Behind the Headlines

Tuesday January 20 2009

Scientists examined the sex organs of male fish to look for feminisation

“The rise in male infertility and the decline in human sperm counts could be linked with chemicals in the environment known as anti-androgens” says The Independent. The newspaper says that these types of chemicals “are able to stop testosterone working” and could be affecting development of men’s reproductive organs.

These results come from a study which tested water from 30 sites near sewage outlets and 1,500 fish. Male fish that were exposed to the highest levels of anti-androgen chemicals were the most likely to show female traits, such as having egg cells in their testes. It is not clear what the source of these chemicals is, but it could be pesticides, industrial pollution or pharmaceutical drugs entering the water system.

This study is of particular concern to ecologists as it concentrated on the effects that these chemicals had on fish. Despite what has been reported in some newspapers it is not yet clear what the implications of these findings are for human health. Further research will be needed to identify the source of these chemicals and establish safe levels of exposure for animals and humans.

Where did the story come from?

This research was conducted by Dr Susan Jobling and colleagues from Brunel University and other research centres in the UK.

The study was funded by Beyond The Basics Ltd, the UK Environment Agency, and the Natural Environment Research Council. It was published in Environmental Health Perspectives, a peer-reviewed journal.

What kind of scientific study was this?

This was a cross-sectional survey looking at the relationship between the levels of different chemicals in UK rivers and the levels of “feminisation” of male fish in these rivers. Feminisation is the taking-on of female characteristics.

The feminisation of male fish in UK rivers is thought to be related to the female hormone oestrogen and related chemicals in the water, which come from human and animal excretion. However, it is not known whether anti-androgens (chemicals that interfere with male hormones) also have an effect.

Anti-androgens have been found to cause problems with testicular development and function in rodents, and these problems resemble a condition known as testicular dysgenesis syndrome in humans. However, the evidence that the same chemicals are causing both human and wildlife endocrine (hormonal) problems and subsequent reproductive problems is weak.

In 2007 The Environment Agency carried out a cross-sectional survey of the chemicals present in effluent from 30 different sewage treatment works across the UK. The agency measured the levels of specific oestrogen-related chemicals at each site.

But the researchers also measured the total oestrogen-like (oestrogenic), oestrogen-blocking (anti-oestrogenic), androgenic (male hormone-like), and anti-androgenic effects of the effluent. This was done by observing the effect that the water samples had on yeasts in the laboratory. These tests do not identify the chemicals causing the effects but show only that the effects are occurring.

The researchers also took 1,083 fish (roach) from the rivers downstream of where the effluent emptied (12 to 71 fish from each site). They looked to see whether male fish had any female characteristics, such as having egg cells in their testes (feminisation) and estimated how much exposure fish had to the chemicals at each site. Exposure was calculated based on the concentration of the various chemicals in the effluent, and how much the effluent would be diluted in the river.

The researchers then used statistical modelling to look at the relationship between feminisation levels and each group of chemicals, both on their own  and when combined.

What were the results of the study?

The researchers found oestrogen-like activity in all 30 effluent sites, and anti-androgenic activity at 20 of these. The levels of oestrogenic and anti-androgenic activity varied between sites.

Statistical models suggested that the level of feminisation of male fish could best be explained by models that took into account levels of both anti-androgens and oestrogens in the water, or solely levels of anti-androgens.

What interpretations did the researchers draw from these results?

The authors concluded that their findings provided strong evidence that the feminisation of fish in UK rivers is related to both anti-androgens and oestrogens. They say that the identity of these anti-androgens is not yet known.

The authors also conclude that this evidence may add support to the theory that hormone disruption in humans and fish can be caused by similar chemicals.

What does the NHS Knowledge Service make of this study?

This study by itself provides evidence of an association between estimated exposure to anti-androgens and oestrogens and feminisation of male fish, but does not prove that the relationship is causal. However, the authors state that the possibility that it is causal is supported by laboratory studies showing that anti-androgens and oestrogens can have an effect on fish feminisation.

The findings of this study are a concern for ecologists, but it is not yet clear what the implications for human health are. Further research will be needed to identify the anti-androgenic chemicals in sewage effluent and determine any possible effects they might have on animals and people.

Analysis by Bazian

Edited by NHS Choices


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