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. 2019 Jun 17;20(12):2947. doi: 10.3390/ijms20122947

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© 2019 by the authors.

Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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Structural formulas of dioxins. There are 75, 135, and 209 possible congeners of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs), respectively. For toxic PCDD/Fs (17 congeners), at least the lateral (para-) positions (2, 3, 7, 8) have chlorine substituents. For dioxin-like polychlorinated biphenyls (DL-PCBs) (12 congeners), there is maximally one chlorine atom in the ortho-positions (2, 2′, 6, 6′) and at least 4 chlorine atoms in the meta-(3, 5, 3′, 5′) and para-(4, 4′) positions.