Polybrominated biphenyls (PBBs), also called brominated biphenyls or polybromobiphenyls, are a group of manufactured chemicals, of the 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. Their chlorine analogs are 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. While once widely used commercially, PBBs are now controlled substances under the Restriction of Hazardous Substances Directive

Restriction of Hazardous Substances Directive

The Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment 2002/95/EC was adopted in February 2003 by the European Union. The RoHS directive took effect on 1 July 2006, and is required to be enforced and become law in each member state...

, which limits their use in electrical and electronic products sold in the EU.

Characteristics

PBBs usually exist as colorless to off-white solids. PBBs soften at 72 degrees Celsius and decompose above 300 degrees Celsius. They have low vapor pressure

Vapor pressure

Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...

, are very soluble in benzene

Benzene

Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....

 and toluene

Toluene

Toluene, formerly known as toluol, is a clear, water-insoluble liquid with the typical smell of paint thinners. It is a mono-substituted benzene derivative, i.e., one in which a single hydrogen atom from the benzene molecule has been replaced by a univalent group, in this case CH3.It is an aromatic...

, and insoluble in water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

. They are degraded by UV light.

Application

PBBs are used as flame retardant

Flame retardant

Flame retardants are chemicals used in thermoplastics, thermosets, textiles and coatings that inhibit or resist the spread of fire. These can be separated into several different classes of chemicals:...

s of the brominated flame retardant group. They are added to plastics used in products such as home electrical appliances, textile

Textile

A textile or cloth is a flexible woven material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw fibres of wool, flax, cotton, or other material to produce long strands...

s, plastic

Plastic

A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

 foams, laptop

Laptop

A laptop, also called a notebook, is a personal computer for mobile use. A laptop integrates most of the typical components of a desktop computer, including a display, a keyboard, a pointing device and speakers into a single unit...

 cabinets, etc. to make them difficult to burn.

Health hazards

Exposure to the coplanar stereoisomer 3,3',4,4',5,5'-hexabromobiphenyl (but not the non-coplanar stereoisomer) in genetically susceptible mice is known to cause immunotoxicity and disorders related to the central nervous system, and even at doses as low as 2.5 mg/kg, excess neonatal fatalities are observed (LD₅₀ is from 5-10mg/kg). The mechanism of toxicity is cellular oxidative stress by aryl hydrocarbon receptor

Aryl hydrocarbon receptor

The Aryl hydrocarbon receptor is a member of the family of basic-helix-loop-helix transcription factors. AhR is a cytosolic transcription factor that is normally inactive, bound to several co-chaperones...

 activation.

There is evidence that pre- and post-natal exposure to PBB in girls leads to menarche

Menarche

Menarche is the first menstrual cycle, or first menstrual bleeding, in female human beings. From both social and medical perspectives it is often considered the central event of female puberty, as it signals the possibility of fertility....

 at an earlier age.

Early studies on the effects of PBBs on human beings concerned the people in Michigan

Michigan

Michigan is a U.S. state located in the Great Lakes Region of the United States of America. The name Michigan is the French form of the Ojibwa word mishigamaa, meaning "large water" or "large lake"....

, USA who consumed PBB-contaminated animal products (see history of PBBs below). A study of 327 girls aged 5–24 years in Michigan found those who were exposed in utero to PBBs at or above a level of 7 ppb

PPB

PPB can stand for:* Party political broadcast, a type of political programming in the United Kingdom* parts-per-billion, a unit of concentration* Portland Police Bureau, a police agency for the city of Portland...

 found had an earlier age at menarche

Menarche

Menarche is the first menstrual cycle, or first menstrual bleeding, in female human beings. From both social and medical perspectives it is often considered the central event of female puberty, as it signals the possibility of fertility....

 compared to a case-control

Case-control

A case-control study is a type of study design in epidemiology. Case-control studies are used to identify factors that may contribute to a medical condition by comparing subjects who have that condition with patients who do not have the condition but are otherwise similar .Case-control studies are...

 group. Michigan dairy farmers exposed to PBBs had significant immune system abnormalities including reduced numbers of circulating blood lymphocytes, increases in lymphocytes with no detectable surface markers, and reduced functional response to specific test antigens. Some residents complained of nausea

Nausea

Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...

, abdominal pain

Abdominal pain

Abdominal pain can be one of the symptoms associated with transient disorders or serious disease. Making a definitive diagnosis of the cause of abdominal pain can be difficult, because many diseases can result in this symptom. Abdominal pain is a common problem...

, loss of appetite, joint pain and lethargy, though it could not be clearly established that PBBs were the cause of these health problems.
Workers who were exposed to PBB during PBB production suffered hypothyroidism

Hypothyroidism

Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone.Iodine deficiency is the most common cause of hypothyroidism worldwide but it can be caused by other causes such as several conditions of the thyroid gland or, less commonly, the pituitary gland or...

, although no deterioration in memory performance was found in PBB-exposed workers in tests conducted several years after final PBB exposure, and there was also no correlation of performance with PBB concentration.

There is stronger evidence that PBBs may have caused skin problems, such as acne

Acne vulgaris

Acne vulgaris is a common human skin disease, characterized by areas of skin with seborrhea , comedones , papules , pustules , Nodules and possibly scarring...

, in consumers of the contaminated food. Some workers exposed to PBBs by breathing and skin contact for days to months also developed acne.

Studies in animals exposed to large amounts of PBBs for a short period or to smaller amounts over a longer period show that PBBs can cause weight loss

Weight loss

Weight loss, in the context of medicine, health or physical fitness, is a reduction of the total body mass, due to a mean loss of fluid, body fat or adipose tissue and/or lean mass, namely bone mineral deposits, muscle, tendon and other connective tissue...

, skin disorders, nervous

Nervous system

The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...

 and immune system

Immune system

An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...

s effects, as well as effects on the liver

Liver

The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

, kidney

Kidney

The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...

s, and thyroid gland.

Possibility of carcinogenicity

It is not known for certain if PBBs could cause cancer

Cancer

Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

 in human beings, but it has been observed that they can lead to cancer in lab mice exposed to very high concentrations of PBBs. Based on such animal tests

Animal testing

Animal testing, also known as animal experimentation, animal research, and in vivo testing, is the use of non-human animals in experiments. Worldwide it is estimated that the number of vertebrate animals—from zebrafish to non-human primates—ranges from the tens of millions to more than 100 million...

, the United States Department of Health and Human Services

United States Department of Health and Human Services

The United States Department of Health and Human Services is a Cabinet department of the United States government with the goal of protecting the health of all Americans and providing essential human services. Its motto is "Improving the health, safety, and well-being of America"...

 has determined that PBBs may reasonably be anticipated to be carcinogen

Carcinogen

A carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes...

s. The International Agency for Research on Cancer

International Agency for Research on Cancer

The International Agency for Research on Cancer is an intergovernmental agency forming part of the World Health Organisation of the United Nations....

 also suggests that PBBs are possibly carcinogenic to humans.

The Michigan PBB contamination incident

Before the 1970s, PBBs were widely used commercially as a flame retardant

Flame retardant

Flame retardants are chemicals used in thermoplastics, thermosets, textiles and coatings that inhibit or resist the spread of fire. These can be separated into several different classes of chemicals:...

. Michigan Chemical Corporation (owned by Velsicol Chemical Corporation

Velsicol Chemical Corporation

Genovique Specialties Corporation was a Rosemont, Illinois based chemical company founded in 1931 that specializes in plasticizers....

) in St. Louis, Michigan

St. Louis, Michigan

St. Louis is a city in Gratiot County in the U.S. state of Michigan. As of the 2000 census, the city population was 4,494. The 2010 census estimate places the population at 7,482.-Geography:...

 was a major producer of the FireMaster range of PBB-based flame retardants. FireMaster BP-6 (a yellow-brown powder) is a mixture of many different PBB congeners with 2,2',4,4',5,5'-hexabromobiphenyl and 2,2',3,4,4',5,5'-heptabromobiphenyl being significant constituents by mass (60-80% and 12-25%, respectively). FireMaster FF-1 (a white powder) is FireMaster BP-6 with the addition of 2% calcium silicate as an anti-caking agent. Mixed bromochlorobiphenyls and polybrominated naphthalenes, as well as lower brominated compounds formed by incomplete bromination, have also been found as minor constituents of FireMaster products.

In 1973, several thousand pound

Pound (mass)

The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...

s of FireMaster BP-6 were accidentally mixed with livestock feed that was distributed to farms in Michigan

Michigan

Michigan is a U.S. state located in the Great Lakes Region of the United States of America. The name Michigan is the French form of the Ojibwa word mishigamaa, meaning "large water" or "large lake"....

, USA. Some 1.5 million chicken

Chicken

The chicken is a domesticated fowl, a subspecies of the Red Junglefowl. As one of the most common and widespread domestic animals, and with a population of more than 24 billion in 2003, there are more chickens in the world than any other species of bird...

s, 30,000 cattle

Cattle

Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...

, 5,900 pig

Pig

A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...

s, and 1,470 sheep then consumed this feed, and became contaminated with PBBs before the error was discovered. These events were dramatized in the 1981 film Bitter Harvest

Bitter Harvest (1981 film)

Bitter Harvest was a 1981 television docudrama about an accidental poisoning of cattle feed in the Midwest in the 1970s. Its plot is based on the 1973 Michigan PBB contamination incident.-Plot:...

.
These events were also dramatized in the book "The Poisoning of Michigan". A 1978 episode of Lou Grant

Lou Grant (TV series)

Lou Grant is an American television drama series starring Ed Asner in the titular role as a newspaper editor. Unusual in American television, this drama series was a spinoff from a sitcom, The Mary Tyler Moore Show. Aired from 1977 to 1982, Lou Grant won 13 Emmy Awards, including "Outstanding Drama...

 ("Slaughter") portrays a similar, but fictionalized account.
One year elapsed before the animals were culled. A study was undertaken on 4,545 people to determine the effects of PBBs on human beings. These include three exposure groups – all people who lived on the quarantined farms, people who received food from these farms and workers (and their families) engaged in PBB manufacture – as well as 725 people with low-level PBB exposure.

All were queried concerning 17 symptoms and conditions possibly related to PBBs. Venous blood

Venous blood

Venous blood is deoxygenated blood in the circulatory system. It runs in the systemic veins from the organs to the heart. Deoxygenated blood is then pumped by the heart to lungs via the pulmonary arteries, one of the few arteries in the body that carries deoxygenated blood .Venous blood is...

was drawn and analyzed for PBB by gas chromatography. Mean serum

Blood plasma

Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...

 PBB levels were found to be 26.9 ppb

PPB

PPB can stand for:* Party political broadcast, a type of political programming in the United Kingdom* parts-per-billion, a unit of concentration* Portland Police Bureau, a police agency for the city of Portland...

 by weight (26.9 µg/kg) in farm residents, 17.1 in recipients, 43.0 ppb in workers, and 3.4 ppb in the low exposure group. No associations could be established between serum PBB levels and symptom prevalence rates.

To evaluate peripheral lymphocyte

Lymphocyte

A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...

 function, T

T cell

T cells or T lymphocytes belong to a group of white blood cells known as lymphocytes, and play a central role in cell-mediated immunity. They can be distinguished from other lymphocytes, such as B cells and natural killer cells , by the presence of a T cell receptor on the cell surface. They are...

 and B cell

B cell

B cells are lymphocytes that play a large role in the humoral immune response . The principal functions of B cells are to make antibodies against antigens, perform the role of antigen-presenting cells and eventually develop into memory B cells after activation by antigen interaction...

 quantitation and in vitro

In vitro

In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...

 responses to three nonspecific mitogen

Mitogen

A mitogen is a chemical substance that encourages a cell to commence cell division, triggering mitosis. A mitogen is usually some form of a protein.Mitogenesis is the induction of mitosis, typically via a mitogen....

s were studied in 34 persons with highest PBB levels (mean: 787 ppb), and in 56 with low levels (mean: 2.8 ppb). Again, no statistically significant differences in lymphocyte function were noted.

Bans and restrictions

Noting the possible hazards on the environment, however, PBBs were listed as one of six controlled substances under the Restriction of Hazardous Substances Directive

Restriction of Hazardous Substances Directive

The Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment 2002/95/EC was adopted in February 2003 by the European Union. The RoHS directive took effect on 1 July 2006, and is required to be enforced and become law in each member state...

 (RoHS), which was enacted into European Law in February 2003. RoHS legislation lists PBBs as a "restricted substance" group. Other countries followed suit, resulting most recently in restriction dates instituted in China on March 1, 2007 and South Korea on July 1, 2007.

Testing for PBB in plastics

Until recently testing for PBB has been cumbersome. Cycle time, inaccuracy, cost and level of expertise required for the test engineer has precluded the implementation of any screening of plastic component in a manufacturing or in a product qualification/validation environment.

Recently, with the introduction of a new analytical instrument IA-Mass, screening of plastic material alongside manufacturing line is possible. A 5 min. detection cycle and a 20 min. quantification cycle is available to test and to qualify plastic parts as they reach the assembly line.

See also

• Polychlorinated biphenyls
• Brominated flame retardant
• RoHS
• IA-Mass