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第一段
1 .OK, so we're been looking at how man-made changes in our environment can affect wildlife.
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2 .Now I'll discuss a particular example.
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3 .Let's take a look at mercury.
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4 .Mercury's one of the 120 or so elements that make up all matter, and it has the symbol Hg.
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5 .It's a shiny, silvery substance.
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6 .You may have seen it in old-fashioned thermometers,
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7 .but it's not used much for domestic purposes now because it's highly toxic.
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第二段
1 .But the problem is that the amount of mercury in the environment's increasing.
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2 .The main reason for this is the power plants used to produce electricity.
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3 .The main source of energy that most of them use is still coal,
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4 .and when it's burned it releases mercury into the atmosphere.
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5 .Some of this gets deposited into lakes and rivers,
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6 .and if it's ingested by a fish it's not excreted,
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7 .it stays in the fish's body and it enters the food chain.
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8 .So it's been known for some time that birds which eat fish may be affected,
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9 .but what wasn't know until quite recently is that those that eat insects can also be affected.
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第三段
1 .So a woman called Claire Varian-Ramos is doing some research on how this is affecting birds.
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第四段
1 .And rather than looking at how many birds are actually killed by mercury poisoning,
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2 .she's looking for more subtle sub-effects.
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3 .And these may be to do with the behaviour of the birds.
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4 .or with the effect of mercury on the way their brain works,
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5 .so whether it leads to problems with memory, for example.
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6 .And she's particularly focusing on the effects of mercury on bird song.
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7 .Now, the process of song learning happens at a particular stage in the birds' development,
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8 .and what you may not know is that a young bird seems to acquire this skill by listening to the songs produced by its father,
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9 .rather than by any other bird.
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第五段
1 .And Varian-Ramos has already found in her research that if young male birds are exposed to mercury,
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2 .if they eat food contaminated with mercury,
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3 .then the songs the produce aren't as complex as those produced by other birds.
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4 .So quite low-level exposure to mercury is likely to have an impact on male birds in a natural situation,
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5 .because it can mean that they're less attractive to female birds,
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6 .and so it can affect their chances of reproduction.
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第六段
1 .Now the way she's carrying out this research is worth thinking about.
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2 .She's using a mixture of studies using birds kept in laboratories,
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3 .and studies carried out outdoors in the wild.
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4 .The lab-based studies have the advantage that you don't get all the variables you would in a natural setting,
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5 .so the experimenter has a much higher level of control,
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6 .and that means they can be more confident about their results in some ways.
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7 .And of course they don't have to worry about going out and finding the birds in order to observe them.
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第七段
1 .So what are the implications here for humans?
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2 .Well, because many birds are migratory,
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3 .they may be transporting mercury far from contaminated sites.
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4 .For example, it's been found that ducks who'd been feeding at a contaminated site were later shot by hunters over a thousand kilometres away,
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5 .and presumably eaten.
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6 .But these birds likely had mercury levels high enough to warrant concern for human consumption.
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第八段
1 .In addition, going back to song learning by birds,
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2 .we saw that this may be affected by mercury contamination.
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3 .Well, we also know that in humans,
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4 .mercury causes developmental delays in the acquisition of language,
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5 .and in fact this process is very similar in the brain regions it involves and even the genes that are involved.
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6 .But mercury contamination has other important implications for humans as well.
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7 .It's now known that an unborn child can be affected if the food eaten by its mother contains high levels of mercury,
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8 .and these effects can be quite substantial.
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第九段
1 .In the end, it comes down to whether more value is placed on human economic wellbeing or environmental wellbeing.
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2 .It's true there are new regulations for mercury emissions from power plants,
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3 .but these will need billions of dollars to implement,
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4 .and increase costs for everyone.
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5 .Some argue that's too much to pay to protect wildlife.
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6 .But as we've seen, the issues go beyond that,
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7 .and I think it's an issue we need to consider very carefully.
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