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85-481: Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism . Toxicity can refer to the effect on a whole organism, such as an animal , bacterium , or plant , as well as the effect on a substructure of the organism, such as a cell ( cytotoxicity ) or an organ such as the liver ( hepatotoxicity ). Sometimes the word is more or less synonymous with poisoning in everyday usage. A central concept of toxicology

170-452: A chemical reaction form a chemical compound . All compounds are substances, but not all substances are compounds. A chemical compound can be either atoms bonded together in molecules or crystals in which atoms, molecules or ions form a crystalline lattice . Compounds based primarily on carbon and hydrogen atoms are called organic compounds , and all others are called inorganic compounds . Compounds containing bonds between carbon and

255-678: A database and is popularly known as the Chemical substances index. Other computer-friendly systems that have been developed for substance information are: SMILES and the International Chemical Identifier or InChI. Often a pure substance needs to be isolated from a mixture , for example from a natural source (where a sample often contains numerous chemical substances) or after a chemical reaction (which often gives mixtures of chemical substances). Stoichiometry ( / ˌ s t ɔɪ k i ˈ ɒ m ɪ t r i / )

340-574: A mixture , referencing them in the chemical substances index allows CAS to offer specific guidance on standard naming of alloy compositions. Non-stoichiometric compounds are another special case from inorganic chemistry , which violate the requirement for constant composition. For these substances, it may be difficult to draw the line between a mixture and a compound, as in the case of palladium hydride . Broader definitions of chemicals or chemical substances can be found, for example: "the term 'chemical substance' means any organic or inorganic substance of

425-618: A "ligand". However, the center does not need to be a metal, as exemplified by boron trifluoride etherate BF 3 OEt 2 , where the highly Lewis acidic , but non-metallic boron center takes the role of the "metal". If the ligand bonds to the metal center with multiple atoms, the complex is called a chelate . In organic chemistry, there can be more than one chemical compound with the same composition and molecular weight. Generally, these are called isomers . Isomers usually have substantially different chemical properties, and often may be isolated without spontaneously interconverting. A common example

510-529: A 14-day period; or causes inflammation which lasts for 14 days in two test subjects. Mild skin irritation is minor damage (less severe than irritation) within 72 hours of application or for three consecutive days after application. Serious eye damage involves tissue damage or degradation of vision which does not fully reverse in 21 days. Eye irritation involves changes to the eye which do fully reverse within 21 days. An Environmental hazard can be defined as any condition, process, or state adversely affecting

595-401: A broad sense but are generally called pathogens rather than toxicants. The biological toxicity of pathogens can be difficult to measure because the threshold dose may be a single organism. Theoretically one virus , bacterium or worm can reproduce to cause a serious infection . If a host has an intact immune system , the inherent toxicity of the organism is balanced by the host's response;

680-416: A chemical reaction takes place and a new substance is formed, the compound iron(II) sulfide , with chemical formula FeS. The resulting compound has all the properties of a chemical substance and is not a mixture. Iron(II) sulfide has its own distinct properties such as melting point and solubility , and the two elements cannot be separated using normal mechanical processes; a magnet will be unable to recover

765-423: A deeply rooted history of not only being aware of toxicity, but also taking advantage of it as a tool. Archaeologists studying bone arrows from caves of Southern Africa have noted the likelihood that some aging 72,000 to 80,000 years old were dipped in specially prepared poisons to increase their lethality. Although scientific instrumentation limitations make it difficult to prove concretely, archaeologists hypothesize

850-442: A dose that without treatment will be lethal to 50% of the population within (respectively) 30 or 60 days. These measures are used more commonly within radiation health physics , for ionizing radiation , as survival beyond 60 days usually results in recovery. A comparable measurement is LCt 50 , which relates to lethal dosage from exposure, where C is concentration and t is time. It is often expressed in terms of mg-min/m . ICt 50

935-413: A given disorder (DiMascio, Soltys and Shader, 1970). These undesirable effects include anticholinergic effects, alpha-adrenergic blockade, and dopaminergic effects, among others. 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 toxic substance, a population-level measure of toxicity

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1020-492: A hatter" and the "Mad Hatter" of the book Alice in Wonderland derive from the known occupational toxicity of hatters who used a toxic chemical for controlling the shape of hats. Exposure to chemicals in the workplace environment may be required for evaluation by industrial hygiene professionals. Hazards in the arts have been an issue for artists for centuries, even though the toxicity of their tools, methods, and materials

1105-436: A metal are called organometallic compounds . Compounds in which components share electrons are known as covalent compounds. Compounds consisting of oppositely charged ions are known as ionic compounds, or salts . Coordination complexes are compounds where a dative bond keeps the substance together without a covalent or ionic bond. Coordination complexes are distinct substances with distinct properties different from

1190-761: A new method of non-toxic lithography . There are many environmental health mapping tools. TOXMAP is a Geographic Information System (GIS) from the Division of Specialized Information Services of the United States National Library of Medicine (NLM) that uses maps of the United States to help users visually explore data from the United States Environmental Protection Agency 's (EPA) Toxics Release Inventory and Superfund programs. TOXMAP

1275-399: 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. This approach is very approximate, but such protection factors are deliberately very conservative, and the method has been found to be useful in

1360-462: A particular molecular identity, including – (i) any combination of such substances occurring in whole or in part as a result of a chemical reaction or occurring in nature". In the field of geology , inorganic solid substances of uniform composition are known as minerals . When two or more minerals are combined to form mixtures (or aggregates ), they are defined as rocks . Many minerals, however, mutually dissolve into solid solutions , such that

1445-486: A physical toxicant if taken in extremely high doses because the concentration of vital ions decreases dramatically with too much water in the body. Asphyxiant gases can be considered physical toxicants because they act by displacing oxygen in the environment but they are inert, not chemically toxic gases. Radiation can have a toxic effect on organisms. Behavioral toxicity refers to the undesirable effects of essentially therapeutic levels of medication clinically indicated for

1530-524: A screening tool. Chemical substance Chemical substances can exist in several different physical states or phases (e.g. solids , liquids , gases , or plasma ) without changing their chemical composition. Substances transition between these phases of matter in response to changes in temperature or pressure . Some chemical substances can be combined or converted into new substances by means of chemical reactions . Chemicals that do not possess this ability are said to be inert . Pure water

1615-437: A separate chemical substance. However, the polymer may be defined by a known precursor or reaction(s) and the molar mass distribution . For example, polyethylene is a mixture of very long chains of -CH 2 - repeating units, and is generally sold in several molar mass distributions, LDPE , MDPE , HDPE and UHMWPE . The concept of a "chemical substance" became firmly established in the late eighteenth century after work by

1700-400: A simple mixture. Typically these have a metal, such as a copper ion, in the center and a nonmetals atom, such as the nitrogen in an ammonia molecule or oxygen in water in a water molecule, forms a dative bond to the metal center, e.g. tetraamminecopper(II) sulfate [Cu(NH 3 ) 4 ]SO 4 ·H 2 O. The metal is known as a "metal center" and the substance that coordinates to the center is called

1785-479: A single chemical substance ( allotropes ). For instance, oxygen exists as both diatomic oxygen (O 2 ) and ozone (O 3 ). The majority of elements are classified as metals . These are elements with a characteristic lustre such as iron , copper , and gold . Metals typically conduct electricity and heat well, and they are malleable and ductile . Around 14 to 21 elements, such as carbon , nitrogen , and oxygen , are classified as non-metals . Non-metals lack

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1870-430: A single manufacturing process. For example, charcoal is an extremely complex, partially polymeric mixture that can be defined by its manufacturing process. Therefore, although the exact chemical identity is unknown, identification can be made with a sufficient accuracy. The CAS index also includes mixtures. Polymers almost always appear as mixtures of molecules of multiple molar masses, each of which could be considered

1955-726: A single rock is a uniform substance despite being a mixture in stoichiometric terms. Feldspars are a common example: anorthoclase is an alkali aluminum silicate, where the alkali metal is interchangeably either sodium or potassium. In law, "chemical substances" may include both pure substances and mixtures with a defined composition or manufacturing process. For example, the EU regulation REACH defines "monoconstituent substances", "multiconstituent substances" and "substances of unknown or variable composition". The latter two consist of multiple chemical substances; however, their identity can be established either by direct chemical analysis or reference to

2040-450: A substance's acute toxicity . A lower LD 50 is indicative of higher toxicity. The term LD 50 is generally attributed to John William Trevan. The test was created by J. W. Trevan in 1927. The term semilethal dose is occasionally used in the same sense, in particular with translations of foreign language text, but can also refer to a sublethal dose. LD 50 is usually determined by tests on animals such as laboratory mice . In 2011,

2125-499: A technical specification instead of particular chemical substances. For example, gasoline is not a single chemical compound or even a particular mixture: different gasolines can have very different chemical compositions, as "gasoline" is primarily defined through source, properties and octane rating . Every chemical substance has one or more systematic names , usually named according to the IUPAC rules for naming . An alternative system

2210-516: A toxic substance 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,

2295-416: A very wide range. The botulinum toxin as the most toxic substance known has an LD 50 value of 1 ng/kg, while the most non-toxic substance water has an LD 50 value of more than 90 g/kg; a difference of about 1 in 100 billion, or 11 orders of magnitude. As with all measured values that differ by many orders of magnitude, a logarithmic view is advisable. Well-known examples are the indication of

2380-400: 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

2465-442: A yellow-grey mixture. No chemical process occurs, and the material can be identified as a mixture by the fact that the sulfur and the iron can be separated by a mechanical process, such as using a magnet to attract the iron away from the sulfur. In contrast, if iron and sulfur are heated together in a certain ratio (1 atom of iron for each atom of sulfur, or by weight, 56 grams (1 mol ) of iron to 32 grams (1 mol) of sulfur),

2550-436: Is glucose vs. fructose . The former is an aldehyde , the latter is a ketone . Their interconversion requires either enzymatic or acid-base catalysis . However, tautomers are an exception: the isomerization occurs spontaneously in ordinary conditions, such that a pure substance cannot be isolated into its tautomers, even if these can be identified spectroscopically or even isolated in special conditions. A common example

2635-704: Is glucose , which has open-chain and ring forms. One cannot manufacture pure open-chain glucose because glucose spontaneously cyclizes to the hemiacetal form. All matter consists of various elements and chemical compounds, but these are often intimately mixed together. Mixtures contain more than one chemical substance, and they do not have a fixed composition. Butter , soil and wood are common examples of mixtures. Sometimes, mixtures can be separated into their component substances by mechanical processes, such as chromatography , distillation , or evaporation . Grey iron metal and yellow sulfur are both chemical elements, and they can be mixed together in any ratio to form

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2720-592: Is a chemical substance made up of a particular kind of atom and hence cannot be broken down or transformed by a chemical reaction into a different element, though it can be transmuted into another element through a nuclear reaction . This is because all of the atoms in a sample of an element have the same number of protons , though they may be different isotopes , with differing numbers of neutrons . As of 2019, there are 118 known elements, about 80 of which are stable – that is, they do not change by radioactive decay into other elements. Some elements can occur as more than

2805-592: Is a resource funded by the US Federal Government. TOXMAP's chemical and environmental health information is taken from NLM's Toxicology Data Network (TOXNET) and PubMed , and from other authoritative sources. Aquatic toxicity testing subjects 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,

2890-402: Is an example of complete combustion . Stoichiometry measures these quantitative relationships, and is used to determine the amount of products and reactants that are produced or needed in a given reaction. Describing the quantitative relationships among substances as they participate in chemical reactions is known as reaction stoichiometry . In the example above, reaction stoichiometry measures

2975-417: Is an example of a chemical substance, with a constant composition of two hydrogen atoms bonded to a single oxygen atom (i.e. H 2 O). The atomic ratio of hydrogen to oxygen is always 2:1 in every molecule of water. Pure water will tend to boil near 100 °C (212 °F), an example of one of the characteristic properties that define it. Other notable chemical substances include diamond (a form of

3060-419: Is equivalent to 10 minutes of 10 mg/m (1 × 100 = 100, as does 10 × 10 = 100). Some chemicals, such as hydrogen cyanide , are rapidly detoxified by the human body, and do not follow Haber's law. In these cases, the lethal concentration may be given simply as LC 50 and qualified by a duration of exposure (e.g., 10 minutes). The material safety data sheets for toxic substances frequently use this form of

3145-440: 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

3230-543: Is more difficult to determine the toxicity of chemical mixtures than a pure chemical because each component displays its own toxicity, and components may interact to produce enhanced or diminished effects. Common mixtures include gasoline , cigarette smoke , and industrial waste . 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. The preclinical toxicity testing on various biological systems reveals

3315-497: Is more useful to compare such substances by therapeutic index , which is simply the ratio of LD 50 to ED 50 . The following examples are listed in reference to LD 50 values, in descending order, and accompanied by LC 50 values, {bracketed}, when appropriate. human, smoking human, inhalation human, oral 3.3 μg/kg 10–1000 μg/kg 0.0000033 0.00001–0.001 human, oral 5.7 μg/kg 0.0000057 2.3–31.5 μg/kg 0.0000023 The LD 50 values have

3400-448: Is often used which relates the probabilities of an outcome for a given individual in a population. One such measure is the LD 50 . 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 " are added to account for uncertainties in data and evaluation processes. For example, if a dose of

3485-423: Is that the effects of a toxicant are dose -dependent; even water can lead to water intoxication when taken in too high a dose, whereas for even a very toxic substance such as snake venom there is a dose below which there is no detectable toxic effect. Toxicity is species-specific, making cross-species analysis problematic. Newer paradigms and metrics are evolving to bypass animal testing , while maintaining

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3570-469: Is the dose that will cause incapacitation rather than death. These measures are commonly used to indicate the comparative efficacy of chemical warfare agents, and dosages are typically qualified by rates of breathing (e.g., resting = 10 L/min) for inhalation, or degree of clothing for skin penetration. The concept of Ct was first proposed by Fritz Haber and is sometimes referred to as Haber's law , which assumes that exposure to 1 minute of 100 mg/m

3655-411: Is the relationships among the weights of reactants and products before, during, and following chemical reactions . Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equals the total mass of the products, leading to the insight that the relations among quantities of reactants and products typically form a ratio of positive integers. This means that if

3740-497: Is used by the Chemical Abstracts Service (CAS). Many compounds are also known by their more common, simpler names, many of which predate the systematic name. For example, the long-known sugar glucose is now systematically named 6-(hydroxymethyl)oxane-2,3,4,5-tetrol. Natural products and pharmaceuticals are also given simpler names, for example the mild pain-killer Naproxen is the more common name for

3825-411: The median lethal dose , LD 50 (abbreviation for " lethal dose , 50%"), LC 50 (lethal concentration, 50%) or LCt 50 is a toxic unit that measures the lethal dose of a given substance . The value of LD 50 for a substance is the dose required to kill half the members of a tested population after a specified test duration. LD 50 figures are frequently used as a general indicator of

3910-459: The EPA currently lists aquatic toxicity as "practically non-toxic" in concentrations greater than 100 ppm. 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. Toxicity of a substance can be affected by many different factors, such as the pathway of administration (whether the toxicant is applied to

3995-558: The No Observed Adverse Effect Level (NOAEL) dose and is helpful for clinical studies. 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 has determined cut-off levels set by governments and scientists (for example, no-observed-adverse-effect levels , threshold limit values , and tolerable daily intake levels). Pesticides provide

4080-475: The U.S. Food and Drug Administration approved alternative methods to LD 50 for testing the cosmetic drug Botox without animal tests. The LD 50 is usually expressed as the mass of substance administered per unit mass of test subject, typically as milligrams of substance per kilogram of body mass, sometimes also stated as nanograms (suitable for botulinum ), micrograms , or grams (suitable for paracetamol ) per kilogram. Stating it this way allows

4165-532: The amounts of the separate reactants are known, then the amount of the product can be calculated. Conversely, if one reactant has a known quantity and the quantity of the products can be empirically determined, then the amount of the other reactants can also be calculated. This is illustrated in the image here, where the balanced equation is: Here, one molecule of methane reacts with two molecules of oxygen gas to yield one molecule of carbon dioxide and two molecules of water . This particular chemical equation

4250-501: The application, but higher tolerance of impurities is usually expected in the production of bulk chemicals. Thus, the user of the chemical in the US might choose between the bulk or "technical grade" with higher amounts of impurities or a much purer "pharmaceutical grade" (labeled "USP", United States Pharmacopeia ). "Chemicals" in the commercial and legal sense may also include mixtures of highly variable composition, as they are products made to

4335-752: The baseline substance is neatly 1 in the negative logarithmic toxin scale. Animal-rights and animal-welfare groups, such as Animal Rights International, have campaigned against LD 50 testing on animals. Several countries, including the UK , have taken steps to ban the oral LD 50 , and the Organisation for Economic Co-operation and Development (OECD) abolished the requirement for the oral test in 2001 (see Test Guideline 401, Trends in Pharmacological Sciences Vol 22, February 22, 2001). A number of procedures have been defined to derive

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4420-408: The chemical combination of the known chemical elements. As of Feb 2021, about "177 million organic and inorganic substances" (including 68 million defined-sequence biopolymers) are in the scientific literature and registered in public databases. The names of many of these compounds are often nontrivial and hence not very easy to remember or cite accurately. Also, it is difficult to keep track of them in

4505-451: The chemical compound (S)-6-methoxy-α-methyl-2-naphthaleneacetic acid. Chemists frequently refer to chemical compounds using chemical formulae or molecular structure of the compound. There has been a phenomenal growth in the number of chemical compounds being synthesized (or isolated), and then reported in the scientific literature by professional chemists around the world. An enormous number of chemical compounds are possible through

4590-460: The chemical industry, manufactured "chemicals" are chemical substances, which can be classified by production volume into bulk chemicals, fine chemicals and chemicals found in research only: The cause of the difference in production volume is the complexity of the molecular structure of the chemical. Bulk chemicals are usually much less complex. While fine chemicals may be more complex, many of them are simple enough to be sold as "building blocks" in

4675-402: The chemical substances of which fruits and vegetables, for example, are naturally composed even when growing wild are not called "chemicals" in general usage. In countries that require a list of ingredients in products, the "chemicals" listed are industrially produced "chemical substances". The word "chemical" is also often used to refer to addictive, narcotic, or mind-altering drugs. Within

4760-419: The chemist Joseph Proust on the composition of some pure chemical compounds such as basic copper carbonate . He deduced that, "All samples of a compound have the same composition; that is, all samples have the same proportions, by mass, of the elements present in the compound." This is now known as the law of constant composition . Later with the advancement of methods for chemical synthesis particularly in

4845-665: The concept of toxicity endpoints. In Ancient Greek medical literature, the adjective τoξικόν (meaning "toxic") was used to describe substances which had the ability of "causing death or serious debilitation or exhibiting symptoms of infection." The word draws its origins from the Greek noun τόξον toxon (meaning "arc"), in reference to the use of bows and poisoned arrows as weapons. English-speaking American culture has adopted several figurative usages for toxicity , often when describing harmful inter-personal relationships or character traits (e.g. " toxic masculinity "). Humans have

4930-505: The earthquake strength using the Richter scale , the pH value , as a measure for the acidic or basic character of an aqueous solution or of loudness in decibels . In this case, the negative decimal logarithm of the LD 50 values, which is standardized in kg per kg body weight, is considered −log 10 (LD 50 ) . The dimensionless value found can be entered in a toxin scale. Water as

5015-775: The effective toxicity is then a combination. In some cases, e.g. cholera toxin , the disease is chiefly caused by a nonliving substance secreted by the organism, rather than the organism itself. Such nonliving biological toxicants are generally called toxins if produced by a microorganism, plant, or fungus, and venoms if produced by an animal. Physical toxicants are substances that, due to their physical nature, interfere with biological processes. Examples include coal dust, asbestos fibres or finely divided silicon dioxide , all of which can ultimately be fatal if inhaled. Corrosive chemicals possess physical toxicity because they destroy tissues, but are not directly poisonous unless they interfere directly with biological activity. Water can act as

5100-531: The element carbon ), table salt (NaCl; an ionic compound ), and refined sugar (C 12 H 22 O 11 ; an organic compound ). In addition to the generic definition offered above, there are several niche fields where the term "chemical substance" may take alternate usages that are widely accepted, some of which are outlined in the sections below. Chemical Abstracts Service (CAS) lists several alloys of uncertain composition within their chemical substance index. While an alloy could be more closely defined as

5185-459: The entire body, lethality to specific organs, major/minor damage, or cause cancer. These are globally accepted definitions of what toxicity is. Anything falling outside of the definition cannot be classified as that type of toxicant. 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

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5270-417: The environment. These hazards can be physical or chemical, and present in air, water, and/or soil. These conditions can cause extensive harm to humans and other organisms within an ecosystem. The EPA maintains a list of priority pollutants for testing and regulation. Workers in various occupations may be at a greater level of risk for several types of toxicity, including neurotoxicity. The expression "Mad as

5355-578: The example of well-established toxicity class systems and toxicity labels . While currently many countries have different regulations regarding the types of tests, numbers of tests and cut-off levels, the implementation of the Globally Harmonized System has begun unifying these countries. Global classification looks at three areas: Physical Hazards (explosions and pyrotechnics), Health Hazards and environmental hazards . The types of toxicities where substances may cause lethality to

5440-471: The exposure time is important (see below). The choice of 50% lethality as a benchmark avoids the potential for ambiguity of making measurements in the extremes and reduces the amount of testing required. However, this also means that LD 50 is not the lethal dose for all subjects; some may be killed by much less, while others survive doses far higher than the LD 50 . Measures such as "LD 1 " and "LD 99 " (dosage required to kill 1% or 99%, respectively, of

5525-432: 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. Considering the limitations of the dose-response concept, a novel Abstract Drug Toxicity Index (DTI) has been proposed recently. DTI redefines drug toxicity, identifies hepatotoxic drugs, gives mechanistic insights, predicts clinical outcomes and has potential as

5610-398: The idea of stereoisomerism – that atoms have rigid three-dimensional structure and can thus form isomers that differ only in their three-dimensional arrangement – was another crucial step in understanding the concept of distinct chemical substances. For example, tartaric acid has three distinct isomers, a pair of diastereomers with one diastereomer forming two enantiomers . An element

5695-414: The iron, since there is no metallic iron present in the compound. While the term chemical substance is a precise technical term that is synonymous with chemical for chemists, the word chemical is used in general usage to refer to both (pure) chemical substances and mixtures (often called compounds ), and especially when produced or purified in a laboratory or an industrial process. In other words,

5780-425: The large number of chemical substances reported in chemistry literature need to be indexed. Isomerism caused much consternation to early researchers, since isomers have exactly the same composition, but differ in configuration (arrangement) of the atoms. For example, there was much speculation about the chemical identity of benzene , until the correct structure was described by Friedrich August Kekulé . Likewise,

5865-409: The literature. Several international organizations like IUPAC and CAS have initiated steps to make such tasks easier. CAS provides the abstracting services of the chemical literature, and provides a numerical identifier, known as CAS registry number to each chemical substance that has been reported in the chemical literature (such as chemistry journals and patents ). This information is compiled as

5950-411: The metallic properties described above, they also have a high electronegativity and a tendency to form negative ions . Certain elements such as silicon sometimes resemble metals and sometimes resemble non-metals, and are known as metalloids . A chemical compound is a chemical substance that is composed of a particular set of atoms or ions . Two or more elements combined into one substance through

6035-405: 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. Skin corrosion and irritation are determined through a skin patch test analysis, similar to an allergic inflammation patch test . This examines the severity of the damage done; when it

6120-399: The number of LD 50 s to some test animal. In biological warfare infective dosage is the number of infective doses per cubic metre of air times the number of minutes of exposure (e.g., ICt 50 is 100 medium doses - min/m ). As a measure of toxicity, LD 50 is somewhat unreliable and results may vary greatly between testing facilities due to factors such as the genetic characteristics of

6205-566: The physiological differences between mice, rats, and humans. Many venomous snakes are specialized predators on mice, and their venom may be adapted specifically to incapacitate mice; and mongooses may be exceptionally resistant. While most mammals have a very similar physiology, LD 50 results may or may not have equal bearing upon every mammal species, such as humans, etc. Note: Comparing substances (especially drugs) to each other by LD 50 can be misleading in many cases due (in part) to differences in effective dose (ED 50 ). Therefore, it

6290-541: The practice of making poison arrows was widespread in cultures as early as the paleolithic era. The San people of Southern Africa have managed to preserved this practice into the modern era, with the knowledge base to form complex mixtures from poisonous beetles and plant derived extracts, yielding an arrow-tip product with a shelf life beyond several months to a year. There are generally five types of toxicities: chemical, biological, physical, radioactive and behavioural. Disease-causing microorganisms and parasites are toxic in

6375-410: The realm of organic chemistry ; the discovery of many more chemical elements and new techniques in the realm of analytical chemistry used for isolation and purification of elements and compounds from chemicals that led to the establishment of modern chemistry , the concept was defined as is found in most chemistry textbooks. However, there are some controversies regarding this definition mainly because

6460-414: The relationship between the quantities of methane and oxygen that react to form carbon dioxide and water. Because of the well known relationship of moles to atomic weights , the ratios that are arrived at by stoichiometry can be used to determine quantities by weight in a reaction described by a balanced equation. This is called composition stoichiometry . Median lethal dose In toxicology ,

6545-423: The relative toxicity of different substances to be compared and normalizes for the variation in the size of the animals exposed (although toxicity does not always scale simply with body mass). For substances in the environment, such as poisonous vapors or substances in water that are toxic to fish, the concentration in the environment (per cubic metre or per litre) is used, giving a value of LC 50 . But in this case,

6630-489: The sample population, animal species tested, environmental factors and mode of administration. There can be wide variability between species as well; what is relatively safe for rats may very well be extremely toxic for humans ( cf. paracetamol toxicity ), and vice versa. For example, chocolate, comparatively harmless to humans, is known to be toxic to many animals . When used to test venom from venomous creatures, such as snakes , LD 50 results may be misleading due to

6715-406: 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 toxicant (solid, liquid, gas), the concentration of the substance, and in the case of gases, the partial pressure (at high ambient pressure, partial pressure will increase for a given concentration as a gas fraction),

6800-456: The species-, organ- and dose-specific toxic effects of an investigational product. The toxicity of substances can be observed by (a) studying the accidental exposures to a substance (b) in vitro studies using cells/ cell lines (c) in vivo exposure on experimental animals. Toxicity tests are mostly used to examine specific adverse events or specific endpoints such as cancer, cardiotoxicity, and skin/eye irritation. Toxicity testing also helps calculate

6885-454: The synthesis of more complex molecules targeted for single use, as named above. The production of a chemical includes not only its synthesis but also its purification to eliminate by-products and impurities involved in the synthesis. The last step in production should be the analysis of batch lots of chemicals in order to identify and quantify the percentages of impurities for the buyer of the chemicals. The required purity and analysis depends on

6970-471: The term even if the substance does follow Haber's law. For disease-causing organisms, there is also a measure known as the median infective dose and dosage. The median infective dose (ID 50 ) is the number of organisms received by a person or test animal qualified by the route of administration (e.g., 1,200 org/man per oral). Because of the difficulties in counting actual organisms in a dose, infective doses may be expressed in terms of biological assay, such as

7055-432: The test population) are occasionally used for specific purposes. Lethal dosage often varies depending on the method of administration ; for instance, many substances are less toxic when administered orally than when intravenously administered. For this reason, LD 50 figures are often qualified with the mode of administration, e.g., "LD 50 i.v." The related quantities LD 50 /30 or LD 50 /60 are used to refer to

7140-458: Was not always adequately realized. Lead and cadmium, among other toxic elements, were often incorporated into the names of artist's oil paints and pigments, for example, "lead white" and "cadmium red". 20th-century printmakers and other artists began to be aware of the toxic substances, toxic techniques, and toxic fumes in glues, painting mediums, pigments, and solvents, many of which in their labelling gave no indication of their toxicity. An example

7225-448: Was the use of xylol for cleaning silk screens . Painters began to notice the dangers of breathing painting mediums and thinners such as turpentine . Aware of toxicants in studios and workshops, in 1998 printmaker Keith Howard published Non-Toxic Intaglio Printmaking which detailed twelve innovative Intaglio -type printmaking techniques including photo etching , digital imaging , acrylic -resist hand-etching methods, and introducing

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