Aquatic and Terrestrial Pollution
AP Environmental Science Topic 8 8:37 English narration · English + 中文 subtitles burned in
Chapters
Transcript
Look at this pond.
看这个池塘。
It is bright green, and it is full of life.
它一片翠绿，充满生命。
Every fish in it is dead.
而里面的鱼全都死了。
Now look at this hill.
再看这座小山。
It is not a hill. It is our rubbish, buried.
它不是山，而是我们埋起来的垃圾。
Two pictures, one mistake: we put things where they do not belong.
两张照片，同一个错误：我们把东西放到了它们不该在的地方。
This is Unit Eight: pollution in water, and pollution on land.
这是第八单元：水中的污染，和陆地上的污染。
By the end you will be able to trace how a lake dies, follow a poison up a food chain, and read a toxicity number.
学完之后，你将能够说清一座湖是怎样死去的， 追踪一种毒物如何沿食物链上升，并读懂毒性数值。
Here is the plan.
本节安排如下。
First, where pollution comes from.
首先是污染来自哪里。
Then eutrophication, the story behind that green pond.
然后是富营养化，也就是那个绿色池塘背后的故事。
Then the poisons that never break down.
接着是永远不会分解的毒物。
Then our waste and our sewage.
然后是我们的垃圾和污水。
Then toxicology, the science of dose.
再然后是毒理学，也就是剂量的科学。
And last, pollution and human health.
最后是污染与人体健康。
Every source of pollution is one of two kinds.
所有污染来源只有两类。
A point source comes from one place you can point at: a factory pipe, a sewage outfall.
点源来自一个你能指出来的地方：一根工厂排污管，一个污水排放口。
You can find it, measure it, and regulate it.
你能找到它、测量它，也能管住它。
A nonpoint source is spread out: farm runoff, city streets, car exhaust.
非点源则是分散的：农田径流、城市街道、汽车尾气。
It comes from everywhere at once, so it is far harder to control.
它同时来自四面八方，所以难控制得多。
Before we add pollution, look at what we take away.
在谈污染之前，先看看我们拿走了什么。
Wetlands and mangroves are natural filters.
湿地和红树林是天然的过滤器。
Their roots trap sediment, take up nutrients and soak up floodwater.
它们的根系拦住泥沙、吸收养分、蓄住洪水。
Young fish grow up safely between them.
幼鱼在它们之间安全长大。
We drain them for farms and clear them for shrimp ponds, and the coast loses its best defence.
我们把它们排干改成农田，砍掉建成虾塘，海岸也就失去了最好的防线。
Now back to that green pond.
现在回到那个绿色的池塘。
Fertiliser washes off the fields into the water, carrying nitrogen and phosphorus.
化肥从农田冲进水里，带来氮和磷。
To algae, that is food.
对藻类来说，这就是食物。
They bloom right across the surface — algal blooms — and block the light, so the plants underneath die.
它们在整个水面上大量繁殖，挡住阳光，下面的水生植物于是死去。
Bacteria rot everything that dies, and burn oxygen while they do it.
细菌分解所有死去的东西，并在这个过程中消耗氧气。
The dissolved oxygen crashes, the water turns hypoxic, and the fish suffocate.
溶解氧骤降，水体缺氧，鱼被憋死。
That is a dead zone.
这就是死区。
It is one case of a bigger idea: human impacts on ecosystems ripple, because the species in them are connected.
它只是一个更大道理的例子：人类对生态系统的影响会层层扩散， 因为其中的物种彼此相连。
In the exam, write that chain as five steps, in order.
在考试中，要按顺序把这条链写成五步。
Extra fertiliser washes into the water.
多余的化肥冲进水里。
The algae grow very fast.
藻类迅速大量繁殖。
The algae soon die.
藻类很快死去。
Decomposers use up the oxygen.
分解者把氧气耗尽。
And the fish die, because there is no oxygen left.
于是鱼死了，因为已经没有氧气了。
The nutrients never poisoned the fish.
养分从来没有毒死鱼。
The bacteria took their air.
是细菌夺走了它们的空气。
Oxygen can be lost a second way, with no nutrients at all.
氧气还可能以第二种方式流失，而且完全不涉及养分。
A power station takes cool water from the river, uses it to carry heat away, and sends it back warm.
发电厂从河里取走凉水，用它带走热量，再把变热的水排回去。
Warm water holds less dissolved oxygen.
温水能溶解的氧更少。
So the same river, just as clean as before, now has less air in it.
于是同一条河，干净程度和以前一样，水里的空气却变少了。
Fish that need cold water move away, or die.
需要冷水的鱼要么离开，要么死亡。
That is thermal pollution.
这就是热污染。
Some pollutants do harm at doses far too small to poison anything.
有些污染物在剂量小到根本毒不死任何东西时，就已经造成伤害。
Your body runs on hormones, chemical messages that fit a receptor the way a key fits a lock.
你的身体依靠激素运行，那是一种化学信号，像钥匙配锁一样与受体结合。
An endocrine disruptor is shaped just enough like a hormone to fit that lock.
内分泌干扰物的形状和激素足够相似，正好能插进那把锁。
Some switch it on when nothing asked.
有的会在没有任何需要时把开关打开。
Others block the real message.
有的则堵住锁，挡住真正的信号。
Certain pesticides and plastic softeners do exactly this.
某些农药和塑料增塑剂做的正是这件事。
Now the poisons that refuse to go away.
现在来看那些赖着不走的毒物。
Persistent organic pollutants, or POPs, include DDT and PCBs.
持久性有机污染物，包括滴滴涕和多氯联苯。
They resist breakdown, so they last for decades and travel right around the world.
它们抗分解，所以能存在几十年，并且能传播到世界各地。
They are fat-soluble — they dissolve in fat, not water — so once they are inside a body they stay there.
它们溶于脂肪而不溶于水，所以一旦进入体内就会留在那里。
Building up within one organism over its life is bioaccumulation.
在一个生物体内不断积累，叫生物累积。
Rising up the food chain is biomagnification.
沿着食物链浓度不断升高，叫生物放大。
Watch what that means.
看看这意味着什么。
The toxin enters the water at a level you would call clean. Plankton take it in and keep it.
毒物进入水中时浓度很低，低到你会觉得这水是干净的。
Small fish eat many plankton and keep all of their toxin.
浮游生物把它吸收进去并留住。
The bird at the top eats them all. The poison never grew. It just ended up in fewer bodies.
小鱼吃掉大量浮游生物，把它们的毒物全都留下。
Read the numbers on the right: four hundredths of a part per million in the plankton, and twenty-five in the osprey.
最上面的鸟又把小鱼全吃了。 毒物的总量从来没有增加，只是集中到了更少的身体里。
Counting all the way from the water, the concentration multiplies two and a half thousand times.
看右边的数字：浮游生物是百万分之零点零四，鱼鹰是百万分之二十五。 从水一路算上来，浓度放大了两千五百倍。
Everything we throw away has to go somewhere.
我们扔掉的每一样东西都得有个去处。
Solid waste disposal starts with a landfill, where most of it is buried.
大部分被埋进垃圾填埋场。
A sanitary landfill lines the base, so the dirty liquid cannot reach the groundwater, and it captures the methane.
卫生填埋场在底部铺了防渗层，使脏水无法渗到地下水，同时收集甲烷。
The rest is burned in incinerators: less volume, but dirtier air.
其余的在焚烧炉里烧掉：体积变小了，但空气更脏。
The exam also names e-waste, old electronics full of toxic metals, and the garbage patches built by ocean dumping.
考试还会考电子垃圾，也就是含有毒金属的旧电器，以及海洋倾倒堆积成的漂浮垃圾带。
The waste reduction methods, in order: reduce, reuse, recycle, and composting for anything organic.
最佳顺序是：减量、重复使用、回收，厨余做堆肥。
Sewage gets its own treatment, in three stages.
污水有自己的处理流程，分三级。
Primary treatment is physical: the sewage sits still and the solids settle out.
一级处理是物理的：污水静置，固体沉降下来。
Secondary treatment is biological: bacteria eat the organic matter that is left.
二级处理是生物的：细菌把剩下的有机物吃掉。
Tertiary treatment is the polish, removing nitrogen and phosphorus, then disinfecting.
三级处理是精处理，去除氮和磷，然后消毒。
Skip that last stage, and the water leaving the plant still feeds a bloom.
如果跳过最后一级，从处理厂流出的水仍然会引发藻华。
Toxicology asks a different question: not what is poisonous, but how much.
毒理学问的是另一个问题：不是什么有毒，而是多少才有毒。
Give a test group bigger and bigger doses and plot the effect against the dose: that is a dose-response curve, and it comes out S-shaped.
给一组实验对象逐渐加大剂量，把效应画出来，曲线呈S形。
The dose that kills half of them is the LD50.
能杀死其中一半的剂量，就是半数致死量。
Now the sentence students get backwards: a lower LD50 means a more toxic chemical, because less of it is needed.
下面这句学生常常记反：半数致死量越低，说明毒性越强，因为用更少的量就够了。
Some chemicals also have a threshold, with no effect below it.
有些化学物质还存在阈值，低于它就没有效应。
Let's do one the exam's way.
我们按考试的方式做一道题。
These are two new chemicals, so ignore the letters on the curve.
这是两种新的化学品，请不要沿用曲线上的字母。
Chemical A has an LD50 of five milligrams per kilogram of body weight.
化学品A的半数致死量是每千克体重五毫克。
Chemical B has an LD50 of five hundred.
化学品B的半数致死量是五百。
Which is more toxic, and what dose of A is lethal to half of a seventy kilogram adult?
哪一个毒性更强？ 对一个七十千克的成年人来说， 多少剂量的A会使一半的人致死？
Pause here and try it. Ready?
先暂停，自己试一试。
Five hundred divided by five is one hundred, and A has the smaller value, so A is one hundred times more toxic.
好了吗？ 五百除以五等于一百，而A的数值更小，所以A的毒性强一百倍。
Now the dose.
再算剂量。
The LD50 is given per kilogram, so multiply by the mass: five times seventy is three hundred and fifty milligrams.
半数致死量是按每千克体重给的，所以要乘以体重： 五乘以七十，等于三百五十毫克。
Less than one gram, while B would need thirty-five grams.
还不到一克，而B需要三十五克。
Harm to people depends on three things: dose, duration, and individual sensitivity.
污染对人的伤害取决于三件事：剂量、持续时间，以及个人的敏感程度。
One big exposure is acute; years of small amounts are chronic.
一次大剂量接触是急性的；多年的小剂量接触是慢性的。
Risk analysis turns that into safe limits.
风险分析把它们转化成安全限值。
Pathogens cause the infectious diseases, and they use the same routes, and the exam wants how each one is transmitted, because the route decides the defence.
病原体引起传染病，走的也是同样的路线；考试要求你说出每一种是怎样传播的， 因为传播途径决定了防治手段。
Cholera and dysentery come from sewage — in drinking water, or in rivers.
霍乱和痢疾来自污水——出现在饮用水里，或者河流里。
Tuberculosis and the viral SARS and MERS are breathed in.
结核病，以及病毒性的非典和中东呼吸综合征，都是吸入的。
Plague arrives in the bite of an infected flea.
鼠疫由受感染的跳蚤叮咬传播。
Malaria, West Nile and Zika ride in the bite of a mosquito, a vector.
疟疾、西尼罗河热和寨卡则随着蚊子的叮咬到来，蚊子就是传播媒介。
And climate change spreads disease: as warm zones push toward the poles, the mosquitoes go with them into places that never had them.
气候变化还会扩散疾病：随着温暖气候带向两极推进， 蚊子也跟着进入从前没有它们的地方。
So the defence is not a drug. It is clean water.
所以真正的防线不是药物，而是干净的水。
Sedimentation lets the large bits settle to the bottom.
沉淀让大颗粒沉到底部。
Filtration removes the solid bits that are left.
过滤除去剩下的固体颗粒。
Carbon takes out bad tastes and smells.
活性炭去掉异味和异臭。
Chlorination kills the harmful microbes.
氯消毒杀死有害微生物。
What comes out is safe drinking water.
出来的就是安全的饮用水。
Clean water and sanitation stop more disease than any medicine, which is why poverty, with neither, is the biggest risk of all.
干净的水和卫生设施比任何药物都更能阻止疾病， 这也是为什么两者都缺的贫困，是最大的风险。
Four ways to protect your marks.
四个保住分数的做法。
First, trace eutrophication in full: nutrients, bloom, decay, oxygen gone, fish dead.
第一，把富营养化完整写出来：养分、藻华、腐烂、缺氧、鱼死。
The bacteria kill the fish, not the fertiliser.
杀死鱼的是细菌，不是化肥。
Second, bioaccumulation is inside one body; biomagnification is up the food chain.
第二，生物累积发生在一个生物体内； 生物放大是沿食物链上升。
Third, a lower LD50 means more toxic, and always multiply by body mass.
第三，半数致死量越低，毒性越强， 而且一定要乘以体重。
Fourth, name the transmission route, because the route decides the defence.
第四，写出传播途径，因为途径决定了防治方法。