Introduction

Endocrine disruption has become one of the 'hottest topics in environmental science today, and in the last few years major, multi-disciplinary research programmes on the issue have been initiated in many countries. However, despite the current intense activity, and the fact that the term 'endocrine disruption' was coined only very recently, for over two decades it has been apparent that exposure to anthropogenic chemicals present in the environment can cause sub-lethal, but still deleterious, effects to wildlife. In many cases reproduction has been adversely affected (such an effect is often quite noticeable, of course, which may well account for why reproduction has received much of the attention), and in at least some of these cases this disruption has been shown to be, or presumed to be, a consequence of disruption of the endocrine control of reproduction.

Most reported examples of what would now be considered cases of endocrine disruption of reproduction in wildlife have occurred in aquatic organisms, or species that feed on aquatic organisms. Thus, for example, some of the most widely reported incidences have been observed in fish (e.g. [1,2]),alligators [3] and fish-eating birds such as gulls and terns [4]. This is probably not coincidental; it seems likely that, on average, aquatic species receive a higher exposure to most pollutants than do terrestrial organisms, for the simple reason that the aquatic environment is the ultimate sink for most wastes. Thus, for example, very high volumes of effluents of domestic and industrial origins are intentionally added to many rivers and inshore marine waters (Tokyo Bay receives about 4.7 km3 of liquid wastes per year, for example), and unintentionally many chemicals (of both natural and man-made origin) are washed from the surrounding land into the aquatic environment.

Exactly which organisms could, or should, be considered 'aquatic' is a moot point. I have 'stretched' the interpretation of an aquatic species to include animals that either spend only part of their lives in water (e.g. many amphibians), or those that live both in water and on land (e.g. many reptiles), but have chosen to exclude other groups of organisms, such as aquatic birds, which other authors may have included. I have also excluded mentioning plants (except here!), even though many are truly aquatic; however, I know of no example of confirmed endocrine disruption in plants (which does not mean that none will ultimately be discovered: plants have hormones, and hence these could, at least theoretically, be disrupted by exposure to exogenous hormone-mimicking chemicals). Due to my particular interest in fish, I have undoubtedly given research into this group prominence. However, I have tried to balance this bias by including discussion of endocrine disruption in other groups of aquatic organisms, covering both vertebrates and invertebrates. My admittedly selective coverage has, nonetheless, allowed me to discuss most, if not all, of the major issues in this area of research.

I have chosen to consider reproductive effects only, despite the fact that it is inevitable that examples of endocrine disruption will include many, and varied, non-reproductive effects; in fact, some have already been reported, e.g. the effects of alkyl phenolic chemicals on growth of fish [5].

I have tried to provide a fairly balanced account. However, in a still very controversial area, with many different, and often powerful, stakeholders, what is balanced to one interested group of people will undoubtedly be biased to another. Such a situation is always going to occur when an issue, which could be very important, is in its infancy; only further research will allow a more informed and reasoned opinion to be reached.

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