Firemaster BP-6
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Product Description
Firemaster BP-6 is a commercial mixture of polybrominated biphenyls (PBBs) that was historically used as a flame retardant in plastics and electronic materials. PBBs are a group of 209 synthetic organic compounds with 1 to 10 bromine atoms attached to a biphenyl structure. Firemaster BP-6, primarily composed of the 2,2',4,4',5,5'-hexabromobiphenyl isomer (also known as BB-153), was used to make products like computer monitors, televisions, textiles, and plastic foams more fire-resistant. However, due to its high toxicity, persistence in the environment, and tendency to bioaccumulate in fatty tissues, it has been associated with serious health risks, including endocrine disruption, liver toxicity, neurodevelopmental effects, and potential carcinogenicity. Following incidents like the Michigan PBB contamination in 1973, which led to widespread human and animal exposure, Firemaster BP-6 was banned in the U.S. and is now restricted or banned in most countries worldwide.
Composition
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Major Congener: 2,2',4,4',5,5'-hexabromobiphenyl (BB-153 or HBB), comprising 56-62.6% of the mixture
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Other Congeners: 2,2',3,4,4',5,5'-heptabromobiphenyl (about 27-33.4%), along with various tetra-, penta-, and hexa-bromobiphenyls
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Trace Components: Bromochlorobiphenyls and polybrominated naphthalenes from incomplete bromination
Uses
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Historical Use: Firemaster BP-6 was primarily used as a flame retardant in thermoplastics, such as acrylonitrile-butadiene-styrene (ABS) for electronic equipment housings, and in other industrial and electrical products.
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Applications: Added to plastics for computer monitors, televisions, textiles, and plastic foams to make them more fire-resistant.
Chemical Properties
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Molecular Formula: C₁₂H₄Br₆ (for hexabromobiphenyl congeners)
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Molecular Weight: 623.59 g/mol (PubChem data)
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Appearance: Yellow-brown powder (mixture); white powder for FF-1 variant (commercial descriptions)
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Melting Point: 220–240°C (approximate for major congener)
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Boiling Point: Decomposes before boiling (>300°C)
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Solubility in Water: <0.1 mg/L (very low, lipophilic)
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Log Kow (Octanol-Water Partition Coefficient): ~8–9 (highly bioaccumulative)
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Vapor Pressure: Negligible at room temperature (non-volatile)
Historical Incident and Environmental Impact
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Michigan Contamination Incident (1973): Several thousand pounds of Firemaster BP-6 were accidentally mixed into livestock feed due to a labeling error at the Michigan Chemical Corporation plant. This led to widespread contamination of dairy and meat products, causing severe health effects in animals and exposure to humans.
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Environmental Persistence: PBBs are highly stable and resist degradation in the environment, allowing them to accumulate in the food chain.
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Current Status: Production of PBBs ceased in 1976. They are now classified as controlled substances under the Toxic Substances Control Act (TSCA) in the U.S. and are banned or restricted in many countries, including the EU under REACH.
Toxicity and Health Effects
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Toxicity: Firemaster BP-6 is highly toxic, acting as an endocrine disruptor, aryl hydrocarbon receptor (AhR) agonist, and cytochrome P450 inducer.
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Health Effects:
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Acute Exposure: Hepatocyte enlargement, vacuolization, necrosis; reduced growth; dermal necrosis in rabbits.
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Intermediate Exposure: Thymic atrophy, adrenal enlargement; fat accumulation; enzyme induction (AHH, cytochrome P450).
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Chronic Exposure: Liver tumors, thyroid hyperplasia; reproductive and developmental toxicity.
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Human Exposure: Elevated PBB levels in serum; potential links to immune suppression, but limited direct carcinogenicity data.
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Current Regulations
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Regulatory Status: PBBs, including Firemaster BP-6 components, are banned in many countries. They are classified as persistent organic pollutants (POPs) and are subject to ongoing monitoring in food chains.
Additional Notes
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Bioaccumulation: PBBs are highly lipophilic and bioaccumulate in fatty tissues of animals and humans.
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Synthesis Methods: Not detailed in the provided information, but typically involves bromination of biphenyl.
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Health Classification: The International Agency for Research on Cancer (IARC) has classified polybrominated biphenyls (PBBs) as Group 2A, meaning they are probably carcinogenic to humans based on sufficient evidence from animal studies.