Citizendia

Labelling transformers containing PCBs.
Labelling transformers containing PCBs.

Polychlorinated biphenyls (PCBs) are a class of organic compounds with 1 to 10 chlorine atoms attached to biphenyl which is a molecule composed of two benzene rings each containing six carbon atoms. An organic compound is any member of a large class of Chemical compounds whose Molecules contain Carbon. Chlorine (ˈklɔriːn from the Greek word 'χλωρóς' ( khlôros, meaning 'pale green' is the Chemical element with Atomic number 17 and Biphenyl (or diphenyl or phenyl benzene or 11'-biphenyl or lemonene) is a solid Organic compound that forms colorless to yellowish crystals Benzene, or benzol, is an organic Chemical compound and a known Carcinogen with the molecular formula C 6 H 6 The chemical formula for all PCBs is C12H10-xClx. A chemical formula is a way of expressing information about the Atoms that constitute a particular Chemical compound, and how the relationship between those atoms changes Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Chlorine (ˈklɔriːn from the Greek word 'χλωρóς' ( khlôros, meaning 'pale green' is the Chemical element with Atomic number 17 and

PCBs were used as coolants and insulating fluids for transformers and capacitors, stabilizing additives in flexible PVC coatings of electrical wiring and electronic components, pesticide extenders, cutting oils, flame retardants, hydraulic fluids, sealants (used in caulking, etc), adhesives, wood floor finishes,[1] paints, de-dusting agents, and in carbonless copy paper. A coolant is a fluid which flows through a device in order to prevent its overheating transferring the heat produced by the device to other devices that utilize or dissipate it A pesticide is a substance or mixture of substances used to kill a pest. Cutting fluids are various fluids that are used in Machining to cool and lubricate the cutting tool Flame retardants are materials that inhibit or resist the spread of Fire. Hydraulic fluids are a large group of fluids used as the motive medium in Hydraulic machinery. A sealant is a viscous material that changes state to become solid once applied and is used to prevent the penetration of Air, Gas, Noise, Dust Caulking is a process used to seal the seams in Wooden Boats or ships and riveted iron or steel ships in order to make them watertight Glue or adhesive is a compound that adheres or bonds two items together Paint is any Liquid, liquifiable or mastic composition which after application to a substrate in a thin layer is converted to an opaque Solid Carbonless copy paper, non-carbon copy paper, or NCR paper is an alternative to Carbon paper, used to make a copy of an original handwritten document without [2]

PCB production was banned in the 1970s due to the high toxicity of most PCB congeners and mixtures. Toxicity is the degree to which a substance is able to damage an exposed organism PCBs are classified as persistent organic pollutants which bioaccumulate in animals. Persistent organic pollutants ( POP s are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at ftudruinsubstance is lost

Chemical structure of PCBs. The possible positions of chlorine atoms on the benzene rings are denoted by numbers assigned to the carbon atoms.
Chemical structure of PCBs. The possible positions of chlorine atoms on the benzene rings are denoted by numbers assigned to the carbon atoms. Chlorine (ˈklɔriːn from the Greek word 'χλωρóς' ( khlôros, meaning 'pale green' is the Chemical element with Atomic number 17 and Benzene, or benzol, is an organic Chemical compound and a known Carcinogen with the molecular formula C 6 H 6 Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6

Contents

Physical and chemical properties

PCB congeners are odorless, tasteless, clear to pale-yellow, viscous liquids. Taste (or more formally gustation) is a form of direct Chemoreception and is one of the traditional five Senses Viscosity is a measure of the resistance of a Fluid which is being deformed by either Shear stress or Extensional stress. Liquid is one of the principal States of matter. A liquid is a Fluid that has the particles loose and can freely form a distinct surface at the boundaries of They are formed by electrophilic chlorination of biphenyl with chlorine gas. In Organic chemistry, an electrophilic aromatic halogenation is a type of Electrophilic aromatic substitution. Biphenyl (or diphenyl or phenyl benzene or 11'-biphenyl or lemonene) is a solid Organic compound that forms colorless to yellowish crystals Chlorine (ˈklɔriːn from the Greek word 'χλωρóς' ( khlôros, meaning 'pale green' is the Chemical element with Atomic number 17 and There are theoretically 209 different PCB congeners, although only about 130 of these were found in commercial PCB mixtures. [3] Commercial PCBs preparations are usually mixtures of 50 or more PCB congeners. [3] Commercial PCB mixtures are clear to pale-yellow, viscous liquids (the more highly chlorinated mixtures are more viscous and more yellow - for example , Aroclor 1260 is a sticky yellowish resin). Resin, not to be confused with Rosin, is a Hydrocarbon Secretion of many Plants particularly coniferous trees. PCBs have low water solubilities — 0. Water ( H2[[oxygen O]] H OH) is the most abundant Molecule on Earth 's surface composing of about 70% of the Earth's surface as Solubility is the characteristic Physical property referring to the ability of a given substance the Solute, to dissolve in a Solvent. 0027-0. 42 ng/L for Aroclors,[2] and low vapor pressures at room temperature, but they have high solubilities in most organic solvents, oils, and fats. The litre or liter (see spelling differences) is a unit of Volume. Vapor pressure (also known as equilibrium vapor pressure or saturation vapor pressure) is the Pressure of a Vapor in equilibrium A solvent is a liquid or gas that dissolves a solid liquid or gaseous Solute, resulting in a Solution. Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water They have high dielectric constants, very high thermal conductivity,[2] high flash points (170-380°C)[2] and are chemically almost inert, being extremely resistant to oxidation, reduction, addition, elimination, and electrophilic substitution. Measurement The relative static permittivity εr can be measured for static Electric fields as follows first the Capacitance of a test In Physics, thermal conductivity, k is the property of a material that indicates its ability to conduct Heat. The flash point of a flammable liquid is the lowest Temperature at which it can form an ignitable mixture in air Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state An addition reaction, in Chemistry, is in its simplest terms an Organic reaction where two or more molecules combine to form a larger one An elimination reaction is a type of Organic reaction in which two Substituents are removed from a molecule in either a one or two-step mechanism. Electrophilic substitution reactions are chemical reactions in which an Electrophile displaces another group typically but not always Hydrogen. [4] The density varies from 1. 182 to 1. 566 kg/L. The litre or liter (see spelling differences) is a unit of Volume. [2] Other physical and chemical properties vary widely across the class. As the degree of chlorination increases, melting point and lipophilicity increase, but vapour pressure and water solubility decrease. Lipophilicity, fat-liking, refers to the ability of a Chemical compound to dissolve in fats oils lipids and non-polar solvents such as Hexane or [2]

PCBs readily penetrate skin, PVC (polyvinyl chloride), and latex (natural rubber); organic solvents such as kerosene increase the rate of skin absorption. Absorption is a route by which substances can exit the body through the Skin. LaTeX (ˈleɪtɛ [5] PCB-resistant materials include Viton, polyethylene, polyvinyl acetate (PVA), polytetrafluoroethylene (PTFE), butyl rubber, nitrile rubber, and Neoprene. Viton is a brand of Synthetic rubber and Fluoropolymer Elastomer commonly used in O-rings and other moulded or extruded Polyethylene or polythene ( IUPAC name poly(ethene) is a Thermoplastic commodity heavily used in consumer products (notably the Polyvinyl acetate ( PVA or PVAc) is a Rubbery Synthetic polymer. In Chemistry, poly(tetrafluoroethene or poly(tetrafluoroethylene ( PTFE) is a synthetic Fluoropolymer which finds numerous applications Butyl rubber &mdashalso known as polyisobutylene and PIB (C4H8n is a Synthetic rubber, a Homopolymer of Nitrile rubber or Buna-N, is a Synthetic rubber Copolymer of Acrylonitrile (ACN and Butadiene. Neoprene or polychloroprene is a family of synthetic Rubbers that are produced by Polymerization of Chloroprene. [5]

PCBs are very stable compounds and do not degrade readily. Chemical decomposition or analysis is the separation of a Chemical compound into elements or smaller compounds They may be destroyed by chemical, thermal, and biochemical processes, though it is extremely difficult to achieve full destruction, and there is the risk of creating extremely toxic dibenzodioxins and dibenzofurans through partial oxidation. Not to be confused with Dioxane or Digoxin. Dioxin is a heterocyclic, organic, antiaromatic compound Dibenzofuran is a Heterocyclic Organic compound with the Chemical structure shown at right Because of the high thermodynamic stability of PCBs, all degradation mechanisms are difficult to sustain. Intentional degradation as a treatment of unwanted PCBs generally requires high heat or catalysis. Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst Environmental and metabolic degradation generally proceeds quite slowly relative to most other compounds.

Alternative names

Commercial PCB mixtures were marketed as Apirolio in Italy, Aroclor by Monsanto in USA and UK, Asbestol in USA, Askarel in USA and UK, Bakola131 in USA, Chlorextol in USA, Clophen by Bayer in Germany, Delor in Czechoslovakia, Fenclor in Italy, Hydol in USA, Inerteen by Westinghouse in the USA, Kanechlor by Kanegafuchi in Japan, Noflamol in USA, Phenoclor and Pyralene by Prodolec in France, Pyranol and Pyrenol by General Electric in USA, Pyroclor in UK, Saft-Kuhl in USA, Santotherm by Mitsubishi in Japan, Sovol and Sovtol in the former USSR, and Therminol in USA. The Monsanto Company ( is a multinational Agricultural biotechnology Corporation. For other uses see Bayer (disambiguation or Beyer or Buyer. Bayer AG (German ˈbaɪə () is a German The, Mitsubishi Group of Companies, or Mitsubishi Companies is a Japanese conglomerate consisting of a range of autonomous businesses which share the Mitsubishi [2][6]

Applications

PCBs were used as coolants and insulating fluids for transformers and capacitors, plasticizers in paints and cements, stabilizing additives in flexible PVC coatings of electrical wiring and electronic components, pesticide extenders, cutting oils, reactive flame retardants, lubricating oils, hydraulic fluids, sealants (for caulking in schools and commercial buildings[1]), adhesives, wood floor finishes (such as Fabulon and other products of Halowax in the U.S.),[1] paints, de-dusting agents, water-proofing compounds, casting agents, vacuum pump fluids, fixatives in microscopy, surgical implants, and in carbonless copy ("NCR") paper. A coolant is a fluid which flows through a device in order to prevent its overheating transferring the heat produced by the device to other devices that utilize or dissipate it A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors A capacitor is a passive electrical component that can store Energy in the Electric field between a pair of conductors Plasticizers are additives that increase the Plasticity or Fluidity of the material to which they are added these include plastics cement concrete wallboard and A pesticide is a substance or mixture of substances used to kill a pest. Cutting fluids are various fluids that are used in Machining to cool and lubricate the cutting tool Flame retardants are materials that inhibit or resist the spread of Fire. A lubricant (sometimes referred to as a "Lube" is a substance (often a liquid introduced between two moving surfaces to reduce the Friction between them improving Hydraulic fluids are a large group of fluids used as the motive medium in Hydraulic machinery. A sealant is a viscous material that changes state to become solid once applied and is used to prevent the penetration of Air, Gas, Noise, Dust Caulking is a process used to seal the seams in Wooden Boats or ships and riveted iron or steel ships in order to make them watertight Glue or adhesive is a compound that adheres or bonds two items together Halowax is a New York-based company that was later owned by Union Carbide. The United States of America —commonly referred to as the Paint is any Liquid, liquifiable or mastic composition which after application to a substrate in a thin layer is converted to an opaque Solid A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial Vacuum. Carbonless copy paper, non-carbon copy paper, or NCR paper is an alternative to Carbon paper, used to make a copy of an original handwritten document without [2]

History

PCBs, originally termed "chlorinated diphenyls," were commercially produced as complex mixtures containing multiple isomers at different degrees of chlorination. This article is about the chemical concept For "isomerism" of atomic nuclei see Nuclear isomer. In the United States, commercial production of PCBs was taken over in 1929 by Monsanto from Swann Chemical Company. Manufacturing levels increased in response to the electrical industry's need for a "safer" cooling and insulating fluid for industrial transformers and capacitors. PCBs were also commonly used as stabilizing additives in the manufacture of flexible PVC coatings for electrical wiring and electronic components to enhance the heat and fire resistance of the PVC. [7]

The toxicity associated with PCBs and other chlorinated hydrocarbons, including polychlorinated naphthalenes was recognized very early due to a variety of industrial incidents [8]. Polychlorinated naphthalene (PCN products are made by chemically reacting Chlorine with Naphthalene, a soft pungent solid made from coal or petroleum and often A conference about the hazards was organized at Harvard School of Public Health in 1937, and a number of publications referring to the toxicity of various chlorinated hydrocarbons were published before 1940 [9]. The Harvard School of Public Health is ( Colloquially HSPH) is one of the professional Graduate schools of Harvard University. Robert Brown reminded chemists in 1947 that Arochlors were "objectionably toxic. Thus the maximum permissible concentration for an 8-hr. day is 1 mg. per cu. m. of air. They also produce a serious and disfiguring dermatitis. "[10] However, PCB manufacture and use continued with few restraints until the 1970s.

PCBs are persistent organic pollutants and have entered the environment through both use and disposal. Persistent organic pollutants ( POP s are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic The environmental transport of PCBs is complex and nearly global in scale. The public, legal, and scientific concerns about PCBs arose from research indicating they were likely carcinogens having the potential to adversely impact the environment and therefore undesirable as commercial products. The term carcinogen refers to any substance Radionuclide or radiation that is an agent directly involved in the promotion of Cancer or in the fatation of its propagation Despite active research spanning five decades, extensive regulatory actions, and an effective ban on their production since the 1970s, PCBs still persist in the environment and remain a focus of attention. [2]

The only North American producer, Monsanto, marketed PCBs under the trade name Aroclor from 1930 to 1977. The Monsanto Company ( is a multinational Agricultural biotechnology Corporation. These were sold under trade names followed by a 4 digit number. The first two digits generally refer to the number of carbon atoms in the biphenyl skeleton (for PCBs this is 12), the second two numbers indicate the percentage of chlorine by mass in the mixture. Thus, Aroclor 1260 has 12 carbon atoms and contains 60% chlorine by mass. An exception is Aroclor 1016, which also has 12 carbon atoms, but has 42% chlorine by mass. Different Aroclors were used at different times and for different applications. In electrical equipment manufacturing in the USA, 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. [2]

Manufacture peaked in the 1960s, by which time the electrical industry had lobbied the U. S. Congress to make them mandatory safety equipment, knowing all the while that they were extremely toxic. In 1966, they were determined by Swedish chemist Dr. Soren Jensen to be an environmental contaminant[11], and it was Dr. Jensen, according to a 1994 article in Sierra, who named them. Previously, they had simply been called "phenols" or referred to by various trade names, such as Aroclor, Kennechlor, Pyrenol, Chlorinol and others. However, Arochlors (chlorinated biphenyls) were known toxins by 1947. Their commercial utility was based largely on their chemical stability, including low flammability, and desirable physical properties, including electrical insulating properties. Fire is the heat and light energy released during a Chemical reaction, in particular a combustion reaction. Their chemical and physical stability has also been responsible for their continuing persistence in the environment, and the lingering interest decades after regulations were imposed to control environmental contamination.

In 1972, PCB production plants existed in Austria, then Federal Republic of Germany, France, Great Britain, Italy, Japan, Spain, USSR, and USA. [2]

From 1973 the use of PCBs was banned in "open" or "dissipative" sources, such as:

However, they continued to be allowed in "totally enclosed uses" such as transformers and capacitors, which, in certain failure modes or out-of-specification conditions, can leak, catch fire, or explode. In Physics, dissipation embodies the concept of a Dynamical system where important mechanical modes such as Waves or Oscillations lose Energy Plasticizers are additives that increase the Plasticity or Fluidity of the material to which they are added these include plastics cement concrete wallboard and A fire retardant is a substance that helps to delay or prevent Combustion. In Chemistry a stabilizer is a chemical which tends to inhibit the reaction between two or more other chemicals Glue or adhesive is a compound that adheres or bonds two items together A railroad tie, cross tie, or railway sleeper is a rectangular object used as a base for Railroad tracks. It was Ward B. Stone of the New York State Department of Environmental Conservation who first published his findings in the early 1970s that PCBs were leaking from transformers and had contaminated the soil at the bottom of utility poles. Concern over the toxicity and persistence (chemical stability) of PCBs in the environment led the United States Congress to ban their domestic production in 1977, although some use continues in closed systems such as capacitors and transformers.

"Enclosed uses" of PCBs include:

In the UK, closed uses of PCBs in new equipment were banned from 1981, when nearly all UK PCB synthesis ceased, but closed uses in existing equipment containing in excess of 5 litres of PCBs were not stopped until December 2000. A capacitor is a passive electrical component that can store Energy in the Electric field between a pair of conductors A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial Vacuum. Hydraulic fluids are a large group of fluids used as the motive medium in Hydraulic machinery. The litre or liter (see spelling differences) is a unit of Volume. [12]

In Japan, PCBs were first produced by Kanegafuchi Chemical Co. Ltd. (Kaneka) in 1954 and production continued until 1972 when the Japanese government banned the production, use, and import of PCBs. [2]

Estimates have put the total global production of PCBs on the order of 1. 5 million tons. The United States was the single largest producer with over 600,000 tons produced between 1930 and 1977. The European region follows with nearly 450,000 tons 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. [13]

Large-scale environmental contamination incidents

New York State

In the United States of America, the General Electric Company (GE) released up to 1,300,000 pounds (590,000 kg) of PCBs into the Hudson River between approximately 1947 and 1977. The United States of America —commonly referred to as the The Hudson River, called Muh-he-kun-ne-tuk, the Great Mohegan by the Iroquois, or as the Lenape Native Americans called it in Unami [14] The PCBs came from the company's two capacitor manufacturing plants at Hudson Falls and Fort Edward in New York State. A capacitor is a passive electrical component that can store Energy in the Electric field between a pair of conductors Hudson Falls is a Village located in Washington County New York. Fort Edward is a Town in Washington County New York, United States. New York ( is a state in the Mid-Atlantic and Northeastern regions of the United States and is the nation's third most populous [14]

In 1976, because of concern over continuing high levels of PCBs in local fish and other aquatic organisms, and the unacceptable risk to the health of consumers of such fish, the New York State Department of Environmental Conservation banned all fishing in the Upper Hudson River, as well as commercial fishing of striped bass and several other species in the Lower Hudson River,[15][14] and also issued advisories restricting the consumption of fish caught within a 20-mile (30 km) long segment of the Hudson River from Hudson Falls to Troy. The New York State Department of Environmental Conservation ( NYSDEC or DEC) is responsible for the conservation improvement and protection of Natural resources The striped bass ( Morone saxatilis, also called rock or rockfish is the state fish of Maryland, Rhode Island, South Carolina, and Troy is a City in New York, US, and the County seat of Rensselaer County. [14][16]

There have been many programs of remediation work to reduce the PCB pollution, mostly paid for by GE. In 1984, approximately 200 miles (320 km) of the Hudson River was designated a Superfund site, and attempts to cleanup the Upper Hudson River began, including the removal in 1977-8 of 180,000 cubic yards (140,000 m³) of contaminated river sediments near Fort Edward. Superfund is the common name for the United States environmental policy officially known as the Comprehensive Environmental Response Compensation and Liability Act [15] In 1991, further PCB pollution was found at Bakers Falls near the former GE Hudson Falls factory, and a program of remediation was started. [15] In August 1995, a 40-mile (64 km) reach of the Upper Hudson was re-opened to fishing but only on a catch-and-release basis. [15] Removal of contaminated soil from Rogers Island was completed in December 1999. Rogers Island is an island on the Hudson River, in Washington County, New York, that once formed part of the third largest City in colonial North [15] In 2002, the United States Environmental Protection Agency announced a further 2,650,000 cubic yards (2,030,000 m³) of contaminated sediments in the Upper Hudson River would be removed.

Indiana

From the late 1950s through 1977, Westinghouse Electric used PCBs in the manufacture of capacitors in its Bloomington, Indiana plant. Founded in 1886 as Westinghouse Electric Company and later renamed Westinghouse Electric Corporation by George Westinghouse. Bloomington is a city and the County seat of Monroe County in the south central region of the U Reject capacitors were hauled and dumped in area salvage yards and landfills. Workers also dumped PCB oil down factory drains which contaminated the city sewage treatment plant. The City of Bloomington gave away the sludge to area farmers and gardeners, creating anywhere from 200 to 2000 sites which remain unaddressed. Over 2 million pounds of PCBs were estimated to have been dumped in Monroe and Owen Counties, which would make it the biggest concentration of PCBs in the world. Although federal and state authorities have been working on the site remediations, many areas remain contaminated. Concerns have been raised regarding the removal of PCBs from the karst limestone topography, and regarding the possible disposal options. Karst topography is a landscape shaped by the dissolution of a layer or layers of soluble Bedrock, usually Carbonate rock such as Limestone To date, the Westinghouse Bloomington PCB Superfund site case does not have a RI/FS (Remedial Investigation/Feasibility Study) and ROD (Record of Decision), although Westinghouse signed a US Department of Justice Consent Decree in 1985. On February 15, 2008, Monroe County approved a plan to clean up the 3 remaining contaminated sites in the City of Bloomington, at a cost of $9. Events 590 - Khosrau II is crowned as king of Persia 1637 - Ferdinand III becomes Holy Roman Emperor 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common 6m to CBS Corp., the successor of Westinghouse. CBS Corporation () is an American Media conglomerate focused on Broadcasting, Publishing, Billboards, and Television [17]

The Great Lakes

Much of the Great Lakes area is still heavily polluted with PCBs, despite extensive remediation work. The Laurentian Great Lakes are a chain of freshwater lakes located in eastern North America, on the Canada–United States border. [18] Locally caught fresh water fish and shellfish are contaminated with PCBs and their consumption is restricted.

Global transport through atmospheric pollution

PCBs have been detected globally in the atmosphere, from the most urbanized areas that are the centers for PCB pollution, to regions north of the Arctic Circle. The atmosphere serves as the primary route for global transport of PCBs, particularly for those congeners with 1 to 4 chlorine atoms.

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/m³ or more. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International In Milwaukee, an atmospheric concentration of 1. 9 ng/m³ has been measured, and this source alone was estimated to account for 120 kg/year of PCBs entering Lake Michigan. Lake Michigan is one of the five Great Lakes of North America, and the only one located entirely within the United States. [19] Concentrations as high as 35 ng/m³, 10 times higher than the EPA guideline limit of 3. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International 4 ng/m³, have been found inside some houses in the U. S. [1]

Volatilization of PCBs in soil was thought to be the primary source of PCBs in the atmosphere, but recent research suggests that ventilation of PCB-contaminated indoor air from buildings is the primary source of PCB contamination in the atmosphere. [20]

Health effects

The toxicity of PCBs to animals was first noticed in the 1970s when emaciated seabird corpses with very high PCB body burdens washed up on beaches. Toxicity is the degree to which a substance is able to damage an exposed organism Since seabirds may die far out at sea and still wash ashore, the true sources of the PCBs were unknown. Where they were found is no reliable indicator of where they had died.

The toxicity of PCBs varies considerably among congeners. The coplanar PCBs, known as non-ortho PCBs because they are not substituted at the ring positions ortho to (next to) the other ring, (i. Arene substitution patterns are part of Organic chemistry IUPAC nomenclature and pinpoint the position of Substituents other than Hydrogen in e. PCBs 77, 126, 169, etc), tend to have dioxin-like properties, and generally are among the most toxic congeners. Not to be confused with Dioxane or Digoxin. Dioxin is a heterocyclic, organic, antiaromatic compound Because PCBs are almost invariably found in complex mixtures, the concept of toxic equivalency factors (TEFs) has been developed to facilitate risk assessment and regulatory control, where more toxic PCB congeners are assigned higher TEF values. One of the most toxic compounds known, 2,3,7,8-tetrachlorodibenzo[p]dioxin, is assigned a TEF of 1. Not to be confused with Dioxane or Digoxin. Dioxin is a heterocyclic, organic, antiaromatic compound [21]

Signs and symptoms

The most commonly observed health effects in people exposed to PCBs are skin conditions such as chloracne and rashes, but these were known to be symptoms of systemic poisoning dating back to the 1922. Health effects, health impacts or health risks are changes in Health resulting from exposure to a source Chloracne is an acne -like eruption of Blackheads Cysts and Pustules associated with over-exposure to certain Halogenated Aromatic A rash is a change of the Skin which affects its color appearance or Texture. Studies in workers exposed to PCBs have shown changes in blood and urine that may indicate liver damage. Blood is a specialized Bodily fluid that delivers necessary substances to the body's cells such as nutrients and oxygen—and transports Waste products Urine is a liquid waste product of the body secreted by the Kidneys by a process of filtration from Blood and Excreted through the Urethra. The liver is a vital organ in the human body and is present in Vertebrates and some other animals In 1968 in Japan, PCB contamination in rice bran oil caused a mass poisoning known as Yushō Disease in over 14000 people. Rice bran oil is the oil extracted from the Germ and inner husk of Rice. (literally oil disease) was a mass poisoning by PCBs which occurred in northern Kyūshū, Japan in 1968 [22] Common symptoms included dermal and ocular lesions, irregular menstrual cycles and a lowered immune response. A lesion is any abnormal tissue found on or in an organism usually damaged by disease or trauma The menstrual cycle is a recurring cycle of physiologic changes that occurs in reproductive-age Females Overt menstruation (where there is blood flow from the An immune system is a collection of mechanisms within an Organism that protects against Disease by identifying and killing Pathogens and Tumor [23][24][25] Other symptoms included fatigue, headache, cough, and unusual skin sores. [26] Additionally, in children, there were reports of poor cognitive development. [23][25][26]
There have also been studies of the health effects of PCBs in the general population and in children of mothers who were exposed to PCBs.
Animals that eat PCB-contaminated food even for short periods of time get liver damage and may die. In 1968 in Japan, 400,000 birds died after eating poultry feed that was contaminated with PCBs. [22] Animals that eat smaller amounts of PCBs in food over several weeks or months develop various kinds of health effects, including anemia; acne-like skin conditions (chloracne); and liver, stomach, and thyroid gland injuries (including hepatocarcinoma). Anemia ( AmE) or anæmia/anaemia ( BrE) (from the Ancient Greek grc-Latn anaîmia, meaning “without blood” is defined as a qualitative Chloracne is an acne -like eruption of Blackheads Cysts and Pustules associated with over-exposure to certain Halogenated Aromatic In Human anatomy, the stomach is a J-shaped hollow muscular organ of the Gastrointestinal tract involved in the second phase of Digestion, following The thyroid is one of the largest Endocrine glands in the body Other effects of PCBs in animals include changes in the immune system, behavioral alterations, and impaired reproduction. An immune system is a collection of mechanisms within an Organism that protects against Disease by identifying and killing Pathogens and Tumor PCBs are not known to cause birth defects in humans, although those that have dioxin-like activity are known to cause a variety of teratogenic effects in animals. Not to be confused with Dioxane or Digoxin. Dioxin is a heterocyclic, organic, antiaromatic compound Teratology stems from the Greek ( Genitive) meaning monster, or marvel and, meaning word, speech.
Women who were exposed to relatively high levels of PCBs in the workplace or ate large amounts of fish contaminated with PCBs had babies that weighed slightly less than babies from women who did not have these exposures. Babies born to women who ate PCB-contaminated fish also showed abnormal responses in tests of infant behavior. Some of these behaviors, such as problems with motor skills and a decrease in short-term memory, lasted for several years. Other studies suggest that the immune system was affected in children born to and nursed by mothers exposed to increased levels of PCBs. The most likely way infants will be exposed to PCBs is from breast milk. Milk is an opaque white liquid produced by the Mammary glands of female Mammals (including Monotremes. Transplacental transfers of PCBs were also reported.
Studies have shown that PCBs alter estrogen levels in the body and contribute to reproduction problems. In the womb, males can be feminized or the baby may be intersex, neither a male nor a female. Also, both sets of reproductive organs may develop. More instances of this are being reported. Biological magnification of PCBs has also led to polar bears and whales that have both male and female sex organs and males that cannot reproduce. This effect is also known as endocrine disruption. Endocrine disruptors (sometimes also referred to as hormonally active agents) are Exogenous substances that act like Hormones in the Endocrine system Endocrine Disrupting Chemicals (EDC's) pose a serious threat to reproduction in top-level predators.

Cancer link

A few studies of workers indicate that PCBs were associated with specific kinds of cancer in humans, such as cancer of the liver and biliary tract. Cancer (medical term Malignant Neoplasm) is a class of Diseases in which a group of cells display uncontrolled A bile duct is any of a number of long tube-like structures that carry Bile. Rats that ate food containing high levels of PCBs for two years developed liver cancer. The Department of Health and Human Services (DHHS) has concluded that PCBs may reasonably be anticipated to be carcinogens. The United States Department of Health and Human Services ( HHS) is a Cabinet department of the United States government with the goal of protecting The term carcinogen refers to any substance Radionuclide or radiation that is an agent directly involved in the promotion of Cancer or in the fatation of its propagation The US Environmental Protection Agency (EPA) and the International Agency for Research on Cancer (IARC) have determined that PCBs are probably carcinogenic to humans. The International Agency for Research on Cancer ( IARC, or CIRC in its French Acronym) is an intergovernmental agency forming part of the World Health PCBs are also classified as probable human carcinogens by the National Cancer Institute, World Health Organization, and the Agency for Toxic Substances and Disease Registry. The National Cancer Institute (NCI is part of the United States Federal government's National Institutes of Health. The United States Agency for Toxic Substances and Disease Registry, ( ATSDR) is an agency for the U Recent research by the National Toxicology Program has confirmed that PCB126 (Technical Report 520) and a binary mixture of PCB126 and PCB153 (Technical Report 531) are carcinogens. The United States Department of Health and Human Services ( HHS) is a Cabinet department of the United States government with the goal of protecting The term carcinogen refers to any substance Radionuclide or radiation that is an agent directly involved in the promotion of Cancer or in the fatation of its propagation

Mechanism of action

As discussed, PCBs exhibit a wide range of toxic effects. These effects may vary depending on the specific PCB. Similar to dioxin, toxicity of coplanar PCBs and mono-ortho-PCBs are thought to be primarily mediated via binding to aryl hydrocarbon receptor (AhR). The Aryl hydrocarbon receptor ( AhR or AHR) is a member of the family of Basic-helix-loop-helix Transcription factors AhR is a cytosolic transcription [27][28] Because AhR is a transcription factor, abnormal activation may disrupt cell function by altering the transcription of genes. In the field of Molecular biology, a transcription factor (sometimes called a sequence-specific DNA binding factor is a Protein that binds to specific sequences Transcription is the synthesis of RNA under the direction of DNA History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance The concept of toxic equivalency factors (TEF) is based on the ability of a PCB to activate AhR.

However, not all effects may be mediated by the AhR receptor. For example, di-ortho-substituted non-coplanar PCBs interfere with intracellular signal transduction dependent on calcium; this may lead to neurotoxicity. In Biology, signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another Calcium (Ca2+ plays a vital role in the Anatomy, Physiology and Biochemistry of Organisms and of the cell, particularly Neurotoxicity occurs when the exposure to natural or artificial toxic substances which are called Neurotoxins alters the normal activity of the Nervous system in [29] Ortho-PCBs may disrupt thyroid hormone transport by binding to transthyretin. The thyroid hormones, Thyroxine ( T4) and Triiodothyronine ( T3) are Tyrosine -based Hormones produced Transthyretin (TTR is a serum and Cerebrospinal fluid carrier of the Thyroid Hormone Thyroxine (T4 [30]

Containment

Landfill – Large quantities of PCBs have been placed in landfill sites, mainly in the form of transformers and capacitors. For other uses see Water treatment and Land reclamation. A landfill, also known as a dump (and historically as Many municipal sites are not designed to contain these pollutants and PCBs are able to escape into the atmosphere or ground water. No emissions above background are seen if the landfill is designed correctly.

Methods of destruction

These can be separated into three distinct categories: physical, microbial, and chemical destruction.

Physical

Incineration – Although PCBs do not ignite themselves, they can be combusted under extreme and carefully controlled conditions. Incineration is a waste treatment technology that involves the Combustion of organic materials and/or substances The current regulations require that PCBs are burnt at a temperature of 1200°C for at least two seconds, in the presence of fuel oil and excess oxygen. A lack of oxygen can result in the formation of PCDDs, PCDFs and dioxins, or the incomplete destruction of the PCBs. Polychlorinated dibenzodioxins ( PCDD s or simply dioxins, are a group of Halogenated Organic compounds which are significant because they act Polychlorinated dibenzofurans ( PCDF s are a group of Halogenated Organic compounds which are toxic environmental Pollutants They are known Not to be confused with Dioxane or Digoxin. Dioxin is a heterocyclic, organic, antiaromatic compound Such specific conditions mean that it is extremely expensive to destroy PCBs on a tonnage scale, and it can only be used on PCB containing equipment and contaminated liquid. This method is not suitable for the decontamination of affected soils.

Ultrasound – In a similar process to combustion, high power ultrasonic waves are applied to water, generating cavitation bubbles. Not to be confused with Supersonic. Ultrasound is cyclic Sound pressure with a Frequency greater than the upper These then implode or fragment, creating microregions of extreme pressures and temperatures where the PCBs are destroyed. Water is thought to undergo thermolysis, oxidising the PCBs to CO, CO2 and hydrocarbons such as biphenyl, with chlorine present as the inorganic ion 16. For the biological process see Decomposition. For chemical decomposition in general see Chemical decomposition. The scope of this method is limited to those congeners which are the most water soluble; those isomers with the least chlorine substitution.

Irradiation – If a deoxygenated mixture of PCBs in isopropanol or mineral oil is subject to irradiation with gamma rays then the PCBs will be dechlorinated to form inorganic chloride and biphenyl. Irradiation is the process by which an item is exposed to Radiation. Isopropyl alcohol (also isopropanol, iso, isopro, Rubbing alcohol, or the abbreviation IPA) is a common name for Mineral oil or liquid Petroleum is a By-product in the Distillation of Petroleum to produce Gasoline and other petroleum Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions The chloride Ion is formed when the element Chlorine picks up one Electron to form an Anion (negatively-charged ion Cl&minus Biphenyl (or diphenyl or phenyl benzene or 11'-biphenyl or lemonene) is a solid Organic compound that forms colorless to yellowish crystals The reaction works best in isopropanol if potassium hydroxide (caustic potash) is added. Potassium hydroxide is the Inorganic compound with the formula K[[hydroxide OH]] Potassium hydroxide is the Inorganic compound with the formula K[[hydroxide OH]] Solvated electrons are thought to be responsible for the reaction. A solvated electron is a Free electron in (solvated in a Solution. If oxygen, nitrous oxide, sulfur hexafluoride or nitrobenzene is present in the mixture then the reaction rate is reduced. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Nitrous oxide, commonly known as " laughing gas," is a Chemical compound with the Chemical formula N 2 O. Sulfur hexafluoride is an Inorganic compound with the formula. Nitrobenzene, also known as nitrobenzol or oil of mirbane, is an Organic compound with the Chemical formula C 6 This work has been done recently in the US often with used nuclear fuel as the radiation source[1][2]. Nuclear fuel is any material that can be consumed to derive Nuclear energy, by analogy to chemical Fuel that is burned to derive energy

Microbial

Much recent work has centered on the study of micro-organisms that are able to decompose PCBs. Biodegradation is the process by which organic substances are broken down by the enzymes produced by living organisms Generally, these organisms work in one of two ways: either they use the PCB as a carbon source, or destruction takes place through reductive dechlorination, with the replacement of chlorine with hydrogen on the biphenyl skeleton. However, there are significant problems with this approach. Firstly, these microbes tend to be highly selective in their dechlorination, with lower chlorinated biphenyls being readily transformed, and with preference to dechlorination in the para and meta positions. A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually Secondly, microbial dechlorination tends to be rather slow acting on PCB as a soil contaminant in comparison to other methods. Soil contamination is caused by the presence of man-made chemicals or other alteration in the natural soil environment Finally, while microbes work well in laboratory conditions, there is often a problem in transferring a successful laboratory strain to a natural system. This is because the microbes can access other sources of carbon, which they decompose in preference to PCBs.

Further recent developments have focused on testing enzymes and vitamins extracted from microbes which show PCB activity. Especially promising seems to be the use of vitamin B12, in which a cobalt ion is in oxidation state (III) under normal redox conditions. Using titanium (III) citrate as a strong reductant converts the cobalt from Co(III) to Co(I), giving a new vitamin known as B12s, which is a powerful nucleophile and reducing catalyst. Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst This can then be used on PCBs, which it dechlorinates in a rapid and selective manner. [31]

Chemical

Many chemical methods are available to destroy or reduce the toxicity of PCBs.

Nucleophilic aromatic substitution is a method of destroying low concentration PCB mixtures in oils, such as transformer oil. nucleophilic aromatic substitution is a Substitution reaction in Organic chemistry in which the Nucleophile displaces a good Leaving group, Substitution of chlorine by polyethylene glycols) occurs in under two hours under a blanket of nitrogen, to prevent oxidation of the oil, to produce aryl polyglycols, which are insoluble in the oil and precipitate out. Poly( Ethylene glycol) (PEG also known as poly( Ethylene oxide) (PEO or polyoxyethylene (POE is the most commercially important type of polyether In the context of organic molecules aryl refers to any Functional group or Substituent derived from a Simple aromatic ring, may it be Phenyl

Between 700 and 925°C, H2 cleaves the carbon-chlorine bond, and cleaves the biphenyl nucleus into benzene yielding HCl without a catalyst. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst This can be performed at lower temperatures with a copper catalyst, and to yield biphenyl. However, since both of these routes require an atmosphere of hydrogen gas and relatively high temperatures, they are prohibitively expensive.

Reaction with highly electropositive metals, or strong reducing agents such as sodium naphthalide, in aprotic solvents results in a transfer of electrons to the PCB, the expulsion of a chloride ion, and a coupling of the PCBs. Electropositivity is a measure of an element's ability to donate Electrons, and therefore form positive Ions. A reducing agent (also called a reductant or reducer) is the element or a compound in a Redox (reduction-oxidation reaction (see Electrochemistry This is analogous to the Wurtz reaction for coupling halogenoalkanes. The Wurtz reaction, named after Charles-Adolphe Wurtz, is a Coupling reaction in Organic chemistry, Organometallic chemistry and recently inorganic The effect is to polymerise many molecules, therefore reducing the volatility, solubility and toxicity of the mixture. This methodology is most successful on low strength PCB mixtures and can also be performed electrochemically in a partly aqueous bicontinuous microemulsion. An emulsion ( IPA: /ɪˈmʌlʃən/ is a mixture of two Immiscible (unblendable liquids

The solution photochemistry of PCBs is based on the transfer of an electron to a photochemically excited PCB from a species such as an amine, to give a radical anion. Photochemistry, a sub-discipline of Chemistry, is the study of the interactions between Atoms, small Molecules, and light (or Electromagnetic radiation Amines are Organic compounds and Functional groups that contain a basic Nitrogen Atom with a Lone pair. This either expels a chloride ion and the resulting aryl radical extracts a hydrogen atom from the solvent, or immediately becomes protonated, leading to the loss of a chlorine atom. In the context of organic molecules aryl refers to any Functional group or Substituent derived from a Simple aromatic ring, may it be Phenyl In chemistry protonation is the addition of a proton ( H[[Cation +]] to an Atom, Molecule, or Ion. It is useful only for water soluble PCBs.

The major pathway for atmospheric destruction of PCBs is via attack by OH radicals. In Chemistry, hydroxide is the most common name for the diatomic Anion OH− consisting of Oxygen and Hydrogen Direct photolysis can occur in the upper atmosphere, but the ultraviolet wavelengths necessary to excite PCBs are shielded from the troposphere by the ozone layer. Photodissociation, photolysis, or photodecomposition is a Chemical reaction in which a Chemical compound is broken down by Photons The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75% of the atmosphere's mass and almost all of its Water vapor and The photochemical mechanisms that give rise to the ozone layer were worked out by the British physicist Sidney Chapman in 1930 It has, however, been shown that higher wavelengths of light (> 300 nm) can degrade PCBs in the presence of a photosensitizer, such as acetone. In Pharmacology, a photosensitizer is a Drug, food or other chemical that increases Photosensitivity of the organism

The Schwartz reaction is the subject of much study, and has significant benefits over other routes. It is advantageous since it proceeds via a reductive process, and thus yields no dioxins through oxidation. The proposed reaction scheme involves the electron transfer from a titanium (III) organometallic species to form a radical anion on the PCB molecule which expels chlorine to eventually form the relatively non-toxic biphenyl. Organometallic chemistry is the study of Chemical compounds containing bonds between Carbon and a Metal.

See also

References

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External links

Appendix

PCB homolog table

For a complete list of PCB congeners, see PCB Congener List. A complete list of Polychlorinated biphenyl (PCB congeners PCB Congener List Explanation of PCB "Descriptors" Congener descriptors give Note that biphenyl, while not technically a PCB congener due to its lack of chlorine substituents, is still typically included in the literature.

PCB HomologCASRNCl SubstituentsNumber of Congeners
Biphenyl92-52-401
Monochlorobiphenyl27323-18-813
Dichlorobiphenyl25512-42-9212
Trichlorobiphenyl25323-68-6324
Tetrachlorobiphenyl26914-33-0442
Pentachlorobiphenyl25429-29-2546
Hexachlorobiphenyl26601-64-9642
Heptachlorobiphenyl28655-71-2724
Octachlorobiphenyl55722-26-4812
Nonachlorobiphenyl53742-07-793
Decachlorobiphenyl2051-24-3101
Biphenyl (or diphenyl or phenyl benzene or 11'-biphenyl or lemonene) is a solid Organic compound that forms colorless to yellowish crystals

Dictionary

polychlorinated biphenyl

-noun

  1. (organic chemistry) A class of aromatic organic compounds formed by the chlorination of the hydrocarbon biphenyl; they have many industrial applications but are damaging to the environment.
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