- The humble stickleback lives under constant threat from
predators such as herons.
-
- Many times a day, a stickleback, eyeing a piece of food,
will have to decide whether it is worth breaking cover to get the food,
and risk getting eaten itself.
-
- The over-bold stickleback will not live long, but the
excessively timid will starve.
-
- Just how bold the little fishes are depends, it seems,
on what kind of water they were brought up in.
-
- Alison Bell, from Glasgow University, UK, has reared
sticklebacks in water that contains tiny concentrations of a synthetic
oestrogen - the kind of level of pollution that you might easily find in
the environment.
-
- She found these fish were significantly more willing
to take risks than those that were reared in pure water.
-
- Alison Bell's work is one of a growing number of studies
that show that animal behaviour can be influenced by environmental chemicals.
-
- Inquisitive lambs
-
- And it suggests that these effects might be seen at very
low concentrations of chemicals - levels which, until now, everyone thought
were simply too low to have an effect.
-
- "There are now lots of studies that show exposure
to low levels of chemicals can affect behaviour," she tells BBC Radio
4's Costing The Earth programme.
-
- "We are barely scratching the surface."
-
- Stuart Rhind and colleagues, at the Macaulay Land Research
Institute near Aberdeen, did something similar.
-
- They took two sets of sheep, and grazed one set on ordinary
grass. The second group they grazed on land that had been fertilised with
sewage sludge.
-
- Sewage sludge contains a complex mixture of chemicals
that go under the general description of "endocrine disrupters"
- chemicals that somehow fool the body into thinking they are natural hormones
(again, the levels in the sludge are very low).
-
- Stuart Rhind could find no differences at all in the
bodies of the two sets of sheep, or their lambs. What he did find, however,
was that the lambs born to the ewes grazed on the sewage sludge behaved
differently to their uncontaminated counterparts.
-
- The male lambs behaved in a much more "feminine
way" - which, in lambs, means being more inquisitive.
-
- "It's not the fact that there has this been this
particular change of behaviour that matters," explains Rhind. "It's
the fact that behaviour has been altered in some way that matters, because
it implies that the developing offspring have had their brains altered."
-
- Boys and girls
-
- If tiny amounts of these chemicals, applied to animals
while in the womb, can alter their brains, what about humans?
-
- It is much harder to do a controlled experiment with
babies, but there is one intriguing piece of research from the Netherlands.
-
- Paediatricians there measured the concentration of two
endocrine-disrupting chemicals in the blood of pregnant women. The levels
were in the range you would expect to get from eating a normal mixed diet.
-
- Then they looked at the behaviour of the children once
they reached school age.
-
- They found that the boys whose mothers had had the most
exposure were more likely to play in a "girly" way - with jewellery,
and dolls, for instance; while the girls whose mothers had been most exposed
were drawn to boyish toys such as guns and trains.
-
- According to investigator Dr Nynke Weisglas Kuperis,
"it was a significant effect, but it is very subtle".
-
- Replicating results
-
- These and many other results with laboratory animals
have led some scientists to call for a radical overhaul of the way chemicals
are tested for safety.
-
- They claim to be able to detect adverse effects at levels
far below those deemed safe by the regulators.
-
- So why aren't the rules changing? Perhaps because this
is an extraordinarily tricky area of science.
-
- While some researchers find these effects, others who
have tried to repeat the experiments in large, well-controlled trials,
have found none at all.
-
- The people who do not find the effects are, by and large,
those working in industry - a fact that leads some academic scientists
to suspect a conspiracy.
-
- But the fact remains that, until these low-dose effects
can be consistently replicated, we are left with worries and suspicions,
but not proof.
-
- - For more, listen to Costing The Earth on BBC Radio
4 on Thursday, 28 April, at 2100 BST. The edition will be archived on the
programme website.
-
- © BBC MMV
-
- http://news.bbc.co.uk/2/hi/science/nature/4492721.stm
|
