There is increasing concern in the media, among politicians and within environmental organizations, about the effects of chemicals in our environment that affect the endocrine systems of wildlife and humans. At its simplest these are referred to as gender-bending' chemicals or environmental estrogens'. The chemicals in question (pesticides, PCBs, plasticizers, petrochemicals, and a variety of industrial chemicals) have been known to decrease human sperm counts, cause fish to change sex', and increase male genital abnormalities. A great deal of pressure has been placed on environmental protection agencies to devise regulatory tests for the effects of these chemicals and to require limitations on their manufacture and release. Fish are increasingly recognized as an excellent model for such tests, in that the aquatic environment may provide early warnings of the effects that these chemicals will have on human health. In addition, the large number of eggs which fish produce provides an excellent model to examine the effects on female fertility. Endocrine Disruption in Fish provides a simple yet extensive background to the field of fish endocrinology in order to assist those toxicologists who have a limited background in either mammalian or fish endocrinology. It shows that environmental estrogens do not simply affect male reproductive potential, but that they may equally well affect the female. It is possible that these chemicals may have a complex effect on the brain, hypothalamus, pituitary, gonad and liver of both sexes. There are many other chemicals which affect both the gonads and other parts of the endocrine system to cause decreased fertility, abnormal sexual differentiation andbehavior, decreased response to stress, immune deficiency or altered basal metabolism. Many thousand man-made chemicals are released into the environment, but very few have been tested for endocrine disrupting activity. This book covers only the minute fraction for which evidence has been collected.

The last half-century has shown a dramatic increase in the standard of living of millions of people in Europe, North America and many parts of the Third World. This has, in many ways been brought about by scientific and technical developments which were initiated in the 1940s and 1950s. Promises were then made that nuclear energy would provide electricity so cheap that it would not need metering, pesticides would end malnutrition throughout the world and plastics and other synthetic chemicals would revolutionise our manufacturing industry and our way of life. Whilst some of these promises have been fulfilled, the problems of long-term health risks to humans and wildlife arising from the use, production and disposal of these products were either unknown or deliberately understated. Nuclear power is rendered economically unviable when the real cost of decommissioning and storage of waste for several millenia is included, and the effects on health of both humans and wildlife of early pest eradication programmes with organochlorine pesticides were well documented in Rachel Carson's "Silent Spring." Evidence of the effects of aerosols and refrigerants on depletion of the ozone layer has led to restriction on the use of CFCs, and there is now increasing evidence of climate change resulting from our profligate use of fossil fuels.