Dioxins and dioxin-like compounds
Dioxins and dioxin-like compounds are compounds that are toxic environmental persistent organic pollutants. They are by-products of various industrial processes - or, in case of dioxin-like PCBs and PBBs, part of intentionally produced mixtures, they include: Polychlorinated dibenzo-p-dioxins, or dioxins. PCDDs are derivatives of dibenzo-p-dioxin. There are 75 PCDD congeners, differing in the number and location of chlorine atoms, seven of them are toxic, the most dangerous being 2,3,7,8-Tetrachlorodibenzodioxin Polychlorinated dibenzofurans, or furans. PCDFs are derivatives of dibenzofuran. There are 135 isomers, ten have dioxin-like properties. Polychlorinated/polybrominated biphenyls, derived from biphenyl, of which twelve are "dioxin-like". Under certain conditions PCBs may form dibenzofurans/dioxins through partial oxidation. Dioxin may refer to 1,4-Dioxin proper, the basic chemical unit of the more complex dioxins; this simple compound has no PCDD-like toxicity. Dioxins have different toxicity depending on the position of the chlorine atoms.
Because dioxins refer to such a broad class of compounds that vary in toxicity, the concept of toxic equivalency factor has been developed to facilitate risk assessment and regulatory control. Toxic equivalence factors exist for seven congeners of ten furans and twelve PCBs; the reference congener is the most toxic dioxin 2,3,7,8-tetrachlorodibenzo-p-dioxin which per definition has a TEF of one. This compound is stable and tends to accumulate in the food chain having a half-life of 7 to 9 years in humans The main characteristics of dioxins are that they are insoluble in water but have a high affinity for lipids. In addition, they tend to associate with organic matter, such as ash and plant leaves. In reference to their importance as environmental toxicants the term dioxins is used exclusively to refer to the sum of compounds from the above groups which demonstrate the same specific toxic mode of action associated with TCDD; these include 12 PCBs. Incidents of contamination with PCBs are often reported as dioxin contamination incidents since it is this toxic characteristic, of most public and regulatory concern.
The toxic effects of dioxins are measured in fractional equivalencies of TCDD, the most toxic and best studied member of its class. The toxicity is mediated through the interaction with a specific intracellular protein, the aryl hydrocarbon receptor, a transcriptional enhancer, affecting a number of other regulatory proteins; this receptor is a transcription factor, involved in expression of many genes. TCDD binding to the AH receptor induces the cytochrome P450 1A class of enzymes which function to break down toxic compounds, e.g. carcinogenic polycyclic hydrocarbons such as benzopyrene. While the affinity of dioxins and related industrial toxicants to this receptor may not explain all their toxic effects including immunotoxicity, endocrine effects and tumor promotion, toxic responses appear to be dose-dependent within certain concentration ranges. A multiphasic dose-response relationship has been reported, leading to uncertainty and debate about the true role of dioxins in cancer rates; the endocrine disrupting activity of dioxins is thought to occur as a down-stream function of AH receptor activation, with thyroid status in particular being a sensitive marker of exposure.
It is important to note that TCDD, along with the other PCDDs, PCDFs and dioxin-like coplanar PCBs are not direct agonists or antagonists of hormones, are not active in assays which directly screen for these activities such as ER-CALUX and AR-CALUX. These compounds have not been shown to have any direct mutagenic or genotoxic activity, their main action in causing cancer is cancer promotion. A mixture of PCBs such as Aroclor may contain PCB compounds which are known estrogen agonists, but on the other hand are not classified as dioxin-like in terms of toxicity. Mutagenic effects have been established for some lower chlorinated chemicals such as 3-chlorodibenzofuran, neither persistent nor an AH receptor agonist; the symptoms reported to be associated with dioxin toxicity in animal studies are wide-ranging, both in the scope of the biological systems affected and in the range of dosage needed to bring these about. Acute effects of single high dose dioxin exposure include wasting syndrome, a delayed death of the animal in 1 to 6 weeks.
By far most toxicity studies have been performed using 2,3,7,8-tetrachlorodibenzo-p-dioxin. The LD50 of TCDD varies wildly between species and strains of the same species, with the most notable disparity being between the similar species of hamster and guinea pig; the oral LD50 for guinea pigs is as low as 0.5 to 2 μg/kg body weight, whereas the oral LD50 for hamsters can be as high as 1 to 5 mg/kg body weight. Between different mouse or rat strains there may be tenfold to thousandfold differences in acute toxicity. Many pathological findings are seen in the liver and other organs; some chronic and sub-chronic exposures can be harmful at much lower levels at particular developmental stages including foetal and pubescent stages. Well established developmental effects are cleft palate, disturbances in tooth development and sexual development as well as endocrine effects. Dioxins have been considered toxic and able to cause reproductive and developmental problems, damage the immune system, inte
In zoology, a folivore is a herbivore that specializes in eating leaves. Mature leaves contain a high proportion of hard-to-digest cellulose, less energy than other types of foods, toxic compounds. For this reason, folivorous animals tend to slow metabolisms. Many enlist the help of symbiotic bacteria to release the nutrients in their diet. Additionally, as has been observed in folivorous primates, they exhibit a strong preference towards immature leaves, which tend to be easier to masticate, tend to be higher in energy and protein, lower in fibre and poisons than more mature fibrous leaves. Herbivory has evolved several times among different groups of animals; the first vertebrates were piscivores insectivores and herbivores. Since a complex set of adaptations was necessary for feeding on fibrous plant materials and only a small proportion of extant tetrapods are obligate herbivores, it could be that early tetrapods made the transition to fledged herbivory by way of omnivory, it has been observed that folivory is rare among flying vertebrates.
Morton attributed this to the fact that leaves are heavy, slow to digest, contain little energy relative to other foods. The hoatzin is an example of a folivorous bird; some bats are folivorous. Arboreal mammalian folivores, such as sloths and some species of monkeys and lemurs, tend to be large and climb cautiously. Similarities in body shape and head- and tooth-structure between early hominoids and various families of arboreal folivores have been advanced as evidence that early hominoids were folivorous. Standard ecological theory predicts large group sizes for folivorous primates, as large groups offer better collective defense against predators and they face little competition for food among each other, it has been observed that these animals frequently live in small groups. Explanations offered for this apparent paradox include social factors such as increased incidence of infanticide in large groups. Folivorous primates are rare in the New World, the primary exception being howler monkeys.
One explanation, offered is that fruiting and leafing occur among New World plants. However a 2001 study found no evidence for simultaneous fruiting and leafing at most sites disproving this hypothesis. Examples of folivorous animals include: Mammals: okapis, sloths, possums and various species of monkey Birds: The hoatzin of the Amazon region and the kakapo of New Zealand Reptiles: iguanas Insects: various kinds of caterpillars, beetles, leaf miners and Orthoptera Others: many land gastropod species Consumer-resource systems Leaf miner, the folivorous strategy of many insects wordquests.info
Surface runoff is the flow of water that occurs when excess stormwater, meltwater, or other sources flows over the Earth's surface. This might occur because soil is saturated to full capacity, because rain arrives more than soil can absorb it, or because impervious areas send their runoff to surrounding soil that cannot absorb all of it. Surface runoff is a major component of the water cycle, it is the primary agent in soil erosion by water. Runoff that occurs on the ground surface before reaching a channel is called a nonpoint source. If a nonpoint source contains man-made contaminants, or natural forms of pollution the runoff is called nonpoint source pollution. A land area which produces runoff that drains to a common point is called a drainage basin; when runoff flows along the ground, it can pick up soil contaminants including petroleum, pesticides, or fertilizers that become discharge or nonpoint source pollution. In addition to causing water erosion and pollution, surface runoff in urban areas is a primary cause of urban flooding which can result in property damage and mold in basements, street flooding.
Surface runoff glaciers. Snow and glacier melt occur only in areas cold enough for these to form permanently. Snowmelt will peak in the spring and glacier melt in the summer, leading to pronounced flow maxima in rivers affected by them; the determining factor of the rate of melting of snow or glaciers is both air temperature and the duration of sunlight. In high mountain regions, streams rise on sunny days and fall on cloudy ones for this reason. In areas where there is no snow, runoff will come from rainfall. However, not all rainfall will produce runoff. On the ancient soils of Australia and Southern Africa, proteoid roots with their dense networks of root hairs can absorb so much rainwater as to prevent runoff when substantial amounts of rain fall. In these regions on less infertile cracking clay soils, high amounts of rainfall and potential evaporation are needed to generate any surface runoff, leading to specialised adaptations to variable streams; this occurs when the rate of rainfall on a surface exceeds the rate at which water can infiltrate the ground, any depression storage has been filled.
This is called flooding Hortonian overland flow, or unsaturated overland flow. This more occurs in arid and semi-arid regions, where rainfall intensities are high and the soil infiltration capacity is reduced because of surface sealing, or in paved areas; this occurs in city areas where pavements prevent water from flooding. When the soil is saturated and the depression storage filled, rain continues to fall, the rainfall will produce surface runoff; the level of antecedent soil moisture is one factor affecting the time. This runoff is called saturated overland flow or Dunne runoff. Soil retains a degree of moisture after a rainfall; this residual water moisture affects the soil's infiltration capacity. During the next rainfall event, the infiltration capacity will cause the soil to be saturated at a different rate; the higher the level of antecedent soil moisture, the more the soil becomes saturated. Once the soil is saturated, runoff occurs. After water infiltrates the soil on an up-slope portion of a hill, the water may flow laterally through the soil, exfiltrate closer to a channel.
This is called throughflow. As it flows, the amount of runoff may be reduced in a number of possible ways: a small portion of it may evapotranspire. Any remaining surface water flows into a receiving water body such as a river, estuary or ocean. Urbanization increases surface runoff by creating more impervious surfaces such as pavement and buildings that do not allow percolation of the water down through the soil to the aquifer, it is instead forced directly into streams or storm water runoff drains, where erosion and siltation can be major problems when flooding is not. Increased runoff reduces groundwater recharge, thus lowering the water table and making droughts worse for agricultural farmers and others who depend on the water wells; when anthropogenic contaminants are dissolved or suspended in runoff, the human impact is expanded to create water pollution. This pollutant load can reach various receiving waters such as streams, lakes and oceans with resultant water chemistry changes to these water systems and their related ecosystems.
A 2008 report by the United States National Research Council identified urban stormwater as a leading source of water quality problems in the U. S; as humans continue to alter the climate through the addition of greenhouse gases to the atmosphere, precipitation patterns are expected to change as the atmospheric capacity for water vapor increases. This will have direct consequences on runoff amounts. Surface runoff can cause erosion of the Earth's surface. There are four main types of soil erosion by water: splash erosion, sheet erosion, rill erosion and gully erosion. Splash erosion is the result of mechanical collision of raindrops with the soil surface: soil particles which are dislodged by the impact move with the surface runoff. Sheet erosion is the overland transport of sediment by runoff without a well d
Institute of Food and Agricultural Sciences
The Institute of Food and Agricultural Sciences is an agriculture, life science and invasive species research facility in Florida affiliated with University of Florida. It is a partnership between federal and county governments that includes an extension office in each of Florida's 67 counties, 13 research and education centers, several demonstration sites, the University of Florida College of Agricultural and Life Sciences, the Center for Tropical Agriculture, portions of the University of Florida College of Veterinary Medicine, the Florida Sea Grant program, the International Program for Food and Natural Resources. IFAS research and development covers natural resource industries that have a $101 billion annual impact; the program is ranked #1 in the nation by the NSF. Because of this mission and the diversity of Florida’s climate and agricultural commodities, IFAS has facilities located throughout Florida. Starting June 1, 2010 IFAS will be under the leadership of Dr. Jack Payne, named Senior Vice President for agriculture and natural resources for the University of Florida on February 26, 2010.
The UF/IFAS research mission is to invent and develop knowledge to enhance the agriculture and natural resources of Florida. Faculty members pursue fundamental and applied research that furthers understanding of natural and human systems. Research is supported by state and federally appropriated funds and supplemented by grants and contracts; the Institute of Food and Agricultural Sciences was awarded $166 million in annual research expenditures in sponsored research for 2018. The Florida Agricultural Experiment Station administers and supports research programs in UF/IFAS; the research program was created in 1887 by federal legislation known as the Hatch Act, a follow-up to the 1862 Morrill Act that established U. S. land-grant universities. The research programs support 350 full-time equivalent faculty members in 16 academic departments on UF’s Gainesville campus and at 13 research and education centers around the state. Most IFAS research can be accessed via the searchable UF/IFAS Electronic Data Information Source.
IFAS supports one of the nation's largest collections of food safety facilities and faculty in the country, is integral in maintaining the National Food Safety Database. Along with researchers specializing in controlling spread of pathogens such as E. coli and Salmonella, IFAS has uniquely specialized research programs dedicated to the science of food packaging and a Center for Food Distribution and Retailing. IFAS microbiologist Lonnie Ingram holds several patents on a unique way to produce cellulosic ethanol using a genetically engineered form of E. coli to break down biomass. A cellulosic ethanol power plant utilizing this method began construction in Louisiana in 2007. Florida is the state most indundated with invasive animal species. Nearly 85 percent of new plants entering the country travel through Miami; as such, much of the UF Department of Entomology and Nematology as well as a Center for Aquatic and Invasive Plants have been dedicated to fighting this problem. IFAS is part of the University of Florida's Emerging Pathogens Institute.
IFAS has been involved in dealing with emerging food safety issues such the recent surge of E. coli and Salmonella infections due to bacteria on fresh produce served at restaurants and grocery stores. Established in 1917 IFAS' Citrus Research and Education Center is the largest citrus research institution in existence with more than 40 laboratories, 250 employees, over 220 acres of groves and greenhouses. Dr. Gary Butcher is recognized as one of the foremost experts on poultry pathogens in the United States; the 1914 Smith-Lever Act provided federal support for land-grant institutions to offer educational programs to enhance the application of useful and practical information beyond their campuses through cooperative extension efforts with states and local communities. UF/IFAS Extension provides Floridians with lifelong learning programs in cooperation with county government, the United States Department of Agriculture, Florida A&M; the wide breadth of educational programming offered in each county responds to the local needs of residents, regulatory agencies, community organizations, industry.
Programs promote sustainable agriculture, teaching environmental stewardship, understanding of food nutrition and safety and parenting skills, providing leadership for youth development through programs like 4-H. By partnering with local government, advisory committees, concerned citizens, commodity groups and the youth of Florida, UF/IFAS Extension creates an important link between the public and research conducted on campus and at 13 research and education centers. Solutions for Your Life is the web site of University of Florida Extension, making IFAS faculty expertise available online under such categories as lawn and garden care, family life and consumer choices, community development, the environment, youth development; the web site is focused on providing relevant solutions. In addition to facilities on the University of Florida campus and Extension offices in each of Florida’s 67 counties, IFAS has 1,255 buildings, 3,190,448 square feet gross, 16,591 acres throughout the state; these facilities are used for teaching and demonstration: 16 on-campus academic departments 13 Research & Education Centers located throughout the state Florida Cooperative Extension Service offices in all 67 counties 6 Research sites/demonstration
The Green Revolution, or Second Agricultural Revolution, is a set of research technology transfer initiatives occurring between 1950 and the late 1960s, that increased agricultural production worldwide in the developing world, beginning most markedly in the late 1960s. The initiatives resulted in the adoption of new technologies, including high-yielding varieties of cereals dwarf wheats and rices, in association with chemical fertilizers and agro-chemicals, with controlled water-supply and new methods of cultivation, including mechanization. All of these together were seen as a'package of practices' to supersede'traditional' technology and to be adopted as a whole. Both the Ford Foundation and the Rockefeller Foundation were involved. One key leader was Norman Borlaug, the "Father of the Green Revolution", who received the Nobel Peace Prize in 1970, he is credited with saving over a billion people from starvation. The basic approach was the development of high-yielding varieties of cereal grains, expansion of irrigation infrastructure, modernization of management techniques, distribution of hybridized seeds, synthetic fertilizers, pesticides to farmers.
The term "Green Revolution" was first used in a speech on 8 March 1968 by the administrator of the U. S. Agency for International Development, William S. Gaud, who noted the spread of the new technologies: "These and other developments in the field of agriculture contain the makings of a new revolution, it is not a violent Red Revolution like that of the Soviets, nor is it a White Revolution like that of the Shah of Iran. I call it the Green Revolution." It has been argued that "during the twentieth century two'revolutions' transformed rural Mexico: the Mexican Revolution and the Green Revolution". With the support of the Mexican government, the U. S. government, the United Nations, the Food and Agriculture Organization, the Rockefeller Foundation, Mexico made a concerted effort to transform agricultural productivity with irrigated rather than dry-land cultivation in its northwest, to solve its problem of lack of food self-sufficiency. In the center and south of Mexico, where large-scale production faced challenges, agricultural production languished.
Increased production meant food self-sufficiency in Mexico to feed its growing and urbanizing population, with the number of calories consumed per Mexican increasing. Technology was seen as a valuable way to feed the poor, would relieve some pressure of the land redistribution process. Mexico was the recipient of Green Revolution knowledge and technology, it was an active participant with financial support from the government for agriculture as well as Mexican agronomists. Although the Mexican Revolution had broken the back of the hacienda system and land reform in Mexico had by 1940 distributed a large expanse of land in central and southern Mexico, agricultural productivity had fallen. During the administration of Manuel Avila Camacho, the government put resources into developing new breeds of plants and partnered with the Rockefeller Foundation. In 1943, the Mexican government founded the International Maize and Wheat Improvement Center, which became a base for international agricultural research.
Agriculture in Mexico had been a sociopolitical issue, a key factor in some regions' participation in the Mexican Revolution. It was a technical issue, enabled by a cohort of trained agronomists, who were to advise peasants how to increase productivity. In the post-World War II era, the government sought development in agriculture that bettered technological aspects of agriculture in regions that were not dominated by small-scale peasant cultivators; this drive for agricultural transformation would have the benefit of keeping Mexico self-sufficient in food and in the political sphere with the Cold War stem unrest and the appeal of Communism. Technical aid can be seen as serving political ends in the international sphere. In Mexico, it served political ends, separating peasant agriculture based on the ejido and considered one of the victories of the Mexican Revolution, from agribusiness that requires large-scale land ownership, specialized seeds and pesticides, a low-wage paid labor force; the government created the Mexican Agricultural Program to be the lead organization in raising productivity.
One of their successes was wheat production, with varieties the agency's scientists helped create dominating wheat production as early as 1951, 1965, 1968. Mexico became the showcase for extending the Green Revolution to other areas of Latin America and beyond, into Africa and Asia. New breeds of maize and wheat produced bumper crops with proper inputs and careful cultivation. Many Mexican farmers, dubious about the scientists or hostile to them came to see the scientific approach to agriculture as worth adopting. In 1960, the Government of the Republic of the Philippines with the Ford Foundation and the Rockefeller Foundation established the International Rice Research Institute. A rice crossing between Dee-Geo-woo-gen and Peta was done at IRRI in 1962. In 1966, one of the breeding lines became a new cultivar, IR8. IR8 required the use of fertilizers and pesticides, but produced higher yields than the traditional cultivars. Annual rice production in the Philippines increased from 3.7 to 7.7 million tons in two decades.
The switch to IR8 rice made the Philippines a rice exporter for the first time in the 20th century. In 1961, India was on the brink of mass famine. Norman Borlaug was invited to India by the adviser to t
A leaf is an organ of a vascular plant and is the principal lateral appendage of the stem. The leaves and stem together form the shoot. Leaves are collectively referred to as foliage, as in "autumn foliage". A leaf is a thin, dorsiventrally flattened organ borne above ground and specialized for photosynthesis. In most leaves, the primary photosynthetic tissue, the palisade mesophyll, is located on the upper side of the blade or lamina of the leaf but in some species, including the mature foliage of Eucalyptus, palisade mesophyll is present on both sides and the leaves are said to be isobilateral. Most leaves have distinct upper surface and lower surface that differ in colour, the number of stomata, the amount and structure of epicuticular wax and other features. Leaves can have many different shapes and textures; the broad, flat leaves with complex venation of flowering plants are known as megaphylls and the species that bear them, the majority, as broad-leaved or megaphyllous plants. In the clubmosses, with different evolutionary origins, the leaves are simple and are known as microphylls.
Some leaves, such as bulb scales, are not above ground. In many aquatic species the leaves are submerged in water. Succulent plants have thick juicy leaves, but some leaves are without major photosynthetic function and may be dead at maturity, as in some cataphylls and spines. Furthermore, several kinds of leaf-like structures found in vascular plants are not homologous with them. Examples include flattened plant stems called phylloclades and cladodes, flattened leaf stems called phyllodes which differ from leaves both in their structure and origin; some structures of non-vascular plants function much like leaves. Examples include the phyllids of liverworts. Leaves are the most important organs of most vascular plants. Green plants are autotrophic, meaning that they do not obtain food from other living things but instead create their own food by photosynthesis, they capture the energy in sunlight and use it to make simple sugars, such as glucose and sucrose, from carbon dioxide and water. The sugars are stored as starch, further processed by chemical synthesis into more complex organic molecules such as proteins or cellulose, the basic structural material in plant cell walls, or metabolised by cellular respiration to provide chemical energy to run cellular processes.
The leaves draw water from the ground in the transpiration stream through a vascular conducting system known as xylem and obtain carbon dioxide from the atmosphere by diffusion through openings called stomata in the outer covering layer of the leaf, while leaves are orientated to maximise their exposure to sunlight. Once sugar has been synthesized, it needs to be transported to areas of active growth such as the plant shoots and roots. Vascular plants transport sucrose in a special tissue called the phloem; the phloem and xylem are parallel to each other but the transport of materials is in opposite directions. Within the leaf these vascular systems branch to form veins which supply as much of the leaf as possible, ensuring that cells carrying out photosynthesis are close to the transportation system. Leaves are broad and thin, thereby maximising the surface area directly exposed to light and enabling the light to penetrate the tissues and reach the chloroplasts, thus promoting photosynthesis.
They are arranged on the plant so as to expose their surfaces to light as efficiently as possible without shading each other, but there are many exceptions and complications. For instance plants adapted to windy conditions may have pendent leaves, such as in many willows and eucalyptss; the flat, or laminar, shape maximises thermal contact with the surrounding air, promoting cooling. Functionally, in addition to carrying out photosynthesis, the leaf is the principal site of transpiration, providing the energy required to draw the transpiration stream up from the roots, guttation. Many gymnosperms have thin needle-like or scale-like leaves that can be advantageous in cold climates with frequent snow and frost; these are interpreted as reduced from megaphyllous leaves of their Devonian ancestors. Some leaf forms are adapted to modulate the amount of light they absorb to avoid or mitigate excessive heat, ultraviolet damage, or desiccation, or to sacrifice light-absorption efficiency in favour of protection from herbivory.
For xerophytes the major constraint drought. Some window plants such as Fenestraria species and some Haworthia species such as Haworthia tesselata and Haworthia truncata are examples of xerophytes. and Bulbine mesembryanthemoides. Leaves function to store chemical energy and water and may become specialised organs serving other functions, such as tendrils of peas and other legumes, the protective spines of cacti and the insect traps in carnivorous plants such as Nepenthes and Sarracenia. Leaves are the fundamental structural units from which cones are constructed in gymnosperms and from which flowers are constructed in flowering plants; the internal organisation of most kinds of leaves has evolved to maximise exposure of the photosynthetic organelles, the chloroplasts, to light and to increase the absorption of carbon dioxide while at the same time controlling water loss. Their surfaces are waterproofed by the plant cuticle and gas exchange between the mesophyll cells and the atmosphere is controlled by minute openings called stomata which open or close to regulate the rate exchange of carbon dioxide and water vapour into
International Standard Serial Number
An International Standard Serial Number is an eight-digit serial number used to uniquely identify a serial publication, such as a magazine. The ISSN is helpful in distinguishing between serials with the same title. ISSN are used in ordering, interlibrary loans, other practices in connection with serial literature; the ISSN system was first drafted as an International Organization for Standardization international standard in 1971 and published as ISO 3297 in 1975. ISO subcommittee TC 46/SC 9 is responsible for maintaining the standard; when a serial with the same content is published in more than one media type, a different ISSN is assigned to each media type. For example, many serials are published both in electronic media; the ISSN system refers to these types as electronic ISSN, respectively. Conversely, as defined in ISO 3297:2007, every serial in the ISSN system is assigned a linking ISSN the same as the ISSN assigned to the serial in its first published medium, which links together all ISSNs assigned to the serial in every medium.
The format of the ISSN is an eight digit code, divided by a hyphen into two four-digit numbers. As an integer number, it can be represented by the first seven digits; the last code digit, which may be 0-9 or an X, is a check digit. Formally, the general form of the ISSN code can be expressed as follows: NNNN-NNNC where N is in the set, a digit character, C is in; the ISSN of the journal Hearing Research, for example, is 0378-5955, where the final 5 is the check digit, C=5. To calculate the check digit, the following algorithm may be used: Calculate the sum of the first seven digits of the ISSN multiplied by its position in the number, counting from the right—that is, 8, 7, 6, 5, 4, 3, 2, respectively: 0 ⋅ 8 + 3 ⋅ 7 + 7 ⋅ 6 + 8 ⋅ 5 + 5 ⋅ 4 + 9 ⋅ 3 + 5 ⋅ 2 = 0 + 21 + 42 + 40 + 20 + 27 + 10 = 160 The modulus 11 of this sum is calculated. For calculations, an upper case X in the check digit position indicates a check digit of 10. To confirm the check digit, calculate the sum of all eight digits of the ISSN multiplied by its position in the number, counting from the right.
The modulus 11 of the sum must be 0. There is an online ISSN checker. ISSN codes are assigned by a network of ISSN National Centres located at national libraries and coordinated by the ISSN International Centre based in Paris; the International Centre is an intergovernmental organization created in 1974 through an agreement between UNESCO and the French government. The International Centre maintains a database of all ISSNs assigned worldwide, the ISDS Register otherwise known as the ISSN Register. At the end of 2016, the ISSN Register contained records for 1,943,572 items. ISSN and ISBN codes are similar in concept. An ISBN might be assigned for particular issues of a serial, in addition to the ISSN code for the serial as a whole. An ISSN, unlike the ISBN code, is an anonymous identifier associated with a serial title, containing no information as to the publisher or its location. For this reason a new ISSN is assigned to a serial each time it undergoes a major title change. Since the ISSN applies to an entire serial a new identifier, the Serial Item and Contribution Identifier, was built on top of it to allow references to specific volumes, articles, or other identifiable components.
Separate ISSNs are needed for serials in different media. Thus, the print and electronic media versions of a serial need separate ISSNs. A CD-ROM version and a web version of a serial require different ISSNs since two different media are involved. However, the same ISSN can be used for different file formats of the same online serial; this "media-oriented identification" of serials made sense in the 1970s. In the 1990s and onward, with personal computers, better screens, the Web, it makes sense to consider only content, independent of media; this "content-oriented identification" of serials was a repressed demand during a decade, but no ISSN update or initiative occurred. A natural extension for ISSN, the unique-identification of the articles in the serials, was the main demand application. An alternative serials' contents model arrived with the indecs Content Model and its application, the digital object identifier, as ISSN-independent initiative, consolidated in the 2000s. Only in 2007, ISSN-L was defined in the