Lipophilicity PCDDs

Both PCDDs and PCDEs are refractory lipophilic pollutants formed by the interaction of chlorophenols. They enter the environment as a consequence of their presence as impurities in pesticides, following certain industrial accidents, in effluents from pulp mills, and because of the incomplete combustion of PCB residues in furnaces. Although present at very low levels in the environment, some of them (e.g., 2,3,7,8-TCDD) are highly toxic and undergo biomagnification in food chains. 

Although these reservoirs may be highly contaminated with PCDD/PCDFs, the chemical and physical properties of these compounds imply that dioxins and furans will stay adsorbed to organic carbon in soils or other particles. On the other hand, mobilization can occur in the presence of lipophilic solvents (leaching into deeper layers of soils and/or groundwater) or in cases of erosion or run-off from topsoil (translocation into the neighbourhood). Experience has shown that transport of PCDD/PCDFs due to soil erosion and run-off does not play a major role in environmental contamination and human exposure (Fiedler 1995, 1999). 

Chlorinated micropoUutants are harmful for man and environment due to their toxicity, persistence, and bioaccumulation. Persistent compounds are very stable and difficult to get metabolized and mineralized by biological and chemical processes in the environment, and as a result, they have become ubiquitous in water, sediments, and the atmosphere bioaccumulation is the result of the lipophilicity of these compounds. Polychlorinated dibenzodioxins and -furans (PCDD/F) are not produced purposely like many of other chlorinated technical products, such as chlorinated biocides DDT, lindane, and toxaphene. The production and use of persistent organic pollutants (POPs), the dirty dozen has now been banned worldwide by the Stockholm protocol. It should be mentioned that about 3000 halogenated products have now been isolated as natural products in plants, microorganisms, and animals," but the total amount of these products is much smaller compared to xenobiotics. 

As PCDDs and PCDFs are lipophilic, the major sources of PCDDs and PCDFs in the diet tend to be fat-containing foods of animal origin. Cows milk is a useful indicator of environmental pollution since cows graze relatively large areas and any PCDDs and PCDFs present on or in grass eaten... 

Farm animals are exposed to PCDD/F via the ingestion of contaminated forage, grains and soil. Owing to its high lipophilicity, dioxin readily bioaccumulates in cattle and has been detected in beef, milk and dairy products. Several studies point out that meat and dairy products account for up to 60% of the total daily human intake of PCDD/Fs in industrialized nations.39,46 PCDD/F levels in beef... 

To review, PCDD/Fs enter the food chain primarily from the atmosphere. Diffusion of gaseous PCDD/Fs to the lipophilic cuticle is the primary mechanism of uptake into plants, although the deposition of particle-bound chemical likely... 

Polychlorinated diphenyl ethers (PCDE) are common impurities in chlorophenol formulations, which were earlier used as fungicides, slimicides, and as wood preservatives. PCDEs are structurally and by physical properties similar to polychlorinated biphenyls (PCB). They have low water solubility and are lipophilic. PCDEs are quite resistant to degradation and are persistent in the environment. In the aquatic environment, PCDEs bioaccumulate. These compounds are found in sediment, mussel, fish, bird, and seal. PCDEs show biomagnification potential, since levels of PCDEs increase in species at higher trophic levels. PCDEs are also detected in human tissue. Despite the persistence and bio accumulation, the significance of PCDEs as environmental contaminants is uncertain. The acute toxicity and Ah-receptor-me-diated (aryl hydrocarbon) activity of PCDEs is low compared to those of polychlorinated di-benzo-p-dioxins (PCDD) and dibenzofurans (PCDF). Due to structural similarity to thyroid hormone, PCDEs could bind to thyroid hormone receptor and alter thyroid function. Furthermore, PCDEs might be metabolized to toxic metabolites. In the environment, it is possible that photolysis converts PCDEs to toxic PCDDs and PCDFs. 

Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorobiphenyls (PCBs), and polychlorophenols (PCPs) are well-known artifacts ubiquitous in the present environment. Due to their lipophilic-ity and resistance to metabolism or chemical degradation these have the potential to accumulate in the food chain and cause toxic effects [1, 2]. Polycyclic aromatic sulfur heterocycles (PASHs) along with different kinds of polycyclic aromatic compounds (PACs) also occur widely in the environment [3,4]. In particular, alkylated dibenzothiophenes have previously been found to be persistent residues in the marine environment after oil spills. Dibenzothiophene and its alkylated derivatives have been found to accumulate in fish and other marine organisms [5-7]. 

Fly ash from municipal waste and industrial waste incinerators contains polychlorinated dibenzo-p-dioxins (PCDDs), including tetrachlorodibenzo-/j-dioxin (TCDD) and polychlorinated dibenzofurans (PCDFs), which are lipophiles, and heavy metals, including chromium, copper, manganese, vanadium, and lead, which are hydrophilesJ29-31 These chemicals have multiple toxicities and are known to impact the human liver, immune system, respiratory system, thyroid, male reproductive function, and CNS J32 34l Several are human carcinogensJ32 35 Enhanced toxic effects are observed in the mixtures of some of theseJ21,22 36 The mixtures of toxicants present in fly ash are complex and the mechanisms for their action on the human body are largely unknown. It is known that occupational exposure to fly... 

Polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF), collectively known as dioxins, comprise a group of, respectively, 75 and 135 individual chemical compounds. These compounds are highly lipophilic and resistant to chemical breakdown, and therefore, they tend to accumulate in the food chain. Many laboratories in Europe are involved in the analysis of environmental and food samples for dioxin compounds, thus creating a requirement for appropriate reference materials. This section describes the certification of five PCDDs and six PCDFs, which are listed below [34] ... 

Polychlorinated dibenzo-y>-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) are chemically classified as halogen-ated (polychlorinated) aromatic hydrocarbons (PHAH). Dioxins are formed as a by-product of chemical processes, whereas PCBs are synthesized by direct chlorination of biphenyls. Due to their lipophilic character, they are concentrated in the food chain and both humans and wildhfe are exposed to them. The major source of human exposure is through the diet, as these substances are concentrated in fatty tissues of beef, poultry, pork and fish, and through cigarette smoking. Moreover, maternal milk contains considerable amounts of PCBs and dioxins. 

Dioxins are a family of the most toxic chlorinated organic compounds known to science, numbering around 75 dioxins and 135 related furans. These can cause cancer and are ECD for humans, even at very low exposure levels, since minute amounts, can bio-accumulate due to their ease of solubility in body fat (dioxins are hydrophobic, water-hating and lipophilic, fat-loving ). Number and position of chlorine atoms in the molecule has a considerable effect on toxicity, and 17 dioxins are classed as highly toxic. These include polychlorinated dioxins (PCDD) and dibenzofurans (PCDF) which are by-products of the chlorine bleaching of paper, the burning of chlorinated hydrocarbons (such as pentachlorophenol, PCB, and PVC) and the incineration of municipal/medical... 

PCDDs and PCDFs have very little solubility in water and exhibit a strong lipophilic character, as shown in Table 21.1 by the high values of n-octanol-water partition coefficients Kow). Therefore, these compounds display strong affinity for sediment, and, consequently, their presence as solute in water is always even lower than solubility in fact, they are associated with the sediment, both suspended and settled. PCDDs and PCDFs are considered semivolatile substances the chemicophysical properties of the seventeen toxic congeners are reported in Table 21.1. 

Due to their stror g lipophilic properties and poor solubility, the PCDDs and PCDFs dissolved in water were generally measured at levels lower than 1 pg/L- If particulate matter is present, most PCDDs and PCDFs are sorbed onto suspended solid material. In this case, the determination should be performed on the aqueous phase and particulate matter as well. In general, the analysis of PCDDs and PCDFs dissolved in water requires large sample volumes, possibly up to hundreds of liters. The use of systems to collect and concentrate the analytes is also recommended [20]. To this aim, solid hydrophobic adsorbents or nonpolar organic solvents are used. 

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