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INTRODUCTION

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Polychlorinated dibenzo-p-dioxins (PCDDs) have been described as the most toxic man-made chemicals known. They are synthetic, lipophilic, and very persistent. They are also relatively controversial. Toxicological studies of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), which is known as the most toxic congener among PCDDs and usually called Dioxin, demonstrate dose-dependent toxic responses to other PCDDs and related chemicals such as the polychlorinated dibenzofurans (PCDFs), which frequently accompany polychlorinated biphenyls (PCBs). (Both PCDFs and PCBs are chemically and biologically similar to PCDDs.) However, the findings from human studies, at least until recently, have been less consistent.

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The animal health effects include but are not limited to: death several weeks after dosing, usually accompanied by a “wasting” or loss of weight syndrome; increase in cancers (found in all animal cancer studies); increased reproductive and developmental disorders including fetal death in utero, malformations, and in offspring dosed in utero, endocrine disruption with altered thyroid and sex hormone blood levels; immune deficiency sometimes leading to death of new born rodents, especially following dosing with infectious agents; liver damage including transient increase in serum liver enzymes as well as the characteristic lesions of hepatocytes to chlorinated organics, enlarged cells, intracytoplasmic lipid droplets, increase in endoplasmic reticulum, enlarged and pleomorphic mitochondria with altered structure of the cristae mitochondriales and enlarged dense intramitochondrial granules; central nervous system and peripheral nervous system changes including altered behavior and change in nerve conduction velocity; altered lipid metabolism with increase in serum lipids; and skin disorders including rash and chloracne (acne caused by chlorinated organic chemicals). Some effects are species specific. Other findings have been reported but with less frequency or consistency.1

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Findings reported in some human studies are similar to those from animal studies. These include an increase in cancers of certain types, including soft tissue sarcomas, Hodgkin's lymphoma, non-Hodgkin's lymphoma, lung cancer, and liver cancer; adverse reproductive and developmental effects following intrauterine and nursing exposure such as lower birth weight and smaller head circumference for gestational age, decreased cognitive abilities, behavioral impairment, and endocrine disruptions including altered thyroid hormone levels; immune deficiency; liver damage; altered lipid metabolism with increase in serum lipids; altered nerve conduction velocity; altered sex ratio in children born to dioxin-exposed women (more females than males); increase in diabetes or altered glucose metabolism in exposed chemical workers and sprayers of dioxin-contaminated Agent Orange herbicide; and behavioral changes including anxiety, difficulty sleeping, and decrease in sexual ability in males.1,2,3,4,5,6,7,8,9,10 Some of the human health effects are subtle such as those reported in the Dutch studies. These effects are not likely to be detected by the clinician on individual patients but only in a larger population-based study. Skin disorders including rash and chloracne are also observed in some exposed persons.

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PCDDs and PCDFs are not manufactured as such, but are usually found as unwanted contaminants ...

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