Dichlorodiphenyltrichloroethane

OVERVIEW

Dichlorodiphenyltrichloroethane (DI-klor-oh-DI-fee-nul-TRI-klor-oh-eth-ane) is a colorless crystalline or white powdery material with a slight aromatic odor. It is far better known by its acronym, DDT. DDT was first synthesized in 1873 by German chemist Othmar Zeidler (1859–1911) as a project for his doctoral thesis. However, the compound was essentially ignored by other chemists and remained a laboratory curiosity for more than sixty years.

KEY FACTS

OTHER NAMES:

DDT; see Overview for additional names

FORMULA:

(ClC₆H₄)₂CHCCl₃

ELEMENTS:

Carbon, hydrogen, chlorine

COMPOUND TYPE:

Halogenated hydrocarbon (organic)

STATE:

Solid

MOLECULAR WEIGHT:

354.49 g/mol

MELTING POINT:

108.5°C (227.3°F)

BOILING POINT:

260°C (500°F)

SOLUBILITY:

Insoluble in water; slightly soluble in ethyl alcohol; soluble in ether, acetone, and benzene

Then, in 1939, Swiss chemist Paul Hermann Müller (1899–1965) discovered that DDT is very effective in killing a wide variety of insects including the common housefly, the mosquito, the louse, and the Colorado beetle. Müller's discovery gave medical workers a powerful tool in preventing a host of infectious diseases carried by these insects, including bubonic plague, dengue fever, elephantitis, encephalitis, leishmaniasis, malaria, sleeping sickness, typhus, yaws, and yellow fever. The compound was used widely during World War II (1939–1945) to control insects in both military and civilian facilities. It was credited for reducing the spread of what is probably the world's most common infectious disease, malaria. Once common throughout the world, malaria was essentially eliminated in Europe and North America as a result of the use of DDT.

In addition to its public health applications, DDT has long been a popular agricultural pesticide. The compound kills many of the insects and other pests that attack crops and reduce the productivity that can be achieved by farmers.

The fate of DDT took a dramatic turn in the 1960s, however, largely as the result of a single book, Silent Spring, written by American biologist and environmentalist Rachel Carson (1907–1964). The book described a situation in which the use of pesticides such as DDT might become so common that the chemical begins to kill off other organisms, such as birds, as well as insects. Carson's book came at a time when scientific evidence of the environmental harm done by pes-ticides was just becoming available. The work was soon adopted by the growing environmental movement as a well-documented warning of what might happen if the uncontrolled use of pesticides did not end. People began to worry about the ill effects of DDT and other pesticides not only on the environment, but also on human health.

In 1972, the U.S. Environmental Protection Agency announced that DDT could no longer be used in the United States because of the risk it posed for human health and the environment. A number of other developed nations soon followed the EPA's action. In 2001, a conference sponsored by the United Nations, called the Stockholm Convention on Persistent Organic Pollutants, adopted a statement calling for the eventual elimination of a dozen pesticides, known as "the dirty dozen," including DDT. Because of its effectiveness against malaria and other infectious diseases, DDT was given a waiver for use by public health officials in nations where the compound had not been banned.

DDT is also known by the following names: 1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane; 1,1′-(2,2,2-trichloroethylidene)bis (4-chlorobenzene); 1,1,1-trichloro-2,2-di(4-chlorophenyl)ethane; 1,1,1-trichloro-2,2-di(p-chlorophenyl) ethane; 1,1-bis(4-chlorophenyl)-2,2,2-trichlorethane; 1,1-bis(p-chlorophenyl)-2,2,2-trichlorethane; 2,2,2-trichloro-1,1-bis (4-chlorophenyl) ethane; and 4,4′-dichlorodiphenyltrichloroethane.

HOW IT IS MADE

DDT is prepared commercially in the reaction between chloral (CCl₃CHO) and chlorobenzene (C₆H₅Cl): CCl₃CHO + 2C₆H₅Cl→(ClC₆H₄)₂CHCCl₃.

COMMON USES AND POTENTIAL HAZARDS

DDT is no longer used in the United States and other nations where it has been banned. It is still used in a number of developing nations for the control of infectious diseases spread by insects that can be killed by DDT. Malaria is the most important of these diseases.

The health hazards posed by DDT are still the subject of intense debate among agricultural scientists, public health experts, and other authorities. Abundant evidence exists to show that DDT can have a variety of harmful effects on animals, ranging from marine algae to bald eagles. The compound may also have serious health effects on humans, including mild to serious damage to the liver, kidneys, and central nervous system. DDT has also been classified as a probable carcinogen by the U.S. Environmental Protection Agency although no definite evidence for that classification is yet available.

Interesting Facts

• Peak use of DDT in the United States occurred in 1958 when about 35 million kilograms (80 million pounds) of the compound were sprayed on U.S. farmlands.
• Extensive data exists to support the advantages of using DDT against malaria. For example, there were more than 2.8 million cases of malaria in Sir Lanka in 1948, before the introduction of DDT. Six years later, after the compound had been put into use in the country, the number of malaria cases dropped to 17. Five years later, after the use of DDT had been discontinued, the number of malaria cases rose to 2.5 million.
• Countries that have banned the use of DDT include Australia (1967), Sweden (1970), Cuba (1970), Germany (1974), Poland (1976), the United Kingdom (1984), Chile (1985), South Korea (1986), Switzerland (1986), and Canada (1989).
• DDT is still manufactured legally in only three countries: China, India, and Indonesia. It may also be produced, although illegally, in Mexico.
• DDT often occurs in combination with two other related compounds, dichlorodiphenyldichloroethane (DDD) and dichlorodiphenyldichloroethylene (DDE).

On the other hand, critics have pointed out that little scientific evidence exists for the belief that DDT is a serious health threat to humans. In one experiment, humans took capsules containing small amounts of DDT every day for 18 months and experienced no measurable health effects as a result. Some observers argue that the benefits gained from using DDT as an agricultural and public health pesticide—benefits such as the elimination of diseases like malaria—far exceed the risks posed by the chemical to human health and the environment.

FOR FURTHER INFORMATION

Carson, Rachel. Silent Spring. Boston: Houghton Mifflin, 1962. "DDT." National Safety Council. http://www.nsc.org/library/chemical/ddt.htm (accessed on December 29, 2005).

"DDT (dichlorodiphenyltrichloroethane)." Extoxnet. http://ace.orst.edu/cgi-bin/mfs/01/pips/ddt.htm (accessed on December 29, 2005).

Dunlap, Thomas. DDT: Scientists, Citizens, and Public Policy. Princeton, NJ: Princeton University Press, 1983.

Edwards, J. Gordon, and Steven Milloy. "100 Things You Should Know about DDT." JunkScience.com. http://www.junkscience.com/ddtfaq.htm (accessed on December 29, 2005).

Karaim, Reed. "Not So Fast with the DDT: Rachel Carson's Warnings Still Apply." American Scholar (June 2005): 53-60.

McGinn, Anne Platt. "Malaria, Mosquitoes, and DDT: The Toxic War against a Global Disease." World Watch (May 1, 2002): 10-17.

"ToxFAQs™ for DDT, DDE, and DDD." Agency for Toxic Substances and Disease Registry. http://www.atsdr.cdc.gov/tfacts35.html (accessed on December 29, 2005).