Polychlorinated biphenyl

Chemical structure of PCBs. The possible positions of chlorine atoms on the benzene rings are denoted by numbers assigned to the carbon atoms.

PCB warning label on a power transformer known to contain PCBs.

A polychlorinated biphenyl (PCB) is a synthetic, organic chlorine compound derived from biphenyl, which is a molecule composed of two benzene rings. The chemical formula for a PCB (CAS number 1336-36-3 ) is C₁₂H_10−xCl_x. There are 209 configurations with 1 to 10 chlorine atoms, of which about 130 are/were used commercially.^[1]:2

Polychlorinated biphenyls were widely used as dielectric and coolant fluids in electrical apparatus, cutting fluids for machining operations, carbonless copy paper and in heat transfer fluids.^[2] Because of PCBs' environmental toxicity and classification as a persistent organic pollutant, PCB production was banned by the United States Congress in 1979 and by the Stockholm Convention on Persistent Organic Pollutants in 2001.^[3] The International Research Agency on Cancer (IRAC), 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.^[4] Many rivers and buildings including schools, parks, and other sites are contaminated with PCBs, and there have been contaminations of food supplies with the toxins.

Some PCBs share a structural similarity and toxic mode of action with dioxin.^[5] Other toxic effects such as endocrine disruption (notably blocking of thyroid system functioning) and neurotoxicity are known.^[6] The maximum allowable contaminant level in drinking water in the United States is set at zero, but because of water treatment technologies, a level of 0.5 parts per billion is the de facto level.^[7]

The bromine analogues of PCBs are polybrominated biphenyls (PBBs), which have analogous applications and environmental concerns.

Physical and chemical properties

PCBs were produced and marketed as mixtures of many congeners. PCB mixtures are characterized by chlorine content. Less-chlorinated PCBs are odorless, tasteless, clear to pale-yellow, viscous liquids, while highly chlorinated mixtures are more viscous and deeper yellow. They are formed by electrophilic chlorination of biphenyl with chlorine gas. PCBs have low water solubilities — 0.0027-0.42 ng/L for Aroclors,^[1] and low vapor pressures at room temperature, but they have high solubilities in most organic solvents, oils, and fats. They have dielectric constants of 2.5~2.7,^[8] very high thermal conductivity,^[1] high flash points (from 170 to 380 °C)^[1] and are chemically fairly inert, being extremely resistant to oxidation, reduction, addition, elimination, and electrophilic substitution.^[9] The density varies from 1.182 to 1.566 kg/L.^[1] Other physical and chemical properties vary widely across the class. As the degree of chlorination increases, melting point and lipophilicity increase, and vapour pressure and water solubility decrease.^[1]

PCBs readily penetrate skin, PVC (polyvinyl chloride), and latex (natural rubber).^[10] PCB-resistant materials include Viton, polyethylene, polyvinyl acetate (PVA), polytetrafluoroethylene (PTFE), butyl rubber, nitrile rubber, and Neoprene.^[10]

The resistance of PCBs to oxidation and reduction in the natural environment makes them very stable compounds, not decomposing readily. They have a long half life (8 to 15 years) and are insoluble in water, which contributes to their stability.^[11] Their destruction by chemical, thermal, and biochemical processes is extremely difficult, and presents the risk of generating extremely toxic dibenzodioxins and dibenzofurans through partial oxidation. Intentional degradation as a treatment of unwanted PCBs generally requires high heat or catalysis (see Methods of destruction below).

Structure and toxicity

Toxic effects vary depending on the specific PCB. In terms of their structure and toxicity, PCBs fall into 2 distinct categories, referred to as coplanar or non-ortho-substituted arene substitution patterns and noncoplanar or ortho-substituted congeners.

Structures of the twelve dioxin-like PCBs

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, and allows them to act like PCDDs, as an agonist of the aryl hydrocarbon receptor (AhR) in organisms. They are considered as contributors to overall dioxin toxicity, and the term dioxins and dioxin-like compounds is often used interchangeably when the environmental and toxic impact of these compounds is considered.^[12][13]

Noncoplanar

Noncoplanar PCBs, with chlorine atoms at the ortho positions cause neurotoxic and immunotoxic effects, but at levels much higher than normally associated with dioxins. They do not activate the AhR, and are not considered part of the dioxin group, and as of 1998 had been of less concern to regulatory bodies.^[14]

Di-ortho-substituted, non-coplanar PCBs interfere with intracellular signal transduction dependent on calcium which may lead to neurotoxicity.^[15] In 2000 it was shown that ortho-PCBs can disrupt thyroid hormone transport by binding to transthyretin.^[16]

Alternative names

Commercial PCB mixtures were marketed under the following names:^[17][18]

Brazil Ascarel Former Czechoslovakia Delor France Phenoclor Pyralène (both used by Prodolec) Germany Clophen (used by Bayer) Italy Apirolio Fenclor

Japan Kanechlor (used by Kanegafuchi) Santotherm (used by Mitsubishi) Pyroclor Former USSR Sovol Sovtol United Kingdom Aroclor xxxx (used by Monsanto Company)            Askarel

United States Aroclor xxxx (used by Monsanto Company) Asbestol Askarel Bakola131 Chlorextol - Allis-Chalmers trade name Hydol Inerteen (used by Westinghouse) Noflamol Pyranol/Pyrenol, Chlorinol (widely used in GE's oil-filled "chlorinol"-branded metal can capacitors, detected by a pungent characteristic odor released by them (especially when they fail) in appliances/consumer & commercial electronic units & motors that utilized them from the early 1960s-late 1970s such as many A/C units, Seeburg Jukeboxes & Zenith TVs) (used by General Electric) Saf-T-Kuhl Therminol FR Series (Monsanto ceased production in 1971[19]).

Aroclor mixtures

The only North American producer, Monsanto Company, marketed PCBs under the trade name Aroclor from 1930 to 1977. These were sold under trade names followed by a 4-digit number. In general, the first two digits refer to the number of carbon atoms in the biphenyl skeleton (for PCBs this is 12); the second two numbers indicate the percentage of chlorine by mass in the mixture. Thus, Aroclor 1260 has 12 carbon atoms and contains 60% chlorine by mass. An exception is Aroclor 1016, which also has 12 carbon atoms, but has 42% chlorine by mass. Aroclor 1016 was prepared by the fractional distillation of Aroclor 1242, which excluded the higher boiling (i.e., more highly chlorinated) congeners.

Different Aroclors were used at different times and for different applications. In electrical equipment manufacturing in the USA, Aroclor 1260 and Aroclor 1254 were the main mixtures used before 1950; Aroclor 1242 was the main mixture used in the 1950s and 1960s until it was phased out in 1971 and replaced by Aroclor 1016.^[1]

Industrial production and commercial applications

Estimates have put the total global production of PCBs on the order of 1.5 million tons. The United States was the single largest producer with over 600,000 tons produced between 1930 and 1977. The European region follows with nearly 450,000 tons through 1984. It is unlikely that a full inventory of global PCB production will ever be accurately tallied, as there were factories in Poland, East Germany, and Austria that produced unknown amounts of PCBs.^[20]

PCB's commercial utility was based largely on their chemical stability, including low flammability, and physical properties, including electrical insulating properties. Use of PCBs is commonly divided into closed and open applications.^[21] Examples of closed applications include coolants and insulating fluids (transformer oil) for transformers and capacitors, such as those used in old fluorescent light ballasts,^[22] hydraulic fluids, lubricating and cutting oils, etc. In contrast, the major open application of PCBs was in carbonless copy ("NCR") paper, which even nowadays results in paper contamination.^[21] Other open applications were as plasticizers in paints and cements, stabilizing additives in flexible PVC coatings of electrical cables and electronic components, pesticide extenders, reactive flame retardants and sealants for caulking in schools and commercial buildings, adhesives, wood floor finishes, such as Fabulon and other products of Halowax in the U.S.,^[23] de-dusting agents, waterproofing compounds, casting agents.^[1] Because of its use as a plasticizer in paints and especially "coal tars" that were used widely to coat water tanks, bridges and other infrastructure pieces, it is recommended that before removing the coal tar by sandblasting it should be tested first to see if PCBs are present.

Aroclor 1254 is routinely used to induce rat liver S9 for mutagenicity tests in biomedical research.^[24]

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.^[1]

Water

Because of their low vapour pressure, PCBs accumulate primarily in the hydrosphere, despite their hydrophobicity, in the organic fraction of soil, and in organisms.

The hydrosphere is the main reservoir. The immense volume of water in the oceans is still capable of dissolving a significant quantity of PCBs.

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 radicals, or directly by photolysis of carbon-chlorine bonds (even if this is a less important process).

Atmospheric concentrations of PCBs tend to be lowest in rural areas, where they are typically in the picogram per cubic meter range, higher in suburban and urban areas, and highest in city centres, where they can reach 1 ng/m³ or more. In Milwaukee, an atmospheric concentration of 1.9 ng/m³ has been measured, and this source alone was estimated to account for 120 kg/year of PCBs entering Lake Michigan.^[25] 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.^[23]

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.^[26]

Biosphere

In biosphere, PCBs can be degraded by either bacteria or eukaryotes, but the speed of the reaction depends on both the number and the disposition of chlorine atoms in the molecule: less substituted, meta- or para- substituted PCBs undergo biodegradation faster than more substituted congeners.

In bacteria, PCBs may be dechlorinated through reductive dechlorination, or oxidized by dioxygenase enzyme.

In eukaryotes, PCBs may be oxidized by the cytochrome P450 enzyme.

Like many lipiphilic toxins, PCBs biomagnify up the food chain. For instance, ducks can accumulate PCBs from eating fish and other aquatic life from contaminated rivers, and these can cause harm to human health or even death when eaten.^[27]

PCBs can be transported by birds from aquatic sources onto land via feces and carcasses.^[28]

Health effects

Labelling transformers containing PCBs

The toxicity of PCBs varies considerably among congeners. The coplanar PCBs, known as nonortho PCBs because they are not substituted at the ring positions ortho to (next to) the other ring, (i.e. PCBs 77, 126, 169, etc.), 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[p]dioxin, a PCDD, is assigned a TEF of 1.^[29]

Exposure and excretion

In general individuals 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.^[30] PCBs collect in body fat and milk fat.^[31] PCB's biomagnify up the food web and are present in fish and waterfowl of contaminated aquifers.^[32] Infants are exposed to PCBs through breast milk or by intrauterine exposure through transplacental transfer of PCBs ^[31] and are at the top of the food chain.^[33]:249ff

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 rashes, 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 and urine that may indicate liver damage. In Japan in 1968, 280 kg of PCB-contaminated rice bran oil was used as chicken feed, resulting in a mass poisoning, known as Yushō disease, in over 1800 people.^[34] Common symptoms included dermal and ocular lesions, irregular menstrual cycles and lowered immune responses.^[35][36][37] Other symptoms included fatigue, headaches, coughs, and unusual skin sores.^[38] Additionally, in children, there were reports of poor cognitive development.^[35]

Women exposed to PCBs before or during pregnancy can give birth to children with lowered cognitive ability, immune compromise, and motor control problems.^[39][40][41]

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 becomes mobilized into the blood when individuals begin to crash diet.^[42] PCBs have shown toxic and mutagenic effects by interfering with hormones in the body. PCBs, depending on the specific congener, have been shown to both inhibit and imitate estradiol, the main sex hormone in females. Imitation of the estrogen compound can feed estrogen-dependent breast cancer 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.

High PCB levels in adults have been shown to result in reduced levels of the thyroid hormone triiodothyronine, 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.^[30][43]

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.^[44] Animals that ingest smaller amounts of PCBs in food over several weeks or months develop various health effects, including anemia; acne-like skin conditions (chloracne); liver, stomach, and thyroid gland injuries (including hepatocarcinoma),, and thymocyte apoptosis.^[30] Other effects of PCBs in animals include changes in the immune system, behavioral alterations, and impaired reproduction.^[30] PCBs that have dioxin-like activity are known to cause a variety of teratogenic effects in animals. Exposure to PCBs causes hearing loss and symptoms similar to hypothyroidism in rats.^[45]

Cancer

In 2013, the International Agency for Research on Cancer (IARC) classified dioxin-like PCBs as human carcinogens.^[46] According to the EPA, PCBs have been shown to cause cancer in animals and evidence supports a cancer-causing effect in humans.^[4] Per EPA, studies have found increases in malignant melanoma and rare liver cancers in PCB workers.^[4]

As of 2012, a review has shown an association between elevated blood levels of PCBs and non-Hodgkin lymphoma.^[47] while studies of PCB workers showed no increased death rates from non-Hodgkin Lymphoma.^[48] In 2013, the International Association for Research on Cancer (IARC) determined that the evidence for PCBs causing non-Hodgkin Lymphoma is "limited" and "not consistent".^[46]

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.^[4]

History

Old power transformers are a major legacy source of PCBs. Even units not originally filled with PCB may be contaminated, since PCB and oil mix freely and any given transformer may have been refilled from hoses or tanks also used with PCBs.

In 1865 the first "PCB-like" chemical was discovered, and was found to be a byproduct of coal tar. Years later in 1881, German chemists synthesized the first PCB in a laboratory. Between then and 1914, large amounts of PCBs were released into the environment, to the extent that there are still measurable amounts of PCBs in feathers of birds currently held in museums.^[49]

In 1935, Monsanto Chemical Company (now 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 isomers at different degrees of chlorination. The electric industry used PCBs as a non-flammable replacement for mineral oil to cool and insulate industrial transformers and capacitors. PCBs were also commonly used as heat stabilizer in cables and electronic components to enhance the heat and fire resistance of PVC.^[50]

In the 1930s, the toxicity associated with PCBs and other chlorinated hydrocarbons, including polychlorinated naphthalenes, was recognized because of a variety of industrial incidents.^[51] 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 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.^[52] In 1947 Robert Brown reminded chemists that Arochlors were "objectionably toxic. Thus the maximum permissible concentration for an 8-hr. day is 1 mg/m³ of air. They also produce a serious and disfiguring dermatitis".^[53]

In 1954 Japan, Kanegafuchi Chemical Co. Ltd. (Kaneka Corporation) first produced PCB's, and continued until 1972.^[1]

Through the 1960s Monsanto Chemical Company knew increasingly more about PCB's 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.^[54]

In 1966, PCBs were determined by Swedish chemist Dr. Soren Jensen to be an environmental contaminant.^[55] Jensen, according to a 1994 article in 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, the then Federal Republic of Germany, France, Great Britain, Italy, Japan, Spain, USSR, and USA.^[1]

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 engaged in data falsification in testing relating to PCBs.^{[56][57][58][59]}

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.^[60][61] 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."^[62]

Existing products containing PCBs which are "totally enclosed uses" such as insulating fluids in transformers and capacitors, vacuum pump fluids, and hydraulic fluid, are allowed to remain in use. ^[63]

The public, legal, and scientific concerns about PCBs arose from research indicating they are likely carcinogens 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.^[1]

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.^[64][65] 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 & 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.^[65] Two businessmen who knowingly sold the contaminated feed ingredient received two-year suspended sentences for their role in the crisis.^[66]

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 USA, 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.^[67] PCBs entered the human food supply by animals grazing on contaminated pastures near the factory, especially in local veal mostly eaten by farmers' families.^[68] The exposed population showed an elevated risk of Non-Hodgkin lymphoma, but not for other specific cancers.^[69]

Japan

In 1968, a mixture of dioxins and PCBs got into rice bran oil produced in northern Kyushu. Contaminated cooking oil sickened more than 1860 people. The symptoms were called Yushō disease.^[34]

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.^[70]

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 EU's upper safe limit of 1.5 pg WHO-TEQ_DFP/μg i.e. 0.12 to 0.3 parts per billion.^[71][72]

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.^[71][73] 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.^[74] 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 1 September 2008. This request for withdrawal of pork products was confirmed in a press release by the Food Safety Authority of Ireland on December 6.^[75]

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.^[76]

Kenya

In Kenya, a number of cases have been reported in the 2010s of thieves selling transformer oil, stolen from electric transformers, 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.^[77]

Slovakia

The chemical plant Chemko in Strážske (east Slovakia) was an important producer of polychlorinated biphenyls for the former communist block (Comecon) until 1984. Chemko contaminated a large part of east Slovakia, especially the sediments of the Laborec river and reservoir Zemplínska šírava.^[78][79]

United Kingdom

Monsanto manufactured PCBs at its chemical plant in 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, from where it continues to be released in waste water discharges.^[80]

Spain

Several cetacean species have very high mean blubber PCB concentrations likely to cause population declines and suppress population recovery. Striped dolphins, bottlenose dolphins and killer whales 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”.^[81]

United States

Alabama

PCBs (manufactured through most of the 20th century) originating from Monsanto Chemical Company in Anniston, Alabama were dumped into Snow Creek, which then spread to Choccolocco Creek, then Logan Martin Lake.^[82] In the early 2000s, class action lawsuits were settled by local land owners, including those on Logan Martin Lake, and 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 the 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.^[83] 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.

Great Lakes

In 1976 environmentalists found PCBs in the sludge at Waukegan Harbor, the southwest end of Lake Michigan. 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%.^[84][85]

Late during the construction of new on- and off-ramps in the M-13 interchange on the Zilwaukee bridge approach, workers uncovered an uncharted landfill containing PCB-contaminated waste, necessitating an environmental cleanup. In August 22, 1989, The Detroit Free Press noted that the clean up costs would cost over $100,000 and delay the opening of the ramps to the M-13 interchange in Zilwaukee, which were scheduled for opening that year.^[86]

Much of the Great Lakes area were still heavily polluted with PCBs in 1988, despite extensive remediation work.^[87] Locally caught fresh water fish and shellfish are contaminated with PCBs, and their consumption is restricted.^[88]

Indiana

From the late 1950s through 1977, Westinghouse Electric used PCBs in the manufacture of capacitors in its 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.^[89] Workers also dumped PCB oil down factory drains, which contaminated the city sewage treatment plant.^[90] The City of Bloomington gave away the sludge to area farmers and gardeners, creating anywhere from 200 to 2000 sites, which remain unaddressed. Over 2 million pounds of PCBs were estimated to have been dumped in Monroe and Owen counties. 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.^[89] 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.^[89]

On 15 February 2008, Monroe County approved a plan to clean up the three remaining contaminated sites in the City of Bloomington, at a cost of $9.6 million to CBS Corp., the successor of Westinghouse. In 1999, Viacom bought CBS, so they are current responsible party for the PCB sites.^[91]

Massachusetts

Pittsfield, in western Massachusetts, was home to the General Electric (GE) transformer and capacitor divisions, and electrical generating equipment built and repaired in Pittsfield powered the electrical utility grid throughout the nation. PCB-contaminated oil routinely migrated from GE's 254-acre (1.03 km²) 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.^[92] PCB-containing solid material was widely used as fill, including oxbows of the Housatonic River.^[92] Fish and waterfowl who live in and around the river contain significant levels of PCBs and are not safe to eat.^[93]

New Bedford Harbor, which is a listed Superfund site,^[94] contains some of the highest sediment concentrations in the marine environment.^[95]

New York

Pollution of the Hudson River is largely due to dumping of PCBs by General Electric from 1947 to 1977.^[96] GE dumped an estimated 1.3 million pounds of PCBs into the Hudson River during these years.^[97] This pollution caused a range of harmful effects to wildlife and people who eat fish from the river or drink the water.^[98]

Love Canal is a neighborhood in Niagara Falls, New York that was heavily contaminated with toxic waste including PCBs.^[99]

Eighteen Mile Creek in Lockport, New York is an EPA Superfund site for PCBs contamination.^[100]

North Carolina

One of the largest deliberate PCB spills in American history occurred in the summer of 1978 when 31,000 gallons of PCB-contaminated oil were illegally sprayed in 3-foot (0.91 m) swaths along the roadsides of some 240 miles (390 km) of North Carolina highway shoulders in 14 counties and at the Fort Bragg Army Base. The crime, known as "the midnight dumpings", occurred over nearly 2 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 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 charages; 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 were strongly opposed in 1982 by local residents.^[101]

In October 2013, at the request of the South Carolina Department of Health and Environmental Control (SCDHEC), the City of Charlotte, North Carolina decided to stop applying sewage sludge to land while authorities investigated the source of PCB contamination.^[102] In February 2014, the City of Charlotte admitted PCBs have entered their sewage treatment centers as well.^[103]

After the 2013 SCDHEC had issued emergency regulations^[104] the City of Charlotte discovered high levels of PCB's entering its sewage waste water treatment plants, where sewage is converted to sewage sludge.^[103] 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.^[102][105] 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.^[106]

Ohio

The Clyde cancer cluster (also known as the Sandusky County cancer cluster) is a childhood cancer cluster that has affected many families in Clyde, Ohio and surrounding areas. PCBs were found in soil in a public park within the area of the cancer cluster.

In 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.^[107]

South Carolina

From 1955 until 1977, the Sangamo Weston plant in Pickens, SC, 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 228 acres (0.92 km²) site of the capacitor plant, its landfills and the polluted watershed, which stretches nearly 1,000 acres (4.0 km²) 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.^[108][109]

In 2009, the state environmental regulators SCDHEC noted fish species in Lake Wateree contained exceptionally high levels of PCB contamination and posted adviseries that fish from the lake were unsafe to eat.

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.^[110]

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, Lake Washington, the Okanogan River, Puget Sound, the Spokane River, the Walla Walla River, the Wenatchee River, and the Yakima River.^[111]1 May 2016 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%), municipal and industrial discharges (20%).^[112] PCBs entered the environment through paint, hydraulic fluids, sealants, inks and have been found in river sediment and wild life. Spokane utilities will spend $300 million to prevent PCBs from entering the river in anticipation of a 2017 federal deadline to do so.^[113] In August 2015 Spokane joined other U.S cities like San Diego and San Jose, California, and Westport, Massachusetts. in seeking damages from Monsanto.^[114]

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.^[115]

Regulation

In 1972 the Japanese government banned the production, use, and import of PCBs.^[1]

In 1973, the use of PCBs in "open" or "dissipative" sources, such as plasticisers in paints and cements, casting agents, fire retardant fabric treatments and heat stabilizing additives for PVC electrical insulation, adhesives, paints and waterproofing, railroad ties was banned in Sweden.

In 1979, concern over the toxicity and persistence (chemical stability) of PCBs in the environment led the United States Congress to ban their domestic production.^[116]

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.^[117]

Containment

Because of its difficult containment, many buildings (at least in the US) with known high PCB dangers have been evacuated and shut down. In many states, including California, laws require any building with such dangers to be sealed and locked, with large warning signs on every entrance point indicating a PCB presence and also a notice to indicate the presence of chemicals known to cause cancer, health problems or reproductive harm. Until a safe solution can be well established, many of these buildings remain undemolished and sealed. Some forms of containment other than building closure and lock-down are noted below.

Large quantities of PCBs have been placed in landfills, mainly in the form of transformers and capacitors. Many municipal sites are not designed to contain these pollutants, and thus PCBs are able to escape into the atmosphere or groundwater.

Methods of destruction

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

Physical

Incineration – Although PCBs do not ignite themselves, they can be combusted under extreme and carefully controlled conditions. The current regulations require that PCBs are burnt at a temperature of 1200 °C (±100 °C) for at least two seconds or 1600 °C (±100 °C) for at least 1.5 seconds, in the presence of fuel oil and excess oxygen.^[118] A lack of oxygen can result in the formation of dioxins/dibenzofurans, or the incomplete destruction of the PCBs. Such specific conditions mean that it is extremely expensive to destroy PCBs on a tonnage scale, and it can only be used on PCB-containing equipment and contaminated liquid. This method is not suitable for the decontamination of affected soils.

Irradiation – If a deoxygenated mixture of PCBs in isopropanol or mineral oil is subjected to irradiation with gamma rays then the PCBs will be dechlorinated to form biphenyl and inorganic chloride. The reaction works best in isopropanol if potassium hydroxide (caustic potash) is added. Solvated electrons are thought to be responsible for the reaction. If oxygen, nitrous oxide, sulfur hexafluoride, or nitrobenzene is present in the mixture then the reaction rate is reduced. This work has been done recently in the US often with used nuclear fuel as the radiation source.^[119][120]

Pyrolysis – Destruction of PCBs with pyrolysis using plasma arc processes, like incineration, uses heat. However, unlike incineration, there is no combustion. The long-chain molecules are broken with extreme temperature provided by an electric arc in an inert environment. Adequate post-pyrolysis treatment of the resultant products is required in order to prevent the risk of back reactions.

Microbial

Much recent work has centered on the study of micro-organisms that are able to decompose PCBs. In general, these organisms work in one of two ways: Either they use the PCB as a carbon source or destruction takes place through reductive dechlorination, with the replacement of chlorine with hydrogen on the biphenyl skeleton. However, there are significant problems with this approach. First, these microbes tend to be highly selective in their dechlorination, with lower chlorinated biphenyls being readily transformed, and with preference to dechlorination in the para and meta positions (this is an advantage however, as ortho dechlorination would transform noncoplanar PCBs into dioxin-like coplanar ones). Second, microbial dechlorination tends to be rather slow-acting on PCB as a soil contaminant in comparison to other methods. Last, while microbes work well in laboratory conditions, there is often a problem in transferring a successful laboratory strain to a natural system. This is because the microbes can access other sources of carbon, which they decompose in preference to PCBs. A low voltage current can stimulate the microbial degradation of PCBs.^[121]

Enzymes and vitamins extracted from microbes that show PCB activity have been tested for use in biodegradation. Especially promising seems to be the use of vitamin B12, in which a cobalt ion is in oxidation state (III) under normal redox conditions. Using titanium (III) citrate as a strong reductant converts the cobalt from Co(III) to Co(I), giving a new vitamin known as B12s, a powerful nucleophile and reducing catalyst can then be used on PCBs, which it dechlorinates in a rapid and selective manner.^[122] In 2005, Shewanella oneidensis biodegraded a high percent of PCBs in soil samples.^[123]

Chemical

Many chemical methods are available to destroy or reduce the toxicity of PCBs. Nucleophilic aromatic substitution is a method of destroying low-concentration PCB mixtures in oils, such as transformer oil. Substitution of chlorine by polyethylene glycols occurs in under two hours under a blanket of nitrogen, to prevent oxidation of the oil, to produce aryl polyglycols, which are insoluble in the oil and precipitate out.

Between 700 and 925 °C, H₂ cleaves the carbon-chlorine bond, and cleaves the biphenyl nucleus into benzene, yielding HCl without a catalyst. This can be performed at lower temperatures with a copper catalyst, and to yield biphenyl. However, since both of these routes require an atmosphere of hydrogen gas and relatively high temperatures, they are prohibitively expensive.

Reaction with highly electropositive metals, or strong reducing agents such as sodium naphthalide, in aprotic solvents results in a transfer of electrons to the PCB, the expulsion of a chloride ion, and a coupling of the PCBs. This is analogous to the Wurtz reaction for coupling halogenoalkanes. The effect is to polymerise many molecules, thereby reducing the volatility, solubility, and toxicity of the mixture. This methodology is most successful on low-strength PCB mixtures and can also be performed electrochemically in a partly aqueous bicontinuous microemulsion.

The solution photochemistry of PCBs is based on the transfer of an electron to a photochemically excited PCB from a species such as an amine, to give a radical anion. This either expels a chloride ion and the resulting aryl radical extracts a hydrogen atom from the solvent or immediately becomes protonated, leading to the loss of a chlorine atom. It is useful only for water-soluble PCBs.

The major pathway for atmospheric destruction of PCBs is via attack by OH radicals. Direct photolysis can occur in the upper atmosphere, but the ultraviolet wavelengths necessary to excite PCBs are shielded from the troposphere by the ozone layer. It has, however, been shown that higher wavelengths of light (> 300 nm) can degrade PCBs in the presence of a photosensitizer, such as acetone.

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

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.

PCB homolog	CASRN	Cl substituents	Number of congeners
Biphenyl (not a PCB)	92-52-4	0	1
Monochlorobiphenyl	27323-18-8	1	3
Dichlorobiphenyl	25512-42-9	2	12
Trichlorobiphenyl	25323-68-6	3	24
Tetrachlorobiphenyl	26914-33-0	4	42
Pentachlorobiphenyl	25429-29-2	5	46
Hexachlorobiphenyl	26601-64-9	6	42
Heptachlorobiphenyl	28655-71-2	7	24
Octachlorobiphenyl	55722-26-4	8	12
Nonachlorobiphenyl	53742-07-7	9	3
Decachlorobiphenyl	2051-24-3	10	1

See also

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

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External links

• ATSDR Toxicological Profile U.S. Department of Health and Human Services
• IARC PCB Monograph
• US EPA PCB Homepage
• National Toxicology Program technical reports searched for "PCB"
• Polychlorinated Byphenyls: Human Health Aspects by the WHO
• Case study of plasma arc process for the destruction of PCBs
• Current Intelligence Bulletin 7: Polychlorinated (PCBs)—NIOSH/CDC (1975)
• It's Your Health - PCBs (Health Canada)
• Introduction to Capacitors oil-filled