chemistry

Polybrominated biphenyl

Polybrominated biphenyl is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Polybrominated biphenyl rather than just read about it. In short: Polybrominated biphenyls (PBBs), also called brominated biphenyls or polybromobiphenyls, are a group of manufactured chemicals that consist of polyhalogenated derivatives of a biphenyl core. Their chlorine analogs are the PCBs.

Key takeaways

Polybrominated biphenyl belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Polybrominated biphenyl to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Polybrominated biphenyl from memory before moving on to harder problems.

Reference excerpt

Polybrominated biphenyls (PBBs), also called brominated biphenyls or polybromobiphenyls, are a group of manufactured chemicals that consist of polyhalogenated derivatives of a biphenyl core. Their chlorine analogs are the PCBs. While once widely used commercially, PBBs are now controlled substances under the Restriction of Hazardous Substances Directive, which limits their use in electrical and electronic products sold in the EU.

Classes of PBBs The family of PBBs consists of 209 possible substances, which are called congeners (PBB = C12H(10−x)Brx (x = 1, 2, ..., 10 = m + n)). The number of isomers for mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, and decabromobiphenyl are 3, 12, 24, 42, 46, 42, 24, 12, 3 and 1, respectively.

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, are very soluble in benzene and toluene, and insoluble in water. They are degraded by UV light.

Application PBBs are used as flame retardants of the brominated flame retardant group. They are added to plastics used in products such as home electrical appliances, textiles, plastic foams, laptop cabinets, etc. to make them difficult to burn. A number of substituted PBBs found application in medicine, namely bromophene and bromofenofos.

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 5–10 mg/kg). The mechanism of toxicity is thought to be related to aryl hydrocarbon receptor activation. There is evidence that pre- and post-natal exposure to PBB can cause early menarche. Early studies on the effects of PBBs on human beings concerned the people in Michigan, United States 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 found had an earlier age at menarche compared to a case-control 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, abdominal pain, 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, 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, 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, skin disorders, nervous and immune systems effects, as well as effects on the liver, kidneys, and thyroid gland.

Possibility of carcinogenicity It is not known for certain if PBBs could cause cancer 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, the United States Department of Health and Human Services has determined that PBBs may reasonably be anticipated to be carcinogens. The International Agency for Research on Cancer also suggests that PBBs are possibly carcinogenic to humans.

Michigan PBB contamination incident

Before the 1970s, PBBs were widely used commercially as a flame retardant. Michigan Chemical Corporation (MCC) in St. Louis, Michigan, which was then owned by Velsicol Chemical Corporation, 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 summer 1973, several thousand pounds of FireMaster BP-6 were accidentally mixed with livestock feed that was distributed to farms in Michigan because the MCC plant also produced a feed precursor ingredient, magnesium oxide, which was sold to the feed manufacturer. Some 1.5 million chickens, 30,000 cattle, 5,900 pigs, and 1,470 sheep then consumed this feed, became contaminated with PBBs and the carcasses were disposed of in landfill sites throughout the state. In 1976, the Michigan Department of Community Health established a PBB registry to gather and analyze data on exposed residents. It now resides at the Rollins School of Public Health at Emory University, and is maintained by epidemiologist Michele Marcus. Michigan Farmer magazine staff members Richard Lehnert and Bonnie Pollard broke the news of the contamination. The magazine continued coverage of the issue until the eventual bankruptcy proceedings of the farm cooperative responsible for the accidental contamination and subsequent distribution of the feed. These events were also portrayed in the 1981 documentary Cattlegate by Jeff Jackson, the true-fiction film Bitter Harvest starring Ron Howard, and in the book The Poisoning of Michigan by Joyce Egginton. A 1978 episode of Lou Grant ("Slaughter") portrays a similar, but fictionalized account. One year elapsed before the animals were culled. This incident is cited amongst a handful of other noxious substances as the driver for President Gerald Ford's reluctant approval in 1976 of the Toxic Substances Control Act, which "remains one of the most controversial regulatory bills ever passed".

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Illustrations

Worked examples

Example 1 — a first encounter with Polybrominated biphenyl

Start with the simplest possible case. Write down what Polybrominated biphenyl claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Polybrominated biphenyl before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Polybrominated biphenyl ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Polybrominated biphenyl

In research: Polybrominated biphenyl appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Polybrominated biphenyl in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Polybrominated biphenyl is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1973 disasters in the United States, 1973 in the environment, Biphenyls, so understanding it makes those chapters shorter.
In everyday life: Look for Polybrominated biphenyl outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Polybrominated biphenyl in 20 minutes

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Frequently asked questions

What is Polybrominated biphenyl in simple terms?

Why does Polybrominated biphenyl matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Polybrominated biphenyl?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Polybrominated biphenyl.