Properties of PCB

The five largest uses for PCBs prior to 1970 were dielectric fluids in capacitors, plasticizers, lubricants, transformer fluids, and hydraulic fluids. They were also used widely in protective coatings, sealers, putty, grinding fluids, printing inks, pattern waxes, carbonless paper, etc. (see Chap. 1). Because of this widespread PCB use they are found throughout the environment [363-365]. A number of important properties of PCBs are discussed below along with information on their distribution and persistence in the environment. 

The scientific community provided much of the original impetus for improved environmental protection in Sweden. Swedish scientists, for instance, focused attention on the health hazards from organic mercury compounds used in agriculture several years before the Minimata poisonings in Japan brought those problems to the attention of the rest of the world.1 The Swedish chemist Soren Jensen was the first to describe the bioaccumulation properties of PCBs, and the pioneering radiation and biochemical re-... 

TABLE 7.2.3 Summary of physical properties of PCB Molecular PCB isomer weight, group CAS no. MW g/mol isomer groups and Aroclor mixtures m.p. Fugacity ratio, F Cl no. °C range at 25°C Le Bas molar volume, VM (cm3/mol) ... 

Sawhney, B.L. (1987) Chemistry and properties of PCBs in relation to environmental effects. In PCBs and the Environment. Waid, Ed., Chapter 2, pp. 48-64. CRC Press Inc., Boca Raton, Florida. 

One possible explanation for this trend Is that bound PCB s derived from an atmospheric source and were associated with soot particles. Several physicochemical properties of PCB s could favor the generation of atmospheric assemblages enriched In less chlorinated Isomers laboratory studies of PCB s demonstrate that there Is a trend toward higher vapor pressure with decreasing chlorine content (37) and that photodecomposition selectively destroys higher... 

The existing information regarding distribution of PCBs in humans is limited. Nevertheless, based on experimental data obtained in animals (see Section 3.4.2.2) and the known physicochemical properties of PCBs, it is reasonable to assume that the lipid soluble PCBs, once cleared from the bloodstream, will accumulate in highest concentration in fatty tissues. Initially, however, PCBs could accumulate in the liver due to its high blood perfusion rate. The availabiUty of PCBs for retention in fatty tissues is intimately linked to metaboUsm (see Section 3.4.3) therefore, it would be expected that the higher chlorinated PCBs would persist for longer periods of time solubiUzed in fatty tissues. 

Anti-estrogenic properties of PCBs also have been examined in numerous studies. Combined exposure of immature rats to 0.32 mg Aroclor 1242 and 0.001 mg 17P-estradiol produced a response similar to estradiol alone, indicating no obvious anti-estrogenic activity, but combined exposure to 0.001 mg... 

To organize a comprehensive review, ATSDR identified expert scientists who do not work for the Agency and have demonstrated expertise in the chemical and physical properties of PCBs, human exposure to PCBs, or the health effects associated with PCB exposure, whether in laboratory animals or... 

General Comments on Chapter 3. The panelists offered several general comments on the profile s presentation of chemical and physical properties of PCBs. First, two panelists thought Chapter 3 should include text that describes, even if generally, how the various chemical and physical properties of PCBs affect environmental distribution and the potential for human exposure. These panelists also recommended that the profile indicate how PCB properties are, to a certain extent, dependent on the number of chlorine atoms in a given congener (e.g., lower-chlorinated PCBs tend to be more water soluble and volatile than the higher-chlorinated PCBs),... 

PCBs are extremely stable to heat, chemical, and biological decomposition. They are excellent insulating and cooling fluids, extensively used for many years in manufacture of transformers and capacitors. PCBs are also used in hydraulic fluids, lubricating oils, paints, adhesive resins, inks, fire retardants, wax extenders, and numerous other products. The chemical and physical properties of PCBs make the remediation of polluted sites difficult. They resist degradation and absorb into soils and colloidal materials in water. Some persist with half-lives of 8-15 years in the environmental compartments. This stability contributes to their dispersion in the environment and long-range air pollution. Because they are lipophilic, these species are stored in fatty tissues and accumulate in the food webs (see Section 2.2). 

From an environmental impact standpoint, the four most important physical properties of PCBs are very low water solubUlty and vapor pressure, high octanol/water partition coefficients, and stability or persistence (NRC, 1979). The five mechanisms by which PCBs can be transported in the soil are as a dissolved material in the water by sorption as an emulsion with water as an immiscible oUy Uquid phase and as a discrete fluid. 

The physical-chemical properties of PCBs vary on a congener-bycongener basis. Commercial PCB fluids are complex mixtures of these PCB congeners. Other chemical compounds were often added as diluents or additives to form commercial PCB-containing fluids. Additionally, various solids and fluids have been contaminated with PCB fluids and PCB-containing fluids. 

Table 6. Selected Environmentally Relevant Properties of PCB Isomer Groups ... 

Polychlorinated biphenyls (PCB) have been analysed for many years in various mediums such as water, sediments, soils and biological mediums. More recently, oil has been added to this list with the implementation of regulations on transformer and reclaimed oils. However, the methods used to analyse PCBs in these oils is not the same as for other mediums since the similarity between the properties of PCBs and the oils could interfere with analysis results. 

The main themes discussed in this book are basic physicochemical properties of PCBs, analytical techniques, human and environmental hazards, combustion byproducts, decontamination processes, destruction techniques and replacement fluids. Obviously, each section cannot claim to be complete but extensive reference lists are provided for readers needing more detailed information. We hope that this review of various PCBs problems and solutions will prove helpful Co readers whatever their background and field of interest. 

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