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HUMAN HEALTH AND ENVIRONMENT: ACID RAIN
Acid rain is precipitation that has fallen through acidic air pollutants, particularly those containing sulfur dioxides and nitrogen dioxides. This precipitation, in the form of rain, snow, or fog, has a more acidic composition than does unpolluted precipitation. When introduced into lakes and ponds, acid rain gradually acidifies the water. When the acid content of the water reaches a certain level, plant and animal life cannot survive. Ironically, lakes and ponds that are acidified become a crystal-clear deep blue, giving the illusion of beauty and health.
Sources of Acid Rain
More than 95 percent of acid rain originates in human actions, chiefly the burning of fossil fuels. The single greatest source of acid rain in the United States is coal-fired power plants, followed by ore smelters and steel mills.
When these and other industries burn fuels, the sulfur and nitrogen in the emissions combine with the oxygen and sunlight in the air to become sulfur dioxide and nitrogen oxides (precursors of sulfuric acid and nitric acids, respectively). Small acid particles are then carried by the wind and combine with moisture to produce acidic rain or snow. Because of higher concentrations of sunlight in the summer months, rain is more strongly acidic in the summertime. Additionally, the rain or snow that falls at the beginning of a storm is more acidic than that which falls later. The ability of a lake to cleanse itself and neutralize its acidity depends on several factors, the most critical of which is bedrock geology.
Effects of Acid Rain
The damage caused to lake and pond habitats is not the worst of the problems created by acid rain. Each year, it is responsible for the destruction of millions of trees in forests in Europe and North America. Scientists have concluded that 75 percent of Europe\'s forests are now experiencing damaging levels of sulfur deposition by acid rain. Forests in every country on the continent are affected.
Doctors believe that acid rain also aggravates and may even cause bronchitis, asthma, and other respiratory problems. People with emphysema and those with a history of heart disease may also suffer from exposure to acid rain. In addition, it may be hazardous to a pregnant woman\'s unborn child.
Acidic precipitation can cause metals such as aluminum, cadmium, lead, and mercury to leach (dissolve and filter) out of the soil. If these metals make their way into water or food supplies (particularly fish), they can cause cancer in humans who consume them.
Acid rain is also responsible for crop damage, which, in turn, contributes to world hunger. Laboratory experiments showed that acid rain can reduce seed yield by up to 23 percent. Actual crop losses are being reported with increasing frequency. A final consequence of acid rain is the destruction of public monuments and structures, with billions of dollars in projected building damage each year.
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GENERAL HEALTH
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