A water-borne chemical is causing oysters to develop into hermaphrodites, which cannot breed, according to British scientists.
By Helen Briggs
BBC News Online science reporter
The pollutant could affect other marine life and further research is needed to find out if it can harm people, say ecologists at Royal Holloway, University of London.
The chemical is widespread in the environment
The substance, nonylphenol - a breakdown product of spermicides, cosmetics and detergents - is discharged through the sewerage system and is widespread in the aquatic environment.
It is a so-called endocrine disruptor - a chemical that can mimic hormones and disrupt normal sexual development.
The researchers looked at the effect of the chemical on Pacific oysters (Crassostrea gigas) raised at a commercial hatchery in Whitstable, Kent.
It caused death and abnormalities in developing embryos and larvae at "environmentally realistic" levels 10 times below the safe limit set by the UK Environment Agency, they say.
Of those that survived, almost a third became hermaphroditic - they possessed the reproductive organs of both sexes.
"These results are worrying," says lead researcher Helen Nice, "not only because of the damage to the oysters themselves, but also because this chemical may well be affecting other organisms sharing their environment."
She says it is vital that effects on vulnerable developmental stages should be considered when chemicals are screened.
"We clearly need further research to find out exactly what harm this chemical does and if it can harm people," she adds.
The Pacific oyster is one of two species of oyster marketed in the UK and throughout Europe.
Professor Michael Thorndyke, who supervised the research, says other types of oyster, as well as molluscs and crustaceans, may also be at risk.
"It has important implications for the numbers and types of animals in the marine environment because it could affect diversity," he says.
Susan Jobling of London's Brunel University, a leading researcher in the field, says nonylphenol is known to interfere with reproduction in fish.
"It is an oestrogen mimic and therefore, when present in the body, it is an impostor," she told BBC News Online.
The Environment Agency says the current environmental quality standard for the chemical is being re-negotiated taking into account any new science and evidence.
"Of extreme importance is the fact that this chemical has been very largely and effectively phased out of use now because of its known endocrine disrupting potential," says a spokesperson.