PBBs

Lowest observed effect level (PbB) (Mg/dl) Heme synthesis and hematological effects Neurological effects Renal system effects Gastrointestinal effects ... 

Except for polybrominated biphenyls (PBB), a limited number of studies regarding the toxicity of aromatic brominated compounds has been performed. Some experiments suggest a moderate acute toxicity of these compounds (ref. 1). 

The polychlorinated biphenyls (PCBs) and polybrominated biphenyls (PBBs) are indnstrial chemicals that do not occur naturally in the environment. The properties, uses, and toxicology of the PCBs are described in detail in Safe (1984), Robertson and Hansen (2001), and Environmental Health Criteria 140. PBBs are described in Safe (1984) and Environmental Health Criteria 152. 

PBBs have also been marketed as mixtures of congeners, produced in this case by the bromination of biphenyl. Their main commercial use has been as lire retardants, for which purpose they were introduced in the early 1970s. The most widely known commercial PBB mixture was Firemaster, first produced in 1970 in the United States, with production discontinued in 1974 following the recognition of pollution problems. 

Many of the components of PCB and PBB mixtures are both lipophilic and stable, chemically and biochemically. Similar to the persistent organochlorine insecticides and their stable metabolites, they can undergo strong bioconcentration and bioaccumulation to reach relatively high concentrations in predators. 

The principal source of pollution by polybrominated biphenyls (PBBs) has been the commercial mixture Firemaster, which was produced in the United States between 1970 and 1974. Production was discontinued in 1974 following a severe pollution incident in Michigan, when Firemaster was accidentally mixed with cattle feed on a farm. In due course, PBBs entered the human food chain via contaminated animal products. Substantial residues were found in humans from the area, and were snbse-quently found to be highly persistent. 

Firemaster is a stable solid, resembling a PCB mixture in its lipophilicity, chemical and thermal stability, and low vapor pressure. Firemaster contains some 80 ont of a possible 209 PBB congeners, but just two of them— 2,2, 4,4, 5,5-hexabromobiphenyl and 2,2, 3,4,4, 5,5, heptabromobiphenyl—account for around 85% of the commercial product (Environmental Health Criteria 152). These two componnds were fonnd to be very slowly eliminated by humans exposed to them during the Michigan incident. A half-life of abont 69 weeks was estimated for 2,4,5,2,4, 5 -HBB. 

PBB mixtures have been used as fire retardants. Many of their constituent congeners are highly persistent, and there was a major environmental accident in the United States in which farm animals and humans became heavily contaminated by them. 

Kaiser, T.E., Reichel, W.L., and Locke, L.H. et al. (1980). Organochlorine insecticides PCB and PBB residues and necropsy data from 29 states. Pesticides Monitoring Journal 13, 145-149. 

Mixed cultures of organisms that were isolated from sediments contaminated with PCBs and polybrominated biphenyls (PBBs) were shown to debrominate PBBs under anaerobic conditions (Morris et al. 1992), and the dominant congener—2,2, 4,4, 5,5 (245-245)-hexabromobiphenyl—could be successively debrominated to 2,2 -dibromobiphenyl. However, in sediments from the most heavily contaminated site containing contaminants in addition to PBBs, very little debromination occurred and the recalcitrance was attributed to the toxicity of the other contaminants (Morris et al. 1993). 

PBBs are therefore not only debrominated microbially under anaerobic conditions, but are also able to induce effective dechlorination of their chlorinated analogs. Debromination may, however, be limited in the presence of other contaminants. 

Substance TBBA replaces PBB/PBDE Polymerized TBBA Phosphorus-based retardants Mineral-based retardants Change base material Separate high and low voltage Reduce voltage... 

The challenge was to avoid the use of hazardous brominated fire retardants such as polybrominated biphenyl (PBB) and pentabromodiphenyl ether (PBDE). The first strategy was to replace PBB and PBDE with tetrabromo-bisphenol-A (TBBA). This has a much lower toxicity, but is still a brominated fire retardant with safety concerns. An improvement... 

Pbb Cknt. FBKK SOj BY WKIGHT Density, 20 20 Grams FREE so, PER 100 Ml. Per Cent. FREE SO, BY Weight Density 20 Grams FREE SO, PER 100 11l. Per Cent. FREE SO, BY Weight Density 20 Grams FREE SO, PER 100 Ml. 

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