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70-489: Because of their longevity, PCBs are still widely in use, even though their manufacture has declined drastically since the 1960s, when a host of problems were identified. With the discovery of PCBs' environmental toxicity , and classification as persistent organic pollutants , their production was banned for most uses by United States federal law on January 1, 1978. The International Agency for Research on Cancer (IARC) rendered PCBs as definite carcinogens in humans. According to

140-429: A trophic cascade can occur. PCBs can cause harm to human health or even death when eaten. PCBs can be transported by birds from aquatic sources onto land via feces and carcasses. PCBs undergo xenobiotic biotransformation, a mechanism used to make lipophilic toxins more polar and more easily excreted from the body. The biotransformation is dependent on the number of chlorine atoms present, along with their position on

210-529: 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

280-453: A bridge for plastic pollution to be transported from terrestrial environments into marine environments. It has been estimated that 88–95% of marine plastic is exported into the ocean by just 10 major rivers. An organism can accumulate PCBs by consuming other organisms that have previously ingested PCBs from terrestrial, freshwater, or marine environments. The concentration of PCBs within an organism will increase over their lifetime; this process

350-401: 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;

420-424: 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

490-414: 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

560-487: 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

630-722: 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

700-399: 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

770-487: 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

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840-532: A scale from 0 to 1. One of the most toxic compounds known, 2,3,7,8-tetrachlorodibenzo[p]dioxin , a PCDD , is assigned a TEF of 1. In June 2020, State Impact of Pennsylvania stated that "In 1979, the EPA banned the use of PCBs, but they still exist in some products produced before 1979. They persist in the environment because they bind to sediments and soils. High exposure to PCBs can cause birth defects, developmental delays, and liver changes." Toxicity Toxicity

910-589: A screening tool. Arene substitution patterns Arene substitution patterns are part of organic chemistry IUPAC nomenclature and pinpoint the position of substituents other than hydrogen in relation to each other on an aromatic hydrocarbon . The toluidines serve as an example for these three types of substitution. Electron donating groups, for example amino , hydroxyl , alkyl , and phenyl groups tend to be ortho / para -directors, and electron withdrawing groups such as nitro , nitrile , and ketone groups, tend to be meta -directors. Although

980-537: A semi-closed application. In contrast, the major open application of PCBs was in carbonless copy ("NCR") paper , which even presently results in paper contamination. Other open applications were lubricating and cutting oils, and as plasticizers in paints and cements, stabilizing additives in flexible PVC coatings of electrical cables and electronic components, pesticide extenders, reactive flame retardants and sealants for caulking , adhesives , wood floor finishes, such as Fabulon and other products of Halowax in

1050-455: A significant quantity of PCBs. As the pressure of ocean water increases with depth, PCBs become heavier than water and sink to the deepest ocean trenches where they are concentrated. A small volume of PCBs has been detected throughout the Earth's atmosphere. The atmosphere serves as the primary route for global transport of PCBs, particularly for those congeners with one to four chlorine atoms. In

1120-516: 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,

1190-415: A treatment of unwanted PCBs generally requires high heat or catalysis (see Methods of destruction below). PCBs readily penetrate skin , PVC (polyvinyl chloride), and latex (natural rubber). PCB-resistant materials include Viton , polyethylene , polyvinyl acetate (PVA), polytetrafluoroethylene (PTFE), butyl rubber , nitrile rubber , and Neoprene . PCBs are derived from biphenyl , which has

1260-400: 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

1330-584: 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,

1400-402: Is called bioaccumulation. PCB concentrations within an organism also change depending upon which trophic level they occupy. When an organism occupies a high trophic level, like orcas or humans , they will accumulate more PCBs than an organism that occupies a low trophic level, like phytoplankton . If enough organisms with a trophic level are killed due to the accumulation of toxins, like PCB,

1470-440: 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

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1540-543: 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

1610-445: 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

1680-625: Is performing more functions in the warmer months, it naturally has a faster metabolism and has less PCB accumulation. However, multiple cold-water periods mixed with toxic PCBs with coplanar chlorine molecules can be detrimental to perch health. Enantiomers of chiral compounds have similar chemical and physical properties, but can be metabolized by the body differently. This was looked at in bowhead whales ( Balaena mysticetus ) for two main reasons: they are large animals with slow metabolisms (meaning PCBs will accumulate in fatty tissue) and few studies have measured chiral PCBs in cetaceans. They found that

1750-423: 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

1820-472: 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

1890-527: Is the primary source of PCB contamination in the atmosphere. In the biosphere , PCBs can be degraded by the sun , bacteria or eukaryotes , but the speed of the reaction depends on both the number and the disposition of chlorine atoms in the molecule: less substituted, meta - or para -substituted PCBs undergo biodegradation faster than more substituted congeners. In bacteria, PCBs may be dechlorinated through reductive dechlorination , or oxidized by dioxygenase enzyme. In eukaryotes, PCBs may be oxidized by

1960-430: Is thought to be linked to PCB 77 metabolism, something that was not measured in this study. Temperature plays a key role in the ecology, physiology and metabolism of aquatic species. The rate of PCB metabolism was temperature dependent in yellow perch ( Perca flavescens ). In fall and winter, only 11 out of 72 introduced PCB congeners were excreted and had halflives of more than 1,000 days. During spring and summer when

2030-643: The U.S. Environmental Protection Agency (EPA), PCBs cause cancer in animals and are probable human carcinogens. Moreover, because of their use as a coolant in electric transformers, PCBs still persist in built environments. Some PCBs share a structural similarity and toxic mode of action with dioxins . Other toxic effects such as endocrine disruption (notably blocking of thyroid system functioning) and neurotoxicity are known. The bromine analogues of PCBs are polybrominated biphenyls (PBBs), which have analogous applications and environmental concerns. An estimated 1.2 million tons have been produced globally. Though

2100-419: The cytochrome P450 enzyme. Like many lipophilic toxins, PCBs undergo biomagnification and bioaccumulation primarily due to the fact that they are easily retained within organisms. Plastic pollution, specifically microplastics , are a major contributor of PCBs into the biosphere and especially into marine environments. PCBs concentrate in marine environments because freshwater systems, like rivers, act as

2170-431: The ortho isomer catechol , the meta isomer resorcinol , and the para isomer hydroquinone : There are three arene substitution isomers of benzenedicarboxylic acid (C 6 H 4 (COOH) 2 ) – the ortho isomer phthalic acid , the meta isomer isophthalic acid , and the para isomer terephthalic acid : These terms can also be used in six-membered heterocyclic aromatic systems such as pyridine , where

Polychlorinated biphenyl - Misplaced Pages Continue

2240-460: The racemic form of tartaric acid "paratartaric acid" (another obsolete term: racemic acid ) in 1830. The use of the prefixes ortho , meta and para to distinguish isomers of disubstituted aromatic rings starts with Wilhelm Körner in 1867, although he applied the ortho prefix to a 1,4-isomer and the meta prefix to a 1,2-isomer. It was the German chemist Karl Gräbe who, in 1869, first used

2310-411: 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

2380-546: 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

2450-510: The PCB metabolism in the liver of four sea turtle species (green, olive ridley , loggerhead and hawksbill), green and hawksbill sea turtles have noticeably higher hydroxylation rates of PCB 52 than olive ridley or loggerhead sea turtles. This is because the green and hawksbill sea turtles have higher P450 2-like protein expression. This protein adds three hydroxyl groups to PCB 52, making it more polar and water-soluble. P450 3-like protein expression that

2520-444: The U.S., de-dusting agents, waterproofing compounds, casting agents. It was also used as a plasticizer in paints and especially "coal tars" that were used widely to coat water tanks, bridges and other infrastructure pieces. Modern sources include pigments , which may be used in inks for paper or plastic products. PCBs are also still found in old equipment like capacitors, ballasts, X-ray machine, and other e-waste. PCBs have entered

2590-963: The US EPA enforced the federal ban as of 1978, PCBs continued to create health problems in later years through their continued presence in soil and sediment, and from products which were made before 1979. In 1988, Japanese scientists Tanabe et al. estimated 370,000 tons were in the environment globally, and 780,000 tons were present in products, landfills, and dumps or kept in storage. The compounds are pale-yellow viscous liquids . They are hydrophobic, with low water solubilities : 0.0027–0.42  ng /L for Aroclors brand , but they have high solubilities in most organic solvents , oils, and fats . They have low vapor pressures at room temperature. They have dielectric constants of 2.5–2.7, very high thermal conductivity , and high flash points (from 170 to 380 °C). The density varies from 1.182 to 1.566 g/cm. Other physical and chemical properties vary widely across

2660-444: The US, Aroclor 1260 and Aroclor 1254 were the main mixtures used before 1950; Aroclor 1242 was the main mixture used in the 1950s and 1960s until it was phased out in 1971 and replaced by Aroclor 1016. One estimate (2006) suggested that 1 million tonnes of PCBs had been produced. 40% of this material was thought to remain in use. Another estimate put the total global production of PCBs on

2730-506: The atmosphere, PCBs may be degraded by hydroxyl radicals , or directly by photolysis of carbon–chlorine bonds (even if this is a less important process). Atmospheric concentrations of PCBs tend to be lowest in rural areas, where they are typically in the picogram per cubic meter range, higher in suburban and urban areas, and highest in city centres, where they can reach 1  ng /m or more. In Milwaukee , an atmospheric concentration of 1.9 ng/m has been measured, and this source alone

2800-516: The average PCB concentrations in the blubber were approximately four times higher than the liver; however, this result is most likely age- and sex-dependent. As reproductively active females transferred PCBs and other poisonous substances to the fetus, the PCB concentrations in the blubber were significantly lower than males of the same body length (less than 13 meters). The toxicity of PCBs varies considerably among congeners . The coplanar PCBs, known as nonortho PCBs because they are not substituted at

2870-399: The average daily water temperature was above 20 °C, persistent PCBs had halflives of 67 days. The main excretion processes were fecal egestion, growth dilution and loss across respiratory surfaces. The excretion rate of PCBs matched with the perch's natural bioenergetics , where most of their consumption, respiration and growth rates occur during the late spring and summer. Since the perch

Polychlorinated biphenyl - Misplaced Pages Continue

2940-449: The class. As the degree of chlorination increases, melting point and lipophilicity increase, and vapour pressure and water solubility decrease. PCBs do not easily break down or degrade, which made them attractive for industries. PCB mixtures are resistant to acids, bases, oxidation, hydrolysis, and temperature change. They can generate extremely toxic dibenzodioxins and dibenzofurans through partial oxidation. Intentional degradation as

3010-665: 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

3080-431: The current meaning is perhaps not obvious. The ortho description was historically used to designate the original compound, and an isomer was often called the meta compound. For instance, the trivial names orthophosphoric acid and trimetaphosphoric acid have nothing to do with aromatics at all. Likewise, the description para was reserved for just closely related compounds. Thus Jöns Jakob Berzelius originally called

3150-411: The easternmost regions of Slovakia. Although deliberate production of PCBs is banned by international treaty, significant amounts of PCBs are still being "inadvertently" produced. Research suggests that 45,000 tons of 'by-product' PCBs are legally produced per year in the US as part of certain chemical and product formulations. Commercial production of PCBs was banned in the United States in 1979, with

3220-775: 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

3290-460: 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

3360-423: The environment through both use and disposal. The environmental fate of PCBs is complex and global in scale. Because of their low vapour pressure , PCBs accumulate primarily in the hydrosphere , despite their hydrophobicity , in the organic fraction of soil , and in organisms including the human body. The hydrosphere is the main reservoir. The immense volume of water in the oceans is still capable of dissolving

3430-419: 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

3500-572: 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

3570-461: The following names: Brazil Czech Republic and Slovakia France Germany Italy Japan Former USSR United Kingdom United States The only North American producer, Monsanto Company , marketed PCBs under the trade name Aroclor from 1930 to 1977. These were sold under trade names followed by a four-digit number. In general, the first two digits refer to the product series as designated by Monsanto (e.g. 1200 or 1100 series);

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3640-473: The formula C 12 H 10 , sometimes written (C 6 H 5 ) 2 . In PCBs, some of the hydrogen atoms in biphenyl are replaced by chlorine atoms. There are 209 different chemical compounds in which one to ten chlorine atoms can replace hydrogen atoms. PCBs are typically used as mixtures of compounds and are given the single identifying CAS number 1336-36-3 . About 130 different individual PCBs are found in commercial PCB products. Toxic effects vary depending on

3710-433: 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

3780-406: 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

3850-449: The most likely to leave the organism. However, some metabolites of PCBs containing ortho – meta protons have increased steric hindrance from the oxygen, causing increased stability and an increased chance of accumulation. Metabolism is also dependent on the species of organism; different organisms have slightly different P450 enzymes that metabolize certain PCBs better than others. Looking at

3920-411: The naming system is Aroclor 1016 which was produced by distilling 1242 to remove the highly chlorinated congeners to make a more biodegradable product. "1016" was given to this product during Monsanto's research stage for tracking purposes but the name stuck after it was commercialized. Different Aroclors were used at different times and for different applications. In electrical equipment manufacturing in

3990-516: The order of 1.5 million tonnes. The United States was the single largest producer with over 600,000 tonnes produced between 1930 and 1977. The European region follows with nearly 450,000 tonnes through 1984. It is unlikely that a full inventory of global PCB production will ever be accurately tallied, as there were factories in Poland, East Germany, and Austria that produced unknown amounts of PCBs. As of 2002, there were still 21,500 tons of PCBs stored in

4060-596: The passage of the Toxic Substances Control Act (TSCA). The utility of PCBs is based largely on their chemical stability, including low flammability and high dielectric constant. In an electric arc, PCBs generate incombustible gases. Use of PCBs is commonly divided into closed and open applications. Examples of closed applications include coolants and insulating fluids ( transformer oil ) for transformers and capacitors , such as those used in old fluorescent light ballasts, and hydraulic fluids considered

4130-544: 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

4200-591: The prefixes ortho -, meta -, para - to denote specific relative locations of the substituents on a disubstituted aromatic ring (namely naphthalene ). In 1870, the German chemist Viktor Meyer first applied Gräbe's nomenclature to benzene . The current nomenclature was introduced by the Chemical Society in 1879. Examples of the use of this nomenclature are given for isomers of cresol , C 6 H 4 (OH)(CH 3 ): There are three arene substitution isomers of dihydroxybenzene (C 6 H 4 (OH) 2 ) –

4270-420: The ring positions ortho to (next to) the other ring, (such as PCBs 77, 126 and 169), tend to have dioxin -like properties, and generally are among the most toxic congeners. Because PCBs are almost invariably found in complex mixtures, the concept of toxic equivalency factors ( TEFs ) has been developed to facilitate risk assessment and regulation, where more toxic PCB congeners are assigned higher TEF values on

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4340-467: The rings. Phase I reactions occur by adding an oxygen to either of the benzene rings by Cytochrome P450 . The type of P450 present also determines where the oxygen will be added; phenobarbital (PB)-induced P450s catalyze oxygenation to the meta-para positions of PCBs while 3-methylcholanthrene (3MC)-induced P450s add oxygens to the ortho – meta positions. PCBs containing ortho – meta and meta – para protons can be metabolized by either enzyme, making them

4410-409: The second two numbers indicate the percentage of chlorine by mass in the mixture. Thus, Aroclor 1260 is a 1200 series product and contains 60% chlorine by mass. It is a myth that the first two digits referred to the number of carbon atoms; the number of carbon atoms do not change in PCBs. The 1100 series was a crude PCB material which was distilled to create the 1200 series PCB product. The exception to

4480-406: 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),

4550-456: 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

4620-513: The specific PCB. In terms of their structure and toxicity, PCBs fall into two distinct categories, referred to as coplanar or non- ortho -substituted arene substitution patterns and noncoplanar or ortho -substituted congeners. Di- ortho -substituted, non-coplanar PCBs interfere with intracellular signal transduction dependent on calcium which may lead to neurotoxicity . ortho -PCBs can disrupt thyroid hormone transport by binding to transthyretin . Commercial PCB mixtures were marketed under

4690-629: The specifics vary depending on the compound, in simple disubstituted arenes, the three isomers tend to have rather similar boiling points. However, the para isomer usually has the highest melting point, and the lowest solubility in a given solvent, of the three isomers. Because electron donating groups are both ortho and para directors, separation of these isomers is a common problem in synthetic chemistry. Several methods exist in order to separate these isomers: The prefixes ortho , meta , and para are all derived from Greek, meaning correct , following , and beside , respectively. The relationship to

4760-427: Was estimated to account for 120 kg/year of PCBs entering Lake Michigan . In 2008, concentrations as high as 35  ng /m, 10 times higher than the EPA guideline limit of 3.4 ng/m, have been documented inside some houses in the U.S. Volatilization of PCBs in soil was thought to be the primary source of PCBs in the atmosphere, but research suggests ventilation of PCB-contaminated indoor air from buildings

4830-458: 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

4900-448: 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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