River sewage pollution found to be disrupting fish hormones
20 January 2009 by Tom Marshall
New research has strengthened the case that polluted river water is harming fish's ability to reproduce by disrupting their hormonal, or endocrine, systems.
Researchers found evidence of endocrine disruption in fish including the roach, pictured.
Scientists found that sewage treatment works are releasing significant volumes of chemicals that inhibit the function of testosterone, the male hormone, into British rivers. They call these chemicals 'anti-androgens'; such pollutants might include compounds used in pharmaceuticals, cleaning products, cancer treatments and pesticides.
These anti-androgens are likely to contribute to fish feminisation - a process whereby male fish develop some female reproductive characteristics, reducing the quality and number of sperm they produce and probably also their ability to compete to pass on their genes. In other studies exposure to anti-androgens has also been linked to damage to human reproductive health.
Scientists already suspected that the female hormone oestrogen could cause feminisation in fish, but it turns out that a whole cocktail of chemicals acting in combination is likely to be behind the problem.
"Our research shows that a much wider range of chemicals than we previously thought is leading to hormone disruption in fish," says Professor Charles Tyler at the University of Exeter, one of the paper's authors. "This means that the pollutants causing these problems are likely to be coming from a wide variety of sources."
Tyler adds that 'the circle is getting tighter' in establishing the hypothesis that similar pollution may also be causing male fertility problems in humans, though he notes that no such connection has yet been proved.
He explains that in the lab exposures to oestrogenic chemicals at the concentrations found in the natural environment do not seem to cause problems of the severity seen in wild fish; when the oestrogens are combined with anti-androgens the mixture is likely to produce the effects seen in polluted rivers.
The study was carried out by the Universities of Brunel, Exeter and Reading with the Centre for Ecology & Hydrology, with statistical modelling support from Beyond the Basics Ltd, and appears in Environmental Health Perspectives. It is based on more than 1000 fish sampled over three years from 30 rivers across England, and on samples of effluent from 43 sewage works.
"We have been working intensively in this field for over ten years," says Dr Susan Jobling at Brunel's Institute for the Environment, lead author on the paper. "The new research findings illustrate the complexities in unravelling chemical causation of adverse health effects in wildlife populations and re-open the possibility of a human-wildlife connection in which effects seen in wild fish and in humans are caused by similar combinations of chemicals."
Something in the water
The University of Exeter is now working with chemists at the University of Sussex to establish exactly what the chemicals in question are, and hence to understand how they are being released into waste water. This will involve both chemical testing of effluent from sewage treatment works and experiments with fish at the works' outlets. Fish accumulate these chemicals in their bile, so can be used to make identifying them easier.
The scientists will also be working with regulators and the water industry to test the chemicals' effects of these anti-androgens in combination with oestrogen and related female hormones to get a realistic analysis on their combined effects in our river systems.
Earlier research from Brunel and Exeter scientists showed how female hormones like oestrogen are leading to the feminisation of male fish. Found in the contraceptive pill as well as some industrial chemicals, oestrogen and associated chemicals enter rivers via sewage treatment works, causing reproductive problems in fish by reducing fertility and in some cases even causing male fish to partially change sex.
One common cause of fertility problems in male humans is called testicular dysgenesis syndrome. This syndrome is known to be caused by exposure to anti-androgens in lab mammals.
The fact the team has proved that anti-androgens as well as oestrogen are being emitted in significant quantities into British rivers certainly provides indirect support for the hypothesis that pollution is behind at least some of the increase in human fertility problems. The researchers say more work is now needed to test this hypothesis.
"In vertebrates the hormonal system is highly conserved; ours is comparatively close to that of fish," Tyler notes, though he also points out that the kinds of exposure to river pollution a human could face is very different from what a fish experiences swimming in a soup of 100,000 chemicals contained within effluent discharges - in some cases throughout the fish's life.
Other researchers also call for caution in connecting the cases of fish and humans. "Are anti-androgens part of the mix of chemicals that could be disrupting wildlife and humans? Yes," says Dr Andrew Johnson, an environmental scientist at the Centre for Ecology & Hydrology in Wallingford who has spent a decade working on endocrine disruption.
"This paper shows that what we already knew was happening to humans is also happening in freshwater," Johnson adds. He explains that research on the hormone-disruption affecting humans has tended to focus on a group of chemicals called phthalates, to which humans are believed to be exposed primarily through cosmetics, and argues that it's not clear that chemicals found in sewage effluent are likely to return to the water supply to affect humans.
Whether the chemicals can do so will depend on exactly which anti-androgens are discovered to be present. If those present are found to be particularly hydrophilic, or water-soluble, it's possible they could get through filtration procedures and return to the drinking water supply, but these filters efficiently remove most pollutants.