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Animal wastes and farm chemicals are also sources of pollution.
動(dòng)物糞便和農(nóng)用化學(xué)品也是污染源。
Fertilizers or chemicals farmers use to help crops grow may wash into ponds, where they cause algae to grow quickly.
農(nóng)民用來幫助作物生長(zhǎng)的肥料或化學(xué)品可能會(huì)被沖入水塘，導(dǎo)致藻類快速生長(zhǎng)。
As algae covers the pond it blocks sunlight.
藻類覆蓋住池塘，擋住陽光。
This lack of sunlight can kill the plants that animals rely on to survive.
缺乏陽光會(huì)殺死動(dòng)物賴以生存的植物。
How do artificial chemicals affect the ocean?
人造化學(xué)物質(zhì)如何影響海洋？
Because the ocean is so big it's hard to tell what effect chemicals have on it.
因?yàn)楹Ｑ筇罅?，很難說化學(xué)物質(zhì)對(duì)它的影響。
But we can see their effects on some of the largest bodies of fresh water on earth.
但我們可以看到它們對(duì)地球上最大的淡水水體的影響。
For example, high levels of chlorine, a chemical use of bleached paper, have been found in Lake Michigan.
例如，在密歇根湖，人們發(fā)現(xiàn)了大量的漂白紙中所含有氯。
Fluorine bromine and other dangerous chemicals have also been found there.
還發(fā)現(xiàn)了氟溴和其他危險(xiǎn)化學(xué)品。
And DDT and PCBs two of the most poisonous and long-lasting substances known continue to threaten aquatic wildlife.
滴滴涕和多氯聯(lián)苯是已知的兩種毒性和持久性最強(qiáng)的物質(zhì)，它們繼續(xù)威脅水中的野生動(dòng)物。
The pollutants found in many of the Great Lakes may be an early warning sign of what to expect in the oceans in the future.
在許多大湖中發(fā)現(xiàn)的污染物可能是預(yù)警信號(hào)，預(yù)示著未來海洋會(huì)出現(xiàn)的情況。
Pesticides also present a problem.
殺蟲劑也是一個(gè)問題。
Farmers use pesticides to kill beetles worms and other animals that damage crops.
農(nóng)民用殺蟲劑殺死甲蟲、蠕蟲和其他破壞農(nóng)作物的動(dòng)物。
But the chemicals and pesticides may harm birds and other animals that feed in the fields.
但是這些化學(xué)物質(zhì)和殺蟲劑，可能會(huì)傷害鳥類和其他在田里覓食的動(dòng)物。
Because agricultural chemicals are usually sprayed over large areas, it's hard to avoid polluting nearby water.
由于農(nóng)用化學(xué)品通常大面積噴灑，很難避免污染附近的水。
And even low levels of chemicals in the water can become harmful, because they build up over time.
即使是水中含量低的化學(xué)物質(zhì)也會(huì)有害，因?yàn)樗鼈儠?huì)隨著時(shí)間的推移而累積。
But water gets polluted in more direct ways too.
但是水也會(huì)以更直接的方式受到污染。
People enjoy lakes and rivers for recreation but they also use them as dumping grounds for industrial wastes.
人們喜歡在湖泊和河流中做各種娛樂活動(dòng)，但也把它們作為工業(yè)廢物的傾倒場(chǎng)。
Along the Detroit River stands a series of abandoned industrial sites.
底特律河沿岸矗立著一系列廢棄的工業(yè)區(qū)。
After having spilled PCBs and other pollutants into the river in the 1970s, many industries simply moved leaving the contaminated sites behind.
在上世紀(jì)70年代，多氯聯(lián)苯和其他污染物排入河流后，許多行業(yè)搬離了這些受污染的地方。
As the site's continued to disintegrate, the pollutants find their way into the river.
隨著的這些地區(qū)中的物質(zhì)不斷分解，污染物進(jìn)入河流。
