PCDDs are found at very low levels in the environment. These levels are measured in nanograms and picograms.  PCDDs are found everywhere in the environment, and most people are exposed to very small background levels of PCDDs when they breath air, consume food or milk, or have skin contact with materials contaminated with PCDDs. For the general population, more than 90% of the daily intake of PCDDs, PCDFs, and other dioxinlike compounds comes from food, primarily meat, dairy products, and fish. PCDDs may be present at much lower levels in fruits and vegetables. The actual intake of PCDDs from food for any one person will depend on the amount and type of food consumed and the level of contamination. Higher levels may be found in foods from areas contaminated with chemicals, such as pesticides or herbicides, containing PCDDs as impurities.
PCDDs have been measured in human milk, cow's milk, and infant formula, so infants are known to be exposed to PCDDs.
Exposure to PCDDs can also occur through skin contact with chlorinated pesticides and herbicides, contaminated soils, or other materials such as PCPtreated wood and PCB transformer fluids.
Background levels of PCDDs in soil are higher than background levels in both air and water. If PCDDs are present at all in outdoor air in rural areas, they are generally present at very low levels or at concentrations near the detection limits for testing equipment. In winter, because of the burning of wood and other fuels for home heating, PCDD levels may be slightly higher than during other seasons. In general, the background air levels of PCDDs in urban areas are higher than in rural areas. The air around people who are smoking cigarettes may also have PCDDs at levels above background levels. Although breathing contaminated air is a minor route of exposure for most people, exposure may be greater in areas near these PCDD sources.
PCDDs have been found in all samples of adipose tissue and blood (serum lipids) from individuals with no known previous exposure. This indicates that all people are exposed to small amounts of PCDDs. The production, use, and disposal of pesticides and phenoxy herbicides, disposal of production waste containing 2,3,7,8TCDD, industrial accidents involving 2,4,5trichlorophenol (2,3,5TCP), and the consumption of PCDDcontaminated food, have all led to increased potential for excess exposure of some groups of people.
Occupational exposure to PCDDs generally occurs through breathing contaminated air, or through skin contact with materials containing PCDDs. Workers with the potential to be exposed to above average levels of PCDDs include those involved in the production or handling of certain chlorinated phenols or chlorinated pesticides or herbicides, and those involved in application of chlorinated pesticides containing PCDDs as impurities. Workers whose jobs involve pressure treatment of wood with PCP and the handling of PCPtreated wood products, chlorination processes at pulp and paper mills, or operation of municipal solid waste or hazardous waste incinerators may have increased exposure to PCDDs. Finally, workers involved in hazardous waste cleanup or cleanup of PCB transformer and/or capacitor fires including emergency service personnel like fire fighters and police who respond to such fires are also at additional risk of exposure to PCDDs. Most of these occupational exposures have been significantly reduced in recent years.
An example of International Chemical Safety Card for most toxic dioxin is presented below.

Route of Exposure Symptoms First Aid
Inhalation  Chloracne. Symptoms may be delayed. Fresh air rest. Refer for medical attention.
Skin MAY BE ABSORBED! Redness. Pain. (See Inhalation). Remove contaminated clothes. Rinse and then wash skin with water and soap. Refer for medical attention.
Eyes Redness. Pain. First rinse with plenty of water for several minutes (remove contact lenses if easily possible) then take to a doctor.
Ingestion (See Inhalation). Give a slurry of activated charcoal in water to drink. Induce vomiting (ONLY IN CONSCIOUS PERSONS!). Refer for medical attention.

Notes for ICSC Information

This chemical is only produced for research purposes but could be generated as a byproduct from chemical processes or fires.

Structure formula of 2,3,7,8-Tetrachlorodibenzo-p-dioxin

3D structure of 2,3,7,8-Tetrachlorodibenzo-p-dioxin

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