Pollutants have been found in British rivers that could account for the decreasing male fertility in the country.
A study that examined wild male fish in rivers developing female reproductive organs found a link between this and the presence of 'anti-androgens' in the water. These drugs, used in medicines such as treatments for prostate cancer and also in pesticides in agriculture, block the function of the male sex hormone testosterone, and thereby reduce male fertility.
It had previously been shown that oestrogen, the female sex hormone, in river water can cause 'feminisation' characteristics in fish, such as male fish developing eggs in their testes, and can lead to male fish actually changing sex. Oestrogen is thought to enter rivers via the sewage system, from the contraceptive pill and from some industries.
These new results, published in the journal Environmental Health Perspectives, implicate anti-androgens in feminisation of fish. The three-year study was carried out by Brunel University and the Universities of Exeter and Reading, and the Centre for Ecology and Hydrology, and looked at over 1,000 fish in rivers around the UK, concentrating on sewage outflow areas. The scientists now warn that this could be a potential reason for the falling fertility rates in human males.
Professor Charles Tyler of the University of Exeter, one of the senior authors, said of the work: 'Our research shows that a much wider range of chemicals than we previously thought is leading to hormone disruption in fish. This means that the pollutants causing these problems are likely to be coming from a variety of sources. Our findings also strengthen the argument for the cocktail of chemicals in our water leading to hormone disruption in fish, and contributing to the rise in male reproductive problems. There are likely to be many reasons behind the rise in male fertility problems in humans, but these findings could reveal one, previously unknown, factor'.
He also says that there is a lack of evidence showing that oestrogen can affect human male fertility, but there is evidence to suggest anti-androgens can affect it. The first stage of follow-up work will be to identify the source of anti-androgenic chemicals and how they get into rivers. Possibilities include that the chemicals enter the rivers from domestic sources or from agricultural land.