Dioxins and Furans
*IARC: International Agency for Research on Cancer.
Polychlorinated dibenzo-para-dioxins (dioxins) and polychlorinated dibenzofurans (furans) are two structurally similar families of compounds that include 75 and 135 congeners, respectively. At least seventeen are considered highly toxic. The overall toxicity of a dioxin containing mixture is assumed to be the Toxic Equivalent (TEQ) of a stated amount of pure 2, 3, 7, 8-tetrachloro-dibenzo-p-dioxin (TCDD), the most potent, hazardous and well-studied dioxin. Dioxins and furans have similar effects on human health, and will be referred to collectively as dioxins.
Dioxins are not commercially produced, but are by products of combustion and industrial processes, including the manufacture of chlorinated chemicals, the incineration of hospital, hazardous and municipal waste, and the bleaching of paper products. Dioxins are stable, persistent compounds that are believed to have a half-life of seven to twenty years in the human body. In the Great Lakes, exposure to dioxin-like compounds has been linked to large -scale hormonal, reproductive and developmental impairment among numerous species of predator birds fish and wildlife; these impacts are primarily transgenerational, affecting the offspring of the exposed organisms.
Approximately 90% of human exposure to dioxin comes from food, especially from beef, fish, and dairy products. Contamination in the food supply comes from dioxin particles that are deposited in water or soil and then proceed up the food chain through fish and livestock, ultimately reaching human tissues through the food we eat. Dioxin bioaccumulates, becoming increasingly concentrated in living tissues as it moves up the food chain.
Dioxins are known to be toxic at extremely low doses. Americans, on average, are exposed to only 1 to 3 picograms per kilogram of body weight per day and the U.S. population revealed an average body burden of 7-8 nano-g/kg of body weight (U.S. EPA, 1982). A 2000 evaluation indicates that adult daily intakes of dioxin and related compounds, including dioxin-like PCBs average 70pgTEQ(DFP)WHO(98)/day. (U.S. EPA, 2000). In most industrialised nations of the world, dioxin body burdens and exposure are in the same range, with levels assumed to be somewhat lower in developing countries, were little testing has been done. The World Health Organization recently lowered by more than half its tolerable daily intake from 10 pg, fixed previously in 1990, to 4 pg/kg bw, based on a recognition that subtle effects may already occur in the general population in developed countries at levels of 2 to 6 picograms.(WFPHA, World Federation of Public Health Associations, 2000).
In 1985, the U.S. EPA declared TCDD (2,3,7,8- Tetra chloro dibenzo dioxin) the most potent synthetic carcinogen yet tested. More recently, IARC has classified TCDD as known human carcinogen. The U.S. EPA estimates that currently U.S. background dioxin exposures may result in upper-bound population cancer risk in the range of one in ten thousand to one in a thousand (one case of cancer out of 10.000 inhabitants or 1 case of cancer out 1000 inhabitants). (WFPHA, 2000).
In humans, there is evidence that high-level exposure to dioxins and furans can cause variations in serum lipid level, microsomal enzyme induction, and gastrointestinal alterations. Other studies of high-level occupational exposure have found associations with some types of cancer, and have concluded that in utero and lactational exposures to dioxins and furans are capable of affecting the hypothalamic/pituitary/thyroid regulatory system in human infants. According to U.S. EPA, effects on humans, including hormonal and metabolic changes, have been documented at dioxin body burdens and exposures only slightly higher than those of the general population.
A single cellular mechanism is thought to be responsible for the wide range of effects dioxins can have. It is believed that dioxins affect organisms by binding to pre-existing cellular receptors designed for hormones, entering the nucleus and manipulating the on or off function of the gene. The genes affected by an impostor like dioxin contain codes for proteins, hormones, enzymes and growth factors, which collectively influence tissue development in the human body. This mechanism is the same in both humans and animals, allowing extrapolation from laboratory experiments involving dioxin effects on animals to a parallel human reaction. (WFPHA, 2000).
There is substantial evidence to indicate that populations of wildlife
species high on the food chain are suffering health damage due to reproductive
and developmental impairment due to background exposures to dioxins and
related compounds. In the Great Lakes, exposure to dioxin-like compounds
has been linked to large-scale hormonal, reproductive, and developmental
impairment among numerous species of predator birds, fish and wildlife;
these impacts are primarily transgenerational, affecting the offspring
of the exposed organisms. (WFPHA, 2000).
Hazardous Substances Data Bank: type Dioxins and Tetrachloro-dibenzofurans.
This site reports a full list of information on the substance as: Human
Health Effects, Animal Toxicity Studies, Environmental Fate & Exposure,
Environmental Standards & Regulations, Chemical/Physical Properties,
Chemical Safety & Handling, Occupational Exposure Standards, Laboratory
Methods, Synonyms and Identifiers.
with toxicity data for furans from the Vermont Safety Information
This site provides a list or toxicity tests results, references for toxicity literature reviews, USA standards and regulations, occupational exposure limits in different states all over the world, and reference to NIHOSH, National Institute for Occupational Safety and Health, analytical standard methods.
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