Scientists working along the southwest coast of Britain have discovered widespread evidence of chemicals disrupting the sexual development of sensitive marine organisms.

In a study published yesterday, the researchers report the first cases in which hormone-disrupting pollutants are believed to be responsible for a gender-bending effect on marine invertebrates living in British estuaries. The finding has caused alarm because the affected species are crucial for the health of the ecosytem, in some cases forming the staple diet of many larger animals.

Researchers at the Marine Biological Association in Plymouth, south-west England, examined clams in estuaries from Southampton to the Severn and found that males at 17 of 23 sites suffered a condition called "intersex," where their testes contain both sperm and eggs. In some cases the male sexual organs contained thousands of eggs and up to 60 per cent of clams were affected.

Some scientists fear that the species may become so badly malformed that they will be unable to reproduce. If that causes a significant drop in their numbers, there will be too little food for animals that feed on them, such as plovers, bar-tailed godwits and other wading birds.

Bill Langston, who led the study, said any knock-on effects could be hard to predict.

"Invertebrates ... support the whole ecosystem by being at the bottom of the food chain. If something goes wrong at the bottom of the chain, there's a risk it could be serious for other species higher up," he said.

One concern is that the clams concentrate the chemicals in their flesh, and so other animals eating them could also begin to show signs of feminization.

Langston's team became aware of the problem when they started to identify the sex of clams in the Devon Avon. The researchers chose the site in the hope that it would be free of chemicals that might interfere with tests on the organisms.

According to the study, published in the journal Biology Letters yesterday, the most likely culprits are industrial hormone-mimicking chemicals, agricultural chemicals, pesticides or natural oestrogen that has found its way into estuaries after passing through sewage treatment works.

Tests conducted by the team show that exposing clams to estradiol, a natural female hormone, or ethinyl estradiol, a similar compound used in the female contraceptive pill, can trigger intersex.

Source:Chinadaily