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29. In two or three well-developed paragraphs, explain how pollutin can come from both natural sources and from human activities. Provide examples of each.
It is true that pollution can come from both natural sources and from human activities. Although we believe that pollution is entirely caused by people, there are some pollutants that occur naturally in the environment. These pollutants usually become hazardous to health when they are concentrated above their normal levels in the environment. For example, in some areas the radioactive gas radon may seep into buildings, where it becomes concentrated. Since it is an odorless gas, people may unknowingly breathe it in. This particular gas causes thousands and thousands of cancer deaths every year in the U.S. Dust, soot, and other particulates are the most common pollutants from natural sources. Particulates are particles in the air that are small enough to breathe into the lungs. They can cause conditions such as chronic bronchitis and emphysema. Another important type of pollution from natural sources are heavy metals. These include the elements arsenic, cadmium, lead, and mercury, and they occur naturally in rocks and soil. Most of these heavy metals can cause nerve damage when they are ingested beyond their threshold dose.
On the other hand, there is pollution caused from human activities. Human activities release thousands of types of chemicals into the environment, but we know little about them and their health effects. Although, there have been recent improvements to help prevent pollution from human activities. In the U.S., most vehicles and factories now have pollution-control devices. Despite all of these preventions, air pollution is still a major health problem. Burning fuels in vehicles, home furnaces, power plants, and factories introduces large amounts of pollutants into the air. These pollutants can include carbon monoxide and many different kinds of particulates. Many premature deaths are also a result of gasoline and coal burning. We are also exposed to industrial chemicals every day. Often, these chemicals can become toxic and dangerous for health. Lastly, much of the pollution in our environment is a result of inadequate waste disposal. Wastewater from cities can carry oil and dozens of toxic chemicals into our waterways, and waste incineration plants can emit toxic products into the air. Even though many methods of disposing waste have improved, problems remain.