Nitrates

NITRATES

NITRATES. Nitrate (NO₃) is a compound of the elements nitrogen and oxygen. Nitrates are important to all living systems. Plants, especially, require it to develop and produce seeds. Nitrogen, the main component of Earth's atmosphere, is a relatively inert substance. To be useful, it must be converted into active forms. Lightning and radiation create nitrates in the atmosphere, where rainstorms carry them to the ground. Bacteria on roots of crops such as alfalfa and clover fix nitrogen in the soil. Microorganisms form nitrates as they break down animal matter. Since the early twentieth century, nitrates have been produced industrially.

Nitrates are present naturally in sewage and in some mineral deposits. Chile's Atacama Desert is the world's leading supplier of the mineralized form. Approximately 86 percent of the nitrate produced in the United States is used for fertilizer, though the chemicals have other uses. Potassium nitrate (KNO 3), also known as saltpeter, is the key ingredient in gunpowder. Saltpeter is formed naturally in warm climates by bacteria decomposing accumulations of excreta and animal refuse. Contact among putrefying material, alkaline soil, plant ashes, air, and moisture causes nitrates to form and penetrate the ground. After evaporation of rainwater, saltpeter appears as white powder on the surface.

Since the temperate climates of Europe and North America did not favor the formation of saltpeter, its supply was a vital concern for American colonists. European countries obtained saltpeter from India. When the American Revolution cut off the colonies from this source, some colonial governments offered bounties and established "artificial nitrate works, " without much success. France saved the Continental Army from running out of gunpowder after having taken great pains to develop its own domestic supply. In the early nineteenth century, salt-peter was discovered in large quantities in caves in Kentucky and Tennessee. This resource helped fuel the Confederate armies during the American Civil War, though 90 percent of their powder likely came from foreign sources that managed to get through the Union blockade. After this period, the United States and Europe imported nitrate from Chile.

As the nineteenth century progressed into the twentieth, demand for nitrate fertilizers increased dramatically. Many countries experimented with methods of converting atmospheric nitrogen. All processes seemed expensive and complex. The outbreak of World War I drove the United States to attempt its own synthetic production by 1917. In preparation, a hydroelectric dam was built at Muscle Shoals, Alabama. Soon after, the process introduced in Germany by Fritz Haber in 1912 proved its superiority and the power plant was abandoned. In the 1930s, it became the foundation of the Tennessee Valley Authority.

Nitrates have become an environmental concern. Elevated levels of nitrogen flowing down the Mississippi River enter the Gulf of Mexico and nourish algal blooms. When algae die and decompose, they consume oxygen, depleting that vital element from the water. Fish and other creatures suffocate in affected areas that can cover thousands of square miles, causing problems for commercial fishing and other coastal industries. Sources of the nitrogen include sewage treatment water, industrial wastes, and atmospheric pollutants; large loads also come from livestock operations and nitrate fertilizer runoff from farm-land. Nitrates infiltrate ground water as well as surface waters. According to the Environmental Protection Agency, when nitrates are present in quantities in excess of ten milligrams per liter, the water supply can pose a potentially fatal threat to infants under six months and to young and pregnant animals.

BIBLIOGRAPHY

Hill, Michael J., ed. Nitrates and Nitrites in Food and Water. New York: Ellis Horwood, 1991.

Keleti, Cornelius. Nitric Acid and Fertilizer Nitrates. New York: Dekker, 1985.

Wilson, W. S., A. S. Ball, and R. H. Hinton. Managing Risks of Nitrates to Humans and the Environment. Cambridge: Royal Society of Chemists, 1999.

Robert P. Multhauf

Christine M. Roane

See also Fertilizers .