The most dangerous form of water pollution results from the dumping of poisonous chemical wastes into the lakes and rivers.These wastes are often colourless,odourless,and tasteless in the water but they can be deadly! What makes things worse is that the water bodies where these chemicals are dumped are often the source of drinking water for millions of people.
Some industries have been dumping toxic chemicals into the water supplies for years.The Great Lakes in North America have been referred to as a “chemical soup” because of the number of chemicals dumped into them.In fact,42 “toxic hot spots” have been identified in the Great Lakes where there are particular problems with the accumulation of toxic chemicals.Thirty-two percent of Canadians and thirteen percent of Americans live in the Great Lakes basin.These 40 million people are exposed to hundreds of potentially dangerous chemicals produced by industries.Many of these chemicals have been found in the bodies of fish and gulls that live in and around the Great Lakes.This proves that the chemicals are in the food chain.
The quality of the water is also threatened by pesticides(杀虫剂) used on farms.These chemicals,which protect the food supply from animal pests,disease,and weeds,are washed from farmers’ fields into rivers and lakes.
There is,however,some good news. Government studies indicate that the levels of many contaminants in the Great Lakes have been declining since the 1970s.Restrictions on the manufacture and use of mercury,many pesticides,and PCBs have resulted in reduced contaminant levels in fish.
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