Every male roach which scientists examined in two rivers, the Nene in Norfolk and the Aire in West Yorkshire, showed signs of feminisation. In the worst cases, large parts of the sperm-producing testes had turned into egg-making ovary tissue. In the least effected, oocytes - the small cells at the start of the production line which leads to fish eggs - were thinly scattered through the testes.
It has been known for years that sewage effluent can feminise fish - male trout kept in cages next to outlet pipes start producing egg yolk protein. Natural oestrogen from women's urine, synthetic oestrogen from the Pill and a variety of industrial chemicals are the culprits. Male flatfish, particularly flounders, also show hermaphrodite signs in estuaries polluted by sewage and industrial effluent. Now the team from Brunel University in west London, which did the work on trout, has shown how universal this disquieting change is for roach.
The results of a three-year investigation, covering 2,000 fish at 20 different sites in England and Wales and funded by the Government's Environment Agency and the Natural Environment Research Council, were unveiled yesterday by Professor John Sumpter, of the University of Middlesex.
On average, 60 per cent of the fish caught in river stretches downstream of sewage works were "intersex". Surprisingly, so were some 25 per cent of those upstream. That is probably caused by sewage effluent from works much further upstream, with the female hormones or their synthetic mimics exerting their effect at an extremely low concentration. Ten per cent of male roach from "pristine" rivers with no sewage works outfalls were also feminised, suggesting the condition may occur naturally at a low level. But the scientists established a link between the quantity of sewage effluent and how sex-changed the fish were.
Professor Sumpter said further research was needed to solve two big unknowns. Were other fish species changed in the same way, and what effect was it having on their breeding? But there is also a great deal of research still to be done on exactly what chemicals are to blame. Earlier research by Brunel and the Ministry of Agriculture, Fisheries and Food found that three hormones found in women's urine were present in sewage effluent at levels high enough to feminise fish.
But the Environment Agency is concerned about a range of industrial chemicals which can be found, at low concentrations, in effluent. It is to review its regulation of polluting companies, and the limits it puts on their effluents, in the light of the growing concern about the effects of sex hormones and their synthetic mimics on wildlife.