The chemicals, known as alkylphenols, could be banned within five years as part of efforts by European governments to move to a "pristine environment". But at present the top 10 discharge sites in Britain are pouring more than 18 tonnes of the chemicals into rivers such as the Tees, Humber and Aire every year.
Almost half of that comes from a single site, ICI Chemicals factory in Wilton, Cleveland, which last year discharged 8.1 tonnes into the Tees estuary, as measured by the Environment Agency.
Alkylphenols are toxic, killing larvae and shrimps at concentrations as low as 10 millionths of a gram per litre. They also mimic the female hormone oestrogen, disrupting the development of young male fish.
Studies in Canada have found that wild roach and Atlantic salmon are particularly affected by the chemicals, a by-product from the manufacture of industrial-strength detergents. Other fish affected include rainbow trout, shrimp and flounder.
Geoff Brighty, the environmental toxicology manager of the Environment Agency, said: "There is experimental data to show that the alkylphenols and derivatives can partly sex-reverse fish: young male fish will grow up to be `intersex', and that applies to any fish. They also make male fish produce an egg protein that only female fish should make. However, we are actually more concerned about the toxic effects, which affect invertebrates like fly larvae at concentrations where the oestrogen-like effects are only beginning to be seen."
The knock-on effects further up the food chain could lead to larger animals starving or being forced to move for nutrition.
An ICI Chemicals spokesman in Wilton said: "There's no denying that this plant does emit this chemical, and nobody is saying that this isn't a polluted river. But the latest research suggests this isn't worse or better than equivalent rivers used for discharge in the US or Europe." He defended ICI's record, saying that emissions had fallen from 40 tonnes in 1997. "That is a considerable success. But we believe that further reduction is necessary and achievable, and we are also encouraging our customers to use alternative products," he said.
The pressure group Friends of the Earth called for a more comprehensive pollution directory, as the Environment Agency's data omits smaller factories and agriculture or sewage treatment works.
Dr Michael Warhurst, the group's pollution campaigner, said: "Fish are threatened by these chemicals, which only add to the problems already caused by hormone pollutants released in sewage effluent."
Representatives of European governments yesterday discussed plans to reduce the level of chemicals released by industry. Dr Brighty said: "There has been some success, since in rivers like the Aire the level of pollution has fallen by a factor of 100 in the past four years. ICI's emissions have fallen by 80 per cent. But we hope that at the European level we could get a ban on these chemicals' discharge into water, perhaps by the middle of the next decade."Reuse content