DDT

Introduction

DDT is the abbreviation for the chemical compound-D ichloro-D iphenyl-T richloroethane. The compound is not naturally occurring. First made over a century ago, it was not until about 50 years later that DDT was shown to be an insecticide—an agent that is lethal to insect species. It is also a nerve poison, although as of 2008 the full details of DDT’s toxic activity are not known.

Originally used during World War II (1939–1945), DDT was sanctioned for use to control crop insect pests after the war. It soon became very popular all over the world. However, only a decade later, the widespread use of DDT had led to the development of resistance to the compound by some target insect species. As well, public concerns of the potential environmental hazards of DDT arose, largely from the publication of Rachel Carson’s book Silent Spring. As a result, DDT was banned for most uses in the United States in 1972.

However, some uses of DDT have continued. For example, the ability of the compound to control mosquito populations has made DDT useful in programs to lessen the spread of the mosquito-transmitted disease malaria. The controlled use of DDT in anti-malaria programs in Africa has been endorsed by the World Health Organization (WHO), despite the compound’s now-rec-ognized health hazards.

Historical Background and Scientific Foundations

DDT was first synthesized in 1874. However, its insecticidal properties were not known until 1942. Then, Paul Muller, who was a chemist at the Swiss company J. P. Geigy (now called Novartis), and who was engaged in research to find new insecticides to protect crop plants, demonstrated that spraying species of flies, gnats, and the Colorado beetle with DDT was lethal. He also demonstrated that the killing was due to the poisoning of the insect’s nervous system. His accomplishments were recognized by the awarding of the 1948 Nobel Prize in physiology or medicine.

By then, the power of DDT to quell the spread of insect-borne diseases had become well-known. The first demonstration of DDT’s potency was dramatic. In 1943, an outbreak of typhus (a sometimes fatal disease caused by two types of a bacteria called Rickettsia that is spread to humans via the bite of a flea or louse) occurred in Naples, Italy. A military commander ordered the use of DDT to treat over one million citizens. Within three weeks the outbreak had been controlled.

The ability of DDT to kill mosquitoes was soon discovered, which almost immediately led to the extensive use of the compound to control malaria (a disease caused by a parasite called Plasmodium, which is spread to humans via the bite of an infected mosquito). Since malaria then afflicted over 300 million people each year and killed at least three million, DDT was hailed as a wonder compound and soon became the most common option in programs designed to halt the disease.

In addition, DDT was licensed to use as an agricultural insecticide. By the late 1940s, DDT sprays and paints were being used routinely by farmers and homeowners to control insect pests.

However, even then, the consequences of extensive DDT use were evident. A 1946 study by the U.S. Department of Agriculture, which was not widely publicized at the time, reported on the development of resistance to DDT by some species of flies and recommended the use of alternate compounds. The agency also published a 1949 study that documented the presence of DDT in milk from cows that had been sprayed with the chemical. Although it recommended that DDT not be used on dairy cattle, the USDA did not consider limiting the sale of the chemical.

The popularity of DDT grew through the 1950s. By 1959, use of DDT in the United States peaked at almost 36,000 tons.

In 1962 the book Silent Spring was published. In the work, author Rachel Carson (1907–1964) warned of the consequences of the widespread and extensive use of DDT on the natural environment and humans, given that relatively little was known of the interactions of DDT with living creatures. The book proved to be prophetic; research over the next decade linked DDT exposure to adverse effects in humans, animals, and birds, both in the short-term and more chronically. Examples of possible longer-term effects include reproductive difficulties, improper development of a fetus, and cancer of the liver and lungs. In a well known example, bald eagle populations in the United States declined due to the accumulation of the pesticide in the bird’s tissue, which led to the production of eggs with thinner, more fragile shells.

A major reason for DDT’s chronic effects is bioaccumulation—the accumulation in tissues of one species that is passed onto species higher in the food chain. As a result, creatures including the bald eagle ingest a much higher level of the toxin than they otherwise would and store the poison in fatty tissues, where it can persist.

As well, DDT can persist in the environment for years. It degrades very slowly, if at all, in soil and breaks

WORDS TO KNOW

HYDROPHOBIC: Compounds do not dissolve easily in water, and are usually non-polar. Oils and other long hydrocarbons are hydrophobic.

INSECTICIDE: A chemical substance used to kill insects.

MALARIA: A group of parasitic diseases common in tropical and subtropical areas, characterized by attacks of chills, fever, and sweating.

TERATOGENIC EFFECT: The combined consequences of the consumption of a harmful substance on a developing fetus.

down in water only after one or several months. Degradation is not necessarily the end of trouble, since two breakdown products can also persist for a long time and cause similar adverse effects as DDT.

The public outcry resulting from Carson’s book and increasing evidence of the environmental and health consequences of DDT led in 1972 to the banning of DDT for all but public health emergencies. Similar actions around the globe led to a plunge in DDT use.

According to estimates from the United Nations Environment Programme (UNEP), the annual world use of DDT declined from almost 70,000 tons in 1981 to only 2,800 tons by 1990.

Impacts and Issues

The ban on all but select uses of DDT has led to a resurgence in some species that had been threatened, as the compound has been gradually removed from the environment over the decades since 1972. An example is the bald eagle, whose recovery in the United States coincided with the ban on DDT.

As of 2008, DDT use is confined almost exclusively to the control of mosquito populations in malaria eradication programs in Africa. The use of DDT as a malaria control declined during the 1990s and was almost completely curbed in 2004 with the implementation of the global treaty on Persistent Organic Pollutants. However, development of mosquito resistance to the alternate chemicals lead some African nations such as South Africa to resume the use of DDT. In 2006 the WHO endorsed the reintroduction of DDT as a malaria control.

Agencies including WHO acknowledge that this use must be carefully controlled, since research has established that the structure of DDT mimics that of several hormones. The levels of DDT can trigger detrimental hormone-induced effects in the womb, following birth, and into adulthood.

The risks of DDT use need to be weighed against the human and economic benefits of lessening the deaths from malaria of over 900,000 Africans annually. Most of the dead are children under the age of 5 years.

See Also Insecticide Use; Predator-Prey Relationships

BIBLIOGRAPHY

Books

Carson, Rachel. Silent Spring. New York: Mariner Books, 2002.

Roberts, Rodger. The Green Killing Fields: The Need for DDT to Defeat Malaria and Reemerging Diseases. Washington: AEI Press, 2007.

Periodicals

McGinn, Anne P. “Malaria, Mosquitoes, and DDT: The Toxic War against a Global Disease.” World Watch15 (2002): 10-17.

Brian D. Hoyle

DDT (dichlorodiphenyltrichloroethane)

DDT is a synthetic chemical compound once used widely in the United States and throughout the world as a pesticide (a chemical substance used to kill weeds, insects, rodents, or other pests). It is probably best known for its dual nature: although remarkably effective in destroying certain living things that are harmful to plants and animals, it can also be extremely dangerous to humans and the environment.

The abbreviation DDT stands for dichlorodiphenyltrichloroethane. DDT was first produced in the laboratory in 1873. For more than half a century, it was little more than a laboratory curiosity—a complicated synthetic (produced by scientists) compound with no apparent use.

Then, in 1939, Swiss chemist Paul Hermann Müller (1899–1965) discovered that DDT was highly poisonous to insects. The discovery was very important because of its potential for use in killing insects that cause disease and eat agricultural crops. For his work, Müller was awarded the Nobel Prize in medicine in 1948.

DDT as an insecticide

During and after World War II (1939–45), DDT became extremely popular among public health workers, farmers, and foresters. Peak production of the compound reached 386 million pounds (175 million kilograms) globally in 1970. Between 1950 and 1970, 22,204 tons (20,000 metric tons) of DDT was used annually in the former Soviet Union. The greatest use of DDT in the United States occurred in 1959, when 79 million pounds (36 million kilograms) of the chemical were sprayed.

By the early 1970s, however, serious questions were being raised about the environmental effects of DDT. Reports indicated that harmless insects (such as bees), fish, birds, and other animals were being killed or harmed as a result of exposure to DDT. The pesticide was even blamed for the near-extinction of at least one bird, the peregrine falcon. Convinced that the environmental damage from DDT was greater than the compound's possible benefits, the U.S. Environmental Protection Agency banned the use of DDT in the United States in 1973. Its use in certain other countries has continued, however, since some nations face health and environmental problems quite different from those of the United States.

DDT's environmental problems arise because of two important properties: persistence and lipid-solubility. The term persistence refers to the fact that DDT does not break down very easily. Once the pesticide has been used in an area, it is likely to remain there for many years. In addition, DDT does not dissolve in water, although it does dissolve in fatty or oily liquids. (The term lipid-solubility is used because fats and oils are

members of the organic family known as lipids.) Since DDT is not soluble in water, it is not washed away by the rain, adding to its persistence in the environment. But since DDT is lipid-soluble, it tends to concentrate in the body fat of animals. The following sequence of events shows how DDT can become a problem for many animals in a food web.

DDT is used today in such African nations as Zimbabwe and Ethiopia to control mosquitoes and the tsetse fly. These two insects cause serious diseases, such as malaria and sleeping sickness. DDT saves lives when used on the tsetse fly in Lake Kariba in Zimbabwe. But once sprayed on

the lake, DDT does not disappear very quickly. Instead, it is taken up by plants and animals that live in the lake. Studies have shown that the concentration of DDT in the lake itself is only 0.002 parts per billion. But algae in the lake have a concentration of 2.5 parts per million. Other members of the food web also accumulate DDT from the organisms they eat. Fish that feed on the algae have DDT levels of 2 parts per million; tiger-fish and cormorants (both of whom live on the algae-eating fish) have levels of 5 and 10 parts per million, respectively; and crocodiles (who eat both tiger-fish and cormorants) have levels as high as 34 parts per million.

Bans on the use of DDT in the United States and some other nations have given ecosystems in those countries a chance to recover. Populations of peregrine falcons, for example, have begun to stabilize and grow once again. Many other animal species are no longer at risk from DDT. Of course, poor nations continue to face a more difficult choice than does the United States, since they must balance the protection of the health of their human populations against the protection of their natural ecosystems.

In December 2000, in a convention organized by the United Nations Environment Program, 122 nations agreed to a treaty banning twelve very toxic chemicals. Included among the twelve was DDT. However, the treaty allowed the use of DDT to combat malaria until other alternatives become available. Before it can take effect, the treaty must be ratified by 50 of the nations that agreed to it in principle.

DDT

DDT ranks among the most infamous acronyms in history. During the mid-twentieth century, its effectiveness at killing insects made it one of the miracle products of wartime investments in science and technology. Yet within thirty years, many industrialized countries banned the synthetic insecticide due to fears of its long-term effects on humans and wildlife. At the turn of the twenty-first century, the devastating resurgence of malaria across the developing world reignited debates over the ethics of using DDT.

The chemical compound that is DDT, dichlorodiphenyl-trichloroethane, was first synthesized in 1873, but not until 1939 did Swiss chemist Paul Müller discover its insecticidal properties. The U.S. military used DDT during World War II to protect soldiers and civilians from the destructive insect-borne diseases typhus and malaria. DDT's persistence and its broad spectrum of action made it extremely successful at killing insects over a long period, in small doses, and at low cost. In response to civilian demand, the U.S. government made the celebrated chemical available to the public in 1945, despite private concerns among federal scientists of potential long-term hazards. The agricultural and public health promise of DDT led to mass aerial spraying programs, and Müller won the 1948 Nobel Prize in physiology or medicine. Production by U.S. companies increased from 10 million pounds in 1944 to more than 100 million pounds in 1951.

Rachel Carson burst the bubble of confidence concerning the safety of DDT in 1962 with her best-selling exposé of the overuse of synthetic chemical pesticides, Silent Spring. The book publicized scientific evidence of the toxic effects of DDT on humans and animals, including nervous system dysfunction, reproductive abnormalities, and cancer. It explained how DDT's insolubility in water and fat-solubility enable it to persist in the soil and water, enter the food chain, and accumulate in the fatty tissues of non-target organisms such as the bald eagle, whose plummeting numbers were linked to DDT-induced eggshell thinning. Silent Spring also showed how mosquitoes and other target insect populations develop genetic resistance to DDT, thereby undermining its efficacy.

Carson criticized the arrogance of entomologists who presumed they could control pests by waging chemical warfare. She made a strong ethical argument for the need to respect the other creatures with which humans share the earth. Although some critics accused her of privileging wildlife over people, she testified to Congress on behalf of "the right of the citizen to be secure in his own home against the intrusion of poisons applied by other persons" (Lear 1997, p. 454). Spurred by increasing evidence of DDT's carcinogenicity, Congress banned the sale of DDT in the United States in 1972. Within three decades DDT was banned in thirty-four countries, and severely restricted in thirty-four others. It continued to be used in several developing nations, primarily in the malaria belt.

Since the 1970s, malaria has become one of the deadliest infectious diseases in the world, killing at least 1.1 million people each year. Children under age five comprise more than half the victims. Many environmentalists and health experts blame malaria's huge resurgence on the overuse of both chemical insecticides and anti-malarial drugs, which led their respective targets—anopheles mosquitoes and plasmodium parasites—to develop genetic resistance. Anti-DDT groups advocate preventive methods, including the use of mosquito nets dipped in the nontoxic insecticide permethrin and the cultivation of fish that consume mosquito larvae, as part of a systematic approach to the disease. In their opinion, DDT should be used only as a last resort due to its well-documented negative effects.

In contrast a strong opposition movement argues that DDT is still the cheapest, most effective anti-malarial measure, and that its declining use is responsible for the recent resurgence of malaria. Pro-DDT groups condemn environmentalists for scaring developing countries from using the chemical, and for caring more about bald eagles than suffering children. They point to scientific studies that fail to confirm evidence of long-term risks of exposure to DDT, and contend that it serves as a crucial insect repellent even in places where mosquitoes have become resistant. From their perspective, it is unethical not to utilize DDT as a first resort against malaria, because its life-saving capacity for millions of people outweighs any potential negative environmental or human health effects.

Despite such conflicting outlooks, a compromise was struck in 2001, when delegates from 127 nations signed an international treaty to phase out twelve toxic, persistent, fat-soluble chemicals, including DDT. After intense debate, developing nations received exemptions permitting them to continue using DDT against the mosquito vectors of malaria until safer, affordable substitutes become available. The Stockholm Convention on Persistent Organic Pollutants entered into force on May 17, 2004.

CHRISTINE KEINER

SEE ALSO Agricultural Ethics;Carson, Rachel;Food Science and Technology.

BIBLIOGRAPHY

Carson, Rachel. (1962). Silent Spring. Boston: Houghton Mifflin. A must-read for anyone interested in the impact of synthetic pesticides on human and environmental health.

Lapkin, Ted. (2003). "DDT and the New Colonialists." Quadrant 47: 16–19. Argues for the use of DDT for malaria control.

Lear, Linda. (1997). Rachel Carson: Witness for Nature. New York: Holt. The definitive biography of Carson.

McGinn, Anne Platt. (2002). "Malaria, Mosquitoes, and DDT." WorldWatch 15: 10–17. Argues against the use of DDT for malaria control.

Russell, Edmund P. (1999). "The Strange Career of DDT: Experts, Federal Capacity, and Environmentalism in World War II." Technology and Culture 40: 770–796. Presents new historical evidence about early DDT research.

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