Levels and congener distributions of PCDDs, PCDFs and dioxin-like PCBs in environmental and human samples: a review

Abstract

The term ''dioxins'' is often used in a confusing way. In toxicological considerations-and also in the present report-the term is used to designate the PCDDs, the PCDFs and the coplanar (''dioxin-like'') PCBs, since these classes of compounds show the same type of toxicity. Because of the large number of congeners, relevant individual congeners are assigned with a toxic equivalency factor (TEF) that relate their toxicity to that of tetrachlorodibenzo-p-dioxin (TCDD) (2,3,7,8-TCDD) and are to be evaluated as dioxins. Each concentration of an individual congener in a mixture is multiplied with its TEF, and the resulting TCDD equivalents are added up and expressed as WHO-endorsed toxic equivalents (WHO-TEQ). Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are mainly the by-products of industrial processes (such as metallurgical processing, bleaching of paper pulp, and the manufacturing of some herbicides and pesticides) but they can also result from natural processes like volcanic eruptions and forest fires. Waste incineration, particularly if combustion is incomplete, is among the largest contributors to the release of PCDDs and PCDFs into the environment. Due to their persistence, PCDDs, PCDFs and PCBs are part of the socalled persistent organic pollutants group of compounds that also include some chlorinated pesticides. Since they have a high lipophilicity and resist transformation, they bio-accumulate in animal and human adipose tissues. Consumption of food is considered as the major source of non-occupational human exposure to PCDD/Fs with foodstuffs from animal origin accounting for more than 90% of the human body burden. With meat, dairy, and fish products being the main contributors. The aim of the present review was to summarize experimental data regarding dioxin emissions from contaminated and uncontaminated biological and environmental samples, from the available literature. The information will be presented chronologically with respect to distribution in human milk, serum; food, water, air, soils and sediments.

A preliminary investigation on emission of polychlorinated dibenzo-p-dioxins/dibenzofurans and dioxin-like polychlorinated biphenyls from coke plants in China

“…CB-118 was the most abundant congener among the dl-PCBs for many thermal related sources, environmental matrices and biological samples (Kim et Zhao et al, 2006;Çok et al, 2007;Srogi, 2008). In this study, the concentration of CB-118 was also the highest one, followed by CB-105, CB-123, CB-156 and CB-77.…”

Reproduction of European eel jeopardised by high levels of dioxins and dioxin-like PCBs?

“…Generally, dioxin-type chemicals produce a wide variety of species specific effects including immunotoxicity, hepatotoxicity, birth defects, endocrine disruption, and the induction of numerous enzymes, most notably that of microsomal cytochrome P4501A1 (CYP1A1) and its associated mono-oxygenase activity, aryl hydrocarbon hydroxylase (Srogi, 2008). In humans and other vertebrates dioxins have been shown to be the risk factors for cancer, immune deficiency, central and peripheral nervous system pathology, endocrine disruption -and many other diseases, as listed by Srogi (2008).…”

“…The half-lives of 2,3,7,8-substituted tetrachlorinated dibenzo-p-dioxin (2,3,7, in rodents, for example, is usually 2-4 weeks but in humans it has been estimated to be 7-11 years, although, with wide individual variation. The half-lives of other PCDD/Fs may vary between six months and 20 years (Srogi, 2008). DL-PCBs are a group of 12 PCBs that share a common toxic mechanism, with the most toxic dioxin compound 2,3,7,8-TetraCDD and, generally are among the most toxic PCB congeners as they incur toxic effects at relatively lower concentrations than those of non-DL-PCBs (NDL-PCBs) (Giesy and Kannan, 1998;McFarland and Clarke, 1989).…”

Fungal enzyme production and biodegradation of polychlorinated dibenzo-p-dioxins and dibenzofurans in contaminated sawmill soil

“…PCDD/Fs contain two aromatic rings with one to eight chlorine atoms ( Figure 5). The toxic congeners have chlorine groups in all of the 2,3,7,8 positions (7 PCDDs and 10 PCDFs), and the most toxic congener is 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) (Srogi, 2008). The toxicity of other congeners is compared to that of 2,3,7,8-TCDD by multiplying their concentration with a Toxic Equivalency Factor (TEF) (Article III, Table 4).…”