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第1段
1 .Listen to part of a lecture in an environmental science class.
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2 .P: Ok. In the last class we were talking about Biofouling. And what did we say, biofouling is, Michael?
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3 .S: That's when different kinds of marine life, uh, marine plants like algae and marine animals like barnacles and mussels attach themselves to the hulls of ships.
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4 .P: Good. Now, that might not seem like that big of a deal, but it actually costs the global shipping industry billions of dollars per year. And that's because?
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5 .S: Having all that stuff attached to its hull makes it harder for a ship to move through the water. So, the ship uses more fuel. P: And?
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6 .S: So the shipping industry spends a lot of money painting the hulls of the ships with special paints to try to stop plants and animals from attaching themselves to the hull.
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7 .P: Ok, and at the very end of class, we said that the first paints that we know for sure were designed specifically to prevent fouling were developed in the mid 18 hundreds. And that's where we'll pick up today.
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8 .Okay, so in the mid 18 hundreds, inventors started taking paint and adding various kinds of biocides, chemicals that would either destroy or at least help control biofouling organisms.
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9 .Some of these paints were somewhat effective at preventing fouling, but many of them were pretty much useless.
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10 .Then in the 1950s, a new biocides compound was developed, a compound called tributyl tin, or TBT.
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11 .TBT-based paints were so effective that they were seen to be the perfect product for preventing biofouling. Any marine life that tried to settle on these paints would die.
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12 .But apart from direct contact with the paint, the TBT was thought to be completely harmless to the environment.
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13 .And then on top of that, the paints were made self-polishing. That is, they were designed so that they very slowly wear off the hull of a ship, so that a fresh layer of paint was always on the surface.
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14 .Although the self-polishing paints introduced significantly more paint into the marine environment, this was thought not to be a problem because TBT was still thought to be completely harmless.
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15 .But then in the 1980s, researchers began to realize that TBT was having a serious negative impact on the marine environment.
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16 .See, TBT accumulates in the sediments on the ocean floor. Animals that feed on these settlements take the TBT into their bodies. And it then makes its way off the food chain as bigger animals prey on smaller ones.
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17 .In the 1990s, the use of TBT began to be phased out. And new laws were put into place to protect the environment.
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18 .Essentially, new paints have to undergo vigorous environmental testing before they can be used commercially.
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19 .On top of that, to be of use to shipping companies, they also have to be inexpensive and work for several years.
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20 .And they have to be effective both import and out at sea. In these two areas, ocean salinity and water cleanliness may vary. And the marine species presence also vary.
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21 .The anti-foul paint that have been able to meet all those requirements haven't been anywhere near as affective as TBT-based paints. And that's led to a large increase in shipping costs. Yes, Michael?
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22 .S: So researchers are still stuck on that idea from the 18 hundreds, taking paint and adding a biocides. Can't they think of anything else?
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23 .P: Well, there's now also some new research being carried out, that's attempting to mimic natural products that are produced by animals.
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24 .For example, there are researchers who are trying to understand the natural glues that animals and plants use to stick to surfaces.
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25 .The idea is if we can understand these glues, then we may be able to develop a product that prevents them from working, which might provide us with a more eco-friendly way of preventing, or at least controlling colonization by biofouling agents.
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