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Dr Katrien Van Look and Professor William Holt.
Institute of Zoology (Zoological Society of London).

Mr Gregory Paull, Dr Eduarda Santos and Professor Charles Tyler.
University of Exeter.

Dr Peter Kille.
Cardiff University.

Environmental contamination is a growing concern for health in both humans and wildlife. It is now well established that some pollutants, known as endocrinedisrupting chemicals (EDCs), can disrupt hormone systems. These chemicals mimic or disrupt hormone function in animals and may be responsible for the observed decline in sperm quality in humans and disruptions in reproductive function in many fish and bird species.

'There is substantial and global evidence for impacts on wildlife from these chemicals', says Katrien Van Look of the Institute of Zoology. 'In particular, fish act as sentinels for chemical pollutants in our freshwater and marine ecosystems and play a central role in hazard identification.'

Some of the most persuasive data supporting the hypothesis that EDCs impact on reproductive health in wildlife have come from studies in fish. The researchers are using zebrafish to study the reproductive effects of EDCs at the molecular and genetic level.

Zebrafish exposed to concentrations of EDCs now typically found in the aquatic environment are assessed for their reproductive condition in terms of sperm quality and general fertilisation and hatching success. 'It is now possible to relate these changes to the effect of these chemicals on gene expression using the powerful genome-level approach of microarrays', says Charles Tyler of the University of Exeter.

The mapping of the zebrafish genome is over 90% complete, which makes it an ideal model for ecotoxicological studies such as these. A microarray is basically a microscope slide on which genes can be individually placed and used to measure the effect of the chemical in terms of its effect on gene expression. The interactions of EDCs switch some genes on and others off, leading to the physiological changes responsible for the observed reproductive dysfunction. The array now established for the zebrafish includes 16,000 individual gene probes.

Assessing sperm motility, fertility and reproductive development in the fish exposed to chemicals, in parallel with the microarray work, enables the researchers to investigate.