The term pollution is derived from the Latin pollutus, which means to be made foul, unclean, or dirty. Anything that corrupts, degrades or makes something less valuable or desirable can be considered pollution. There is, however, a good deal of ambiguity and contention about what constitutes a pollutant. Many reserve the term for harmful physical changes in our environment caused by human actions. Others argue that any unpleasant or unwanted environmental changes whether natural or human-caused constitute pollution. This broad definition could include smoke from lightening-ignited forest fires, ash and toxic fumes from volcanoes, or bad-tasting algae growing naturally in a lake. Some people include social issues in their definition of pollution, such as noise from a freeway, visual blight from intrusive billboards, or cultural pollution when the worst aspects of modern society invade a traditional culture. As you can see, these definitions depend on the observer's perspective...