UV absorbing organic chemicals (UV filters) are increasingly used in sunscreens, personal care products and in the protection of materials against UV irradiation. They enter the aquatic environment, where contamination is widespread. A considerable number of UV filters have hormonal activities in vitro, and some have estrogenic activity in fish. In fathead minnows, estrogenic 3-benzylidene camphor and benzophenone-2 caused feminization of male fish, alteration of gonads, and decrease in fertility and reproduction. Besides effects on the sex hormone system, inhibition of enzymes involved in the thyroid and glucocorticoid system have been demonstrated in mammals. At present it is unknown, what kind of genes or gene clusters related to these hormone systems and additional physiological functions are affected by UV filters. This project will focus in more detail on open questions on molecular, biochemical and reproductive effects of UV filters in zebrafish, a species not yet studied in that respect, and of which microarrays offer major advantages for global gene expression analysis. Effects of the UV filters 4-methyl-benzylidene-camphor (4MBC) and 2-ethyl-hexyl-4-trimethoxycinnamate (EHMC) will be investigated in the model organism Danio rerio (zebrafish). These studies aim at understanding the ecotoxicological effects of UV filters, elucidating the modes of action, and to contribute to the hazard and risk assessment of these largely used personal care products for aquatic ecosystems.