Endocrine disruptors

Many chemical substances of natural or anthropogenic origin are suspected or known to be endocrine disruptors. They can influence the endocrine system of organisms by a direct and/or an indirect interaction. Among the compounds which have been included in the 'old' POPs group are DDT and its metabolites, polychlorobiphenyl (PCBs), and PCDDs and PCDFs. Among the DDT isomers, the

Table 2 TEFs for PCDD, PCDF, and dioxin-like PCBs according to WHO risk-assessment approach (1997)a

Congener

Mammals

Birdsb

Fishb

Polychlorodibenzodioxins

2,3,7,8-T4CDD

1

1

1

1,2,3,7,8-P5CDD

1

1

1

1,2,3,4,7,8-H6CDD

0.1

0.05

0.5

1,2,3,6,7,8-H6CDD

0.1

0.01

0.01

1,2,3,7,8,9-H6CDD

0.1

0.1

0.01

1,2,3,4,6,7,8-H7CDD

0.01

<0.001

<0.001

O8CDD

0.0001

<0.0001

<0.0001

Polychlorodibenzofurans

2,3,7,8-T4CDF

0.1

1

0.05

1,2,3,7,8-P5CDF

0.05

0.1

0.05

2,3,4,7,8-P5CDF

0.5

1

0.5

1,2,3,4,7,8-H6CDF

0.1

0.1

0.1

1,2,3,6,7,8-H6CDF

0.1

0.1

0.1

1,2,3,7,8,9-H6CDF

0.1

0.1

0.1

2,3,4,6,7,8-H6CDF

0.1

0.1

0.1

1,2,3,4,6,7,8-H7CDF

0.01

0.01

0.01

1,2,3,4,7,8,9-H7CDF

0.01

0.01

0.01

O8CDF

0.0001

<0.0001

<0.0001

Non-ortho-polychlorobiphenyls

[77] 3,3',4,4'-T4CB

0.0001

0.05

0.0001

[81] 3,4,4',5-T4CB

0.0001

0.1

0.0005

[126] 3,3',4,4',5-P5CB

0.1

0.1

0.005

[169] 3,3',4,4',5,5'-H6CB

0.01

0.001

0.00005

Mono-ortho-polychlorobiphenyls

[105] 2,3,3',4,4'-P5CB

0.0001

0.0001

<0.000005

[114] 2,3,4,4',5-P5CB

0.0005

0.0001

<0.000005

[118] 2,3',4,4',5-P5CB

0.0001

0.00001

<0.000005

[123] 2',3,4,4',5-P5CB

0.0001

0.00001

<0.000005

[156] 2,3,3',4,4',5-H6CB

0.0005

0.0001

<0.000005

[157] 2,3,3',4,4',5'-H6CB

0.0005

0.0001

<0.000005

[167] 2,3',4,4',5,5'-H6CB

0.00001

0.00001

<0.000005

[189] 2,3,3',4,4',5,5'-H7CB

0.0001

0.00001

<0.000005

aSeveral TEF systems were defined during the last two decades. WHO proposed an update of its 1997 TEFs in 2005. bBased on a limited data set.

aSeveral TEF systems were defined during the last two decades. WHO proposed an update of its 1997 TEFs in 2005. bBased on a limited data set.

o,p'-DDT is the most active chemical species with estrogenic activity while an antiestrogenic effect has been reported forp',p'-dichlorodiphenyldichloroethylene (DDE). In in vitro studies, chlorinated biphenyl mixtures (PCBs) show an affinity for the estrogenic receptors while in mammals, in vivo, they show an uterotrophic effect. The antiestrogenic effects of TCDD have been investigated thoroughly in in vivo studies, where it has been determined that TCDD influences uterus weight and reduces the number of estrogen and progesterone receptors in organisms. In vitro, this compound also elicits an antiestrogenic effect, and finally a further effect which is called the 'downregulation' of estrogen receptors. In particular, TCDD is an exogenous agonist for the arylhydrocarbon (Ah)-receptor, which when activated increases the estrogen receptors degradation rate, induces the estradiol metabolizing enzymes, and inhibits gene expression controlled by estradiol or growth promoters.

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