BBC reporter Bernadette Kehoe: "Some scientists have suggested the chemicals are linked to the fall in male sperm counts"

Environmental campaigners say chemicals that interfere with the hormone system are causing increasing damage in the rivers and coastal waters of Britain.

The chemicals are known as endocrine disrupters (EDCs), or "gender benders".

They include some pesticides, dioxins (which can be given off by incinerators), and many other synthetic substances.

These EDCs mimic natural hormones, the body's chemical messengers, or block the cells that act as hormone receptors.

Effects on sexual development

That causes disruption of the endocrine system which controls growth and reproduction.

The campaigners say the effects of EDCs are now known to be damaging the endocrine systems of fish in the estuaries of the Mersey, the Tees and the Tyne.

In the Thames estuary and other major British rivers, they say they have found flounders which have become feminised.

Seals are at risk from EDCs

Other species affected include female dogwhelks in North Sea shipping lanes and close to main ports, which are developing penises.

Both common and grey seals have been found with suppressed immune systems.

And otters are suffering from lower fertility and reduced penis size.

The campaign groups which have sounded the alarm are Friends of the Earth, Greenpeace, the Marine Conservation Society, the Whale and Dolphin Conservation Society, and the World Wide Fund for Nature.

Most chemicals' effects unclear

They say that little is known on the toxicity of about 100,000 chemicals currently available for use.

And they say this means "a global-scale experiment is being conducted where humans and the environment are being exposed to unpredictable cocktails of chemicals".

A growing risk in the food chain

EDCs are among the chemicals which concentrate in body fat, and their effect becomes more marked as they move up the food chain.

So someone who eats a lot of fish could expect to be absorbing EDCs in their diet.

Like many other chemicals, their effects tend to be more severe in children. And one EDC may work with another chemical to produce an effect that neither could achieve in isolation.

Although scientists have identified only about 100 chemicals as EDCs, the groups say these are believed to be just the tip of the iceberg.

A failsafe approach

They want industry to take responsibility for eliminating the threat of EDCs in the marine environment, and to make the transition to clean production of safer chemicals.

And they say the government should act on the precautionary principle, refusing to allow chemicals to be discharged unless they have been proven to be safe beyond reasonable doubt.