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Endocrine Disruptors

3. Do EDCs affect wildlife?

  • 3.1 What are the most illustrative examples of effects on wildlife?
  • 3.2 How reliable is the evidence in wildlife?

Several studies performed in the wild or with wildlife in the laboratory have shown that exposure to certain endocrine disrupting chemicals (EDCs) has adverse effects in some populations. These vary from subtle changes in body function and sexual behaviour to permanent effects on sex organ development. Most of the information comes from Europe and North America.

Some EDCs disappear quickly from the environment, while others persist. Aquatic animals – especially predators – have been most affected, but effects have also been found in animals living on land. Some of the damage observed in certain animals is likely to be due to endocrine disruption. In most cases, however, the link between exposure to EDCs and endocrine disruption is unclear. More...

3.1 What are the most illustrative examples of effects on wildlife?

3.1.1 Mammals: exposure to organochlorines (PCBs, DDE) has adversely affected Baltic seals’ reproductive and immune systems, causing large population declines. These seals show signs of damaged endocrine systems, but exactly how these chemicals are causing these effects is not known. More...

3.1.2 Birds: Eggshell thinning and altered sex organ development have been observed in birds of prey exposed to the pesticide DDT, resulting in severe population declines. Birth defects have been found in fish-eating birds, which are directly related to exposure to another chemical, PCB, but the precise linkage to the possible underlying endocrine disturbance is uncertain. More...

3.1.3 Reptiles: A presumed pesticide spill in Lake Apopka (Florida, USA) provides a well-publicised example of potential endocrine disrupting chemical (EDC) effects on the decrease in alligator numbers. The alligators had a variety of sex organ and other developmental abnormalities attributed to exposure to high levels of various organochlorine contaminants that can affect the endocrine balance. Even though several explanations have been proposed, the precise cause of the changes in the alligators remains unknown. More...

3.1.4 Amphibians: Population declines in amphibians, such as frogs, have been seen in both unpolluted and polluted habitats worldwide. Currently, there is not enough information to know whether EDCs are the cause. More...

3.1.5 Fish: There is extensive evidence that chemicals found in the waste outflows from pulp and paper mills and sewage treatment plants can affect reproduction and development in fish. A variety of endocrine changes are involved, but it is not yet fully clear which chemicals are responsible for the changes or how they work. More...

3.1.6 Invertebrates (animals without backbones): Exposure to tributyltin (TBT), a chemical used in antifouling paints, provides the clearest example in invertebrates of an endocrine effect caused by an environmental contaminant. The females of certain marine organisms, such as snails, slugs, whelks and periwinkles, develop male sex organs when exposed to TBT. This has resulted in worldwide declines in their populations. This ‘ masculinisation effect’ is probably due to increases in the levels of male hormones in the females caused by TBT. More...

3.2 How reliable is the evidence in wildlife?

It has been suggested that wildlife studies provide early warnings about possible harmful effects on humans of exposure to endocrine disrupting chemicals (EDCs). But because there is such a variety of species and only a few have been studied, it is important not to jump to conclusions about EDCs. In addition, studies on the potential effects of EDCs on wildlife have mainly concentrated on individuals, rather than whole populations or communities of animals.

The way in which disturbances in sexual and reproductive functions, and impaired offspring survival, affect whole populations is difficult to quantify. Overall, the current scientific knowledge provides evidence that some abnormalities seen in wildlife are caused by chemicals that function as EDCs. However, in most cases, the evidence of a causal link between the abnormalities and exposure to particular chemicals is weak, and most effects have been observed in areas where chemical contamination is high. More...


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