Science Interviews


Sun, 9th Sep 2012

Chemicals in sewage sludge cause physiological changes in sheep

Stewart Rhind, James Hutton Institute

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Chris -   Industry has revolutionised the way that we live.  In the developed world we enjoy high quality lifestyles, healthcare breakthroughs, and a range of gadgets and devices that make life cheap and easy.  This ranges from plastic baby bottles to printed circuit boards, and even non-stick frying pans.  But the result is that we’re all being exposed to low-levels of mixtures of chemicals that, together, might be having serious impacts upon our health.  Sheep exposed naturally to these same substances are showing signs of changes to their fertility, reproductive organs, brains, and bones.  Aberdeen Scientist, Stuart Rhind...

Stuart -   We’re investigating the potential effects of environmental chemicals, most of which are man-made chemicals, collectively referred to as Endocrine Disrupting Compounds, EDCs.  Now, what that means is multiple chemicals coming from many, many different sources, which have one thing in common, they interfere with the normal actions of physiological systems in animals.

Chris -   How?

sewage inletsStuart -   Well, their actions can probably be at the gene level, affecting gene expression, or they can interfere with enzyme systems in cells.  We see changes in cellular structures.  We see changes in organ structures.  We see changes in animal behaviour, the incidence of diseases, etc.  It comes in many, many different forms because there are many chemicals acting in many different ways.

Chris -   And what are the consequences of those actions?  Do we know exactly how they affect living systems and who’s vulnerable?  Is it just humans?

Stuart -   Well, the short answer is that, no, we don’t know.  But what this work that we’ve been doing is beginning to show is that the actions of multiple chemicals together, each of them at levels far too low to be considered in any way harmful, may have consequences for the functioning of many different organs and for animal health and well-being, particularly for reproduction.  Now, when you ask "which animals," well, the short answer is, all animals.  And when I say all, I don’t just mean mammals.  I mean, all animals, all the way from bacteria, through all sorts of worms and molluscs, all the way up to humans.

Chris -   Gosh!  So pretty comprehensive. And, of course, if you fiddle with one bit of the ecosystem, it will have knock-on effects.

Stuart -   That’s right.  We’re talking about extremely complex systems here.  Not only are we talking about potentially up to 100,000 chemicals acting on probably, dozens of different systems.  We’re talking about different species responding in different ways.  But the overall effect is that we might be upsetting ecosystems on which humans depend for their survival.  I mean, to take a simple example, if as I said, we could be perturbing populations of bacteria and soil, also, populations of many other organisms such as earthworms, which are fundamental to the processing of nutrients, which is then used by our crop plants.  Now, if, by introducing these chemicals to the soil in increased amounts, we start to perturb those populations, we start to change the whole ecosystem, perhaps reducing the population of one species and increasing that with another, we may upset these processes.  If we upset these processes, perhaps we could be compromising our crop production, with all the consequences of that for an increasing human population.

Chris -   Difficult to study and very difficult to make predictions, a bit like Neils Bohr said, "predictions are always difficult to make, especially about the future."  So, how are trying to get a handle on what the impacts might be?

Stuart -   When we started this work, in 1997, I was charged with investigating endocrine disrupting compounds.  My first problem was that these chemicals are known to be present in very, very low levels.  So in order to study them, I wanted to find a way of increasing animal exposure, but not in a big way.  Not like it’s done in the lab where you take one chemical and you maybe go from very low levels up to what would be considered pharmacological levels, the kind of levels you’d take with a drug to cure a disease; huge amounts.  I wanted to get away from that, I wanted a subtle change, something that was real world if you like. So I came up with the concept of using sewage sludge. All our drains, from our domestic and industrial facilities, all ultimately end up in our sewage system which goes into a sewage farm where it is processed.  Two products come out, one is “pure” water, and the other is solid waste.  But because of our human lifestyle, it contains all the products that we use.  It contains our medicines, illegal drugs, things from plastics, from cleaning agents.  So, we’re using this sludge as a tool.  In many parts of the world, it is recycled to land as fertiliser.  By putting it onto pasture, something that’s done routinely, we can study the effects of introducing these extra chemicals on animals exposed to that treated pasture.

Chris -   It’s grazing animals.

Dolly the sheepStuart -   This is sheep in this case.  So, sheep are our experimental model and we’re applying sludge to the pasture as a fertiliser.

Chris -   And what are you measuring about the sheep?

Stuart -   First of all, we’re measuring the concentrations of selected endocrine disruptors in the tissues of sheep to get an idea of how much of these chemicals are actually present.  Now there is a second part and that is, what are the consequences for the function of various organs, and that’s where a number of collaborators in many different countries come in.  And they’ve been able to demonstrate subtle changes in multiple organs.

Chris - What are you comparing the sheep grazing the sewage treated grass with because obviously it’s one thing to do an observation, it’s another to say, well, we’ve got cause and effect here?

Stuart -   We have a control group of animals, that is, an untreated group. They are treated in exactly the same way as those exposed to the sewage sludge except that instead of using sewage sludge as fertilizer we use and inorganic, man-made fertilizer that we know contains absolutely minimal levels of these pollutants. We can’t guarantee that the effects we see are a function of the chemicals, these endocrine disruptors, but our results taken in conjunction with what is known in the literature, we believe it to be the most likely explanation.

Chris -   That being the case, what is the implication for us humans?

Stuart -   In my personal opinion, if things went to their logical extreme, we could threaten the viability of ecosystems on which we depend and we could ultimately threaten our own fertility as a species. We already have evidence of declining sperm count, increased incidence of requirements for IVF (in-vitro fertilisation), particularly in certain countries. I think we do need to understand possible consequences for the health of the ecosystems on which we depend for our own survival.  

Chris -   Stuart Rhind, from Aberdeen University.


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