Impairments of Endocrine Functions: Causes and Consequences - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 191

Steroid

Cytoplasm

Nucleus

Receptor complex

Receptor

Protein

DNA

Increased transcription
of responsive genes

Proteins

FIGURE 8.1
Regulatory role of steroidal hormones. (After Landis, W.G., Yu, M.H., Introduction to Environmental Toxicology.
Impacts of Chemicals upon Ecological Systems , Lewis Publishers, Boca Raton, FL, 2004. With permission.)

Hormone

EDC 1 EDC 2

Response

No effect

Hormonal receptor Hormonal receptor

Hormonal Mimic Hormonal Block

e hormonal response is decreased.

e hormonal response is increased.

EDC = endocrine disruptor compound

FIGURE 8.2
Mechanisms of action of endocrine disrupters; principle of lock and key.

8.2.2.2 What Are Endocrine Disruptors?

For the EU, “An endocrine disruptor is an exogenous substance or mixture that alters
function(s) of the endocrine system and consequently causes adverse health effects in an
intact organism, or its progeny, or (sub)populations” (EU 1998). The US Environmental
Protection Agency (1997) has adopted the definition proposed by Kavlock et al. (1996): “An
exogenous agent that interferes with the synthesis, secretion, transport, binding, action, or
elimination of natural hormones in the body which are responsible for the maintenance