Polychlorinated dibenzodioxins levels

Polychlorinated dibenzodioxins and dibenzofurans (PCDD/Fs), in contrast to other chlorinated chemicals, have never been commercially manufactured nor are of any benefit or known use. PCDD/Fs are ubiquitous contaminants, which are released as byproducts of incomplete combustion or as impurities in chemical processes, and that their levels in the environment are increasing. 

Consequently, they are able to integrate pollutant levels over a broad area by bioaccumulation (Furness, 1993). A bird egg, unlike a mammalian fetus, is an isolated and independent metabolic system. In addition, persistent, bioaccumulative and lipophilic pollutants (e.g. PCBs, polychlorinated dibenzodioxins and furans) are known to biomagnify in the egg yolk and result in concentrations of orders of magnitude higher than the ambient concentrations in the diet of the female bird (Kleinow et al., 1999). The contaminant levels in waterbird eggs, therefore, provide important and useful information for monitoring changes in environmental quality. 

Schecter, A., Furst, P., Furst, C., Meemken, H.A., Groebel, W., Vu, D.Q., 1989b. Levels of polychlorinated dibenzodioxins and dibezofurans in cow s milk and in soy bean derived infant formulas sold in the United States and other countries. Chemosphere 19, 913-918. 

Phiet PH, Anh TK, Vu DQ, et al. 1989. Preliminary observations on the clinical histories, polychlorinated dibenzodioxin and dibenzofiiran tissue levels and 2,3,7,8-TCDD toxic equivalents of potentially dioxin-exposed patients living in the south of Vietnam. Chemosphere 19 937-940. 

Another major exposure route for humans is via contaminated food. For example, North America s Great Lakes, which are the largest body of freshwater in the world, are polluted with about 362 contaminants that were found in quantifiable amounts in the water, sediment, and biota (IJC 1983 USEPA 1994). The critical pollutants were identified as PCBs, DDT, dieldrin, toxaphene, mirex, methyl mercury, benzofa) pyrene, hexachlorobenzene, polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and alkylated lead. Some of these pollutants biomagnify in the aquatic food chain and can be detected in increased levels in cooked Great Lakes fish. Consequently, the blood serum levels of these chemicals are significantly increased in consumers of contaminated Great Lakes sport fish compared to people who do not eat such fish (Flumphrey 1983 Fiore et al. 1989 Sonzogni et al. 1991). 

The acute toxicity exerted by PCBs is generally low. The most prominent effect is the pronounced induction of the MFO system in different tissues, with increased de novo synthesis and increased levels in several cytP450 isozymes. The PCBs in the environment occur as a mixture of congeners and every congener exerts specific toxicity, with some PCBs exerting exclusive effects. One such effect is the capability for planar PCBs to bind to and stimulate the cytoplasmatic aryl hydrocarbon receptor in the cell, the same receptor that is stimulated by the highly toxic polychlorinated dibenzodioxins (PCDDs) (see below). 

The severe health effects observed in the Japanese Yusho incident of 1968 were attributed to the ingestion of polychlorinated biphenyls (PCBs). At that time, the forefront of analytical chemistry was represented by the determination of trace components at the parts per million (ppm) concentration level. It was not until about ten years later that analytical methodology was able to detect polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzodioxins (PCDDs) at concentrations of 10 parts per billion (ppb) or less in the presence of PCBs. The significance of the determinations lies in the assessment of risk to human populations exposed to undegraded PCBs and to mixtures of chemically similar compounds of concern derived from uncontrolled reactions such as might occur when a PCB filled transformer undergoes eventful failure. 

Since 1979, many studies have identified other chlorinated aromatic compounds present in trace levels in the PCBs, or produced as incomplete oxidation products in PCB fires . These compounds include polychlorinated dibenzofurans (PCDFs), polychlorinated biphenylenes (PCBPs), polychlorinated pyrenes (PCPYs), and polychlorinated chrysenes (PCCYs), Polychlorinated dibenzodioxins (PCDDs) have also been detected from fires where trichlorobenzenes were present with PCBs as the dielectric fluid Animal tests and industrial incidents have shown some... 

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