INTRODUCTION

Since the middle of the last century there has been a tremendous growth in the number and range of chemicals used for manufacturing processes. It has been estimated that 95% of all man-made compounds have been produced in the last 50 years. Inevitably, some of these chemicals pollute the environment. This may be caused by deliberate release, such as products to manage agriculture (e.g. herbicides, fungicides and pesticides); incidental release, such as waste products of industrial processes (e.g. sulphur dioxide and acid rain, dioxins, detergents and heavy metals); accidental chemical spills (e.g. oil tanker disasters, sewerage outflows); or the pervasive and continuous pollution of substances merely because of lack of proper controls and care. This environmental pollution, and the effects it might have on nature, has been recognised for many years and was highlighted by well-known scientists and ecologists (Carson, 1962). The stability and persistence of many man-made chemicals in the environment with their eventual distribution throughout the food chain is of very real concern and, although the apocalyptic forecasts of the destruction of nature from chemical pollution might now appear excessive, there have been enough examples of the effects of environmental chemicals on reducing animal populations for the need to be vigilant. Some classic examples of the effects of environmental chemicals on reproduction in vertebrates serve to illustrate this point. From 1950 to the 1970s, the organochlorine DDT (1,1,1-trichloro-2, 2-bis (p-chlorophenyl) ethane) was used profligately as a general pesticide.