Polychlorinated Compounds

Thus, [C] X TEE = TEQ i , i , where [C] = environmental concentration of planar polychlorinated compound. The TEQ is an estimate of the concentration of TCDD that would produce the same effect as the given concentration of the dioxin-like chemical. 

PAHs can be bioconcentrated or bioaccumulated by certain aquatic invertebrates low in the food chain that lack the capacity for effective biotransformation (Walker and Livingstone 1992). Mollusks and Daphnia spp. are examples of organisms that readily bioconcentrate PAH. On the other hand, fish and other aquatic vertebrates readily biotransform PAH so, biomagnification does not extend up the food chain as it does in the case of persistent polychlorinated compounds. As noted earlier, P450-based monooxygenases are not well represented in mollusks and many other aquatic invertebrates (see Chapter 4, Section 4.2) so, this observation is not surprising. Oxidation catalyzed by P450 is the principal (perhaps the only) effective mechanism of primary metabolism of PAH. 

Coplanar PCBs, PCDDs, and PCDFs express Ah-receptor-mediated toxicity (Chapter 6, Section 6.2.4). Binding to the receptor leads to induction of cytochrome P4501 and a number of associated toxic effects. Again, toxic effects are related to the extent of binding to this receptor and appear to be additive, even with complex mixtures of planar polychlorinated compounds. Induction of P4501A1/2 has been widely used as the basis of a biomarker assay. Residue data can be used to estimate TEQs for dioxin (see Chapter 7, Section 7.2.4). 

The results obtained with sample 1485 in theses SPME conditions are given Table 10.1, column 12. They are very similar to those obtained at ambient temperature but less volatile compounds, eluted after a-cedrol, could be observed. Except for the polychlorinated compound (84) of unknown origin, they are degradation products of resin acids resulting from ageing and their presence, even in small amounts, is indicative of a conifer resin. 

Rordorf, B. F. (1985a) Thermodynamic and thermal properties of polychlorinated compounds the vapor pressures and flow tube kinetic... 

Interaction effects of PCDDs with other polychlorinated compounds or mixtures are not extensively documented. For example, certain polychlorinated hexachlorobiphenyls (PCBs) have a low toxic potency to induce cleft palate deformities in mice (Bimbaum et al. 1985). However, mixtures of 2,3,7,8-TCDD and 2,3,4,5,3, 4 -hexachlorobiphenyl resulted in a tenfold increase in incidence of cleft palate in mice. Thus, the toxicity of compounds such as 2,3,7,8-TCDD may be enhanced by compounds of relatively low acute toxicity, such as selected PCBs. Bimbaum etal. (1985) concluded that the widespread environmental occurrence of such combinations suggests a need for further evaluation of the mechanism of this interaction. 

Caution Most polychlorinated compounds show some toxicity. These compounds should be handled in a hood. 

The reactions include an unusual Diels-Alder reaction and a very useful synthetic method, the dechlorination of polychlorinated compounds. At the present time this procedure is the best one available for the removal of chlorine from an organic molecule. The end product, 7,7-dimethoxybicyclo[2.2.1]heptene, is an interesting and useful intermediate in bicyclic chemistry it has a reactive double bond and a protected carbonyl group in the 7-position. 

Finally, when we are running out of cyclohexane, the process terminates by the interaction of two radical species, e.g. two chlorine atoms, two cyclohexyl radicals, or one of each species. The combination of two chlorine atoms is probably the least likely of the termination steps, since the Cl-Cl bond would be the weakest of those possible, and it was light-induced fission of this bond that started off the radical reaction. Of course, once we have formed cyclohexyl chloride, there is no reason why this should not itself get drawn into the radical propagation steps, resulting in various dichlorocyclohexane products, or indeed polychlorinated compounds. Chlorination of an alkane will give many different products, even when the amount of chlorine used is limited to molar ratios, and in the laboratory it is not going to be a particularly useful process. 

Because 2,4,5-T is often contaminated with dioxins and other polychlorinated compounds, it is no longer used. It was the compound used in "Agent Orange" and proved to be an agricultural and social disaster. 

Anaerobic bioreactors have been used since the 1880s to treat wastewaters with large amounts of suspended solids. However, anaerobic reactors are sensitive to toxic pollutants and vulnerable to process upsets, and have been used mainly for municipal sludge digestion. For methane production the sequential metabolism of the anaerobic consortia must be balanced, and the methanogens in particular are vulnerable to process upsets. Recently, anaerobic-aerobic processes (Figure 1.1) have been developed for the mineralization of xenobiotics. These processes take advantage of an anaerobic reactor for the initial reductive dechlorination of polychlorinated compounds or the reduction of nitro substituents to amino substituents. If the reduced compounds are more readily mineralized in an aerobic reactor, an anaerobic-aerobic process is feasible. 

Harrigan GG, Goetz GH, Luesch H, Yang S, Likos J (2001) Dysideaprolines A-F and Barbaleucamides A-B, Novel Polychlorinated Compounds from a Dysidea Species. J Nat Prod 64 1133... 

Rordorf, B.F. (1985) Thermodynamic properties of polychlorinated compounds The vapor pressure and enthalpies of sublimation of ten-para-dioxins. Thermochim. Acta 85, 435—438. 

The method involves chloroform extraction of acidified waste water samples and rotary evaporation without heat. After redissolving in chloroform the samples were analysed directly by high performance liquid chromatography on a microparticulate silica gel column. A number of solvent combinations are possible and 98 2 cyclohexane-acetic acid is preferred. The minimum detectable concentration is lppm (without sample concentration) and the coefficient of variation is 1-2%. The type of separation achieved with a microparticulate silica gel column is shown in Fig. 4.1. The first peak as determined by gas chromatographic-mass spectrometric analysis, consisted of a complex mixture of polychlorinated compounds, including octa-, hepta- and hexachlorodibenzo-/ -... 

Carbonyl compounds, -halogenated anilines, benzidines, nitro compounds, phenols, polychlorinated compounds, alkylbenzene, sulphonates, alkyl sulphonates, alkylbenzene sulphonates, carbamates [155]... 

Chlorination is carried out in the liquid phase at 120 with a conversion rate of 40 per cent to limit the formation of polychlorinated compounds. Chlorination takes place mainly at the middle of the chain. The mixture of mono-, di- and polychlorinated derivatives and unconverted paraffin is sent to the dehydrochlorination reactor, which operates between 300 and 350"C in the presence of siiico-alumina. The monochlorinated derivatives are converted with a conversion yield of more than 99 per cent to mono-olefins with an internal double bond. The dehydrochlorination of di- and polychlorinated paraffins yields diolefms and polyolefins. 

GC/ECD is the most applied method for the determination of toxaphene congeners in fish and other matrices. Due to the limited selectivity of the ECD, coelutions of toxaphene components with other polychlorinated compounds such as PCBs cannot be identified. However, since B8-1413 (P-26), B9-1679 (P-50), and B9-1025 (P-62) are very abundant in fish, a significant interference (> 30%) by other toxaphene congeners can be excluded. The risk of interferences can be reduced by analyzing the same sample on two different stationary phases. Since identical disturbances on both systems are not very likely, comparable concentrations increases the confidence in the obtained results. De Boer et al. and Shoelb et al. used multidimensional gas chromatography with ECD as an alternative to avoid interferences [67,68]. 

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