• What are dioxins?

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      dev@edge.studio

1. General

Dioxins belong to a special group of persistent environmental chemicals. Number of studies including those by WHO (World Health Organisation) have shown several risky effects of Dioxins on human health, such as dermal toxicity, immunotoxicity, reproductive effects and teratogenicity, endocrine disruption and carcinogenicity. In terms of dioxin release into the environment, the incineration of solid wastes is the worst anthropogenic source.

2. Family of Dioxins


Figure 1: Family of Dioxins: PCDDs, PCDFs and co-PCB’s

The name dioxin is generally used for the family of structurally and chemically related chlorinated congeners (Fig. 1):

  • polychlorinated dibenzo-para-dioxins (PCDDs)
  • polychlorinated dibenzofurans (PCDFs)
  • co-planar polychlorinated biphenyls (co-PCBs).
    Among some 419 types of dioxin-related compounds identified, only 29 of these are currently considered to have significant toxicity, with 2,3,7,8-TCDD (tetrachlorodibenzo-para-dioxin) being the most toxic.

    3. Toxicity Equivalence of Dioxins

    The concept of toxic equivalency factors (TEFs) has been used to facilitate risk assessment and regulatory control of exposure to these mixtures. TEF values for individual congeners in combination with their chemical concentration can be used to calculate TEQs (the total 2,3,7,8- TCDD toxicity equivalence quantity) contributed by all dioxin-like congeners in the mixture using the following equation:

    TEQ = S (TEFi × PCDDi) + S (TEFj × PCDFj) + S (TEFk × PCBk)

    Table 1 summarises WHO’s recent assessment of TEFs, which are most commonly used.


    Congener


    TEF value


    Congener


    TEF value
    Dibenzo-p-dioxins

     

    Non-ortho PCBs

     
    2,3,7,8-TCDD

    1

    PCB 77

    0.0001
    1,2,3,7,8-PnCDD

    1

    PCB 81

    0.0001
    1,2,3,4,7,8-HxCDD

    0.1

    PCB 126

    0.1
    1,2,3,6,7,8-HxCDD

    0.1

    PCB 169

    0.01
    1,2,3,7,8,9-HxCDD

    0.1

     

     
    1,2,3,4,6,7,8-HpCDD

    0.01

    Mono-ortho PCBs

     
    OCDD

    0.0001

    PCB 105

    0.0001
     

     

    PCB 114

    0.0005
    Dibenzofurans

     

    PCB 118

    0.0001
    2,3,7,8-TCDF

    0.1

    PCB 123

    0.0001
    1,2,3,7,8-PnCDF

    0.05

    PCB 156

    0.0005
    2,3,4,7,8-PnCDF

    0.5

    PCB 157

    0.0005
    1,2,3,4,7,8-HxCDF

    0.1

    PCB 167

    0.00001
    1,2,3,6,7,8-HxCDF

    0.1

    PCB 189

    0.0001
    1,2,3,7,8,9-HxCDF

    0.1

     

     
    2,3,4,6,7,8-HxCDF

    0.1

     

     
    1,2,3,4,6,7,8-HpCDF

    0.01

     

     
    1,2,3,4,7,8,9-HpCDF

    0.01

     

     
    OCDF

    0.0001

     

     

    Table 1: WHO TEFs for human risk assessment

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