PbB

Lead may be determined in a variety of biological materials such as blood, urine, soft tissues, teeth, bones, hairs, leaves and wood. From the viewpoint of occupational and environmental toxicology the determination of lead in blood is of greatest importance, since the concentration of lead in whole blood (PbB) is considered to be the best indicator of current lead exposure in humans and mammals (Alessio et al., 1979 Ewers et al.. 1991 Lauwerys, 1975 Vahter, 1982 WHO, 1977, 1980). Therefore, the problems of PbB determination are broadly discussed in this chapter, whereas the techniques and problems of lead determination in other biological matrices such as teeth, bones, plant and animal tissues are reviewed to a minor extent. 

The determination of PbB is of prime importance with respect to the diagnosis of lead poisoning and to the assessment of hazardous conditions both in occupationally exposed people and in the general population. It is generally agreed that the concentrations of lead in air. food and water are less relevant for assessing health hazards for humans than the amount of lead actually absorbed and this is what actually is reflected by PbB (WHO, 1977, 1980). 

In interpreting PbB levels one must consider the fact that they refiect a dynamic equilibrium between exposure (intake and absorption), distribution, and eiimination. Under 

Blood contains lead in three forms a major fraction (about 95%) bound to erythrocytes, a protein-bound fraction in plasma, and a diffusible fraction that represents the metabolically active form of circulating blood. Since the major fraction of PbB is bound to erythrocytes, some authors have proposed expression of results in / g/100 mL of erythrocytes so that variations in the hematocrit value are taken into account. However, the biological validity of this correction is still controversial. With the improvement of the analytical sensitivity and reliability of the methods for measuring low levels of lead in biologicai materials, it is likely that, in future, the concentration of diffusible lead in plasma as an index of metabolically active lead will be further evaluated (Lauwerys, 1983). 

Kinetic studies in man show that the lead body burden consists essentially of three compartments (1) a rapid exchange pool in blood and soft tissues (2) an intermediate exchange pool in muscles, skin and bone marrow (3) a slow exchange pool in dense bones and teeth (biological half-life about 20 years). The amount of lead stored in the latter compartment increases throughout life (Steenhout, 1982 Steenhout and Pourtois, 1981). 

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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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