Dioksin and Furan

Dioxins and Furans
Written by Anna Reani, hb
Thursday, 02 April 2009 13:56
Studies show that dioxins and furans are present in trace amounts throughout the environment. Minute amounts may be found in the air we breathe, food we eat, water we drink, soil and dust we come in contact with, and in consumer products.
Dioxins and furans are two families of related chemical compounds known as polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans. Of these, 17 (including the most toxic, 2,3,7,8-TCDD) pose a major health risk. Similar in chemical structure and biological properties, dioxins and furans are usually found together in the environment as complex mixtures. The toxicity of each compound depends on the number and position of the chlorine atoms within the molecules.
Why all the concern?
For many people, the word dioxin provokes fear because it has often been described as one of the most toxic substances known to man. Much of this concern has focused on the most toxic member of the dioxin and furan family - 2,3,7,8-TCDD.
This was the contaminant in the weedkiller 2,4,5-T, also used by the U.S. military in 'Agent Orange', and in the oil sprayed on the unpaved roads of Times Beach, Missouri, in the early 1970s. Although most can be broken down by sunlight, dioxins and furans are not biodegradable. They do not dissolve in water and can attach to particles of soil, dust and sediment. As a result, they can persist unchanged in the environment, mainly in soil and sediment, for years. They also can accumulate in animals, wildlife and human body tissues.
Effects on humans
Studies have been done on people who have been accidentally exposed to high levels of dioxins and furans - at work, as a result of improper waste disposal, or from eating contaminated cooking oil.
Chloracne, a skin disorder, is the most common human health effect. Extreme exposures also lead to other effects on the skin, liver, immune system, reproduction system, senses and behavior. The effects of long-term, low-level human exposure are still being investigated. Current scientific evidence does not indicate a link between normal, everyday exposure and long-term health effects such as cancer, coronary disease and impaired reproduction.
How are dioxins and furans produced?
Dioxins and furans are unwanted byproducts created in manufacturing other chemicals such as some disinfectants, wood preservatives and herbicides. They are also emitted during combustion processes such as the incineration of municipal and industrial waste, wood and gasoline burning.
Detecting dioxins and furans
The recent development of very sensitive and accurate analytical methods enables scientists to detect concentrations of dioxins and furans as low as parts per trillion and parts per quadrillion. At these very minute levels, dioxins and furans have been found in some soil, air, water, wildlife, food and human fat samples.
To understand these minute figures, just imagine a grain of salt in an Olympic-sized pool as a 'parts per trillion', or the area of a dollar bill compared to the area of Canada as a 'parts per quadrillion'. Higher levels (in the parts per billion range) have been measured in chemical wastes and in sediment samples obtained near properties contaminated with industrial wastes.
How much are we exposed to?
A federal-Ontario assessment has estimated the average daily multimedia exposure (from air, water, food, soil, consumer products) of adult Canadians to dioxins and furans is about 2 to 4 picograms of 2,3,7,8-TCDD toxic equivalents (TEQ) per kilogram of body weight. While human exposure is mostly from food, breathing urban air is also an important contributor. Drinking water and coming into contact with contaminated soils or consumer products provide far less exposure.
How much is safe?
Although recommended safe levels are usually developed based on the effects of 2,3,7,8- TCDD, it is possible to calculate tolerable levels of exposure for all dioxins and furans. This is done by taking the concentrations of the 17 most toxic dioxins and furans, multiplying each one by a toxic equivalency factor (TEF) - its toxicity relative to 2,3,7,8-TCDD - and adding up all the corrected concentrations expressed as 2,3,7,8-TCDD toxic equivalents (TEQ).
Source : Environmental Dept. Canada