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Polybrominated diphenyl ethers or PBDE, are organobromine compound
Organobromine compound
Organobromine compounds are organic compounds that contain carbon bonded to bromine. The most pervasive is the naturally produced bromomethane. One prominent application is the use of polybrominated diphenyl ethers as fire-retardants. A variety of minor organobromine compounds are found in...

s that are used as flame retardants. Like other brominated flame retardants, PBDEs have been used in a wide array of products, including building materials, electronics, furnishings, motor vehicles, airplanes, plastics, polyurethane
Polyurethane
A polyurethane is any polymer composed of a chain of organic units joined by carbamate links. Polyurethane polymers are formed through step-growth polymerization, by reacting a monomer with another monomer in the presence of a catalyst.Polyurethanes are...

 foams, and textiles. They are structurally akin to the PCB
Polychlorinated biphenyl
Polychlorinated biphenyls are a class of organic compounds with 2 to 10 chlorine atoms attached to biphenyl, which is a molecule composed of two benzene rings. The chemical formula for PCBs is C12H10-xClx...

s and other polyhalogenated compound
Polyhalogenated compound
Polyhalogenated compounds are any compounds with multiple substitutions of halogens. They are of particular interest and importance because halogens generally are highly reactive and also bioaccumulate in humans, and comprise a superset of which has many toxic and carcinogenic industrial...

s, consisting of two halogen
Halogen
The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...

ated aromatic rings. PBDEs are classified according to the average number of bromine
Bromine
Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...

 atoms in the molecule. The health hazards of these chemicals have attracted increasing scrutiny, and they have been shown to reduce fertility in humans at levels found in households. Their chlorine analogs are polychlorinated diphenyl ethers
Polychlorinated diphenyl ethers
Polychlorinated diphenyl ethers are structurally similar to polychlorinated biphenyls , both which may be toxic polyhalogenated compounds and some PCDE congeners have been reported to cause toxic responses similar to those caused by some of the non-ortho-substituted PCBs, which are mediated by the...

 (PCDEs). Because of their toxicity and persistence, their industrial production is to be eliminated under the Stockholm Convention
Stockholm Convention on Persistent Organic Pollutants
Stockholm Convention on Persistent Organic Pollutants is an international environmental treaty, signed in 2001 and effective from May 2004, that aims to eliminate or restrict the production and use of persistent organic pollutants .- History :...

, a treaty to control and phase out major persistent organic pollutants (POP).

Classes of PBDEs



The family of PBDEs consists of 209 possible substances, which are called congeners (PBDE = C12H10−xBrxO (x = 1, 2, ..., 10 = m + n)). Congeners include dibromodiphenyl ethers, tribromodiphenyl ethers, tetrabromodiphenyl ethers, pentabromodiphenyl ether
Pentabromodiphenyl ether
Pentabromodiphenyl ether is a brominated flame retardant which belongs to the group of polybrominated diphenyl ethers...

s, hexabromodiphenyl ethers, heptabromodiphenyl ethers, octabromodiphenyl ethers, nonabromodiphenyl ether, and decabromodiphenyl ether
Decabromodiphenyl ether
Decabromodiphenyl ether is a brominated flame retardant which belongs to the group of polybrominated diphenyl ethers ....

. In the United States, PBDEs are marketed with trade names: DE-60F, DE-61, DE-62, and DE-71 applied to pentaBDE mixtures; DE-79 applied to octaBDE mixtures; DE 83R and Saytex 102E applied to decaBDE mixtures. The available commercial PBDE products are not single compounds or even single congeners but rather a mixture of congeners.

Lower brominated PBDEs


These species average 1-5 bromine
Bromine
Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...

 atoms per molecule and are regarded as more dangerous because they more efficiently bioaccumulate
Bioaccumulation
Bioaccumulation refers to the accumulation of substances, such as pesticides, or other organic chemicals in an organism. Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at which the substance is lost...

. Lower-brominated PBDEs have been known to affect hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...

 levels in the thyroid
Thyroid
The thyroid gland or simply, the thyroid , in vertebrate anatomy, is one of the largest endocrine glands. The thyroid gland is found in the neck, below the thyroid cartilage...

 gland. Studies have linked them to reproductive and neurological risks at certain concentrations or higher.

Higher brominated PBDEs


These species average more than 5 bromine
Bromine
Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...

 atoms per molecule.

The commercial mixture, named pentabromodiphenyl ether, contains the pentabromo derivative predominantly (50-62%), however the mixture also contains tetrabromides (24-38%) and hexabromides (4-8%), as well as traces of the tribromides (0-1%). In similar manner, commercial octabromodiphenyl ether is a mixture of homologs: hexa-, hepta-, octa-, nona-, and decabromides.

Health and environmental concerns


Since the 1990s, scientists have questioned the safety of PBDEs. People are exposed to low levels of PBDEs through ingestion of food and by inhalation. PBDEs bioaccumulate in blood, breast milk, and fat tissues. Personnel associated with the manufacture of PBDE-containing products are exposed to highest levels of PBDEs. Bioaccumulation is of particular concern in such instances, especially for personnel in recycling and repair plants of PBDE-containing products. People are also exposed to these chemicals in their domestic environment because of their prevalence in common household items. Studies in Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

 have found significant concentrations of PBDEs in common foods such as salmon
Salmon
Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...

, ground beef
Ground beef
Beef mince, ground beef, hamburger meat , hamburg or minced meat is a minced meat food, made of beef finely chopped by a mincer. It is used in many recipes including hamburgers and cottage pie...

, butter
Butter
Butter is a dairy product made by churning fresh or fermented cream or milk. It is generally used as a spread and a condiment, as well as in cooking applications, such as baking, sauce making, and pan frying...

, and cheese
Cheese
Cheese is a generic term for a diverse group of milk-based food products. Cheese is produced throughout the world in wide-ranging flavors, textures, and forms....

. PBDEs have also been found at high levels in indoor dust, sewage sludge, and effluents from wastewater treatment plants. Increasing PBDE levels have been detected in the blood of marine mammal
Marine mammal
Marine mammals, which include seals, whales, dolphins, and walruses, form a diverse group of 128 species that rely on the ocean for their existence. They do not represent a distinct biological grouping, but rather are unified by their reliance on the marine environment for feeding. The level of...

s such as harbor seal
Harbor Seal
The harbor seal , also known as the common seal, is a true seal found along temperate and Arctic marine coastlines of the Northern Hemisphere...

s.

There is also growing concern that PBDEs share the environmental long life and bioaccumulation
Bioaccumulation
Bioaccumulation refers to the accumulation of substances, such as pesticides, or other organic chemicals in an organism. Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at which the substance is lost...

 properties of polychlorinated dibenzodioxins.

Case studies


Studies show that children in the United States, Norway, Australia, and the Faroe Islands have higher levels of PBDEs than adults. In the United States, children's blood concentrations average 62 parts per billion (ppb) and range from 24 to 114 ppb. Published studies express concern because exposure to PBDEs impairs development of the nervous system. PBDEs have also been shown to have hormone-disrupting effects, in particular, on estrogen and thyroid hormones. Experiments with animals have shown that deiodination, active transport, sulfation, and glucuronidation may be involved in disruption of thyroid homeostasis after perinatal exposure to PBDEs during critical developmental time points in utero and days after birth. These adverse effects on hepatic mechanism of thyroid hormone disruption during development have been shown to persist into adulthood. The U.S. Environmental Protection Agency (EPA) noted that PBDEs are particularly toxic to the developing brains of animals. Peer-reviewed studies have shown that even a single dose administered to mice during development of the brain can cause permanent changes in behavior, including hyperactivity.

Swedish scientists first reported substances related to PentaBDE were accumulating in human breast milk. Studies by the Swedish Society for Nature Conservation found for the first time very high levels of higher brominated PBDEs (BDE-209) in eggs of Peregrine falcon
Peregrine Falcon
The Peregrine Falcon , also known as the Peregrine, and historically as the Duck Hawk in North America, is a widespread bird of prey in the family Falconidae. A large, crow-sized falcon, it has a blue-gray back, barred white underparts, and a black head and "moustache"...

s. Two forms of PBDEs, Penta and Octa, are no longer manufactured in the United States because of health and safety concerns. Based on a comprehensive risk assessment under the Existing Substances Regulation 793/93/EEC, the EU has completely banned the use of Penta and Octa BDE since 2004. However, both chemicals are still found in furniture and foam items made before the phase-out was completed. The most-common PBDEs that are used in electronics are in a form known as Deca. Deca is banned in Europe for this use and in some U.S. states. For PBDE, EPA has set reference dose of 7 micrograms per kilogram of body weight, which is "believed to be without appreciable effects". However, Linda Birnbaum, PhD, a senior toxicologist with the EPA notes concern: "What I see is another piece of evidence that supports the fact that levels of these chemicals in children appear to be higher than the levels in their parents; I think this study raises a red flag. Previous study by EWG in 2003 published test results showing that the average level of fire-retardants in breast milk from 20 American mothers was 75 times higher than the average levels measured in Europe.

It has been postulated that increasing levels of PBDEs in the environment could be correlated with the increasing incidence of feline hyperthyroidism. However, a study in 2007 found that no association could be detected between hyperthyroid cats and serum PBDE levels.

An experiment conducted at Woods Hole Oceanographic Institution
Woods Hole Oceanographic Institution
The Woods Hole Oceanographic Institution is a private, nonprofit research and higher education facility dedicated to the study of all aspects of marine science and engineering and to the education of marine researchers. Established in 1930, it is the largest independent oceanographic research...

 in 2005 showed that the isotopic signature
Isotopic signature
An isotopic signature is a ratio of stable or unstable isotopes of particular elements found in an investigated material...

 of methoxy-PBDEs found in whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...

 blubber
Blubber
Blubber is a thick layer of vascularized adipose tissue found under the skin of all cetaceans, pinnipeds and sirenians.-Description:Lipid-rich, collagen fiber–laced blubber comprises the hypodermis and covers the whole body, except for parts of the appendages, strongly attached to the musculature...

 contained carbon-14
Carbon-14
Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon with a nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues , to date archaeological, geological, and hydrogeological...

, the naturally occurring radioactive isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...

 of carbon. Methoxy-PBDEs are produced by some marine species. If the methoxy-PBDEs in the whale had come from artificial (human-made) sources, they would have contained only carbon-12 and no carbon-14 due to the fact that virtually all PBDEs that are produced artificially use petroleum as the source of carbon; all carbon-14 would have long since completely decayed from that source. The isotopic signatures of the PBDEs themselves were not evaluated. The carbon-14 may instead be in methoxy groups enzymatically added to man-made PBDEs.

A 2010 study found that children with higher concentrations of PBDEs in their umbilical cord blood at birth scored lower on tests of mental and physical development between the ages of one and six. Developmental effects were particularly evident at four years of age, when verbal and full IQ scores were reduced 5.5 to 8.0 points for those with the highest prenatal exposures.

Regulations of PBDEs


As of June 1, 2006 the State of California began prohibiting the manufacture, distribution, and processing of flame-retardant products containing pentabrominated diphenyl ether (pentaBDE) and octabrominated diphenyl (octaBDE). PBDEs are ubiquitous in the environment, and, according to the EPA, exposure may pose health risks. According to U.S. EPA's Integrated Risk Information System, evidence indicates that PBDEs may possess liver toxicity, thyroid toxicity, and neurodevelopmental toxicity. In June 2008, the U.S. EPA set a safe daily exposure level ranging from 0.1 to 7 ug per kg body weight per day for 4 most common PBDEs. In April 2007, the legislature of the state of Washington passed a bill banning the use of PBDEs. The State of Maine Department of Environmental Protection found that all PBDEs should be banned. In August, 2003, the State of California outlawed the sale of penta- and octa- PBDE and products containing them, effective January 1, 2008. In May 2007, the legislature of the state of Maine
Maine
Maine is a state in the New England region of the northeastern United States, bordered by the Atlantic Ocean to the east and south, New Hampshire to the west, and the Canadian provinces of Quebec to the northwest and New Brunswick to the northeast. Maine is both the northernmost and easternmost...

 passed a bill phasing out the use of DecaBDE.

The European Union decided to ban the use of two classes of flame retardants, in particular, polybrominated diphenyl ethers (PBDEs) and polybrominated biphenyls (PBBs) in electric and electronic devices. This ban was formalised in the RoHS Directive, and an upper limit of 1 g/kg for the sum of PBBs and PBDEs was set. In February 2009, the Institute for Reference Materials and Measurements (IRMM)
Institute for Reference Materials and Measurements
The Institute for Reference Materials and Measurements , located in Geel, Belgium, is one of the seven institutes of the Joint Research Centre , a Directorate-General of the European Commission ....

 released two certified reference materials (CRMs) to help analytical laboratories better detect these two classes of flame retardants. The reference materials were custom-made to contain all relevant PBDEs and PBBs at levels close to the legal limit.

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