DDT

DDT (dichloro-diphenyl-trichloro-ethane) is an insecticide that was first used worldwide in 1946 to increase agricultural production and to reduce disease vectors (carriers). Although formulated in 1874, DDT's insecticidal properties were not discovered until 1936. Paul Muller of Switzerland won the Nobel Prize for that discovery in 1948.

The neurotoxin DDT interferes with the action potential along neurons. It affects insects and vertebrates by means of this same primary mechanism. It has a greater effect on insects simply because they are smaller and absorb it more readily. At a high enough dosage, DDT can have as detrimental an effect on vertebrates, including humans. Symptoms of DDT toxicity include apprehension, headache, anorexia, nausea, hyper-excitability, muscle fibrillation, respiratory arrest, coma, and death.

DDT is relatively inert and stable, and is nearly insoluble in water. This combination of attributes allows it to be stored easily in fat. As a result, fatty tissues act as biological magnifiers by slowing the excretion of DDT after it is absorbed. Like other fat-soluble compounds, DDT is transferred up the food chain more efficiently than are water-soluble compounds, thereby achieving higher concentrations among carnivores. Because DDT toxicity is a function of concentration, this biomagnification is most likely to cause problems for a predator species, such as eagles, ospreys, and falcons, at the end of a long food chain.

During the 1950s, United States efforts to control Dutch elm disease consisted primarily of killing its vector, elm bark beetles, with DDT. Soon after, communities in the Midwest and Northeast began to notice an accumulation of dead robins and other birds. Roy Barker discovered that earthworms were consuming DDT sprayed on the elm trees which was seeping into the soil. Robins in turn ate the earthworms, receiving a lethal dose of DDT from as few as eleven worms. Birds that did not die often suffered reduced fertility.

Other predatory bird species also appeared to decline during the 1940s and 1950s. Hawk Mountain, Pennsylvania, is a stopover for many migrating hawks and eagles. From 1935 to 1939, 40 percent of the eagles were yearlings. Between 1955 and 1959, only 20 percent were yearlings. The percentage of juveniles in eagle populations along the Mississippi, Illinois, and Susquehanna Rivers also declined after 1947. In 1950, there were two hundred mating pairs of ospreys at the mouth of the Connecticut River; by 1970 the number had dropped to six. One study suggested that DDT interfered with calcium deposition in eggshells, thereby potentially reducing the reproduction rate of susceptible bird species. However, subsequent studies found no correlation between DDT levels and eggshell thickness either in nature or in controlled experiments.

DDT may adversely affect whole ecosystems. In the 1950s, the Canadian government instituted a policy of eradicating the spruce budworm. This native insect attacks several species of evergreens. Millions of acres of the Northwest Miramichi watershed were sprayed to save balsams, the pulp industry's most valuable cash crop. Soon trout and salmon began to turn up dead along the streams. Their prey, caddis fly larvae, stonefly nymphs, and blackfly larvae, were being killed along with the spruce budworm. In 1959, the watershed produced less than a third of the smolt (young salmon) it had produced before the most recent spraying.

Rachel Carson's book Silent Spring, was released in 1962 and documented the adverse effects of DDT on the environment. Her book catalyzed the modern American environmental movement. Over the years a variety of objections have been made to her characterization of DDT as an absolute detriment to human and ecological health. For example, studies on the role of DDT in breast cancer have yielded ambiguous results. It is also possible that the correlation between DDT use and the decline of fish and bird populations was caused by the simultaneous use of other pollutants such as PCBs.

The Environmental Protection Agency banned DDT in 1971 as a potential human carcinogen. Since then most countries have banned the chemical for agricultural purposes. However, DDT continues to be a cheap and effective way to kill mosquitoes that transmit malaria, requiring lower concentrations than those for agricultural use.

In 2000, more than 100 governmental and nongovernmental agencies gathered to formulate a treaty to completely phase out DDT and eleven other pollutants. The World Health Organization warned that a sudden worldwide ban on DDT could result in an epidemic of malaria in countries that cannot afford other effective insecticides. Until safe, affordable alternatives are developed, DDT will continue to be used in many countries where malaria is endemic, and its residues will be found in soils and human breast milk around the world. span>

see also Carson, Rachel; Pesticides; Silent Spring.

Brian R. West

Bibliography

Carson, Rachel. Silent Spring. Boston, MA: Houghton Mifflin, 1962.

DDT and Its Derivatives: Environmental Aspects. Geneva, Switzerland: World Health Organization, 1989.

Internet Resources

Note for the Press No. 15. World Health Organization. <http://www.who.org>.

DDT (Dichlorodiphenyl trichloroethane)

DDT, dichlorodiphenyl trichloroethane, was synthesized in 1874, but its insecticidal properties were first identified in 1939 by P.H. Mueller. He received the Nobel Prize for his discovery, which coincided with the outbreak of World War II, when DDT was used extensively to keep soldiers free of head and body lice. DDT also proved very effective against mosquitoes, which transmit a serious global human disease, malaria, as well as yellow fever. After the war, DDT was developed extensively as an agricultural pesticide.

DDT has an extremely low volatility and may be the least soluble chemical known, which makes it extremely persistent in soils and aquatic sediments. It has relatively low acute mammalian toxicity and is toxic to a wide range of insects. It kills insects by affecting the transmission of nerve impulses, probably by influencing the delicate balance of sodium and potassium within the neuron.

More than four billion pounds of DDT have been used throughout the world since 1940. Production in the United States peaked in 1961 when 160 million pounds were manufactured. Large economic benefits have resulted from the control of many serious agricultural and forestry pests, including Colorado potato beetle, cotton boll weevil, and pests of fruit, vegetables, corn, and tobacco. In forestry, its greatest success occurred in combating spruce budworm and gypsy moth. However, its major impact lay in the control of mosquitoes that transmit malaria, as well as body lice and fleas; many millions of lives have been saved through these uses.

DDT's potentially adverse environmental effects were brought to public attention by Rachel Carson in her book Silent Spring (1963). Carson emphasized the great persistence of DDT in soils and river sediments and focused on the bioconcentration of DDT through the trophic levels of food chains. One result of the bioaccumulation of DDT was the thinning of the eggshells of predatory birds such as bald eagles, peregrine falcons, golden eagles, hawks, and pelicans, resulting in embryonic death and decreasing populations of these species. DDT bioconcentrates because it has low water solubility and high fat solubility, that is, a high lipid-to-water partition coefficient (e.g., it can concentrate into fatty tissues from water). In the 1960s large DDT residues in human tissues and human milk began to be reported, probably from the consumption of food containing traces of DDT. DDT in body fat was reported to cause convulsions in laboratory rats; it also reached human fetuses by crossing the placenta. However, few serious effects on human health were officially recorded.

Many pests began to develop resistance to DDT, necessitating the progressive use of more of the pesticide to control such pests. In 1972 the use of DDT in the United States was banned on environmental grounds, including the widespread contamination of the environment with DDT, its ability to bioconcentrate, and its effects on endangered bird species.

Suitable alternatives to DDT were found in the United States and other industrialized countries that also banned its use in the 1970s. However, tropical developing countries that used inexpensive DDT extensively to control malaria and other pests faced a significant dilemma. Moreover, although the United States no longer used DDT, it continued to manufacture and export very large quantities to developing countries and how much DDT is still used. It is difficult to say with accuracy exactly which countries still use DDT. Some countries use it illegally, others only in small quantities. And information is often impossible to obtain because questionnaires from an organization like the World Health Organization (WHO) generally have only a 50 to 60 percent response rate. Nonetheless, it is known that poorer countries in Central and South America, Africa, and Asia, as well as the large nation of China, continue to utilize sizable quantities of DDT.

see also Bioaccumulation; Carson, Rachel; Federal Insecticide, Rodenticide and Fungicide Act; Integrated Pest Management; Persistent Organic Pollutants (POPS); Pesticides.

Internet Resource

"World Wildlife Federation DDT Report." Available from http://www.worldwildlife.org/toxics.

Clive A. Edwards

DDT

DDT (dichloro-diphenyl-trichloroethane) is perhaps the most recognized of all insecticides because it's use helped reveal the many hazards associated with synthetic (man-made) pesticides. This colorless, odorless, insoluble toxic pesticide contains up to fourteen chemical compounds. It is known for its ability to eradicate (destroy) pesky insects such as flies, lice, and mosquitoes, as well as agricultural pests. Although first synthesized in 1874 by German chemist Othmar Zeidler, DDT was not used as an insecticide until 1939. It was then that Swiss scientist Paul Hermann Muller (1899-1965) discovered its insect-killing properties.

DDT is very durable. In some applications it is effective for 12 years. Water cannot wash it away and it resists breakdown by light and air. Its strength and persistence have resulted in DDT's transfer to "non-target" living organisms. Once in an ecosystem (an inter-related community of animals, plants, and bacteria), it can pass on from crops to birds and from water to fish, eventually affecting the whole food chain.

DDT Exposure

When ingested by humans, DDT is stored in body fats and can be passed on to nursing babies. Low levels of DDT in humans are harmless but large concentrations can cause severe health problems such as liver cancer. When applied to an insect, DDT is easily absorbed through the body surface. After attacking the nervous system, DDT causes paralysis. Some insects have a resistance to DDT, thereby making the insecticide ineffective. These resistant insects are able to reproduce and pass this trait on to their offspring.

Many problems arise when larger animals are exposed to DDT or eat smaller animals that have ingested (eaten) the toxin (poison). For example, while DDT is more toxic to fish than birds, it still causes widespread bird deaths. With high levels of exposure, DDT causes convulsions and paralyzes the birds' nerve centers. In smaller concentrations, it can weaken their egg shells and can cause sharp declines in the species' reproductive rate. DDT ingestion by peregrine falcons is thought to have caused their almost complete extinction in most regions of the United States.

The Benefits of DDT

The benefits of DDT were demonstrated in the 1940s when it was used in World War I (1939-1945) to clear out mosquito-infested areas prior to invasion. Even after the war, the use of DDT in the United States almost completely wiped out malaria (an infectious disease characterized by severe chills and fever) and yellow fever. In tropical areas, the use of DDT has helped save millions of lives that would otherwise have been lost to disease. DDT was also routinely applied as a crop dust or water spray on orchards, gardens, fields, and forests. At one point it was registered for use on 334 agricultural crops.

In 1962 Rachel Carson's (1907-1964) landmark book, Silent Spring, exposed the dangers of unregulated pesticide use. Spurred by public pressure, state and federal governments turned their attention to the regulation of pesticides. In 1972, the United States Environmental Protection Agency (EPA) banned the use of DDT. Today, DDT is restricted in the United States, Europe, and Japan. However, many other countries still use DDT widely for malaria control, delousing, and the eradication of other disease-spreading insects.

DDT or 2,2-bis( p -chlorophenyl)-1,1,1,-trichloroethane, chlorinated hydrocarbon compound used as an insecticide . First introduced during the 1940s, it killed insects that spread disease and fed on crops, and Swiss scientist Paul Müller was awarded the 1948 Nobel Prize in Physiology or Medicine for discovering (1939) DDT's insecticidal properties. DDT, however, is toxic to many animals, including humans, and it is not easily degraded into nonpoisonous substances and can remain in the environment and the food chain for prolonged periods. By the 1960s its harmful effects on the reproductive systems of fish and birds were apparent in the United States, where the insecticide had been heavily used for agricultural purposes. After the United States banned its use in 1972, the affected wildlife population recovered, particularly the bald eagle and the osprey. Nevertheless, DDT use continues in parts of the world, particularly in tropical regions, to control the mosquitoes that spread malaria . In 2001 the Stockholm Convention on Persistent Organic Pollutants called for the phasing out of DDT once a cost-effective alternative becomes available.

Bibliography: See D. Kinkela, DDT and the American Century (2011).

DDT (dichlorodiphenyltrichloroethane) An organochlorine compound that was first synthesized in 1874. In 1939 the Swiss chemist Paul Hermann Müller (1899–1965) discovered its insecticidal properties, for which he was awarded the 1948 Nobel Prize in Physiology or Medicine. DDT was used widely to control arthropod parasites of humans and then as an agricultural and horticultural insecticide. Its use was curtailed, and abandoned in many countries, because the chemical stability that allowed it to remain effective for long periods also caused its accumulation along food-chains and because target insects were acquiring resistance to it.

DDT Dichlorodiphenyltrichloroethane; a colourless organic crystalline compound, (ClC₆H₄)₂CH(CCl₃), made by the reaction of trichloromethanal with chlorobenzene. DDT is the best known of a number of chlorine-containing pesticides used extensively in agriculture in the 1940s and 1950s. The compound is stable, accumulates in the soil, and concentrates in fatty tissue, reaching dangerous levels in carnivores high in the food chain. Restrictions are now placed on the use of DDT and similar pesticides.

DDT (dichlorodiphenyltrichloroethane) Organic compound used as an insecticide. It acts as a contact poison, disorganizing the nervous system. Effective against most insect pests, it proved to have long-lasting toxic effects and many species developed resistance. It is now banned in many countries.

DDT (chlorophenothane, dicophane) n. a powerful insecticide that was formerly widely used. The quantities now present in the environment – in the form of stores accumulated in animal tissues – have led to its use being restricted.

DDT • abbr. dichlorodiphenyltrichloroethane, a synthetic organic compound introduced in the 1940s as an insecticide and now widely banned.

DDT dichlorodiphenyltrichloroethane (insecticide)