IUPAC name:2,3,7,8-tetrachlorodibenzo-para-dioxin
ISO name (common): TCDD
Molecular Formula:C12H4Cl4O2
Structural Formula:

                     H        Cl
                      \      /
      H                C -- C
       \             //      \\
        C == C - O - C        C - Cl
       /      \       \      /
 Cl - C        C - O - C == C
       \\     //             \     
        C -- C                H
       /      \   
     Cl        H    

Molecular Mass: 322
CAS number: 1746-01-6
Melting point:305-306°C
IARC rating: Group 1 carcinogen
Appearance: Colourless to white crystalline powder

Ratmale LD50oral: 22.0 µg/kg
Ratfemale LD50oral: 45.0 µg/kg
Hamster LD50oral: 1,157-5,051µg/kg
Rabbit LD50oral:115.0µg/kg

2,3,7,8-Tetrachlorodibenzo-p-dioxin is produced as an unwanted contaminant during the manufacture of chlorobenzenes, chlorophenols and their derivatives such as 2, 4, 5-trichlorophenoxy acetic acid and 2-(2,4,5-trichlorophenoxy)propionic acid.

Of the 210 dioxin-like compounds, TCDD has the highest potency.

The most commonly reported symptom related to TCDD exposure in man has been chloracne. The acne-like lesions of the skin may develop a few weeks after the exposure and may persist for over a year following the cessation of exposure. Other skin problems which have been reported include hyperpigmentation, hirsutism, increased skin fragility, and vesicular eruptions on exposed areas of the skin.

In rats TCDD induces lipid peroxidation, this leads to general cell membrane damage which will ultimately produce death.

USEPA; Health Risk Assessment Approach for 2,3,7,8-Tetrachlorodibenzo-p-Dioxin p.1 (1985) EPA 600/8-85-013
USEPA; Ambient Water Quality Criteria Doc: 2,3,7,8-Tetrachlorodibenzo-p-dioxin p.C-15 (1980) EPA 400/5-80-072
Stohs SJ et al; Biochem Biophys Res Commun 111:3 854-9 (1983)

The dioxin shown in the write-up above, 2,3,7,8-tetrachloro-dibenzo-p-dioxin (dioxin TCDD) is one of the most potent synthetic toxins known. It is fatal to rats) in doses of 22 micrograms per kilogram of bodyweight. (It takes 15,100 or more micrograms of arsenic oxide per kilogram body weight to kill a rat). Also studies in animals have shown it to be very carcinogenic.

In 1976 an explosion at a chemical factory in Seveso Italy released about 2 kilograms of TCDD into the environment, contaminating 10 square miles of land. Although no immediate deaths occured, 2,000 people had to be treated for dioxin poisoning, and 600 were evacuated from their homes.

TCDD has a half-life in soil of 2-9 years, and up to 32 days in air, leading to stringent guidelines on it's usage.

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