Polychlorinated biphenyl 48230 225554783 2008-07-14T08:10:51Z Albambot 6552142 robot Removing: [[lt:Polichlorintieji bifenilai]] [[Image:PCB-labelling.jpg|thumb|right|Labelling transformers containing PCBs.]] '''Polychlorinated biphenyls''' ('''PCB'''s) are a class of [[organic compound]]s with 1 to 10 [[chlorine]] atoms attached to [[biphenyl]] which is a molecule composed of two [[benzene ring]]s each containing six carbon atoms. The [[chemical formula]] for all PCBs is '''[[Carbon|C]]'''<sub>12</sub>'''[[Hydrogen|H]]'''<sub>10-x</sub>'''[[Chlorine|Cl]]'''<sub>x</sub>. PCBs were used as [[coolant]]s and insulating fluids for transformers and capacitors, stabilizing additives in flexible [[PVC]] coatings of electrical wiring and electronic components, [[pesticide]] extenders, [[cutting oil]]s, [[flame retardant]]s, [[hydraulic fluid]]s, [[sealant]]s (used in [[caulking]], etc), [[adhesive]]s, wood floor finishes,<ref name="rudel2008">{{cite journal | author=Rudel, R A, Seryak, L M, and Brody, J G | title=PCB-containing wood floor finish is a likely source of elevated PCBs in resident's blood, household air and dust: a case study of exposure | journal=Environmental Health | volume= | pages = 2 | year=2008 | doi = 10.1186/1476-069X-7-2 <!--Retrieved from CrossRef by DOI bot-->}}</ref> [[paint]]s, [[de-dusting agent]]s, and in [[carbonless copy paper]].<ref name="unepbangkok"/> PCB production was banned in the 1970s due to the high [[toxicity]] of most PCB [[congeners]] and mixtures. PCBs are classified as [[persistent organic pollutant]]s which [[bioaccumulate]] in animals. [[Image:Polychlorinated biphenyl structure.svg|300px|thumb|right|Chemical structure of PCBs. The possible positions of [[chlorine]] atoms on the [[benzene ring]]s are denoted by numbers assigned to the [[carbon]] atoms.]] ==Physical and chemical properties== PCB [[congener]]s are [[odor]]less, [[taste]]less, clear to pale-yellow, [[viscosity|viscous]] [[liquid]]s. They are formed by [[Electrophilic halogenation|electrophilic chlorination]] of [[biphenyl]] with [[chlorine]] gas. There are theoretically 209 different PCB congeners, although only about 130 of these were found in commercial PCB mixtures.<ref name="unep">{{cite book | author=UNEP Chemicals | title=Guidelines for the Identification of PCBs and Materials Containing PCBs | issue=1 | publisher=United Nations Environment Programme | year=1999 | pages=p.2 | url=http://www.chem.unep.ch/pops/pdf/PCBident/pcbid1.pdf | accessdate=2007-11-07}}</ref> Commercial PCBs preparations are usually mixtures of 50 or more PCB congeners.<ref name="unep"/> Commercial PCB mixtures are clear to pale-yellow, viscous liquids (the more highly chlorinated mixtures are more viscous and more yellow - for example , Aroclor 1260 is a sticky yellowish [[resin]]). PCBs have low [[water (molecule)|water]] [[solubility|solubilities]] — 0.0027-0.42 [[nanogram|ng]]/[[litre|L]] for Aroclors,<ref name="unepbangkok"/> and low [[vapor pressure]]s at room temperature, but they have high solubilities in most organic [[solvent]]s, oils, and [[fat]]s. They have high [[dielectric constant]]s, very high [[thermal conductivity]],<ref name="unepbangkok"/> high [[flash point]]s (170-380°C)<ref name="unepbangkok"/> and are chemically almost inert, being extremely resistant to [[oxidation]], [[reduction (chemistry)|reduction]], [[addition reaction|addition]], [[elimination reaction|elimination]], and [[electrophilic substitution]].<ref>{{cite web | author=Amy Boate, Greg Deleersnyder, Jill Howarth, Anita Mirabelli, and Leanne Peck | title=Chemistry of PCBs | year=2004 | url=http://wvlc.uwaterloo.ca/biology447/modules/intro/assignments/Introduction2a.htm | accessdate=2007-11-07}}</ref> The density varies from 1.182 to 1.566 [[kilogram|kg]]/[[litre|L]].<ref name="unepbangkok"/> Other physical and chemical properties vary widely across the class. As the degree of chlorination increases, melting point and [[lipophilicity]] increase, but vapour pressure and water solubility decrease.<ref name="unepbangkok"/> PCBs readily penetrate [[Absorption (skin)|skin]], [[PVC]] (polyvinyl chloride), and [[latex]] (natural rubber); organic solvents such as kerosene increase the rate of skin absorption.<ref name="anzecc">{{cite book | title = Identifying PCB-Containing Capacitors | publisher = Australian and New Zealand Environment and Conservation Council (ANZECC) | pages = pp.4-5 | year = 1997 | isbn = 0 642 54507 3 | url = http://www.environment.gov.au/settlements/publications/chemicals/scheduled-waste/pubs/pcbid.pdf| accessdate = 2007-07-07}}</ref> PCB-resistant materials include [[Viton]], [[polyethylene]], [[polyvinyl acetate]] (PVA), [[polytetrafluoroethylene]] (PTFE), [[butyl rubber]], [[nitrile rubber]], and [[Neoprene]].<ref name="anzecc"/> PCBs are very stable compounds and do not [[Chemical decomposition|degrade]] readily. They may be destroyed by chemical, thermal, and biochemical processes, though it is extremely difficult to achieve full destruction, and there is the risk of creating extremely toxic [[dioxins|dibenzodioxins]] and [[dibenzofurans]] through partial oxidation. Because of the high thermodynamic stability of PCBs, all degradation mechanisms are difficult to sustain. Intentional degradation as a treatment of unwanted PCBs generally requires high heat or [[catalysis]]. Environmental and metabolic degradation generally proceeds quite slowly relative to most other compounds. ==Alternative names== Commercial PCB mixtures were marketed as ''Apirolio'' in Italy, ''Aroclor'' by [[Monsanto]] in USA and UK, ''Asbestol'' in USA, ''Askarel'' in USA and UK, ''Bakola131'' in USA, ''Chlorextol'' in USA, ''Clophen'' by [[Bayer]] in Germany, ''Delor'' in Czechoslovakia, ''Fenclor'' in Italy, ''Hydol'' in USA, ''Inerteen'' by [[Westinghouse Electric Corporation (1886)|Westinghouse]] in the USA, ''Kanechlor'' by Kanegafuchi in Japan, ''Noflamol'' in USA, ''Phenoclor'' and ''Pyralene'' by [[Prodolec]] in France, ''Pyranol'' and ''Pyrenol'' by [[General Electric]] in USA, ''Pyroclor'' in UK, ''Saft-Kuhl'' in USA, ''Santotherm'' by [[Mitsubishi]] in Japan, ''Sovol'' and ''Sovtol'' in the former USSR, and ''Therminol'' in USA.<ref name="unepbangkok">{{cite web|title=Proceedings of the Subregional Awareness Raising Workshop on Persistent Organic Pollutants (POPs), Bangkok, Thailand | publisher=''[[United Nations Environment Programme]]'' | year=1997 |date=November 25-28th, 1997 | url=http://www.chem.unep.ch/pops/POPs_Inc/proceedings/bangkok/FIEDLER1.html | accessdate=2007-12-11}}</ref><ref name="jof2003">{{cite web | title=Brand names of PCBs — What are PCBs? | publisher=Japan Offspring Fund / Center for Marine Environmental Studies (CMES), Ehime University, Japan | year=2003 | url=http://tabemono.info/report/former/pcd/2/2_2/e_1.html | accessdate=2008-02-11}}</ref> ==Applications== PCBs were used as [[coolant]]s and insulating fluids for [[transformer]]s and [[capacitor]]s, [[plasticizer]]s in paints and cements, stabilizing additives in flexible [[PVC]] coatings of electrical wiring and electronic components, [[pesticide]] extenders, [[cutting fluid|cutting oils]], reactive [[flame retardant]]s, [[lubricant|lubricating oils]], [[hydraulic fluid]]s, [[sealant]]s (for [[caulking]] in schools and commercial buildings<ref name="rudel2008"/>), [[adhesive]]s, wood floor finishes (such as ''Fabulon'' and other products of [[Halowax]] in the [[U.S.]]),<ref name="rudel2008"/> [[paint]]s, [[de-dusting agent]]s, water-proofing compounds, casting agents, [[vacuum pump]] fluids, [[fixative]]s in microscopy, surgical implants, and in [[carbonless copy paper|carbonless copy ("NCR") paper]].<ref name="unepbangkok"/> ==History== PCBs, originally termed "chlorinated diphenyls," were commercially produced as complex mixtures containing multiple [[isomer]]s at different degrees of chlorination. In the United States, commercial production of PCBs was taken over in 1929 by Monsanto from Swann Chemical Company. Manufacturing levels increased in response to the electrical industry's need for a "safer" cooling and insulating fluid for industrial transformers and capacitors. PCBs were also commonly used as stabilizing additives in the manufacture of flexible PVC coatings for electrical wiring and electronic components to enhance the heat and fire resistance of the PVC.<ref>{{cite book | title = Health Concerns and Environmental Issues with PVC-Containing Building Materials in Green Buildings | author = Karlyn Black Kaley, Jim Carlisle, David Siegel, Julio Salinas | publisher = Integrated Waste Management Board, California Environmental Protection Agency, USA | month = October | year = 2006 | pages = p.11 | format = pdf | url=http://www.ciwmb.ca.gov/publications/GreenBuilding/43106016.pdf | accessdate = 2007-08-03}}</ref> The toxicity associated with PCBs and other chlorinated hydrocarbons, including [[polychlorinated naphthalene]]s was recognized very early due to a variety of industrial incidents <ref>{{cite journal | title = The problem of possible systemic effects from certain chlorinated hydrocarbons | journal= Journal of Industrial Hygiene and Toxicology | author= Drinker, C.K., M.F. Warren, and G.A. Bennet | year = 1937 | volume= 19 | issue= 7 | pages = 283}} </ref>. A conference about the hazards was organized at [[Harvard School of Public Health]] in 1937, and a number of publications referring to the toxicity of various chlorinated hydrocarbons were published before 1940 <ref> {{cite journal| title= The early history of scientific and medical research on 'agent orange' |author= Butler, D.A.| journal= Brooklyn Journal of Law and Policy | year= 2005| volume= 13| issue=2 | pages=527 | url=http://brooklaw.edu/students/journals/bjlp/jlp13ii_butler.pdf }}</ref>. Robert Brown reminded chemists in 1947 that Arochlors were "objectionably toxic. Thus the maximum permissible concentration for an 8-hr. day is 1 mg. per cu.m. of air. They also produce a serious and disfiguring dermatitis."<ref> {{cite journal | author = Brown, R. M. | title= The toxicity of the 'Arochlors' | journal= Chemist-Analyst| volume= 36| pages= 33| year= 1947 | url=http://chemport.cas.org/cgi-bin/sdcgi?APP=ftslink&action=reflink&origin=npg&version=1.0&coi=1:CAS:528:DyaH2sXjs1WntA%3D%3D&pissn=0028-0836&pyear=1967&md5=58285ba11405fbe2e87bf46712d4f63d }}</ref> However, PCB manufacture and use continued with few restraints until the 1970s. PCBs are [[persistent organic pollutant]]s and have entered the environment through both use and disposal. The environmental transport of PCBs is complex and nearly global in scale. The public, legal, and scientific concerns about PCBs arose from research indicating they were likely [[carcinogens]] having the potential to adversely impact the environment and therefore undesirable as commercial products. 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.<ref name="unepbangkok"/> The only North American producer, [[Monsanto]], marketed PCBs under the trade name '''Aroclor''' from 1930 to 1977. These were sold under trade names followed by a 4 digit number. The first two digits generally refer to the number of carbon atoms in the biphenyl skeleton (for PCBs this is 12), the second two numbers indicate the percentage of chlorine by mass in the mixture. Thus, Aroclor 1260 has 12 carbon atoms and contains 60% chlorine by mass. An exception is Aroclor 1016, which also has 12 carbon atoms, but has 42% chlorine by mass. Different Aroclors were used at different times and for different applications. In electrical equipment manufacturing in the USA, Aroclor 1260 and Aroclor 1254 were the main mixtures used before 1950, Aroclor 1242 was the main mixture used in the 1950s and 1960s until it was phased out in 1971 and replaced by Aroclor 1016.<ref name="unepbangkok"/> Manufacture peaked in the 1960s, by which time the electrical industry had lobbied the U.S. Congress to make them mandatory safety equipment, knowing all the while that they were extremely toxic{{Fact|date=July 2007}}. In 1966, they were determined by Swedish chemist Dr. Soren Jensen to be an environmental contaminant<ref>{{cite journal | author=S. Jensen |title=Report of a new chemical hazard | journal=New Sci.|volume=32|pages=612|date=1966}}</ref>, and it was Dr. Jensen, according to a 1994 article in [[Sierra]], who named them. Previously, they had simply been called "phenols" or referred to by various trade names, such as Aroclor, Kennechlor, Pyrenol, Chlorinol and others. However, Arochlors (chlorinated biphenyls) were known toxins by 1947. Their commercial utility was based largely on their chemical stability, including low [[fire|flammability]], and desirable physical properties, including electrical insulating properties. Their chemical and physical stability has also been responsible for their continuing persistence in the environment, and the lingering interest decades after regulations were imposed to control environmental contamination. In 1972, PCB production plants existed in Austria, then Federal Republic of Germany, France, Great Britain, Italy, Japan, Spain, USSR, and USA.<ref name="unepbangkok"/> From 1973 the use of PCBs was banned in "open" or "[[dissipative]]" sources, such as: * [[plasticiser]]s in paints and cements * casting agents * [[fire retardant]] fabric treatments and [[Heat stabilizer|heat stabilizing additives]] for PVC electrical insulation * [[adhesives]] * paints and water-proofing * [[railway sleeper]]s However, they continued to be allowed in "totally enclosed uses" such as transformers and capacitors, which, in certain failure modes or out-of-specification conditions, can leak, catch fire, or explode. It was Ward B. Stone of the New York State Department of Environmental Conservation who first published his findings in the early 1970s that PCBs were leaking from transformers and had contaminated the soil at the bottom of utility poles. Concern over the toxicity and persistence (chemical stability) of PCBs in the environment led the United States Congress to ban their domestic production in 1977, although some use continues in closed systems such as capacitors and transformers. "Enclosed uses" of PCBs include: * [[capacitor]]s * insulating fluids in transformers * [[vacuum pump]] fluids * [[hydraulic fluid]]s In the UK, closed uses of PCBs in new equipment were banned from 1981, when nearly all UK PCB synthesis ceased, but closed uses in existing equipment containing in excess of 5&nbsp;[[litres]] of PCBs were not stopped until December 2000.<ref name="defra05">{{cite web|title=Guidance on municipal waste strategies, Section 5.12 Equipment which contains low volumes of PCBs | publisher=UK Department of the Environment, Transport and the Regions | page=p.17 | year=2001 | url=http://www.defra.gov.uk/environment/waste/management/guidance/mwms/pdf/mwms.pdf | accessdate=2008-01-29}}</ref> In Japan, PCBs were first produced by Kanegafuchi Chemical Co. Ltd. (Kaneka) in 1954 and production continued until 1972 when the Japanese government banned the production, use, and import of PCBs.<ref name="unepbangkok"/> 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.<ref>{{cite journal | author=Breivik K, Sweetman A, Pacyna JM, Jones KC | title=Towards a global historical emission inventory for selected PCB congeners - a mass balance approach 1. Global production and consumption | journal=The Science of the Total Environment | volume=290 |date=2002 | pages=181–198 | doi=10.1016/S0048-9697(01)01075-0}}</ref> ==Large-scale environmental contamination incidents== ===New York State=== In the [[United States of America]], the [[General Electric Company]] (GE) released up to {{convert|1300000|lb|kg|sigfig=2}} of PCBs into the [[Hudson River]] between approximately 1947 and 1977.<ref name="epa_ge">{{cite web|title=Hudson River PCBs — Background and Site Information | publisher=[[United States Environmental Protection Agency]] | url=http://www.epa.gov/hudson/background.htm | accessdate=2007-12-31}}</ref> The PCBs came from the company's two [[capacitor]] manufacturing plants at [[Hudson Falls]] and [[Fort Edward (town), New York|Fort Edward]] in [[New York State]].<ref name="epa_ge"/> In 1976, because of concern over continuing high levels of PCBs in local fish and other aquatic organisms, and the unacceptable risk to the health of consumers of such fish, the [[New York State Department of Environmental Conservation]] banned all fishing in the Upper Hudson River, as well as commercial fishing of [[striped bass]] and several other species in the Lower Hudson River,<ref name="epa_superfund_cleanup">{{cite web|title=Hudson River PCBs | publisher=[[United States Environmental Protection Agency]] | date=2007-06-27 | url=http://www.epa.gov/Region2/superfund/npl/0202229c.pdf | accessdate=2007-12-31}}</ref><ref name="epa_ge"/> and also issued advisories restricting the consumption of fish caught within a {{convert|20|mi|km|sigfig=1|adj=on}} long segment of the Hudson River from Hudson Falls to [[Troy, New York|Troy]].<ref name="epa_ge"/><ref name="nysdec">{{cite web|title="Hudson River Virtual Tour — Chapter 9: PCB Pollution in the Hudson | publisher=[[New York State Department of Environmental Conservation]] | url=http://www.dec.ny.us/lands/25974.html | accessdate=2007-12-31}}</ref> There have been many programs of remediation work to reduce the PCB pollution, mostly paid for by GE. In 1984, approximately {{convert|200|mi|km}} of the Hudson River was designated a [[Superfund]] site, and attempts to cleanup the Upper Hudson River began, including the removal in 1977-8 of {{convert|180000|cuyd|m3}} of contaminated river sediments near Fort Edward.<ref name="epa_superfund_cleanup"/> In 1991, further PCB pollution was found at Bakers Falls near the former GE Hudson Falls factory, and a program of remediation was started.<ref name="epa_superfund_cleanup"/> In August 1995, a {{convert|40|mi|km|adj=on}} reach of the Upper Hudson was re-opened to fishing but only on a catch-and-release basis.<ref name="epa_superfund_cleanup"/> Removal of contaminated soil from [[Rogers Island (New York)|Rogers Island]] was completed in December 1999.<ref name="epa_superfund_cleanup"/> In 2002, the [[United States Environmental Protection Agency]] announced a further {{convert|2650000|cuyd|m3}} of contaminated sediments in the Upper Hudson River would be removed. ===Indiana=== {{Refimprovesect|date=December 2007}} 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. Workers also dumped PCB oil down factory drains which contaminated the city sewage treatment plant.{{Fact|date=May 2007}} The City of Bloomington gave away the sludge to area farmers and gardeners, creating anywhere from 200 to 2000 sites which remain unaddressed. Over 2 million pounds of PCBs were estimated to have been dumped in Monroe and Owen Counties, which would make it the biggest concentration of PCBs in the world.{{Fact|date=May 2007}} Although federal and state authorities have been working on the site remediations, many areas remain contaminated. Concerns have been raised regarding the removal of PCBs from the [[karst]] limestone topography, and regarding the possible disposal options. To date, the Westinghouse Bloomington PCB Superfund site case does not have a RI/FS (Remedial Investigation/Feasibility Study) and ROD (Record of Decision), although Westinghouse signed a US Department of Justice Consent Decree in 1985.{{Fact|date=May 2007}} On [[February 15]] [[2008]], Monroe County approved a plan to clean up the 3 remaining contaminated sites in the City of Bloomington, at a cost of $9.6m to [[CBS Corporation|CBS Corp.]], the successor of Westinghouse. <ref>{{cite web|title=Monroe Co. approves PCB clean up|url=http://www.webcitation.org/query?url=http%3A%2F%2Fwww.indystar.com%2Fapps%2Fpbcs.dll%2Farticle%3FAID%3D%2F20080218%2FLOCAL%2F802180394&date=2008-02-18|publisher=IndyStar.com|accessdate=2008-02-18}}</ref> ===The Great Lakes=== Much of the [[Great Lakes]] area is still heavily polluted with PCBs, despite extensive remediation work.<ref>{{cite journal | author=Bette Hileman | title=The Great Lakes cleanup effort | journal=Chemistry and Engineering | volume=8 | date=[[1988-02-08]] | pages=22–39}}</ref> Locally caught fresh water fish and shellfish are contaminated with PCBs and their consumption is restricted. ==Global transport through atmospheric pollution== PCBs have been detected globally in the atmosphere, from the most urbanized areas that are the centers for PCB pollution, to regions north of the Arctic Circle. The atmosphere serves as the primary route for global transport of PCBs, particularly for those congeners with 1 to 4 chlorine atoms. Atmospheric concentrations of PCBs tend to be lowest in rural areas, where they are typically in the [[picogram]] per cubic meter range, higher in suburban and urban areas, and highest in city centres, where they can reach 1&nbsp;[[nanogram|ng]]/[[metre|m]]³ or more. In [[Milwaukee]], an atmospheric concentration of 1.9&nbsp;ng/m³ has been measured, and this source alone was estimated to account for 120&nbsp;[[kilogram|kg]]/year of PCBs entering [[Lake Michigan]].<ref name="weth2005">{{cite journal | author=Wethington, D M III and Hornbuckle, K C | title=Milwaukee, WI, as a Source of Atmospheric PCBs to Lake Michigan | journal=Environmental Science | volume=39 | issue=1 | pages=57–63 | year=2005 | doi=10.1021/es048902d}}</ref> Concentrations as high as 35&nbsp;[[nanogram|ng]]/[[metre|m]]³, 10&nbsp;times higher than the [[United States Environmental Protection Agency|EPA]] guideline limit of 3.4&nbsp;ng/m³, have been found inside some houses in the U.S.<ref name="rudel2008"/> Volatilization of PCBs in soil was thought to be the primary source of PCBs in the atmosphere, but recent research suggests that ventilation of PCB-contaminated indoor air from buildings is the primary source of PCB contamination in the atmosphere.<ref name="jamshidi2007">{{cite journal | author=Jamshidi A, Hunter S, Hazrati S, and Harrad S | title=Concentrations and Chiral Signatures of Polychlorinated Biphenyls in Outdoor and Indoor Air and Soil in a Major U.K. Conurbation | journal=Environmental Science Technology | volume=41 | issue=7 | pages=2153–2158 | year=2007 | doi=10.1021/es062218c}}</ref> == Health effects == The [[toxicity]] of PCBs to animals was first noticed in the 1970s when emaciated seabird corpses with very high PCB body burdens washed up on beaches. Since seabirds may die far out at sea and still wash ashore, the true sources of the PCBs were unknown. Where they were found is no reliable indicator of where they had died. The toxicity of PCBs varies considerably among congeners. The coplanar PCBs, known as non-ortho PCBs because they are not substituted at the ring positions [[Arene substitution patterns|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 regulatory control, where more toxic PCB congeners are assigned higher TEF values. One of the most toxic compounds known, [[dioxin|2,3,7,8-tetrachlorodibenzo[p]dioxin]], is assigned a TEF of 1.<ref>{{cite journal| author=Van den Berg M | journal=Environ Health Perspect. | volume=106 | issue=12 | month=Dec | year=1998 | pages=775–792 | doi = 10.2307/3434121 | title = Toxic Equivalency Factors (TEFs) for PCBs, PCDDs, PCDFs for Humans and Wildlife}}</ref> ===Signs and symptoms=== *'''Humans''' :The most commonly observed [[health effects]] in people exposed to PCBs are skin conditions such as [[chloracne]] and [[rash]]es, but these were known to be symptoms of systemic poisoning dating back to the 1922. Studies in workers exposed to PCBs have shown changes in [[blood]] and [[urine]] that may indicate [[liver]] damage. In 1968 in Japan, PCB contamination in [[rice bran oil]] caused a mass poisoning known as [[Yushō Disease]] in over 14000 people.<ref name="jsta">{{cite web | title=Contamination of rice bran oil with PCB used as the heating medium by leakage through penetration holes at the heating coil tube in deodorization chamber | publisher=''[http://shippai.jst.go.jp/en/Search Japan Science and Technology Agency]'' | url=http://shippai.jst.go.jp/en/Detail?fn=2&id=CB1056031 | accessdate=2007-12-11}}</ref> Common symptoms included dermal and ocular [[lesion]]s, irregular [[menstrual cycle]]s and a lowered [[immune response]].<ref name=NCBI>[http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_uids=11386736&dopt=Abstract Polychlorinated biphenyls, polychlorinated dibenzo...[Environ Res. 2001&#93; - PubMed Result<!-- Bot generated title -->]</ref><ref name=RARE>{{RareDiseases|8326}}</ref><ref name=FOX>[http://www.foxriverwatch.com/baby_studies_pcbs_2.html PCB Baby Studies Part 2<!-- Bot generated title -->]</ref> Other symptoms included fatigue, headache, cough, and unusual skin sores.<ref name=HEALTH>[http://www.healthgoods.com/Education/Health_Information/General_Health/environmental_diseases.htm Environmental Diseases from A to Z<!-- Bot generated title -->]</ref> Additionally, in children, there were reports of poor cognitive development.<ref name=NCBI /><ref name=FOX /><ref name=HEALTH /> :There have also been studies of the health effects of PCBs in the general population and in children of mothers who were exposed to PCBs. *'''Animals''' :Animals that eat PCB-contaminated food even for short periods of time get liver damage and may die. In 1968 in Japan, 400,000 birds died after eating poultry feed that was contaminated with PCBs.<ref name="jsta"/> Animals that eat smaller amounts of PCBs in food over several weeks or months develop various kinds of health effects, including [[anemia]]; acne-like skin conditions ([[chloracne]]); and liver, [[stomach]], and [[thyroid]] gland injuries (including hepatocarcinoma). Other effects of PCBs in animals include changes in the [[immune system]], behavioral alterations, and impaired reproduction. PCBs are not known to cause birth defects in humans, although those that have [[dioxin]]-like activity are known to cause a variety of [[teratogenic]] effects in animals. *'''Effects during pregnancy/breastfeeding''' :Women who were exposed to relatively high levels of PCBs in the workplace or ate large amounts of fish contaminated with PCBs had babies that weighed slightly less than babies from women who did not have these exposures. Babies born to women who ate PCB-contaminated fish also showed abnormal responses in tests of infant behavior. Some of these behaviors, such as problems with motor skills and a decrease in short-term memory, lasted for several years. Other studies suggest that the immune system was affected in children born to and nursed by mothers exposed to increased levels of PCBs. The most likely way infants will be exposed to PCBs is from breast [[milk]]. Transplacental transfers of PCBs were also reported. :Studies have shown that PCBs alter estrogen levels in the body and contribute to reproduction problems. In the womb, males can be feminized or the baby may be intersex, neither a male nor a female. Also, both sets of reproductive organs may develop. More instances of this are being reported. Biological magnification of PCBs has also led to polar bears and whales that have both male and female sex organs and males that cannot reproduce. This effect is also known as [[endocrine disruptor|endocrine disruption]]. Endocrine Disrupting Chemicals ([[EDC]]'s) pose a serious threat to reproduction in top-level predators. === Cancer link === A few studies of workers indicate that PCBs were associated with specific kinds of [[cancer]] in humans, such as cancer of the liver and [[biliary tract]]. Rats that ate food containing high levels of PCBs for two years developed liver cancer. The [[Department of Health and Human Services]] (DHHS) has concluded that PCBs may reasonably be anticipated to be [[carcinogen]]s. The [[United States Environmental Protection Agency|US Environmental Protection Agency]] (EPA) and the [[International Agency for Research on Cancer]] (IARC) have determined that PCBs are probably carcinogenic to humans. PCBs are also classified as probable human carcinogens by the [[National Cancer Institute]], [[World Health Organization]], and the [[Agency for Toxic Substances and Disease Registry]]. Recent research by the [[National Toxicology Program]] has confirmed that PCB126 (Technical Report 520) and a binary mixture of PCB126 and PCB153 (Technical Report 531) are [[carcinogens]]. ===Mechanism of action=== As discussed, PCBs exhibit a wide range of toxic effects. These effects may vary depending on the specific PCB. Similar to dioxin, toxicity of coplanar PCBs and mono-ortho-PCBs are thought to be primarily mediated via binding to [[aryl hydrocarbon receptor]] (AhR).<ref>{{cite journal |author=Safe S |title=Polychlorinated biphenyls (PCBs) and polybrominated biphenyls (PBBs): biochemistry, toxicology, and mechanism of action |journal=Crit. Rev. Toxicol. |volume=13 |issue=4 |pages=319–95 |year=1984 |pmid=6091997 | doi = 10.3109/10408448409023762 <!--Retrieved from CrossRef by DOI bot-->}}</ref><ref>{{cite journal |author=Safe S, Bandiera S, Sawyer T, Robertson L, Safe L, Parkinson A, Thomas PE, Ryan DE, Reik LM, Levin W |title=PCBs: structure-function relationships and mechanism of action |journal=Environ. Health Perspect. |volume=60 |issue= |pages=47–56 |year=1985 |pmid=2992927 | doi = 10.2307/3429944 <!--Retrieved from CrossRef by DOI bot-->}}</ref> Because AhR is a [[transcription factor]], abnormal activation may disrupt cell function by altering the [[Transcription (genetics)|transcription]] of [[gene]]s. The concept of toxic equivalency factors (TEF) is based on the ability of a PCB to activate AhR. However, not all effects may be mediated by the AhR receptor. For example, di-ortho-substituted non-coplanar PCBs interfere with intracellular [[signal transduction]] dependent on [[Calcium in biology|calcium]]; this may lead to [[neurotoxicity]].<ref>{{cite journal |author=Simon T, Britt JK, James RC |title=Development of a neurotoxic equivalence scheme of relative potency for assessing the risk of PCB mixtures |journal= |volume= |issue= |pages= |year=2007 |pmid=17475378}}</ref> Ortho-PCBs may disrupt [[thyroid hormone]] transport by binding to [[transthyretin]].<ref>{{cite journal |author=Chauhan KR, Kodavanti PR, McKinney JD |title=Assessing the role of ortho-substitution on polychlorinated biphenyl binding to transthyretin, a thyroxine transport protein |journal=Toxicol. Appl. Pharmacol. |volume=162 |issue=1 |pages=10–21 |year=2000 |pmid=10631123 | doi = 10.1006/taap.1999.8826 <!--Retrieved from CrossRef by DOI bot-->}}</ref> == Containment == [[Landfill]] &ndash; Large quantities of PCBs have been placed in landfill sites, mainly in the form of transformers and capacitors. Many municipal sites are not designed to contain these pollutants and PCBs are able to escape into the atmosphere or ground water. No emissions above background are seen if the landfill is designed correctly. == Methods of destruction == These can be separated into three distinct categories: physical, microbial, and chemical destruction. === Physical === [[Incineration]] &ndash; 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 for at least two seconds, in the presence of fuel oil and excess oxygen. A lack of oxygen can result in the formation of [[PCDD]]s, [[PCDF]]s and [[dioxin]]s, 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. [[Ultrasound]] &ndash; In a similar process to combustion, high power ultrasonic waves are applied to water, generating cavitation bubbles. These then implode or fragment, creating microregions of extreme pressures and temperatures where the PCBs are destroyed. Water is thought to undergo [[thermolysis]], oxidising the PCBs to CO, CO<sub>2</sub> and hydrocarbons such as biphenyl, with chlorine present as the inorganic ion 16. The scope of this method is limited to those congeners which are the most water soluble; those isomers with the least chlorine substitution. [[Irradiation]] &ndash; If a deoxygenated mixture of PCBs in [[isopropanol]] or [[mineral oil]] is subject to irradiation with [[gamma rays]] then the PCBs will be dechlorinated to form inorganic [[chloride]] and [[biphenyl]]. The reaction works best in isopropanol if [[potassium hydroxide]] (''[[caustic potash]]'') is added. [[Solvated electron]]s 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[http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=10116942][http://www.patentstorm.us/patents/6132561.html]. === Microbial === Much recent work has centered on the study of micro-organisms that are able to [[biodegradation|decompose]] PCBs. Generally, these organisms work in one of two ways: either they use the PCB as a carbon source, or destruction takes place through reductive dechlorination, with the replacement of chlorine with hydrogen on the biphenyl skeleton. However, there are significant problems with this approach. Firstly, these [[microbe]]s 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. Secondly, microbial dechlorination tends to be rather slow acting on PCB as a [[soil contaminant]] in comparison to other methods. Finally, while microbes work well in laboratory conditions, there is often a problem in transferring a successful laboratory strain to a natural system. This is because the microbes can access other sources of carbon, which they decompose in preference to PCBs. Further recent developments have focused on testing enzymes and vitamins extracted from microbes which show PCB activity. Especially promising seems to be the use of vitamin B12, in which a cobalt ion is in oxidation state (III) under normal redox conditions. Using titanium (III) citrate as a strong reductant converts the cobalt from Co(III) to Co(I), giving a new vitamin known as B12s, which is a powerful nucleophile and reducing [[catalyst]]. This can then be used on PCBs, which it dechlorinates in a rapid and selective manner.<ref>{{cite journal |author=Woods SL, Trobaugh DJ |title=Polychlorinated Biphenyl Reductive Dechlorination by Vitamin B12s: Thermodynamics and Regiospecificity |journal=Environ. Sci. Technol. |volume=33 |issue= |pages=857–863 |year=1999| doi = 10.1021/es9804823 <!--Retrieved from CrossRef by DOI bot-->}}</ref> === Chemical === [http://www.ec.gc.ca/pcb/destruction/eng/c44_e.htm 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 glycol]]s) 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, [[Hydrogen|H]]<sub>2</sub> cleaves the carbon-chlorine bond, and cleaves the biphenyl nucleus into benzene yielding [[Hydrogen chloride|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 [[electropositivity|electropositive]] metals, or strong [[reducing agent]]s 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, therefore reducing the volatility, solubility and toxicity of the mixture. This methodology is most successful on low strength PCB mixtures and can also be performed electrochemically in a partly aqueous bicontinuous micro[[emulsion]]. 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 [[protonation|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 [[hydroxide|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. == See also == * [[GE]] * [[Bay mud]] * [[Organochlorine compound]] * [[Polybrominated biphenyls]] * [[Neal Stephenson|Neal Stephenson's]] novel ''[[Zodiac (novel)|Zodiac]]'' involves PCBs and their impact on the environment. == References == <references/> == External links == * [http://www.atsdr.cdc.gov/toxprofiles/tp17.pdf ATSDR Toxicological Profile] U.S. Department of Health and Human Services * [http://monographs.iarc.fr/ENG/Monographs/suppl7/suppl7.pdf IARC PCB Monograph] * [http://www.epa.gov/pcb/ US EPA PCB Homepage] * [http://ntp-server.niehs.nih.gov/ntpweb/index.cfm?objectid=08481142-D3A0-C8AE-408773AC4B6D89C5 National Toxicology Program technical reports] * [http://www.inchem.org/documents/cicads/cicads/cicad55.htm Polychlorinated Byphenyls: Human Health Aspects] by the [[WHO]] ==Appendix== ===PCB homolog table=== For a complete list of PCB congeners, see [[PCB Congener List]]. Note that biphenyl, while not technically a PCB congener due to its lack of chlorine substituents, is still typically included in the literature. {| class="wikitable" width="50%" border="1" |- ! PCB Homolog ! CASRN ! Cl Substituents ! Number of Congeners |- | [[Biphenyl]] | 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 |- |} {{HealthIssuesOfPlastics}} [[Category:Organochlorides]] [[Category:Flame retardants]] [[Category:Hazardous air pollutants]] [[Category:IARC Group 2A carcinogens]] [[Category:Persistent organic pollutants]] [[Category:Soil contamination]] [[Category:synthetic materials]] [[cs:Polychlorované bifenyly]] [[da:Polyklorerede bifenyler]] [[de:Polychlorierte Biphenyle]] [[es:Bifenilos policlorados]] [[eo:Poliklorizita bifenilo]] [[fr:Polychlorobiphényle]] [[gl:PCB]] [[ko:폴리염화 비페닐]] [[it:Policlorobifenili]] [[he:PCB]] [[nl:Polychloorbifenyl]] [[ja:ポリ塩化ビフェニル]] [[no:Polyklorerte bifenyler]] [[nn:PCB]] [[pl:Polichlorowane bifenyle]] [[pt:Bifenilpoliclorado]] [[ru:Полихлорированные дифенилы]] [[sr:Полихлоровани бифенили]] [[fi:Polykloorattu bifenyyli]] [[sv:Polyklorerade bifenyler]] [[zh:多氯聯苯]]