• Biological activity
• Biological warfare
• California Proposition 65 (1986)
• Carcinogen
• Drunkenness
• Indicative limit value
• List of highly toxic gases
• Mutagen
• Nephrotoxicity
• Neurotoxicity
• Ototoxicity
• Paracelsus
• Physiologically-based pharmacokinetic modelling.
• Poison
• Reference dose
• Registry of Toxic Effects of Chemical Substances (RTECS) - toxicity database
• Soil contamination
• Teratogen
• Toxic tort
• Toxication
• Toxicophore
• Toxin
• Toxica, a disambiguation page

References

1. ^ United Nations Economic Commission for Europe Globally Harmonized System of Classification and Labelling of Chemicals
2. ^ EPA implementation of Global Harmonization
3. ^ Globally Harmonized System of Classification and Labelling of Chemicals – Part 2, Physical Hazards
4. ^ ^{a b} Globally Harmonized System of Classification and Labelling of Chemicals – Part 3, Health Hazards
5. ^ ^{a b} Globally Harmonized System of Classification and Labelling of Chemicals – Part 4, Environmental Hazards
6. ^ EPA: Ecological risk assessment

External links

• Agency for Toxic Substances and Disease Registry
• Chemical and Other Safety Information – Oxford University
• Whole Effluent, Aquatic Toxicity Testing FAQ

Categories: Toxicology

See Also:

What Links Here:

Recently Viewed Pages:

• Plant Pathology: Blogs
• Diphacinone: Blogs
• For Specific Crops: Blogs
• Ryanodine: Blogs
• Business and Economy: Blogs
• Calcium Phosphide: Blogs
• Soil Steam Sterilization: Blogs
• Pest Control: Encyclopedia
• Agriculture: Encyclopedia
• Pest Control: Answers

Most Popular Pages:

• Convulsant: Blogs
• For Specific Crops: Blogs
• Ancient Egypt: Blogs
• Diphacinone: Blogs
• Plant Pathology: Blogs
• Difethialone: Blogs
• Calcium Phosphide: Blogs
• Soil Steam Sterilization: Blogs
• Toxic: Web Search
• Business and Economy: Blogs

Related 'Toxic' Searches: