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第1段
1 . Listen to part of a lecture in a botany class.
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2 .In yesterday's class, we finished the chapter on outdoor remediation by watching a documentary about how large plots of mushrooms are being planted to assist in cleaning up the land at old oil refinery sites.
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3 . The mushrooms help clean up the pollution by absorbing the oil out of the soil, and then they are safely discarded.
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4 . Now let's switch our focus from the outdoor environment to the indoor environment.
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5 .In the United States, the first evidence we had that house plants can alter the quality of indoor air was documented and provided by the government's space program, NASA.
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6 . See, NASA researchers were attempting to design environments for people to live in in outer space.
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7 . Consequently, they built BIO home in the mid 1980s.
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8 . BIO home was a small, tightly sealed living space constructed with synthetic materials.
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9 . There was no ventilation. The problem was that it soon became apparent that people living in BIO home were having physical reactions to those materials, things like wheezing and coughing.
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10 .Well, at one point, the NASA researchers decided to place quite a number of plants in BIO home.
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11 .Sure enough, the inhabitants complaints cleared up. S: Could that have just been a coincidence?
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12 .Not according to the prior research that NASA had done.
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13 .In their experiment, individual low light plants that they knew didn't require a lot of sunlight had each been placed in separate sealed glass containers.
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14 .Then a single isolated chemical was injected into each container.
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15 .For example, fromaldehyde was one of the chemicals selected since it's quite a common chemical.
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16 .Or rather more precisely, I should say that formaldehyde is present in a lot of things in many new homes, most noticeably in the first several months when products are new.
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17 . S: Oh, like in what sort of things?
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18 . Well, let's see. Um, just off the top of my head, plywood paneling, uh, furniture, kitchen cabinets, insulation, the list goes on. It's quite extensive.
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19 . Now, as far as the experiment goes, well, in the glass containers that contained a plant, the different airborne chemicals that were used decreased and decreased substantially.
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20 . However, in the glass chambers, with no plant, the chemical levels stayed the same.
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21 . S: Are they all the same species of plant?
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22 .Great question. The answer is no.
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23 . And because of that, researchers noticed that certain varieties of plants were more effective than others at removing particular chemicals.
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24 . And that's clearly supported by even more recent research.
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25 .For instance, one species of fern, called the Boston fern, has been found to be unusually effective in terms of targeting formaldehyde
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26 . It's dramatically better at it than most other plants are.
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27 . S: So the leaves of the plants make this happen?
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28 . Well, that's what you think, right?
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29 .And the leaves do help to some extent. But what most people don't know is that actually the majority of the purification process takes place near the roots of the plant.
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30 . See, it's the microorganisms that live around the roots of the plant that break down chemicals.
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31 .They are most responsible. They turn the chemicals into food for the plant.
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32 .Each plant species has different kinds of microorganisms that thrive around its root base.
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33 . S: I'm curious, were there any negative effects for the plants in these situations?
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34 . Did their effectiveness decrease after the plants' cells had taken all this stuff in?
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35 . Not at all. Further research done after that NASA study has revealed to us that plants' ability to remove chemicals from the air actually improves overtime.
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36 . It turns out the microorganisms actually adapt.
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37 .They increase in number to meet higher concentrations of chemical.
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38 . So essentially, it's a win-win situation for both the plant and the person.
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39 .Now, it's also interesting to note that over the year, the subsequent research, we've come to realize that the soil itself is actually something that can be taken out of the equation.
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40 . As far as the microorganisms are concerned, the air purification process becomes most efficient if we use a mixture that's made up of only two ingredients, carbon pellets and rocks. Why?
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41 . Well, the contaminated air can move more easily down to the root zone through the small gaps between the rocks.
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42 .And that's really all you need.
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