[en] There is an increasing concern about environmental exposure to multiple chemicals and adverse changes in reproductive development, function, or behaviour in wildlife. The major group of environmental chemicals, such as organochlorine pesticides, polychlorinated biphenyls (PCBs) and other xenoestrogens are currently known to have estrogenic effects in vertebrates or fishes. Recent studies suggest that past exposure to such estrogenic compounds may affects the risk of developing breast cancer, precocious puberty, or impaired fertility in man.