For other uses: see DDT (disambiguation).

DDT was developed as the first of the modern insecticides early in World War II. It was initially used with great effect to combat mosquitoes spreading malaria, typhus, and other insect-borne human diseases among both military and civilian populations. The Swiss chemist Paul Hermann Müller was awarded the Nobel Prize in Physiology or Medicine in 1948 "for his discovery of the high efficiency of DDT as a contact poison against several arthropods".

DDT is a highly lipophilic colorless solid with a weak, chemical odor that is nearly insoluble in water but has a good solubility in most organic solvents, fat, and oils. DDT is also known under the chemical names 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane and dichloro-diphenyl-trichloroethane (from which the abbreviation was derived).

In the early 1960s, an American activist named Rachel Carson published the book Silent Spring, which alleged that DDT caused cancer and harmed bird reproduction by thinning egg shells. The book resulted in a large public outcry which eventually led to the pesticide being banned for agricultural use in the USA, and was one of the signature events in the birth of the environmental movement. It was subsequently banned for use in many countries in the 1970s due to its allegedly negative environmental impact. There is still a great controversy regarding the extent of this impact and the reduced use of DDT to fight human diseases.

Properties

DDT is a colourless crystalline substance which is practically insoluble in water but highly soluble in fats and most organic solvents.

DDT is created by the reaction of trichloroethanol with chlorobenzene (C₆H₅Cl). Trade or other names for DDT include Anofex, Cesarex, Chlorophenothane, Dedelo, p,p'-DDT, Dichlorodiphenyltrichloroethane, Dinocide, Didimac, Digmar, ENT 1506, Genitox, Guesapon, Guesarol, Gexarex, Gyron, Hildit, Ixodex, Kopsol, Neocid, OMS 16, Micro DDT 75, Pentachlorin, Rukseam, R50 and Zerdane.

DDT is persistent in the environment. It has a reported half life of 26 days in river water (U.S. EPA, 1989), but 15 years in most soils. It is also immobile in most soils. Routes of loss and degradation include runoff, volatilization, photolysis and biodegradation (aerobic and anaerobic). These processes generally occur slowly. Breakdown products in the soil environment are DDE (1,1-dichloro-2,2-bis(p-dichlorodiphenyl)ethylene) and DDD (1,1-dichloro-2,2-bis(p-chlorophenyl)ethane), which are also highly persistent and have similar chemical and physical properties.

DDT has potent insecticidal properties; it kills by opening sodium channels in insect neurons, causing the neuron to fire spontaneously. This leads to uncontrolled spasming and eventual death. Insects with certain mutations in their sodium channel gene may be resistant to DDT and other similar insecticides.

History

DDT was first synthesized in 1873, but its insecticidal properties were not discovered until 1939, by the Swiss scientist Paul Hermann Müller, who was awarded the 1948 Nobel Prize in Physiology and Medicine for his efforts. DDT is the best-known of a number of chlorine-containing pesticides used in the 1940s and 1950s. It was used extensively during World War II by Allied troops and certain civilian populations to control insect typhus and malaria vectors (as a result nearly eliminating typhus). Civilian suppression used a spray on interior walls, which kills mosquitoes that rest on the wall after feeding to digest their meal; resistant strains are repelled from the area. Entire cities in Italy were dusted to control the typhus carried by lice. DDT also sharply reduced the incidence of biting midges in Great Britain.

DDT was responsible for eradicating malaria from Europe and North America. Though today malaria is thought of as a tropical disease, it was more widespread prior to an extensive malaria eradication program carried out in the 1950s. Though this program was highly successful worldwide (reducing mortality rates from 192 per 100,000 to a low of 7 per 100,000), it was less effective in tropical regions due to the continuous life-cycle of the parasite and poor infrastructure. It was not pursued aggressively in sub-Saharan Africa due to perceived difficulties, with the result that mortality rates there were never reduced to the same dramatic extent, and now constitute the bulk of malarial deaths worldwide, especially following the resurgence of the disease as a result of microbe resistance to drug treatments and the spread of the deadly malarial variant caused by Plasmodium falciparum.

DDT was also extensively used as an agricultural insecticide after 1945. DDT spraying in agricultural contexts was often orders of magnitudes greater in quantity than that employed for public health purposes, which required as little as 2g/m² of DDT; by comparison, a single cotton field may have used a ton of DDT.

By the 1950s, in some uses, doses of DDT and other insecticides had to be doubled or tripled as resistant insect strains developed. In addition, the evidence began to grow that the chemical became more concentrated at higher levels in the food chain.

The banning of DDT

In 1962 Rachel Carson's book Silent Spring was published. The book argued that pesticides, and especially DDT, were poisoning both wildlife and the environment and also endangering human health. The public reaction to Silent Spring launched the modern environmental movement, and DDT became a prime target of the growing anti-chemical and anti-pesticide movements during the 1960s. However, to date, there is not a single known human death from DDT poisoning.

DDT was first banned from use in Norway and Sweden in 1970 and was not banned in the United Kingdom until 1984. During the late 1960's, pressure grew within the United States for a ban on DDT. In January 1971, the US District Court of Appeals ordered Ruckelshaus to begin the deregistration procedure for DDT. Initially, after a six-month review process, the EPA's first Administrator William Ruckelshaus rejected an outright ban, citing studies from the EPA's internal staff that stated that DDT was not an imminent danger to human health and wildlife. However, the findings of these staff members were criticized, as they were performed mostly by economic entonomologists inherited from the United States Department of Agriculture, whom many environmentalists felt were biased towards agribusiness and tended to minimize concerns about human health and wildlife. The decision not to ban thus created public controversy.

The EPA held seven months of hearings in 1971-1972, with scientists giving evidence both for and against the use of DDT. At the end of the hearings, the hearing examiner, Edmund Sweeney, ruled that the scientific evidence provided no basis for banning DDT. In the summer of 1972 Ruckelshaus reviewed evidence collected during the agency's hearings as well as reports prepared by two DDT study groups (the Hilton and Mrak Commissions ) that had both come to the opposite conclusion. He did not actually attend any of the EPA commission's hearings however, and according to his aides did not read any transcripts of it. Ruckelshaus overturned Sweeny's ruling and announced a ban on virtually all uses of DDT in the U.S., where it was classified in EPA Toxicity Class II. Ruckelshaus argued that the pesticide was "a warning that man may be exposing himself to a substance that may ultimately have a serious effect on his health." (Tren & Bate, 2004)(Milloy, 1999).

Statements made by Charles Wurster, the chief scientist for the Environmental Defense Fund, the organization chiefly behind the move to ban DDT, support the view that it was important for the EPA and environmentalists to succeed in banning DDT, so that their success would afford them greater powers to act in other areas. Wurster is quoted in the Seattle Times of October 5, 1969, as saying: "If the environmentalists win on DDT, they will achieve a level of authority they have never had before. In a sense, much more is at stake than DDT." (Tren & Bate, 2004).

The 1970s ban in the U.S. took place amid a climate of public mistrust of the scientific and industrial community, following such fiascos as Agent Orange, Love Canal, and use of the hormone diethylstilbestrol (DES). In addition, the fact that the bald eagle was placed on the endangered species list in large part because of the overuse of DDT was also a strong factor leading to its banning in the United States.

As of 2004, DDT continues to be used in other (primarily tropical) countries where mosquito-borne malaria and typhus are greater health problems than DDT's potential toxicity. Use of DDT to control mosquitoes is primarily done inside buildings and through inclusion in household products and selective spraying; this greatly reduces the risk of strong environmental impact.

Groups such as the WWF officially support a gradual phase-out and eventual total ban on DDT, arguing that DDT is environmentally persistent and thus any use represents a hazard. [1]

Critics of the ban argue that one should not confuse use with abuse; i.e. that most of the alleged problems stem from over-application, so do not justify banning responsible use for disease control purposes.

Environmental impact

DDT is an organochlorine. Some organochlorines have been shown to have weak estrogenic activity, that is, they are chemically similar enough to estrogen to trigger hormonal responses in contaminated animals. This sort of activity has been observed in DDT in laboratory studies involving mouse and rat test subjects, but available epidemiological evidence does not indicate that these effects have occurred in humans as a result of DDT exposure.

DDT and its metabolic products accumulate through the food chain, with apex predators such as raptors having a higher concentration of the chemicals than other animals sharing the same environment. In particular, DDT has been cited as a major reason for the decline of the bald eagle in the 1950's and 1960's, which was of particularly symbolic interest in that the eagle is the national bird of the United States. Other bird species are relatively unaffected; for example, the chicken.

DDT is not particularly toxic to humans, compared to other widely used pesticides. In particular, no link to cancer has yet been established. Numerous studies have been conducted, including one in which humans voluntarily ingested 35 mg of DDT daily for almost two years. DDT is often applied directly to clothes and used in soap, with no demonstrated ill effects.

Controversy remains in some scientific circles over DDT's actual toxicity, however. Some scientists have protested that the laboratory animal studies done in 1969 (and which led to the banning of DDT in much of the developed world) which showed that DDT caused an increase in liver cancer was inconsistent with observations in the wild, given that DDT had been used widely during the preceding three decades with no increase in liver cancer in any of the human populations among whom it had been sprayed.

When the World Health Organization investigated the 1969 mouse study, they found that both experimental and control groups had developed a surprising number of tumors. Further investigation revealed that the food fed to both groups were moldy and contained aflatoxin, a carcinogen. When the tests were repeated using uncontaminated foods, neither group developed abnormal numbers of tumors.

DDT and malaria

Malaria infects between 300 million and 500 million people every year. The World Health Organisation estimates that around 1 million people die from malaria every year. Most of those deaths (90%) occur in Africa and mostly in children under the age of 5. The economic impact includes costs of health care, working days lost to sickness, days lost in education, decreased productivity due to brain damage from cerebral malaria, and loss of investment and tourism (Tren & Bate, 2004).

Most of the prior use of DDT was in agriculture. Current use for disease control require only a small fraction of the amounts used previously and is much less likely to cause environmental problems. Such limited use of DDT has not become ineffective due to resistance in areas where it is used inside homes. Swaziland, Mozambique and Ecuador are other examples of countries that have very successfully reduced malaria incidence with DDT. However, its use has been greatly limited in many other countries due to reluctance by aid agencies in the developed world to fund DDT spraying and opposition from Western environmental groups. (Africa fighting malaria FAQ, 2005).

There are insecticide alternatives to DDT, and Vietnam is often mentioned as a country that has seen a continued decline in malaria cases after involuntarily switching from DDT in 1991. However, Vietnam's neighbour Thailand has continued to use DDT and has a much smaller malaria rate despite similar conditions. The insecticide alternatives are generally more expensive, which limits their use in poor nations and in situations where anti-malarial efforts are already underfunded. It is doubtful that they are more environmentally friendly or as efficient, easy to use and safe for humans as DDT. Bhutan, Myanmar, Sri Lanka, and India have seen large increases in malaria cases after the ban (Roberts, 2004)(Africa fighting malaria FAQ, 2005).

In the period from 1934-1955 there were 1.5 million cases of malaria in Sri Lanka resulting in 80,000 deaths. After an extensive anti-mosquito program with DDT there were only 17 cases reported in 1963 and the program was halted. Malaria later rebounded to 600,000 cases in 1968 and the first quarter of 1969. Some proponents of DDT consider this an example of environmentalism trumping public wellbeing even though the use of DDT was ended more due to the lack of continuing need than due to environmental concerns. Spraying with DDT was resumed but many of the local mosquitos had acquired resistance to DDT in the interim, presumably because of the continued use of DDT for crop protection, and so it was not nearly as effective as it had been previously. Switching to the more-expensive malathion in 1977 reduced the malaria infection rate to 3,000 by 2004.

In many African nations, the problems resulting from malaria are viewed as greater than the potential dangers of DDT. After South Africa stopped using DDT in 1996, the number of malaria cases in KwaZulu Natal province rose from 8,000 to 42,000 cases. By 2000, there had been an approximate 400 percent increase in malaria deaths. Today, thanks to DDT, the number of deaths from malaria in the region is less than 50. South Africa could afford and did try newer alternatives to DDT but they proved less effective (Tren & Bate, 2004). Uganda also began permitting its use in anti-malarial efforts despite a threat that its agricultural products to Europe could be banned as a result. (EU warns Uganda over plans to use DDT to fight malaria, 2005). The country states it cannot achieve its development goals without first eliminating malaria with DDT. The GDP shows a striking co-relation between malaria and poverty, where malaria is estimated to reduce per capita growth by 1.3 percent per annum. (Lirri & Ntabadde, 2005).

Malaria cases increased in South America after the ban. Only Ecuador, which has continued to use DDT, has seen a reduction in the number of malaria cases in recent years. Other mosquito-borne diseases are also on the rise. Until the 1970s, DDT was used to eradicate the aedes aegypti mosquito from most tropical regions of the Americas. The reinvasion of aedes aegypti since then has brought devastating outbreaks of dengue fever, dengue hemorrhagic fever, and a renewed threat of urban yellow fever (Bate, 2001).

Dr. Elizabeth Whelan, the president of the American Council on Science and Health claims that 60 million or more lives "have been needlessly lost since the ban on DDT took effect. ... It's a real tragedy that DDT has been so demonized over the years by activist organizations such as Environmental Defense and the regulatory bodies that they have duped." Whelan's estimates come from estimates that 2.5 million people die of malaria each year: mostly African children and pregnant mothers. According to the U.N. World Health Organization (WHO), malaria kills one child under the age of 5 every 30 seconds. Some detractors have raised questions about the credibility of the American Council on Science and Health, since according to the Congressional Quarterly's Public Interest Profiles Whelan's organization received more than 75 percent of their funding from the chemical and pharmaceutical industry. See the article on ACSH for more details.

External links

Environmental impact

• Microbial Degradation of Pesticides
• DDT and its Derivatives - Environmental Aspects
• Areobic pathway of DDT metabolization
• Anaeobic pathway of DDT metabolization
• Pesticide residues in food 2000 : DDT
• Pesticide residues in food - 1984
• Environmental Fate Evaluation of DDT, Chlordane and Lindane
• DDT, Eggshells, and Me
• EPA : Pesticides and Public Health

Malaria and DDT

• Time to Spray DDT, a New York Times column by Nicholas Kristof
• 100 things you should know about DDT
• Malaria clock
• Millions Dead of Malaria Because of Ban, More Deaths Likely
• Africa Malaria Day and DDT in Uganda
• The Mosquito Killer, a New Yorker article about Fred Soper by Malcolm Gladwell
• How many must die?
• Rachel Carson's Ecological Genocide
• Better Living Through Chemistry
• The DDT ban myth
• Malaria and the DDT Story
• Who's Kidding W.H.O.? Strange Doings
• In Defense of DDT
• The Malaria Project at the Center for Study of Responsive Law
• Without DDT, malaria bites back
• Malaria and DDT
• Murderous ban on DDT defended by scientists
• Adolf Hitler: My parts per million in his downfall

References

• Africa fighting malaria FAQ Retrieved Feb. 16, 2005.
• Bailey, Ronald (12 June 2002). Silent Spring at 40: Rachel Carson’s classic is not aging well Reason Online,
• Bate, Roger (24 April 2001). Without DDT, malaria bites back spiked-online.com
• EU warns Uganda over plans to use DDT to fight malaria (February 2, 2005) EUbusiness.com
• Lirri, Evelyn & Ntabadde, Asha (February 15, 2005). Experts Defend DDT Use Allafrica.com
• Lundholm, C. E. (1997) DDE-induced eggshell thinning in birds: Effects of p,p′-DDE on the calcium and prostaglandin metabolism of the eggshell gland. Comparative Biochemistry and Physiology Part C: Pharmacology, Toxicology and Endocrinology Volume 118, Issue 2 , October 1997, Pages 113-128
• Milloy, Steven J. (1999). 100 things you should know about DDT. Retrieved Feb. 16, 2005.
• Risebrough, Robert W. (1998). Endocrine Disrupters and Bald Eagles: A Response.
• Roberts, Donald R. (2004). PhD Testimony, United States Senate, Committee on Foreign Relations.
• Tren, Richard & Bate, Roger (2004). South Africa's War against Malaria: Lessons for the Developing World. Cato Policy Analysis No. 513.