Male flatfish in the Merseyside area are changing sex due to the levels of oestrogen in the water from human contraceptive pills.
A team of scientists from the University of Liverpool and Cefas examined flounders, Platichthys flesus, caught in the Dee area and in the Mersey area to compare levels of vitellogenin (VTG) plasma in their blood.
VTG is a protein which causes egg yolk production in female fish, and ordinarily, you don't find any of it, or only very tiny amounts, in male fish.
However, male fish have a gene which can be turned on if sufficient oestrogen (the female sex hormone) is present in their water, causing them to produce VTG. Previous studies on trout and other fish have shown that VTG can build up in fish kept in estrogen polluted areas, causing the build up of eggs in the testes of male fish.
The report says that males and immature female flounders caught in the Mersey had abnormally high VTG levels in their plasma due to the presence of natural and synthetic oestrogens and xenoestrogens in the water. Those fish from the comparatively less polluted River Dee did not.
The study also showed a seasonal effect of VTG concentrations in males, with levels being highest during mid-winter.
The results suggest that as much as 0.5% of the Mersey flounders may be affected by the hormones.
For more details see: Kleinkauf A, Scott AP, Stewart C, Simpson MG, Leah RT. (2004) - Abnormally elevated VTG concentrations in flounder (Platichthys flesus) from the Mersey estuary - a continuing problem. Ecotoxicology and Environmental Safety. 2004 Jul;58(3):356-64.