With many of the world's fastest growing countries in the process of industrializing and modernizing, there is reason to believe that destruction will continue to increase well beyond that year. DAir Pollution A significant portion of industry and transportation is based on the burning of fossil fuels, such as gasoline. As these fuels are burned, chemicals and particulate matter are released into the atmosphere. Although a vast number of substances contribute to air pollution, the most common contain carbon, sulfur, and nitrogen. These chemicals interact with one another and with ultraviolet radiation in sunlight in various dangerous ways. Smog, usually found in urban areas with large numbers of automobiles, is formed when nitrogen oxides react with hydrocarbons in the air to produce aldehydes and ketones. Smog can cause serious health problems. When sulfur dioxide and nitrous oxide are transformed into sulfuric acid and nitric acid in the atmosphere and come back to earth in precipitation, they form acid rain. Acid rain is a serious global problem because few species are capable of surviving in the face of such acidic conditions. Acid rain has made numerous lakes so acidic that they no longer support fish populations. Acid rain is also thought to be responsible for the decline of many forest ecosystems worldwide. Germany's Black Forest has suffered dramatic losses, and recent surveys suggest that similar declines are occurring throughout the eastern United States. Water Pollution Estimates suggest that nearly 1.5 billion people lack safe drinking water and that at least 5 million deaths per year can be attributed to waterborne diseases. Water pollution may come from point or nonpoint sources. Point sources discharge pollutants at specific locations-from, for example, factories, sewage treatment plants, or oil tankers.The technology exists for point sources of pollution to be monitored and regulated, although political factors may complicate matters. Nonpoint sources-runoff water containing pesticides and fertilizers from acres of agricultural land, for example-are much more difficult to control. Pollution arising from nonpoint sources accounts for a majority of the contaminants in streams and lakes. With almost 80 percent of the planet covered by oceans, people have long acted as if those bodies of water could serve as a limitless dumping ground for wastes. Raw sewage, garbage, and oil spills have begun to overwhelm the diluting capabilities of the oceans, and most coastal waters are now polluted. Beaches around the world are closed regularly, often because of high amounts of bacteria from sewage disposal, and marine wildlife is beginning to suffer. FGroundwater Depletion Water that seeps through porous rocks and is stored beneath the ground is called groundwater. Worldwide, groundwater is 40 times more abundant than fresh water in streams and lakes, and although groundwater is a renewable resource, reserves are replenished relatively slowly. In the United States, approximately half the drinking water comes from groundwater. Presently, groundwater in the United States is being withdrawn approximately four times faster than it is being naturally replaced. The Ogallala Aquifer, a huge underground reservoir stretching under eight states of the Great Plains, is being drawn down at rates exceeding 100 times the replacement rate, suggesting that agricultural practices depending on this source of water may have to change within a generation. When groundwater is depleted in coastal regions, oceanic salt water commonly intrudes into freshwater supplies. Saltwater intrusion is threatening the drinking water of many areas along the Gulf and Atlantic coasts. The EPA has estimated that, on average, 25 percent of usable groundwater is contaminated, although in some areas as much as 75 percent is contaminated. Contamination arises from leaking underground storage tanks, poorly designed industrial waste ponds, and seepage from the deep-well injection of hazardous wastes into underground geologic formations. Because groundwater is recharged and flows so slowly, once polluted it will remain contaminated for extended periods.
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