The existence of chemicals in our environment and food that may disrupt endocrine systems and affect
developmental processes and physiological functions in animals and humans has become a major focus of
scientists in the fields of Environmental chemistry, toxicology and medicine over the last years. Many classes of
chemicals, both of natural and anthropogenic origin, have been claimed to possess endocrine-disrupting potential.
While presently most attention is given to potential interactions of chemicals with the sex steroid systems, there
also exists a wide body of evidence for interactions of similar classes of chemicals with the thyroid hormone
system. Thyroid hormones, as well as sex steroids, are very important in normal structural and functional
development of sexual organs and the brain. In many cases very close interactions and linkages between sex
steroids and thyroid hormones appear to exist both on a molecular and physiological level. Therefore it is
important to include potential disruptions of the thyroid system in the evaluation of the possible impact of
chemicals in food and environment on health and normal development of vertebrate species.
The main focus of the second period of the project: "Reproductive and developmental effects of PHAHs on
amphibians - a mechanistic approach" is the development and validation of in vitro test-systems and whole
organism based test systems to screen effects of organohalogen contaminants on the thyroid hormone system. The
ultimate objective is to provide a sound scientific basis which is essential and needed to be able to quantify the real
toxicological risk for humans and wildlife from various chemicals disturbing the thyroid hormone system.