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Polychlorinated biphenyls (PCBs) are
organochlorine compound Organochlorine chemistry is concerned with the properties of organochlorine compounds, or organochlorides, organic compounds that contain one or more carbon–chlorine bonds. The chloroalkane class (alkanes with one or more hydrogens substituted ...
s with the formula C12 H10−''x'' Cl''x''; they were once widely used in the manufacture of carbonless copy paper, as heat transfer fluids, and as
dielectric In electromagnetism, a dielectric (or dielectric medium) is an Insulator (electricity), electrical insulator that can be Polarisability, polarised by an applied electric field. When a dielectric material is placed in an electric field, electric ...
and
coolant A coolant is a substance, typically liquid, that is used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corr ...
fluids for electrical equipment. They are highly toxic and
carcinogen A carcinogen () is any agent that promotes the development of cancer. Carcinogens can include synthetic chemicals, naturally occurring substances, physical agents such as ionizing and non-ionizing radiation, and biologic agents such as viruse ...
ic chemical compounds, formerly used in industrial and consumer electronic products, whose production was banned internationally by the
Stockholm Convention on Persistent Organic Pollutants Stockholm Convention on Persistent Organic Pollutants is an international environmental treaty, signed on 22 May 2001 in Stockholm and effective from 17 May 2004, that aims to eliminate or restrict the production and use of persistent organi ...
in 2001. Because of their longevity, PCBs are still widely in use, even though their manufacture has declined drastically since the 1960s, when a multitude of problems was identified. With the discovery of PCBs' environmental
toxicity Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacteria, bacterium, or plant, as well as the effect o ...
, and classification as
persistent organic pollutant Persistent organic pollutants (POPs) are organic compounds that are resistant to degradation through chemical, biological, and photolytic processes. They are toxic and adversely affect human health and the environment around the world. Because ...
s, 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 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 Neurotoxicity is a form of toxicity in which a biological, chemical, or physical agent produces an adverse effect on the structure or function of the central and/or peripheral nervous system. It occurs when exposure to a substance – specifical ...
are known. The
bromine Bromine is a chemical element; it has chemical symbol, symbol Br and atomic number 35. It is a volatile red-brown liquid at room temperature that evaporates readily to form a similarly coloured vapour. Its properties are intermediate between th ...
analogues of PCBs are
polybrominated biphenyl Polybrominated biphenyls (PBBs), also called brominated biphenyls or polybromobiphenyls, are a group of manufactured chemicals that consist of polyhalogenated compound, polyhalogenated derivatives of a biphenyl core. Their chlorine analogs are t ...
s (PBBs), which have analogous applications and environmental concerns. An estimated 1.2 million tons have been produced globally. Though 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.


Physical and chemical properties


Physical properties

The compounds are pale-yellow
viscous Viscosity is a measure of a fluid's rate-dependent resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for example, syrup h ...
liquid Liquid is a state of matter with a definite volume but no fixed shape. Liquids adapt to the shape of their container and are nearly incompressible, maintaining their volume even under pressure. The density of a liquid is usually close to th ...
s. They are hydrophobic, with low
water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...
solubilities: 0.0027–0.42  ng/L for Aroclors brand, but they have high solubilities in most organic
solvent A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...
s, oils, and
fat In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food. The term often refers specif ...
s. They have low
vapor pressure Vapor pressure or equilibrium vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. The equilibrium vapor pressure is an indicat ...
s at room temperature. They have
dielectric constant The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insul ...
s of 2.5–2.7, very high
thermal conductivity The thermal conductivity of a material is a measure of its ability to heat conduction, conduct heat. It is commonly denoted by k, \lambda, or \kappa and is measured in W·m−1·K−1. Heat transfer occurs at a lower rate in materials of low ...
, and high
flash point The flash point of a material is the "lowest liquid temperature at which, under certain standardized conditions, a liquid gives off vapours in a quantity such as to be capable of forming an ignitable vapour/air mixture". The flash point is somet ...
s (from 170 to 380 °C). The density varies from 1.182 to 1.566 g/cm3. Other physical and chemical properties vary widely across the class. As the degree of chlorination increases, melting point and
lipophilicity Lipophilicity (from Greek λίπος "fat" and φίλος "friendly") is the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such compounds are called lipophilic (translated ...
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
dibenzofuran Dibenzofuran (DBF) is a heterocyclic organic compound with the chemical structure shown at right. It is an aromatic compound that has two benzene rings fused to a central furan ring. All the numbered carbon atoms have a hydrogen atom bonded to each ...
s through partial oxidation. Intentional degradation as a treatment of unwanted PCBs generally requires high heat or
catalysis Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...
(see Methods of destruction below). PCBs readily penetrate
skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...
, PVC (polyvinyl chloride), and
latex Latex is an emulsion (stable dispersion) of polymer microparticles in water. Latices are found in nature, but synthetic latices are common as well. In nature, latex is found as a wikt:milky, milky fluid, which is present in 10% of all floweri ...
(natural rubber). PCB-resistant materials include Viton,
polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including bott ...
, polyvinyl acetate (PVA),
polytetrafluoroethylene Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene, and has numerous applications because it is chemically inert. The commonly known brand name of PTFE-based composition is Teflon by Chemours, a corporate spin-of ...
(PTFE),
butyl rubber Butyl rubber, sometimes just called butyl, is a synthetic rubber, a copolymer of isobutylene with isoprene. The abbreviation IIR stands for isobutylene isoprene rubber. Polyisobutylene, also known as "PIB" or polyisobutene, (C4H8)n, is the homop ...
,
nitrile rubber Nitrile rubber, also known as nitrile butadiene rubber, NBR, Buna-N, and acrylonitrile butadiene rubber, is a synthetic rubber derived from acrylonitrile (ACN) and butadiene. Trade names include Perbunan, Nipol, Krynac and Europrene. This rubber is ...
, and
Neoprene Neoprene (also polychloroprene) is a family of synthetic rubbers that are produced by polymerization of chloroprene.Werner Obrecht, Jean-Pierre Lambert, Michael Happ, Christiane Oppenheimer-Stix, John Dunn and Ralf Krüger "Rubber, 4. Emulsion Rub ...
.


Structure and toxicity

PCBs are derived from
biphenyl Biphenyl (also known as diphenyl, phenylbenzene, 1,1′-biphenyl, lemonene or BP) is an organic compound that forms colorless crystals. Particularly in older literature, compounds containing the functional group consisting of biphenyl less one ...
, which has the formula C12H10, sometimes written (C6H5)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 . About 130 different individual PCBs are found in commercial PCB products. Toxic effects vary depending on 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. ;Coplanar or non-''ortho'' :The coplanar group members have a fairly rigid structure, with their two phenyl rings in the same plane. It renders their structure similar to polychlorinated dibenzo-''p''-dioxins (PCDDs) and
polychlorinated dibenzofurans Polychlorinated dibenzofurans (PCDFs) are a family of organic compounds with one or several of the hydrogens in the dibenzofuran structure replaced by chlorines. For example, 2,3,7,8-tetrachlorodibenzofuran (TCDF) has chlorine atoms substitut ...
, and allows them to act like PCDDs, as an agonist of the
aryl hydrocarbon receptor The aryl hydrocarbon receptor (also known as AhR, AHR, ahr, ahR, AH receptor, or as the dioxin receptor) is a protein that in humans is encoded by the AHR gene. The aryl hydrocarbon receptor is a transcription factor that regulates gene express ...
(AhR) in organisms. They are considered as contributors to overall dioxin toxicity, and the term
dioxins and dioxin-like compounds Dioxins and dioxin-like compounds (DLCs) are a group of chemical compounds that are persistent organic pollutants (POPs) in the environmental pollutant, environment. They are mostly by-products of burning or various industrial processes or, in the ...
is often used interchangeably when the environmental and toxic impact of these compounds is considered. ;Noncoplanar :Noncoplanar PCBs, with chlorine atoms at the ''ortho'' positions can cause neurotoxic and immunotoxic effects, but only at concentrations much higher than those normally associated with dioxins. However, as they are typically found at much higher levels in biological and environmental samples they also pose health concerns, particularly to developing animals (including humans). As they do not activate the AhR, they are not considered part of the dioxin group. Because of their lower overt toxicity, they have typically been of lesser concern to regulatory bodies. Di-''ortho''-substituted, non-coplanar PCBs interfere with intracellular
signal transduction Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a biochemical cascade, series of molecular events. Proteins responsible for detecting stimuli are generally termed receptor (biology), rece ...
dependent on
calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...
which may lead to
neurotoxicity Neurotoxicity is a form of toxicity in which a biological, chemical, or physical agent produces an adverse effect on the structure or function of the central and/or peripheral nervous system. It occurs when exposure to a substance – specifical ...
. ''ortho''-PCBs can disrupt
thyroid hormone File:Thyroid_system.svg, upright=1.5, The thyroid system of the thyroid hormones triiodothyronine, T3 and T4 rect 376 268 820 433 Thyroid-stimulating hormone rect 411 200 849 266 Thyrotropin-releasing hormone rect 297 168 502 200 Hypothalamus r ...
transport by binding to
transthyretin Transthyretin (TTR or TBPA) is a transport protein in the plasma and cerebrospinal fluid that transports the thyroid hormone thyroxine (T4) and retinol to the liver. This is how transthyretin gained its name: ''transports thyroxine and retinol' ...
.


Mixtures and trade names

Commercial PCB mixtures were marketed under the following names: Brazil * Ascarel Czech Republic and Slovakia *Delor France *Phenoclor *Pyralène (both used by Prodolec) Germany *Clophen (used by
Bayer Bayer AG (English: , commonly pronounced ; ) is a German multinational pharmaceutical and biotechnology company and is one of the largest pharmaceutical companies and biomedical companies in the world. Headquartered in Leverkusen, Bayer' ...
) Italy *Apirolio *Fenclor Japan *Kanechlor (used by Kanegafuchi) *Santotherm (used by
Mitsubishi The is a group of autonomous Japanese multinational companies in a variety of industries. Founded by Yatarō Iwasaki in 1870, the Mitsubishi Group traces its origins to the Mitsubishi zaibatsu, a unified company that existed from 1870 to 194 ...
) *Pyroclor Former USSR *Sovol *Sovtol United Kingdom *Aroclor xxxx (used by
Monsanto Company The Monsanto Company () was an American agrochemical and agricultural biotechnology corporation founded in 1901 and headquartered in Creve Coeur, Missouri. Monsanto's best-known product is Roundup, a glyphosate-based herbicide, developed in ...
) *Askarel United States *Aroclor xxxx (used by
Monsanto Company The Monsanto Company () was an American agrochemical and agricultural biotechnology corporation founded in 1901 and headquartered in Creve Coeur, Missouri. Monsanto's best-known product is Roundup, a glyphosate-based herbicide, developed in ...
) *Asbestol *Askarel *Bakola131 *Chlorextol –
Allis-Chalmers Allis-Chalmers was a United States, U.S. manufacturer of machinery for various Industry (economics), industries. Its business lines included list of agricultural machinery, agricultural equipment, heavy equipment, construction equipment, electric ...
trade name *Dykanol (Cornell-Dubilier) *Hydol *Inerteen (used by Westinghouse) *Noflamol *Pyranol/Pyrenol, Clorinol (used in
General Electric General Electric Company (GE) was an American Multinational corporation, multinational Conglomerate (company), conglomerate founded in 1892, incorporated in the New York (state), state of New York and headquartered in Boston. Over the year ...
's oil-filled "clorinol"-branded metal can
capacitor In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...
s. Utilized from the early 1960s to late 1970s in air conditioning units, Seeburg jukeboxes and Zenith televisions) * Saf-T-Kuhl * Therminol FR Series (
Monsanto The Monsanto Company () was an American agrochemical and agricultural biotechnology corporation founded in 1901 and headquartered in Creve Coeur, Missouri. Monsanto's best-known product is Roundup, a glyphosate-based herbicide, developed ...
ceased production in 1971).


Aroclor mixtures

The only North American producer,
Monsanto Company The Monsanto Company () was an American agrochemical and agricultural biotechnology corporation founded in 1901 and headquartered in Creve Coeur, Missouri. Monsanto's best-known product is Roundup, a glyphosate-based herbicide, developed in ...
, 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); 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 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 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.


Production

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 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. , there were still 21,500 tons of PCBs stored in 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 the passage of the Toxic Substances Control Act (TSCA).


Applications

The utility of PCBs is based largely on their chemical stability, including low
flammability A combustible material is a material that can burn (i.e., sustain a flame) in air under certain conditions. A material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort a ...
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
coolant A coolant is a substance, typically liquid, that is used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corr ...
s and insulating fluids ( transformer oil) for
transformer In electrical engineering, a transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple Electrical network, circuits. A varying current in any coil of the transformer produces ...
s and
capacitor In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...
s, such as those used in old fluorescent light ballasts, and
hydraulic fluid A hydraulic fluid or hydraulic liquid is the medium by which power is transferred in hydraulic machinery. Common hydraulic fluids are based on mineral oil or water. Examples of equipment that might use hydraulic fluids are excavators and backho ...
s considered 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
plasticizer A plasticizer ( UK: plasticiser) is a substance that is added to a material to make it softer and more flexible, to increase its plasticity, to decrease its viscosity, and/or to decrease friction during its handling in manufacture. Plasticizer ...
s in paints and cements, stabilizing additives in flexible PVC coatings of electrical cables and electronic components,
pesticide Pesticides are substances that are used to control pests. They include herbicides, insecticides, nematicides, fungicides, and many others (see table). The most common of these are herbicides, which account for approximately 50% of all p ...
extenders, reactive
flame retardant Flame retardants are a diverse group of chemicals that are added to manufactured materials, such as plastics and textiles, and surface finishes and coatings. Flame retardants are activated by the presence of an combustion, ignition source and pr ...
s and
sealant Sealant is a substance used to block the passage of fluids through openings in materials, a type of Seal (mechanical), mechanical seal. In building construction ''sealant'' is sometimes synonymous with ''caulk'' (especially if acrylic latex or ...
s for
caulk Caulk (also known as caulking and calking) is a material used to Seal (mechanical), seal Joint (building), joints or seams against leakage in various structures and piping. The oldest form of caulk consisted of fibrous materials driven into ...
ing,
adhesive Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. The use of adhesives offers certain advantage ...
s, wood floor finishes, such as ''Fabulon'' and other products of Halowax in 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
pigment A pigment is a powder used to add or alter color or change visual appearance. Pigments are completely or nearly solubility, insoluble and reactivity (chemistry), chemically unreactive in water or another medium; in contrast, dyes are colored sub ...
s, 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.


Environmental transport and transformations

PCBs have entered the environment through both use and disposal. The environmental fate of PCBs is complex and global in scale.


Water

Because of their low
vapour pressure Vapor pressure or equilibrium vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. The equilibrium vapor pressure is an indicat ...
, PCBs accumulate primarily in the
hydrosphere The hydrosphere () is the combined mass of water found on, under, and above the Planetary surface, surface of a planet, minor planet, or natural satellite. Although Earth's hydrosphere has been around for about 4 billion years, it continues to ch ...
, despite their
hydrophobicity In chemistry, hydrophobicity is the chemical property of a molecule (called a hydrophobe) that is seemingly intermolecular force, repelled from a mass of water. In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to b ...
, in the organic fraction of
soil Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...
, and in
organism An organism is any life, living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have be ...
s including the human body. The hydrosphere is the main reservoir. The immense volume of water in the oceans is still capable of dissolving 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.


Air

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 the atmosphere, PCBs may be degraded by
hydroxyl radical The hydroxyl radical, •HO, is the neutral form of the hydroxide ion (HO–). Hydroxyl radicals are highly reactive and consequently short-lived; however, they form an important part of radical chemistry. Most notably hydroxyl radicals are pr ...
s, or directly by
photolysis Photodissociation, photolysis, photodecomposition, or photofragmentation is a chemical reaction in which molecules of a chemical compound are broken down by absorption of light or photons. It is defined as the interaction of one or more photons wi ...
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 To help compare different '' orders of magnitude'', the following lists describe various ''mass'' levels between 10−67 kg and 1052 kg. The least massive thing listed here is a graviton, and the most massive thing is the observable univer ...
per cubic meter range, higher in suburban and urban areas, and highest in city centres, where they can reach 1  ng/m3 or more. In
Milwaukee Milwaukee is the List of cities in Wisconsin, most populous city in the U.S. state of Wisconsin. Located on the western shore of Lake Michigan, it is the List of United States cities by population, 31st-most populous city in the United States ...
, 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. It is the second-largest of the Great Lakes by volume () and depth () after Lake Superior and the third-largest by surface area (), after Lake Superior and Lake Huron. To the ...
. In 2008, concentrations as high as 35  ng/m3, 10 times higher than the EPA guideline limit of 3.4 ng/m3, 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 is the primary source of PCB contamination in the atmosphere.


Biosphere

In the
biosphere The biosphere (), also called the ecosphere (), is the worldwide sum of all ecosystems. It can also be termed the zone of life on the Earth. The biosphere (which is technically a spherical shell) is virtually a closed system with regard to mat ...
, PCBs can be degraded by the
sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
,
bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...
or
eukaryote The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...
s, 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 In organochlorine chemistry, reductive dechlorination describes any chemical reaction which cleaves the covalent bond between carbon and chlorine via reductants, to release chloride ions. Many modalities have been implemented, depending on the ...
, or oxidized by
dioxygenase Dioxygenases are oxidoreductase enzymes. Aerobic organism, Aerobic life, from simple single-celled bacteria species to complex eukaryotic organisms, has evolved to depend on the oxidizing power of dioxygen in various metabolic pathways. From energ ...
enzyme. In eukaryotes, PCBs may be oxidized by the
cytochrome P450 Cytochromes P450 (P450s or CYPs) are a Protein superfamily, superfamily of enzymes containing heme as a cofactor (biochemistry), cofactor that mostly, but not exclusively, function as monooxygenases. However, they are not omnipresent; for examp ...
enzyme. Like many lipophilic toxins, PCBs undergo
biomagnification Biomagnification, also known as bioamplification or biological magnification, is the increase in concentration of a substance, e.g a pesticide, in the tissue (biology), tissues of organisms at successively higher levels in a food chain. This inc ...
and
bioaccumulation Bioaccumulation is the gradual accumulation of substances, such as pesticides or other chemicals, in an organism. Bioaccumulation occurs when an organism absorbs a substance faster than it can be lost or eliminated by catabolism and excretion. T ...
primarily due to the fact that they are easily retained within organisms. Plastic pollution, specifically
microplastics Microplastics are "synthetic solid particles or polymeric matrices, with regular or irregular shape and with size ranging from 1 μm to 5 mm, of either primary or secondary manufacturing origin, which are insoluble in water." Microplastics a ...
, 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 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 is called bioaccumulation. PCB concentrations within an organism also change depending upon which
trophic level The trophic level of an organism is the position it occupies in a food web. Within a food web, a food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the ...
they occupy. When an organism occupies a high trophic level, like
orcas The orca (''Orcinus orca''), or killer whale, is a toothed whale and the largest member of the oceanic dolphin family. The only extant species in the genus '' Orcinus'', it is recognizable by its black-and-white-patterned body. A cosmopoli ...
or
human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...
s, they will accumulate more PCBs than an organism that occupies a low trophic level, like
phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater Aquatic ecosystem, ecosystems. The name comes from the Greek language, Greek words (), meaning 'plant', and (), mea ...
. If enough organisms with a trophic level are killed due to the accumulation of toxins, like PCB, 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.


Biochemical metabolism


Overview

PCBs undergo xenobiotic biotransformation, a mechanism used to make
lipophilic Lipophilicity (from Greek language, Greek λίπος "fat" and :wikt:φίλος, φίλος "friendly") is the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such compounds are c ...
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 the rings. Phase I reactions occur by adding an oxygen to either of the benzene rings by
Cytochrome P450 Cytochromes P450 (P450s or CYPs) are a Protein superfamily, superfamily of enzymes containing heme as a cofactor (biochemistry), cofactor that mostly, but not exclusively, function as monooxygenases. However, they are not omnipresent; for examp ...
. 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 the most likely to leave the organism. However, some metabolites of PCBs containing ''ortho''–''meta'' protons have increased
steric hindrance Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is generally a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape ( conformation) and reactivi ...
from the oxygen, causing increased stability and an increased chance of accumulation.


Species dependent

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 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 In chemistry, hydroxylation refers to the installation of a hydroxyl group () into an organic compound. Hydroxylations generate alcohols and phenols, which are very common functional groups. Hydroxylation confers some degree of water-solubility ...
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 is thought to be linked to PCB 77 metabolism, something that was not measured in this study.


Temperature dependent

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 The yellow perch (''Perca flavescens''), commonly referred to as perch, striped perch, American perch or preacher is a freshwater perciform fish native to much of North America. The yellow perch was described in 1814 by Samuel Latham Mitchill fr ...
(''Perca flavescens''). In fall and winter, only 11 out of 72 introduced PCB congeners were excreted and had
halflives Halflives is an alternative rock band from Modena, Italy. Following several lineup changes, the band is now a solo project composed of frontwoman Linda Battilani. After releasing their debut 8-track record "Empty Rooms" in 2017, they toured Eur ...
of more than 1,000 days. During spring and summer when 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 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.


Sex dependent

Enantiomer In chemistry, an enantiomer (Help:IPA/English, /ɪˈnænti.əmər, ɛ-, -oʊ-/ Help:Pronunciation respelling key, ''ih-NAN-tee-ə-mər''), also known as an optical isomer, antipode, or optical antipode, is one of a pair of molecular entities whi ...
s of chiral compounds have similar chemical and physical properties, but can be metabolized by the body differently. This was looked at in
bowhead whale The bowhead whale (''Balaena mysticetus''), sometimes called the Greenland right whale, Arctic whale, and polar whale, is a species of baleen whale belonging to the family Balaenidae and is the only living representative of the genus '' Balaena' ...
s (''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 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).


Health effects

The toxicity of PCBs varies considerably among congeners. The
coplanar In geometry, a set of points in space are coplanar if there exists a geometric plane that contains them all. For example, three points are always coplanar, and if the points are distinct and non-collinear, the plane they determine is unique. How ...
PCBs, known as nonortho PCBs because they are not substituted at 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 a scale from 0 to 1. One of the most toxic compounds known, 2,3,7,8-tetrachlorodibenzo ioxin, 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."


Exposure and excretion

In general, people are exposed to PCBs overwhelmingly through food, much less so by breathing contaminated air, and least by skin contact. Once exposed, some PCBs may change to other chemicals inside the body. These chemicals or unchanged PCBs can be excreted in feces or may remain in a person's body for years, with half lives estimated at 10–15 years. PCBs collect in
body fat Adipose tissue (also known as body fat or simply fat) is a loose connective tissue composed mostly of adipocytes. It also contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, Blood vessel, vascular endothel ...
and milk fat. PCBs biomagnify up the
food web A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Position in the food web, or trophic level, is used in ecology to broadly classify organisms as autotrophs or he ...
and are present in fish and overflow of contaminated aquifers. Human infants are exposed to PCBs through
breast milk Breast milk (sometimes spelled as breastmilk) or mother's milk is milk produced by the mammary glands in the breasts of women. Breast milk is the primary source of nutrition for newborn infants, comprising fats, proteins, carbohydrates, and a var ...
or by intrauterine exposure through transplacental transfer of PCBs and are at the top of the food chain. Workers recycling old equipment in the electronics recycling industry can also be exposed to PCBs.


Signs and symptoms


Humans

The most commonly observed health effects in people exposed to extremely high levels of PCBs are skin conditions, such as chloracne and
rash A rash is a change of the skin that affects its color, appearance, or texture. A rash may be localized in one part of the body, or affect all the skin. Rashes may cause the skin to change color, itch, become warm, bumpy, chapped, dry, cracke ...
es, but these were known to be symptoms of acute systemic poisoning dating back to 1922. Studies in workers exposed to PCBs have shown changes in
blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood is com ...
and
urine Urine is a liquid by-product of metabolism in humans and many other animals. In placental mammals, urine flows from the Kidney (vertebrates), kidneys through the ureters to the urinary bladder and exits the urethra through the penile meatus (mal ...
that may indicate
liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...
damage. In Japan in 1968, 280 kg of PCB-contaminated
rice bran oil Rice bran oil is the oil extracted from the hard outer brown layer of rice called bran. It is known for its high smoke point of and mild flavor, making it suitable for high-temperature cooking methods such as stir frying and deep frying. It i ...
was used as chicken feed, resulting in a mass poisoning, known as Yushō disease, in over 1800 people. Common symptoms included dermal and ocular
lesion A lesion is any damage or abnormal change in the tissue of an organism, usually caused by injury or diseases. The term ''Lesion'' is derived from the Latin meaning "injury". Lesions may occur in both plants and animals. Types There is no de ...
s, irregular
menstrual cycle The menstrual cycle is a series of natural changes in hormone production and the structures of the uterus and ovaries of the female reproductive system that makes pregnancy possible. The ovarian cycle controls the production and release of eg ...
s and lowered
immune response An immune response is a physiological reaction which occurs within an organism in the context of inflammation for the purpose of defending against exogenous factors. These include a wide variety of different toxins, viruses, intra- and extracellula ...
s. Other symptoms included fatigue, headaches, coughs, and unusual skin sores. Additionally, in children, there were reports of poor cognitive development. Women exposed to PCBs before or during pregnancy can give birth to children with lowered cognitive ability, compromised immune systems, and motor control problems. There is evidence that crash dieters that have been exposed to PCBs have an elevated risk of health complications. Stored PCBs in the
adipose tissue Adipose tissue (also known as body fat or simply fat) is a loose connective tissue composed mostly of adipocytes. It also contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, Blood vessel, vascular endothel ...
become mobilized into the blood when individuals begin to crash diet. PCBs have shown toxic and
mutagen In genetics, a mutagen is a physical or chemical agent that permanently changes genetic material, usually DNA, in an organism and thus increases the frequency of mutations above the natural background level. As many mutations can cause cancer in ...
ic effects by interfering with
hormone A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs or tissues by complex biological processes to regulate physio ...
s in the body. PCBs, depending on the specific congener, have been shown to both inhibit and imitate
estradiol Estradiol (E2), also called oestrogen, oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of female reproductive cycles such as estrous and menstrual cycles. Estradiol is responsible ...
, the main sex hormone in females. Imitation of the estrogen compound can feed estrogen-dependent
breast cancer Breast cancer is a cancer that develops from breast tissue. Signs of breast cancer may include a Breast lump, lump in the breast, a change in breast shape, dimpling of the skin, Milk-rejection sign, milk rejection, fluid coming from the nipp ...
cells, and possibly cause other cancers, such as uterine or cervical. Inhibition of estradiol can lead to serious developmental problems for both males and females, including sexual, skeletal, and mental development issues. In a cross-sectional study, PCBs were found to be negatively associated with testosterone levels in adolescent boys. High PCB levels in adults have been shown to result in reduced levels of the thyroid hormone
triiodothyronine Triiodothyronine, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate. Production of T3 and its prohormone thyroxi ...
, which affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate. It also resulted in reduced immunity and increased thyroid disorders.


Animals

Animals that eat PCB-contaminated food, even for short periods of time, suffer liver damage and may die. In 1968 in Japan, 400,000 birds died after eating poultry feed that was contaminated with PCBs. Animals that ingest smaller amounts of PCBs in food over several weeks or months develop various health effects, including
anemia Anemia (also spelt anaemia in British English) is a blood disorder in which the blood has a reduced ability to carry oxygen. This can be due to a lower than normal number of red blood cells, a reduction in the amount of hemoglobin availabl ...
; acne-like skin conditions ( chloracne); liver,
stomach The stomach is a muscular, hollow organ in the upper gastrointestinal tract of Human, humans and many other animals, including several invertebrates. The Ancient Greek name for the stomach is ''gaster'' which is used as ''gastric'' in medical t ...
, and
thyroid The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans, it is a butterfly-shaped gland located in the neck below the Adam's apple. It consists of two connected lobes. The lower two thirds of the lobes are connected by ...
gland injuries (including hepatocarcinoma), and
thymocyte A thymocyte is an immune cell present in the thymus, before it undergoes transformation into a T cell. Thymocytes are produced as stem cells in the bone marrow and reach the thymus via the blood. Thymopoiesis describes the process which turns thy ...
apoptosis Apoptosis (from ) is a form of programmed cell death that occurs in multicellular organisms and in some eukaryotic, single-celled microorganisms such as yeast. Biochemistry, Biochemical events lead to characteristic cell changes (Morphology (biol ...
. Other effects of PCBs in animals include changes in the
immune system The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic ...
, behavioral alterations, and impaired reproduction. PCBs that have dioxin-like activity are known to cause a variety of
teratogenic Teratology is the study of abnormalities of physiological development in organisms during their life span. It is a sub-discipline in medical genetics which focuses on the classification of congenital abnormalities in dysmorphology caused by ...
effects in animals. Exposure to PCBs causes hearing loss and symptoms similar to hypothyroidism in rats.


Cancer

In 2013, the
International Agency for Research on Cancer The International Agency for Research on Cancer (IARC; ) is an intergovernmental agency forming part of the World Health Organization of the United Nations. Its role is to conduct and coordinate research into the causes of cancer. It also cance ...
(IARC) classified dioxin-like PCBs as human
carcinogen A carcinogen () is any agent that promotes the development of cancer. Carcinogens can include synthetic chemicals, naturally occurring substances, physical agents such as ionizing and non-ionizing radiation, and biologic agents such as viruse ...
s. According to the U.S. EPA, PCBs have been shown to cause cancer in animals and evidence supports a cancer-causing effect in humans. Per the EPA, studies have found increases in malignant melanoma and rare liver cancers in PCB workers. In 2013, the IARC determined that the evidence for PCBs causing
non-Hodgkin lymphoma Non-Hodgkin lymphoma (NHL), also known as non-Hodgkin's lymphoma, is a group of blood cancers that includes all types of lymphomas except Hodgkin lymphomas. Symptoms include enlarged lymph nodes, fever, night sweats, weight loss, and tiredn ...
is "limited" and "not consistent". In contrast an association between elevated blood levels of PCBs and non-Hodgkin lymphoma had been previously accepted. PCBs may play a role in the development of cancers of the immune system because some tests of laboratory animals subjected to very high doses of PCBs have shown effects on the animals' immune system, and some studies of human populations have reported an association between environmental levels of PCBs and immune response.


Lawsuits related to health effects

In the early 1990s, Monsanto faced several lawsuits over harm caused by PCBs from workers at companies such as Westinghouse that bought PCBs from Monsanto and used them to build electrical equipment. Monsanto and its customers, such as Westinghouse and GE, also faced litigation from third parties, such as workers at scrap yards that bought used electrical equipment and broke them down to reclaim valuable metals. Monsanto settled some of these cases and won the others, on the grounds that it had clearly told its customers that PCBs were dangerous chemicals and that protective procedures needed to be implemented. In 2003, Monsanto and Solutia Inc., a Monsanto corporate spin-off, reached a $700 million settlement with the residents of West Anniston, Alabama, who had been affected by the manufacturing and dumping of PCBs. In a trial lasting six weeks, the jury found that "Monsanto had engaged in outrageous behavior, and held the corporations and its corporate successors liable on all six counts it considered – including negligence, nuisance, wantonness and suppression of the truth." In 2014, the Los Angeles Superior Court found that Monsanto was not liable for cancers claimed to be from PCBs permeating the food supply of three plaintiffs who had developed non-Hodgkin's lymphoma. After a four-week trial, the jury found that Monsanto's production and sale of PCBs between 1935 and 1977 were not substantial causes of the cancer. In 2015, the cities of Spokane, San Diego, and San Jose initiated lawsuits against Monsanto to recover cleanup costs for PCB contaminated sites, alleging that Monsanto continued to sell PCBs without adequate warnings after they knew of their toxicity. Monsanto issued a media statement concerning the San Diego case, claiming that improper use or disposal by third-parties, of a lawfully sold product, was not the company's responsibility. In July 2015, a St Louis county court in Missouri found that Monsanto, Solutia, Pharmacia and Pfizer were not liable for a series of deaths and injuries caused by PCBs manufactured by Monsanto Chemical Company until 1977. The trial took nearly a month and the jury took a day of deliberations to return a verdict against the plaintiffs from throughout the USA. Similar cases are ongoing. "The evidence simply doesn't support the assertion that the historic use of PCB products was the cause of the plaintiffs' harms. We are confident that the jury will conclude, as two other juries have found in similar cases, that the former Monsanto Company is not responsible for the alleged injuries," a Monsanto statement said. In May 2016, a Missouri state jury ordered Monsanto to pay $46.5 million to three plaintiffs whose exposure to PCB caused non-Hodgkin lymphoma. In December 2016, the state of Washington filed suit in King County. The state sought damages and clean up costs related to PCBs. In March 2018
Ohio Attorney General The Ohio attorney general is the chief legal officer of the state of Ohio in the United States. The office is filled by general election, held every four years. The Ohio attorney general is Republican Dave Yost. History The office of the att ...
Mike DeWine Richard Michael DeWine ( ; born January 5, 1947) is an American politician and attorney serving as the 70th List of governors of Ohio, governor of Ohio since 2019. A member of the Republican Party (United States), Republican Party, he served a ...
also filed a lawsuit against
Monsanto The Monsanto Company () was an American agrochemical and agricultural biotechnology corporation founded in 1901 and headquartered in Creve Coeur, Missouri. Monsanto's best-known product is Roundup, a glyphosate-based herbicide, developed ...
over health issues posed by PCBs. On November 21, 2019, a federal judge denied a bid by Monsanto to dismiss a lawsuit filed by LA County calling the company to clean up cancer-causing PCBs from Los Angeles County waterways and storm sewer pipelines. The lawsuit calls for Monsanto to pay for cleanup of PCBs from dozens of waterways, including the LA River, San Gabriel River and the Dominguez Watershed. In June 2020, Bayer agreed to pay $650 million to settle local lawsuits related to Monsanto's pollution of public waters in various areas of the United States with PCBs. In 2023, over 90 Vermont school districts joined a lawsuit against Monsanto alleging that PCBs created by the company were used in the construction of their schools. The
Vermont Attorney General The Vermont attorney general is a statewide elected executive official in the U.S. state of Vermont who is elected every two years. It was created by an act of the Vermont General Assembly in 1790, repealed in 1797, and revived in 1904. The office ...
's office also filed its own lawsuit against Monsanto related to the use of its PCBs.


History

In 1865, the first "PCB-like" chemical was discovered, and was found to be a byproduct of
coal tar Coal tar is a thick dark liquid which is a by-product of the production of coke and coal gas from coal. It is a type of creosote. It has both medical and industrial uses. Medicinally it is a topical medication applied to skin to treat psoria ...
. Years later in 1876, German chemist Oscar Döbner (Doebner) synthesized the first PCB in a laboratory. Since then, large amounts of PCBs were released into the environment, to the extent that there are even measurable amounts of PCBs in feathers of birds currently held in museums before the production of PCBs peaked. In 1935, Monsanto Chemical Company (later Solutia Inc) took over commercial production of PCBs from Swann Chemical Company which had begun in 1929. PCBs, originally termed "chlorinated diphenyls", were commercially produced as mixtures of
isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...
s at different degrees of chlorination. The electric industry used PCBs as a non-flammable replacement for
mineral oil Mineral oil is any of various colorless, odorless, light mixtures of higher alkanes from a mineral source, particularly a distillate of petroleum, as distinct from usually edible vegetable oils. The name 'mineral oil' by itself is imprecise, ...
to cool and insulate industrial transformers and capacitors. PCBs were also commonly used as
heat stabilizer Polyvinyl chloride (alternatively: poly(vinyl chloride), colloquial: vinyl or polyvinyl; abbreviated: PVC) is the world's third-most widely produced synthetic polymer of plastic (after polyethylene and polypropylene). About 40 million tons of ...
in cables and electronic components to enhance the heat and fire resistance of PVC. In the 1930s, the toxicity associated with PCBs and other chlorinated hydrocarbons, including polychlorinated naphthalenes, was recognized because of a variety of industrial incidents. Between 1936 and 1937, there were several medical cases and papers released on the possible link between PCBs and its detrimental health effects. In 1936, a U.S.
Public health Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals". Analyzing the de ...
Service official described the wife and child of a worker from the Monsanto Industrial Chemical Company who exhibited blackheads and pustules on their skin. The official attributed these symptoms to contact with the worker's clothing after he returned from work. In 1937, a conference about the hazards was organized at Harvard School of Public Health, and a number of publications referring to the toxicity of various chlorinated hydrocarbons were published before 1940. In 1947, Robert Brown reminded chemists 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". In 1954, Kanegafuchi Chemical Co. Ltd. (Kaneka Corporation) first produced PCBs, and continued until 1972. Through the 1960s Monsanto Chemical Company knew increasingly more about PCBs' harmful effects on humans and the environment, per internal leaked documents released in 2002, yet PCB manufacture and use continued with few restraints until the 1970s. In 1966, PCBs were determined by Swedish chemist Sören Jensen to be an environmental contaminant. Jensen, according to a 1994 article in ''Sierra (magazine), Sierra'', named chemicals PCBs, which previously, had simply been called "phenols" or referred to by various trade names, such as Aroclor, Kanechlor, Pyrenol, Chlorinol and others. In 1972, PCB production plants existed in Austria, West Germany, France, the UK, Italy, Japan, Spain, the USSR and the US. In the early 1970s, Ward B. Stone of the New York State Department of Environmental Conservation (NYSDEC) first published his findings that PCBs were leaking from transformers and had contaminated the soil at the bottom of utility poles. There have been allegations that Industrial Bio-Test Laboratories#Polychlorinated biphenyls, Industrial Bio-Test Laboratories engaged in data falsification in testing relating to PCBs. In 2003, Monsanto and Solutia Inc., a Monsanto corporate spinoff, reached a US$700 million settlement with the residents of Anniston, Alabama, West Anniston, Alabama, who had been affected by the manufacturing and dumping of PCBs. In a trial lasting six weeks, the jury found that "Monsanto had engaged in outrageous behavior, and held the corporations and its corporate successors liable on all six counts it considered – including negligence, nuisance, wantonness and suppression of the truth." Existing products containing PCBs which are "totally enclosed uses" such as insulating fluids in transformers and capacitors, vacuum pump fluids, and
hydraulic fluid A hydraulic fluid or hydraulic liquid is the medium by which power is transferred in hydraulic machinery. Common hydraulic fluids are based on mineral oil or water. Examples of equipment that might use hydraulic fluids are excavators and backho ...
, are allowed to remain in use in the US. The public, legal, and scientific concerns about PCBs arose from research indicating they are likely
carcinogen A carcinogen () is any agent that promotes the development of cancer. Carcinogens can include synthetic chemicals, naturally occurring substances, physical agents such as ionizing and non-ionizing radiation, and biologic agents such as viruse ...
s having the potential to adversely impact the environment and, therefore, undesirable as commercial products. 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.


Pollution due to PCBs


Belgium

In 1999, the Dioxin Affair occurred when 50 kg of PCB transformer oils were added to a stock of recycled fat used for the production of 500 tonnes of animal feed, eventually affecting around 2,500 farms in several countries. The name ''Dioxin Affair'' was coined from early misdiagnosis of dioxins as the primary contaminants, when in fact they turned out to be a relatively small part of the contamination caused by thermal reactions of PCBs. The PCB congener pattern suggested the contamination was from a mixture of Aroclor 1260 and 1254. Over 9 million chickens, and 60,000 pigs were destroyed because of the contamination. The extent of human health effects has been debated, in part because of the use of differing risk assessment methods. One group predicted increased cancer rates, and increased rates of neurological problems in those exposed as neonates. A second study suggested carcinogenic effects were unlikely and that the primary risk would be associated with developmental effects due to exposure in pregnancy and neonates. Two businessmen who knowingly sold the contaminated feed ingredient received two-year suspended sentences for their role in the crisis.


Italy

The Italian company Caffaro, located in Brescia, specialized in producing PCBs from 1938 to 1984, following the acquisition of the exclusive rights to use the patent in Italy from Monsanto. The pollution resulting from this factory and the case of Anniston, in the US, are the largest known cases in the world of PCB contamination in water and soil, in terms of the amount of toxic substance dispersed, size of the area contaminated, number of people involved and duration of production. The values reported by the local health authority (ASL) of Brescia since 1999 are 5,000 times above the limits set by Ministerial Decree 471/1999 (levels for residential areas, 0.001 mg/kg). As a result of this and other investigations, in June 2001, a complaint of an environmental disaster was presented to the Public Prosecutor's Office of Brescia. Research on the adult population of Brescia showed that residents of some urban areas, former workers of the plant, and consumers of contaminated food, have PCB levels in their bodies that are in many cases 10–20 times higher than reference values in comparable general populations. PCBs entered the human food supply by animals grazing on contaminated pastures near the factory, especially in local veal mostly eaten by farmers' families. The exposed population showed an elevated risk of Non-Hodgkin lymphoma, but not for other specific cancers.


Japan

In 1968, a mixture of dioxins and PCBs got into rice bran oil produced in northern Kyushu. Contaminated cooking oil sickened more than 1,860 people. The symptoms were called Yushō disease. In Okinawa, high levels of PCB contamination in soil on Kadena Air Base were reported in 1987 at thousands of parts per million, some of the highest levels found in any pollution site in the world.


Republic of Ireland

In December 2008, a number of Irish news sources reported testing had revealed "extremely high" levels of dioxins, by toxic equivalent, in pork products, ranging from 80 to 200 times the European Union, EU's upper safe limit of 1.5 pg WHO-TEQDFP/μg i.e. 0.12 to 0.3 parts per billion. Brendan Smith (politician), Brendan Smith, the Minister for Agriculture, Fisheries and Food, stated the pork contamination was caused by PCB-contaminated feed that was used on 9 of Ireland's 400 pig farms, and only one feed supplier was involved. Smith added that 38 beef farms also used the same contaminated feed, but those farms were quickly isolated and no contaminated beef entered the food chain. While the contamination was limited to just 9 pig farms, the Irish government requested the immediate withdrawal and disposal of all pork-containing products produced in Ireland and purchased since September 1, 2008. This request for withdrawal of pork products was confirmed in a press release by the Food Safety Authority of Ireland on December 6. It is thought that the incident resulted from the contamination of fuel oil used in a drying burner at a single feed processor, with PCBs. The resulting combustion produced a highly toxic mixture of PCBs, dioxins and furans, which was included in the feed produced and subsequently fed to a large number of pigs.


Kenya

In Kenya, a number of cases have been reported in the 2010s of thieves selling transformer oil, stolen from electric
transformer In electrical engineering, a transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple Electrical network, circuits. A varying current in any coil of the transformer produces ...
s, to the operators of roadside food stalls for use in deep frying. When used for frying, it is reported that transformer oil lasts much longer than regular cooking oil. The downside of this misuse of the transformer oil is the threat to the health of the consumers, due to the presence of PCBs.


Slovakia

The chemical plant Chemko in Strážske (east Slovakia) was an important producer of polychlorinated biphenyls for the former communist bloc (Comecon) until 1984. Chemko contaminated a large part of east Slovakia, especially the sediments of the Laborec river and reservoir Zemplínska šírava.


Slovenia

Between 1962 and 1983, the Iskra (company), Iskra Kondenzatorji company in Semič (White Carniola, Southeast Slovenia) manufactured
capacitor In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...
s using PCBs. Due to the wastewater and improperly disposed waste products, the area (including the Krupa (Lahinja), Krupa and Lahinja rivers) became highly contaminated with PCBs. The pollution was discovered in 1983, when the Krupa river was meant to become a water supply source. The area was sanitized then, but the soil and water are still highly polluted. Traces of PCBs were found in food (eggs, cow milk, walnuts) and Krupa is still the most PCB-polluted river in the world.


Spain and Portugal

Several cetacean species have very high mean blubber PCB concentrations likely to cause population declines and suppress population recovery. Striped dolphins, bottlenose dolphins and orcas were found to have mean levels that markedly exceeded all known marine mammal PCB toxicity thresholds. The western Mediterranean Sea and the south-west Iberian Peninsula were identified as "hotspots".


United Kingdom

Monsanto The Monsanto Company () was an American agrochemical and agricultural biotechnology corporation founded in 1901 and headquartered in Creve Coeur, Missouri. Monsanto's best-known product is Roundup, a glyphosate-based herbicide, developed ...
manufactured PCBs at its chemical plant in Newport, Wales, Newport, South Wales, until the mid- to late-1970s. During this period, waste matter, including PCBs, from the Newport site was dumped at a disused quarry near Groes-faen, west of Cardiff, and Penhros landfill site from where it continues to be released in waste water discharges.


United States

Monsanto was the only company that manufactured PCBs in the US. Its production was entirely halted in 1977. (Kimbrough, 1987, 1995) On November 25, 2020, U.S. District Judge Fernando M. Olguin rejected a proposed $650 million settlement from Bayer, the company which acquired Monsanto in 2018, and allowed Monsanto-related lawsuits involving PCB to proceed.


Alabama

PCBs originating from Monsanto Chemical Company in Anniston, Alabama, Anniston, Alabama, were dumped into Snow Creek, which then spread to Choccolocco Creek, then Logan Martin Lake. In the early 2000s, class action lawsuits were settled by local land owners, including those on Logan Martin Lake, and Lay Dam, Lay Reservoir (downstream on the Coosa River), for the PCB pollution. Donald Stewart, former Senator from Alabama, first learned of the concerns of hundreds of west Anniston residents after representing a church which had been approached about selling its property by Monsanto. Stewart went on to be the pioneer and lead attorney in the first and majority of cases against Monsanto and focused on residents in the immediate area known to be most polluted. Other attorneys later joined in to file suits for those outside the main immediate area around the plant; one of these was the late Johnnie Cochran. In 2007, the highest pollution levels remained concentrated in Snow and Choccolocco Creeks. Concentrations in fish have declined and continue to decline over time; sediment disturbance, however, can resuspend the PCBs from the sediment back into the water column and food web.


California

San Francisco Bay has been contaminated by PCBs, "a legacy of PCBs spread widely across the land surface of the watershed, mixed deep into the sediment of the Bay, and contaminating the Bay food web". Levels of PCBs in fish and shellfish exceed thresholds for safe consumption. Signs around the Bay warn anglers of which species to avoid. State water quality regulators set a Total Maximum Daily Load for PCBs require city and county governments around the Bay to implement control measures to limit PCBs in urban runoff. An important part of the second, revised version of this permit was the requirement for municipalities to install green infrastructure with a goal of reducing pollutant levels in stormwater.


Connecticut

In New Haven, the decommissioned English Station has a high concentration of PCB contamination due to the chemicals used in the running of the plant. This, along with asbestos contamination, has made cleaning and demolishing the abandoned site extremely difficult. The PCB contamination has spread to the soil, and to the river, where locals will sometimes fish unaware of the danger.


Great Lakes

In 1976, environmentalists found PCBs in the sludge at Waukegan, Illinois, Waukegan Harbor, the southwest end of
Lake Michigan Lake Michigan ( ) is one of the five Great Lakes of North America. It is the second-largest of the Great Lakes by volume () and depth () after Lake Superior and the third-largest by surface area (), after Lake Superior and Lake Huron. To the ...
. They were able to trace the source of the PCBs back to the Outboard Marine Corporation that was producing boat motors next to the harbor. By 1982, the Outboard Marine Corporation was court-ordered to release quantitative data referring to their PCB waste released. The data stated that from 1954 they released 100,000 tons of PCB into the environment, and that the sludge contained PCBs in concentrations as high as 50%. In 1989, during construction near the Zilwaukee, Michigan, Zilwaukee bridge, workers uncovered an uncharted landfill containing PCB-contaminated waste which cost $100,000 to clean up. Much of the Great Lakes area were still heavily polluted with PCBs in 1988, despite extensive remediation work.


Indiana

From the late 1950s through 1977, Westinghouse Electric used PCBs in the manufacture of capacitors in its Bloomington, Indiana, Bloomington, Indiana, plant. Reject capacitors were hauled and dumped in area salvage yards and landfills, including Bennett's Dump, Neal's Landfill and Lemon Lane Landfill. 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 2,000 sites, which remain unaddressed. Over 1,000 tons of PCBs were estimated to have been dumped in Monroe County, Indiana, Monroe and Owen County, Indiana, Owen counties. Although federal and state authorities have been working on the sites' environmental remediation, many areas remain contaminated. Concerns have been raised regarding the removal of PCBs from the karst limestone topography, and regarding the possible disposal options. To date, the Westinghouse Bloomington PCB Superfund site case does not have a Remedial Investigation/Feasibility Study (RI/FS) and Record of Decision (ROD), although Westinghouse signed a US Department of Justice Consent Decree in 1985. The 1985 consent decree required Westinghouse to construct an incinerator that would incinerate PCB-contaminated materials. Because of public opposition to the incinerator, however, the State of Indiana passed a number of laws that delayed and blocked its construction. The parties to the consent decree began to explore alternative remedies in 1994 for six of the main PCB contaminated sites in the consent decree. Hundreds of sites remain unaddressed as of 2014. Monroe County will never be PCB-free, as noted in a 2014 Indiana University program about the local contamination. On February 15, 2008, Monroe County approved a plan to clean up the three remaining contaminated sites in the City of Bloomington, at a cost of United States dollar, $9.6 million to CBS Corporation, CBS Corp., the successor of Westinghouse. In 1999, Viacom bought CBS, so they are current responsible party for the PCB sites.


Massachusetts

Pittsfield, Massachusetts, Pittsfield, in western Massachusetts, was home to the General Electric Pittsfield Plant, General Electric (GE) transformer, capacitor, and electrical generating equipment divisions. The electrical generating division built and repaired equipment that was used to power the electrical utility grid throughout the nation. PCB-contaminated oil routinely migrated from GE's industrial plant located in the very center of the city to the surrounding groundwater, nearby Silver Lake, and to the Housatonic River, which flows through Massachusetts, Connecticut, and down to Long Island Sound. PCB-containing solid material was widely used as fill, including meander, oxbows of the Housatonic River. Fish and waterfowl which live in and around the river contain significant levels of PCBs and are not safe to eat. EPA designated the Pittsfield plant and several miles of the river as a Superfund site in 1997, and ordered GE to remediate the site. EPA and GE began a cleanup of the area in 1999. New Bedford, Massachusetts#Geography, New Bedford Harbor, which is a listed Superfund site, contained some of the highest sediment concentrations of PCBs in the marine environment. Cleanup of the area began in 1994 and is mostly complete as of 2020. Investigations into historic waste dumping in the Bliss Corner, Massachusetts, Bliss Corner neighborhood have revealed the existence of PCBs, among other hazardous materials, buried in soil and waste material.


Missouri

In 1982, Martha C. Rose Chemical Inc. began processing and disposing of materials contaminated with PCBs in Holden, Missouri, a small rural community about east of Kansas City. From 1982 until 1986, nearly 750 companies, including General Motors Corp., Commonwealth Edison, Illinois Power Co. and West Texas Utilities, sent millions of pounds of PCB contaminated materials to Holden for disposal. Instead, according to prosecutors, the company began storing the contaminated materials while falsifying its reports to the EPA to show they had been removed. After investigators learned of the deception, Rose Chemical was closed and filed for bankruptcy. The site had become the nation's largest waste site for the chemical PCB. In the four years the company was operational, the EPA inspected it four times and assessed $206,000 in fines but managed to collect only $50,000. After the plant closed the state environmental agency found PCB contamination in streams near the plant and in the city's sewage treatment sludge. A 100,000 square-foot warehouse and unknown amounts of contaminated soil and water around the site had to be cleaned up. Most of the surface debris, including close to 13 million pounds of contaminated equipment, carcasses and tanks of contaminated oil, had to be removed. Walter C. Carolan, owner of Rose Chemical, and five others pleaded guilty in 1989 to committing fraud or falsifying documents. Carolan and two other executives served sentences of less than 18 months; the others received fines and were placed on probation. Cleanup costs at the site are estimated at $35 million.


Montana

Two launch facilities at Malmstrom Air Force Base showed PCB levels higher than the thresholds recommended by the Environmental Protection Agency when extensive sampling began of active U.S. intercontinental ballistic missile bases to address specific cancer concerns in 2023.


New York

Pollution of the Hudson River is largely due to dumping of PCBs by
General Electric General Electric Company (GE) was an American Multinational corporation, multinational Conglomerate (company), conglomerate founded in 1892, incorporated in the New York (state), state of New York and headquartered in Boston. Over the year ...
from 1947 to 1977. GE dumped an estimated 1.3 million pounds of PCBs into the Hudson River during these years. The PCBs came from the company's two capacitor manufacturing plants at Hudson Falls, New York, Hudson Falls and Fort Edward (town), New York, Fort Edward, New York. This pollution caused a range of harmful effects to wildlife and people who eat fish from the river or drink the water. In 1984, EPA declared a 200-mile (320 km) stretch of the river, from Hudson Falls to New York City, to be a Superfund site requiring cleanup. Extensive remediation actions on the river began in the 1970s with the implementation of Clean Water Act#Point sources, wastewater discharge permits and consequent control or reduction of wastewater discharges, and sediment removal operations, which have continued into the 21st century. Love Canal is a neighborhood in Niagara Falls, New York, Niagara Falls, New York, that was heavily contaminated with toxic waste including PCBs. Eighteen Mile Creek (Niagara County), Eighteen Mile Creek in Lockport (town), New York, Lockport, New York, is an EPA Superfund site for PCBs contamination. PCB pollution at the Government Plaza, Binghamton, State Office Building in Binghamton, New York, Binghamton was responsible for what is now considered to be the first indoor environmental disaster in the United States. In 1981, a transformer explosion in the basement spewed PCBs throughout the entire 18-story building. The contamination was so severe that cleanup efforts kept the building closed for 13 years.


North Carolina

One of the largest deliberate PCB spills in American history occurred in the summer of 1978 when 31,000 gallons (117 m^3) of PCB-contaminated oil were illegally sprayed by the Ward PCB Transformer Company in swaths along the roadsides of some of North Carolina highway shoulders in 14 counties and at the Fort Bragg Army Base. The crime, known as "Warren County PCB Landfill, the midnight dumpings", occurred over nearly two weeks, as drivers of a black-painted tanker truck drove down one side of rural Piedmont highways spraying PCB-laden waste and then up the other side the following night. Under Governor Jim Hunt, James B. Hunt, Jr., state officials then erected large, yellow warning signs along the contaminated highways that read: "CAUTION: PCB Chemical Spills Along Highway Shoulders". The illegal dumping is believed to have been motivated by the passing of the Toxic Substances Control Act (TSCA), which became effective on August 2, 1978, and increased the expense of chemical waste disposal. Within a couple of weeks of the crime, Robert Burns and his sons, Timothy and Randall, were arrested for dumping the PCBs along the roadsides. Burns was a business partner of Robert "Buck" Ward Jr., of the Ward PCB Transformer Company, in Raleigh. Burns and sons pleaded guilty to state and Federal criminal charges; Burns received a three to five-year prison sentence. Ward was acquitted of state charges in the dumping, but was sentenced to 18 months prison time for violation of TSCA. Cleanup and disposal of the roadside PCBs generated controversy, as the Governor's plan to pick up the roadside PCBs and to bury them in a landfill in rural Warren County, North Carolina, Warren County were strongly opposed in 1982 by local residents. In October 2013, at the request of the South Carolina Department of Health and Environmental Control (SCDHEC), the City of Charlotte, North Carolina, Charlotte, North Carolina, decided to stop applying biosolids, sewage sludge to land while authorities investigated the source of PCB contamination. In February 2014, the City of Charlotte admitted PCBs have entered their sewage treatment centers as well. After the 2013 SCDHEC had issued emergency regulations, the City of Charlotte discovered high levels of PCBs entering its sewage waste water treatment plants, where sewage is converted to sewage sludge. The city at first denied it had a problem, then admitted an "event" occurred in February 2014, and in April that the problem had occurred much earlier. The city stated that its very first test with a newly changed test method revealed very high PCB levels in its sewage sludge farm field fertilizer. Because of the widespread use of the contaminated sludge, SCDHEC subsequently issued PCB fish advisories for nearly all streams and rivers bordering farm fields that had been applied with city waste.


Ohio

The Clyde cancer cluster (also known as the Sandusky County cancer cluster) is a childhood cancer, childhood cancer cluster that has affected many families in Clyde, Ohio, Clyde, Ohio, and surrounding areas. PCBs were found in soil in a public park within the area of the cancer cluster. In Akron, Ohio, Akron, Ohio, soil was contaminated and noxious PCB-laden fumes had been put into the air by an electrical transformer deconstruction operation from the 1930s to the 1960s.


South Carolina

From 1955 until 1977, the Sangamo Weston plant in Pickens, South Carolina, used PCBs to manufacture capacitors, and dumped 400,000 pounds of PCB contaminated wastewater into the Twelve Mile Creek. In 1990, the EPA declared the site of the capacitor plant, its landfills and the polluted watershed, which stretches nearly downstream to Lake Hartwell as a Superfund site. Two dams on the Twelve Mile Creek are to be removed and on Feb. 22, 2011 the first of two dams began to be dismantled. Some contaminated sediment is being removed from the site and hauled away, while other sediment is pumped into a series of settling ponds. In 2013, the state environmental regulators issued a rare emergency order, banning all sewage sludge from being land applied or deposited on landfills, as it contained very high levels of PCBs. The problem had not been discovered until thousands of acres of farm land in the state had been contaminated by the hazardous sludge. A criminal investigation to determine the perpetrator of this crime was launched.


Washington

As of 2015, several bodies of water in the state of Washington were contaminated with PCBs, including the Columbia River, the Duwamish River, Green Lake (Seattle), Green Lake, Lake Washington, the Okanogan River, Puget Sound, the Spokane River, the Walla Walla River, the Wenatchee River, and the Yakima River. A study by Washington State published in 2011 found that the two largest sources of PCB flow into the Spokane River were City of Spokane stormwater (44%) and municipal and industrial discharges (20%). PCBs entered the environment through paint, hydraulic fluids, sealants, inks and have been found in river sediment and wildlife. Spokane utilities will spend $300 million to prevent PCBs from entering the river in anticipation of a 2017 federal deadline to do so. In August 2015 Spokane joined other U.S. cities like San Diego and San Jose, California, San Jose, California, and Westport, Massachusetts, Westport, Massachusetts, in seeking damages from Monsanto.


Wisconsin

From 1954 until 1971, the Fox River in Appleton, Wisconsin, had PCBs deposited into it from Appleton Paper/NCR, P.H. Gladfelter, Georgia-Pacific and other notable local paper manufacturing facilities. The Wisconsin DNR estimates that after wastewater treatment the PCB discharges to the Fox River due to production losses ranged from 81,000 kg to 138,000 kg. (178,572 lbs. to 304,235 lbs). The production of Carbon Copy Paper and its byproducts led to the discharge into the river. Fox River clean up is ongoing.


Pacific Ocean

Polychlorinated biphenyls have been discovered in organisms living in the Mariana Trench in the Pacific Ocean. Levels were as high as 1,900 nanograms per gram of Amphipoda, amphipod tissue in the organisms analyzed.


Regulation


Japan

In 1972 the Japanese government banned the production, use, and import of PCBs.


Sweden

In 1973, the use of PCBs in "open" or "dissipative" sources (such as Plasticizer, plasticisers in paints and cements, casting agents, fire retardant fabric treatments and Heat stabilizer, heat stabilizing additives for PVC electrical insulation,
adhesive Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. The use of adhesives offers certain advantage ...
s, paints and waterproofing, railroad ties) was banned in Sweden.


United Kingdom

In 1981, the UK banned closed uses of PCBs in new equipment, and nearly all UK PCB synthesis ceased; closed uses in existing equipment containing in excess of 5 litres of PCBs were not stopped until December 2000.


United States

In 1976, concern over the toxicity and persistence (chemical stability) of PCBs in the environment led the United States Congress to ban their domestic production, effective January 1, 1978, pursuant to the Toxic Substances Control Act of 1976, Toxic Substances Control Act. To implement the law, EPA banned new manufacturing of PCBs, but issued regulations that allowed for their continued use in electrical equipment for economic reasons. EPA began issuing regulations for PCB usage and disposal in 1979. The agency has issued guidance publications for safe removal and disposal of PCBs from existing equipment. EPA defined the "maximum contaminant level goal" for public water systems as zero, but because of the limitations of water treatment technologies, a level of 0.5 parts per billion is the actual regulated level (maximum contaminant level).


Methods of destruction


Physical

PCBs were technically attractive because of their inertness, which includes their resistance to combustion. Nonetheless, they can be effectively destroyed by incineration at 1000 °C. When combusted at lower temperatures, they convert in part to more hazardous unintentional persistent organic pollutants, including polychlorinated dibenzofurans and dibenzo-p-dioxins. When conducted properly, the combustion products are water, carbon dioxide, and hydrogen chloride. In some cases, the PCBs are combusted as a solution in kerosene. PCBs have also been destroyed by pyrolysis in the presence of alkali metal carbonates. Thermal desorption is highly effective at removing PCBs from soil.


Chemical

PCBs are fairly chemically unreactive, this property being attractive for its application as an inert material. They resist oxidation. Many chemical compounds are available to destroy or reduce the PCBs. Commonly, PCBs are degraded by basic mixtures of glycols, which displace some or all chloride. Also effective are reductants such as sodium or sodium naphthalene. Vitamin B12 has also shown promise.


Microbial

The use of microorganisms to degrade PCBs from contaminated sites, relying on multiple microorganisms' co-metabolism, is known as bioremediation of polychlorinated biphenyl. Some micro-organisms biodegradation, degrade PCBs by reducing the C-Cl bonds. Microbial dechlorination tends to be rather slow-acting in comparison to other methods. Enzymes extracted from microbes can show PCB activity. In 2005, ''Shewanella oneidensis'' biodegraded a high percentage of PCBs in soil samples. A low voltage current can stimulate the microbial degradation of PCBs.


Fungal

There is research showing that some ligninolytic fungi can degrade PCBs.


Bioremediation

The remediation, or removal, of PCBs from estuarian and coastal river sediments is quite difficult due to the overlying water column and the potential for resuspension of contaminants during the removal process. The most common method of PCB extraction from sediments is to dredge an area and dispose of the sediments in a landfill. This method is troubling for a number of reasons, namely that it has a risk of resuspension of the chemicals as the sediments are disturbed, and this method can be very damaging to ecosystems. A potential cost effective, low risk remediation technique is bioremediation. Bioremediation involves the use of biota to remediate sediments. Phytoremediation, the use of plants to remediate soils, has been found to be effective for a broad range of contaminants such as mercury PCB and PAHs in terrestrial soils. A promising study conducted in New Bedford Harbor found that ''Ulva rigida'', a type of seaweed common throughout the world, is effective at removing PCB from sediments. During a typical bloom in New Bedford Harbor, ''U. rigida'' forms a thick mat that lies on top of and in contact with the sediment. This allows for ''U. rigida'' to uptake large amounts of PCB from the sediment with concentrations of PCB in ''U. rigida'' reaching 1580 μg kg−1 within 24 hours of the bloom. Live tissue tended to take up higher concentrations of PCB than dead tissue, but this is not to say that dead tissue did not still take up large amounts of PCB as well.


Homologs

For a complete list of the 209 PCB congeners, see PCB congener list. Note that biphenyl, while not technically a PCB congener because of its lack of chlorine substituents, is still typically included in the literature.


See also

* Bay mud * Organochlorine compound * Polybrominated biphenyl * ''Zodiac (novel), Zodiac'', a novel by Neal Stephenson which involves PCBs and their impact on the environment.


References


External links


ATSDR Toxicological Profile
U.S. Department of Health and Human Services
IARC PCB Monograph


– US EPA
National Toxicology Program technical reports searched for "PCB"


by the WHO
Current Intelligence Bulletin 7: Polychlorinated (PCBs)
��NIOSH/CDC (1975)

(Health Canada) {{Electric transformers Chloroarenes Flame retardants Endocrine disruptors IARC Group 2A carcinogens Soil contamination Synthetic materials Electric transformers Suspected testicular toxicants Suspected fetotoxicants Suspected female reproductive toxicants Persistent organic pollutants under the Convention on Long-Range Transboundary Air Pollution Persistent organic pollutants under the Stockholm Convention Monsanto Biphenyls