On the Earth's surface, the atmosphere, land, and water contain compounds that were not present in them centuries ago. This is because air, soil, and water pollution have reached into almost every part of the globe in the past 100 years. Today, sensitive equipment can detect tiny amounts of chemicals in the environment. Many scientists believe these instruments will soon show there is no spot on Earth free from pollution.
Before waste management experts can clean up large or small amounts of pollution, they must understand the specific substances that contaminate the environment. Contamination assessment has two purposes: to evaluate the overall pollution problem at a site and to measure the types and amounts of these hazardous substances.
Contamination assessment is done using equipment but also by simply observing a site. Sensitive equipment detects minute amounts of compounds, but the body's senses are also useful in evaluating contamination. People living within sight of factory smokestacks or alongside rivers covered by a toxic sheen need only their eyes and nose to detect pollution. Sight, taste, and smell often provide the first warnings of environmental dangers. Some contaminants, however, are not detectable by the senses, and analysis must be done on reliable equipment.
The antipollution laws set forth by the Clean Air and the Clean Water Acts of the 1970s could not be met without accurate equipment and trained scientists. Increase in knowledge about the chemicals in air, land, and water came by using improved machines that could measure various chemicals at low concentrations. The engineers who designed the equipment faced one challenge that is characteristic of environmental sampling: Polluting chemicals are usually part of complex mixtures. For example, a gram of soil has thousands of compounds and many thousand living microorganisms. Environmental engineers had to design instruments capable of finding chemicals lurking at minuscule levels within these complex mixtures.
Scientists who study the environment by analyzing environmental samples view the world from the ecosystem level down to molecular and even atomic levels. They must track small amounts of chemicals because many pollutants cause harm to living tissue in amounts as low as one hundredth of a milligram (mg), so it is critical to have the ability to measure low concentrations. Contamination is now measured routinely to the molecular level in environmental laboratories.
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Essay, Research Paper: 
