How do Chemicals in the Environment affect Fertility?
There are many things that men and women can do individually to maximise the fertility, but what about the environment in which we live and the air we breathe? Chris Smith spoke to Professor Paul Fowler from Aberdeen University who looks at how these factors play a role...
Paul - Well, in the modern world, we’re exposed to a very large range of chemicals all at the same time. So, what interests me is models where the exposure is to the foetus, which is a sensitive life stage, is also an exposure to a complex cocktail.
One of your previous speakers already alluded to smoking and I study the effects of maternal smoking on the human foetus because, really, there is no totally adequate animal model for that. When you look at the effects on the foetus you can see changes in the liver and also defects in both the developing testes and the developing ovary. This matches to increased risk for the offspring of having reduced fertility in adulthood.
Chris - The thing is, ever since Walter Raleigh and all his pals went and got tobacco off of the Americas and brought it back and got us all hooked on it, people have been smoking, but populations have not declined. Populations have grown and they’ve grown faster and faster until more recently, so it can‘t just be smoking. There must be something else which is also affecting people’s fertility?
Paul - Well, that is a very good point to make, although taking one of the other points your speakers mentioned, increasingly leaving your fertility till later will exacerbate the problems. But we’re also exposed to a very large range of both natural and synthetic chemicals, some of which are persistent, some of which are not persistent.
But some of these chemicals are what we call “endocrine disrupting” compounds, and what they can do is to alter how the body’s endogenous hormones, our own hormones, our own endocrine system works. So, an example would be something like phthalates which may block the effects of the androgen receptor…
Chris - These are in plastic bottles, aren’t they?
Paul - That’s correct, yes. And the effect of that in the developing male foetus would be reduced masculinisation.
Chris - Essentially, we’re living in a world which is more polluted than previously; we’ve made more artificial things than we ever had in the past, and we’re basted in these substances - the environments full of them. We’re being exposed, and because they might look chemically a bit like some of the hormones that we naturally have in our body, there might be a knock-on effect to our own physiology, the way our body works. Because of exposure to these chemicals, one of those consequences could be affecting our reproductive development?
Paul - That is correct. Although the thing to bear in mind is that some of these compounds do indeed have close relationships. One would be bisphenol A, which looks like oestrogen and, indeed, bisphenol A can act like an oestrogen, but it’s a much weaker oestrogen than the oestrogen in our own bodies.
Chris - How are you looking at this; how are you attempting to study this?
Paul - The other model we use is a sheep exposed to sewage sludge which contains if I may be it this way, a rich digestion of the modern world. Right from pharmaceuticals, to agricultural run off, to air pollution.
Chris - But sheep don’t eat sewage do they, so how do the sheep get in contact with the sewage sludge?
Paul - Well, sewage sludge is a wonderful fertiliser. So it is widely used in many European countries, including the UK, as a fertiliser. We found that if you pasture pregnant sheep on sewage sludge fertilised fields, then you can get defects in development of the foetus. So smaller testes, lower testosterone, reduced numbers of eggs, and some of those defects persist in some of the animals into adulthood.
Chris - Are they transgenerational? In other words, if an animal is affected in this way, when itself then comes to breed, do it’s offspring suffer similarly?
Paul - There is some evidence of that in other studies. We’ve not been able to do that with the sheep model. If you think about how long it takes to breed successive generations of sheep, and the patience of funders, that’s difficult to do. There is evidence of transgenerational effects of smoking, for instance.
Chris - It’s a worry though isn’t it because if we’re exposed to these chemicals because we’ve messed up the environment? And, obviously, you’re looking at sheep, and that’s one example, but you can see how with these things being in the environment we may ourselves also be being exposed. But if the effects don’t go away, or we’ve done something to ourselves and we can pass those effects onto our offspring, that’s a real concern.
Paul - It is a concern. Although one of the things to, perhaps, just take a little bit of comfort from is given that we’re exposed to very complex cocktails of chemicals, the net outcome for the individual is very difficult to predict. That said, it’s only sensible that proper risk assessments are done on the chemicals that are used in order to determine their likely risk both to humans, and to economically important species.
Chris - Just very briefly in 30 seconds, actually what evidence have you got that what is happening in the sheep could be happening in us?
Paul - Allan Pacey did say the data on falling sperm counts is controversial and some of the studies are very poor, and I agree utterly with that statement. However increasingly, the series of publications recently suggest that the decrease in sperm counts in humans probably is genuine.