世界那么大，凈土有幾何

一直以來，人類不僅從環境中獲取資源，還習慣于把環境當成垃圾場，向其中直接排放廢氣、廢水、固體廢棄物。從天空到陸地，從河流到海洋，哪里有人類的足跡，哪里就少不了污染。然而，世界這么大，總有人類到不了的地方，我們還能否心存一絲希望—在這個星球上，尚有逃過人類破壞的一方凈土？答案也許會讓人失望……

Pollution， by definition， is something introduced into the environment that harmfully disrupts it. While nature sometimes produces its own damaging contaminants1）—wildfires send up billows of smoke and ash， volcanoes belch2） noxious gases—humans are responsible for the lion’s share3） of the pollution plaguing the planet today.

Wherever we go， we seem to have a knack4） for leaving our rubbish and waste behind. Visit even the most remote outpost on the planet and you will witness this first hand5）. Still， the world is a big place. Might there be some last holdouts free from the taint of our pollution？ Answering that question works best if we break down the environment into6） four realms—the sky， land， freshwater and ocean.

Sky and Land

Air pollution comes in many forms. Smog is mostly composed of particulate matter7） and ozone. And its impact on human health and the environment can be severe. In India alone， ozone pollution causes crop losses equivalent to $1.2 billion per year. In terms of human health， outdoor air pollution costs an estimated one million lives per year， while air pollution produced in homes—usually a by-product of cooking fires—kills around two million people annually.

When carbon monoxide， nitrogen dioxide and other primary pollutants （those that are injected directly into the atmosphere） find their way high into the atmosphere， they often get transformed through chemical reactions into what scientists refer to as secondary pollutants. Some of these pollutants can linger for months. Others， like methane8）， are less reactive and may circulate the globe for years until they are eventually broken down or find their way to the ground via snow or rain.

Pollution expelled into the air gets transported vast distances by winds and atmospheric currents. For instance， Indonesia has recently been clearing large tracts of forest with fire to create new palm oil plantations—and Singapore now contends with significant haze9） problems due to its neighbour’s slash-and-burn tendencies. Smoke pollution can travel even further than that， however： Fires used for farming in South America and southern Africa are a major source of air pollution for the entire southern hemisphere. On occasions， pollution emitted from one source region can find its way around the globe more than once.

So based on what we know about atmospheric currents and pollution distribution， it’s safe to say that there are no places on the planet guaranteed to be fully free from air pollution. And therefore that goes for the land surface too.

That said， however， there are places where the air is cleaner. In general， the Southern Hemisphere’s air is better than the Northern Hemisphere’s， just by virtue of10） the fact that fewer people live there. While pollution does move around the world， there is less mixing between the hemispheres due to barrier-like wind patterns. The South Pole， therefore， probably contains the cleanest air on Earth given its remoteness. But as Helen ApSimon， a professor of air pollution studies points out， there’s still a massive pollution-caused hole in the ozone layer hovering over Antarctica， and deposits of black carbon can be readily spotted on that continent’s snow.

Water

Air pollution， unfortunately， also affects water， and therefore cancels out hope that perfectly clean freshwater bodies exist. But while pollution from the air does settle in water， it’s actually pollution from land that acts as the primary contaminant for freshwater resources. Chemicals， fertilisers11） and waste seep into groundwater and wash into lakes， streams and rivers， often winding up12） in the ocean. The result is dead zones—swathes13） of fresh or saltwater devoid of life. Dead zones occur when nutrient loads from land cause massive microbial14） blooms， which in turn deplete the water of oxygen. These tubs of death are found all over the world， but the Gulf of Mexico’s Mississippi River Delta is perhaps the most infamous example.

Raw sewage15） and industrial waste are primary culprits wreaking havoc16） on freshwater. In many countries， “sanitation” refers only to removing waste from homes—not treating it before returning it to the environment. By some estimates， 80% of wastewater generated in developing countries is discharged directly into local waterways. That figure can be worse on a case-to-case basis： New Delhi dumps 99% of its wastewater into the Yamuna River， for example， while Mexico City pumps all of its liquid refuse17） into the Mezquital Valley. That is the main source of pollution all over the world.

According to Asit Biswas18）’s research， none of South Asia’s 1.65 billion people have access to clean， safe tap water； more than half of China’s rivers and lakes are too polluted to drink； and 72% of samples collected from Pakistan’s water supply system were found to be unfit for human consumption.

As with the air， freshwater bodies furthest from humans are probably also the cleanest. Canada’s far northern lakes and rivers， along with the Arctic and Antarctic’s freshwater are likely candidates for least-polluted bodies of water. Glacial layers that formed prior to the Industrial Revolution as well as sub-glacier lakes trapped far below the surface could in fact be pristine. Antarctica’s Lake Vostok， for instance， is buried under ice that is 400，000 years old. But these water bodies are clean because humans cannot physically get to them—other than by using drills.

Ocean

Even the oceans， which remain largely unexplored and occupy a whopping19） 70% of the Earth’s surface， have not escaped our pollution’s reaches. Today， an estimated 60%～80% of marine pollution originates from land， reaching the water through harbours， dirty beaches and polluted waterways that drain into the sea. Of that pollution， plastic is the most pervasive20）. That’s because most plastic takes centuries—perhaps even longer—to completely disappear.

Surprisingly， some of the remotest places in the ocean are also some of the most polluted， thanks to the patterns of the currents. Midway Atoll， a speck21） of land in the middle of the North Pacific， for example， is uninhabited save22） for scientists who visit for a few weeks at a time. But it’s covered in washed up debris， which often fatally finds its way into the digestive system of seabirds living there.

Likewise， the deep sea was once thought to be largely cut off from the human world， but the more we explore， the more we are coming to terms with the fact that that is not the case. “I’ve done a lot of work on the bottom of the ocean with submarines and ROVs [remote operated vehicles]， and there’s human debris everywhere，” says Lisa Levin， a biological oceanographer at Scripps Institution of Oceanography in San Diego， California. “It brings home23） the fact that human beings are an integral part of marine ecosystems now.”

On the deep-sea floor， the most readily identifiable pollution tends to be cans and bottles， though discarded fishing gear， ropes， metal objects， military ammunition24） and even old shoes regularly turn up， too. The diversity of garbage represents the fact that， historically， “people used the ocean as a dumping ground，” Levin says. In addition to the things we can see， much more is likely buried under the sediment25）， she adds， while other forms of pollution cannot be spotted by the human eye， such as microplastic—former bottles and bags that have broken down into ever smaller particles. Those tiny plastic pieces fill the ocean and “are probably impossible to ever clean up，” says Jenni Brandon， a graduate student in biological oceanography at the Scripps Institution.

Plastic pollution is not the only man-made waste contaminating the ocean， however. Oil spills regularly occur all over the world， even if the majority of them escape the notice of Western media. Persistent chemicals such as polychlorinated biphenyls （PCBs） also leach into the water from land， and then travel up the marine food chain.

And not all marine pollution is physical. Noise pollution caused by things like ship engine noise and sonar26） is becoming an increasing problem that has been implicated in whale， dolphin and squid deaths. “There are some places that don’t have physical debris—or at least where we haven’t found physical debris，” Brandon says. “But it would be hard to find anywhere that hasn’t had any human impacts.”

Some human impacts on the marine realm can also be completely unexpected. In 2007， for example， several amphipod crustaceans scooped up from water 11 km below the surface of the Pacific Ocean turned out to have cow DNA within their guts. “How do you get cow to the bottom of the Kermadec Trench？” Levin says. “I’m sure it was just a ship dumping its leftovers.”

While a burger for lunch may or may not harm those trench-dwelling creatures， it does demonstrate just how deeply our influence on the planet reaches. Whether our contaminants take the form of a discarded lunch， human excrement27） or billions of metric tonnes of airborne pollutants， we’re left with an unfortunate but clear answer： There probably is no place on Earth without pollution. In other words， as Biswas says， “We human beings have done a wonderful job of contaminating the environment around us.”

污染，就其定義而言，是指某些物質進入環境并對其造成有害的破壞。大自然有時會自發生成破壞性污染物，比如野火會產生滾滾的濃煙和灰燼，火山會噴射出有毒的氣體。然而，對當今全球蔓延的大部分污染負有責任的都是人類。

無論走到哪里，我們似乎都習慣于留下垃圾和廢棄物。即使前往地球上最偏遠的邊區村落，你都能親眼看到這一點。然而，地球是一個廣袤之地，是否還有未被人類污染的最后陣地呢？要想完滿地回答這個問題，我們可以將環境劃分為四個領域—天空、陸地、淡水和海洋。

天空和陸地

空氣污染的形式多種多樣。灰霾主要由顆粒物和臭氧組成，會對人類健康和環境產生嚴重的影響。僅在印度，臭氧污染每年給農作物造成的損失就相當于12億美元。就人類健康而言，室外空氣污染預計每年導致一百萬人喪生，而主要由烹飪用火引起的室內空氣污染每年會導致約兩百萬人喪生。

當一氧化碳、二氧化氮和其他原生污染物（指那些直接排放到大氣中的污染物）進入高空大氣的時候，它們通常會經過化學反應轉化成科學家們所說的次生污染物。這類污染物中，有一些可以在空中停留幾個月，而像甲烷等另一些不易發生反應的污染物則有可能會在地球上循環流通多年，直到最終被分解，或通過雪或雨落到地面。

排放到空氣中的污染物可以被風和氣流帶到很遠的地方。例如，印度尼西亞最近一直在火燒大片森林，以開辟新的棕櫚油種植園，而新加坡目前全力應對的嚴重煙霾問題就源于與它相鄰的印度尼西亞這種刀耕火種的態勢。然而，煙塵污染傳播的距離更遠：南美洲和非洲南部為耕作而燃燒的大火就是整個南半球空氣污染的主要來源。有時，某污染發源地排放的污染物會不止一次地擴散到全球。

那么，基于我們對氣流和污染傳播的了解，我們可以有把握地說，這個星球上沒有任何地方可以保證完全沒有空氣污染。由此說來，陸地表面的情況也是如此。

不過，就算這樣，還是有些地方的空氣更潔凈些。大體來說，南半球的空氣質量要優于北半球，原因就在于那里的人口更少。雖然污染會在全球流動，但由于像屏障似的風帶的存在，南北半球之間很少交互污染。因此，鑒于南極遠離人煙，那里很可能擁有地球上最潔凈的空氣。但是，正如從事空氣污染研究的海倫·艾普西蒙教授指出的那樣，懸浮在南極洲上空的臭氧層中仍有一個由污染造成的巨大的臭氧空洞，在那片陸地的積雪上很容易看到黑碳沉積物。

淡水

很不幸，空氣污染也會波及淡水，所以別指望有絕對干凈的淡水水體存在了。不過，盡管空氣中的污染物的確會融入淡水中，但淡水資源的首要污染源實際上是陸地。化學物質、肥料和廢水會滲入地下水，被沖入湖泊、溪流和河流中，最終通常會以匯入海洋而告終。污染的結果就是出現死亡水域—無生命存在的淡水或咸水區域。死亡水域之所以會出現，是因為大量來自陸地的營養性污染物引起微生物的大量繁殖，從而耗盡了水域中的氧氣。這些盆狀死亡水域遍布全球，但墨西哥灣的密西西比河三角洲或許是最為臭名昭著的例子。

未經處理的污水和工業廢水是造成淡水嚴重污染的罪魁禍首。在許多國家，“環境衛生”僅指將垃圾從家里清除出去—不做任何處理就讓其返回到環境中。根據一些估算，發展中國家產生的80%的污水都被直接排放到了當地水道中。就個案來說，數據可能更糟糕。例如，新德里將99%的廢水排入了亞穆納河，而墨西哥城將其所有液態垃圾倒進了梅茲奎塔爾河谷。這就是全球的主要污染源。

根據阿西特.比斯瓦斯的研究，南亞的16.5億人中無人能喝到干凈、安全的自來水；中國半數以上的河流和湖泊因污染嚴重而無法飲用；巴基斯坦供水系統的采樣中有72%經測試發現不適合人類飲用。

和空氣一樣，距離人類最遠的淡水水體很可能也是最干凈的。加拿大最北端的湖泊和河流以及北極和南極的淡水很可能就屬于污染最少的淡水水體之列。事實上，工業革命之前形成的冰層和深埋于冰面以下的冰下湖可能都是純凈的。例如，南極洲的福斯多克湖被埋在冰層下長達40萬年。但是，這些水體純凈的原因是人類無法真正接觸到它們—除非使用鉆孔機。

海洋

海洋覆蓋了地球表面的70%之多，其絕大部分區域尚未被人類勘探，即便如此，它也未能逃過人類的污染。目前，預計有60%～80%的海洋污染源于陸地，污染物通過港口、骯臟的海灘以及與海洋相通的水道進入海域。塑料制品在海洋污染中最為普遍，因為絕大多數塑料制品需要幾百年—甚至可能需要更長的時間—才能完全消失。

不可思議的是，因為洋流模式的影響，海洋中某些最為偏遠的地方也是污染最嚴重的一些地方。例如，中途島環礁是北太平洋中部的一個小島，那里沒有居民居住，只有科學家會前往調研，每次調研持續幾周。但是島上覆蓋著被沖上岸的垃圾。這些垃圾通常會進入當地海鳥的消化系統中，具有致命的作用。

同樣，人們曾認為深海的大部分區域都與人類世界隔絕，但是我們探測得越深入，我們就越是不得不接受一個現實：事實并非如此。“我曾利用潛水艇和水下機器人（遙控操作裝置）對海底做了大量的研究，發現那里到處都是人類的垃圾，”加州圣迭哥市斯克利普斯海洋研究所的海洋生物學家麗莎·萊文說道，“這清楚地表明，人類目前已經是海洋生態系統中一個不可分割的組成部分了。”

在深海的海床上，最容易識別的污染物往往是金屬罐和瓶子，不過廢棄漁具、繩子、金屬物體、軍事裝備甚至舊鞋子也會不時地出現。萊文說，垃圾的多樣性表明，從歷史上看，“人們都把海洋當做了傾倒垃圾的場所”。除了我們可以看到的這些東西，可能還有更多污染物被埋在沉積物的下面，她補充說道，而還有一些形式的污染是人類肉眼無法看到的，比如微塑料，它是由被丟棄的瓶子和袋子分解而成的更小的顆粒。那些微小的塑料碎片遍布海洋，并且“可能永遠無法清除干凈”，斯克利普斯研究所海洋生物學專業研究生詹尼·布蘭登說。

然而，塑料污染并不是污染海洋的唯一人造垃圾。石油泄漏事故在世界各地經常發生，盡管其中大部分事故都逃過了西方媒體的關注。多氯聯苯等持久性化學物質也會從陸地流入海洋，隨后往上進入海洋食物鏈。

海洋污染并不都是有形的。由輪船發動機和聲吶造成的噪音污染已成為一個日益嚴重的問題，鯨魚、海豚和魷魚的死亡可能都與此有關。“有些地方確實沒有有形的垃圾—或者至少是我們沒在那里發現有形垃圾，”布蘭登說，“但是我們很難找到一個未受人類影響的地方。”

人類對海洋領域的某些影響也可能完全出人意料。例如，在2007年，人們在太平洋水下11公里處撈出很多端足目甲殼動物，結果發現它們的內臟中竟含有奶牛的DNA。“人類是如何把奶牛帶到克馬德克海溝的底部呢？”萊文說，“我敢肯定這是輪船傾倒殘羹剩菜引起的。”

午餐吃的漢堡也許不一定會傷害到那些生存在海溝里的生物，但這的確表明了我們對地球的影響有多深。無論我們的污染物是以丟棄的午餐、人類排泄物還是以數十億噸的空氣污染物的形式存在，我們都面臨一個不幸而明確的回答：地球上可能已經沒有未被污染的地方了。換言之，正如比斯瓦斯所說：“在污染周遭環境方面，我們人類真是成績卓著。”

17.refuse [?refju?s] n. 廢料，廢物；垃圾

18.Asit Biswas：阿西特.比斯瓦斯，印度環境學家，因專注于水資源管理研究而聞名，是第三世界水管理中心的創始人。

19.whopping [?w?p??] adj. 巨大的，龐大的

20.pervasive [p?（r）?ve?s?v] adj. 遍布的；流行的，普遍的

21.speck [spek] n. 一點點

22.save [se?v] prep. 除……之外

23.bring home：以強調的形式清楚地顯示（或證實），（向……）活生生地揭示

24.ammunition [??mj??n??（?）n] n. 軍事裝備

25.sediment [?sed?m?nt] n. 沉積物

26.sonar [?s??nɑ?（r）] n. 聲吶（聲波或超聲波水下探測系統，用于測定水下潛艇方位或海洋深度等）

27.excrement [?ekskr?m?nt] n. 排泄；糞便