Ddt

For other uses, see DDT (disambiguation).

DDT
IUPAC name	4,4\'-(2,2,2-trichloroethane- 1,1-diyl)bis(chlorobenzene)
Identifiers
CAS number	[50-29-3]
SMILES	Clc1ccc(cc1)C(c2ccc(Cl)cc2)C(Cl)(Cl)Cl
Properties
Molecular formula	C14H9Cl5
Molar mass	354.49 g/mol
Density	1.55 g/cm³ Record of DDT in the GESTIS Substance Database from the BGIA, accessed on {{{Date}}}
Melting point	108.5–109 °C
Boiling point	185–187 °C (at 7 Pa)
Hazards
EU classification	Yes
Main hazards	T, N
R-phrases	R25 R40 R48/25 R50/53
S-phrases	(S1/2) S22 S36/37 S45 S60 S61
LD50	113 mg/kg (rat)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

DDT (from its trivial name, Dichloro-Diphenyl-Trichloroethane) is one of the best known synthetic pesticides. It is a chemical with a long, unique, and controversial history.

First synthesized in 1874, DDT\'s insecticidal properties were not discovered until 1939. In the early years of World War II, DDT was used with great effect to control mosquitoes spreading malaria, typhus, and other insect-borne diseases among both military and civilian populations. The Swiss chemist Paul Hermann Müller of Geigy Pharmaceutical 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."NobelPrize.org: The Nobel Prize in Physiology or Medicine 1948 Accessed July 26, 2007. After the war, DDT was made available for use as an agricultural insecticide, and soon its production and use skyrocketed.Environmental Health Criteria 9: DDT and its derivatives, World Health Organization, 1979.

In 1962, Silent Spring by American biologist Rachel Carson was published. The book catalogued the environmental impacts of the indiscriminate spraying of DDT in the US and questioned the logic of releasing large amounts of chemicals into the environment without fully understanding their effects on ecology or human health. The book suggested that DDT and other pesticides may cause cancer and that their agricultural use was a threat to wildlife, particularly birds.Carson, Rachel (1962). Silent Spring. Boston: Houghton Mifflin.  Its publication was one of the signature events in the birth of the environmental movement. Silent Spring resulted in a large public outcry that eventually led to most uses of DDT being banned in the US in 1972.J. Paull, Rachel Carson, A Voice for Organics - the First Hundred Years, Journal of Bio-Dynamics Tasmania, (86) 37-41, 2007. DDT was subsequently banned for agricultural use worldwide, but its limited use in disease vector control continues to this day in certain parts of the world and remains controversial.Paull, John, Toxic Colonialism, New Scientist, (2628) 25, 03 November 2007.

Along with the passage of the Endangered Species Act, the US ban on DDT is cited by scientists as a major factor in the comeback of the bald eagle in the contiguous US.Stokstad E (2007). "Species conservation. Can the bald eagle still soar after it is delisted?". Science 316 (5832): 1689–90. doi:10.1126/science.316.5832.1689. PMID 17588911. 

Contents 1 Properties and chemistry 2 History 2.1 Use in the 1940s and 1950s 2.2 Concerns about environmental effects 2.3 Restrictions on usage 2.4 U.S. ban 3 Environmental impact 4 Effects on human health 4.1 Toxicity 4.1.1 Acute 4.1.2 Chronic 4.2 Cancer 4.2.1 Breast cancer 4.3 Developmental and reproductive toxicity 5 DDT use against malaria 5.1 Overall effectiveness of DDT against malaria 5.2 Mosquito resistance to DDT 5.3 Residents\' resistance to use of DDT 5.4 Human exposure associated with DDT spraying for disease vectors 5.5 Criticism of restrictions on DDT use 5.6 Alternatives to DDT 5.6.1 DDT versus other insecticides 5.6.2 DDT versus non-chemical vector control 6 References 7 External links 7.1 US Government 7.2 Toxicity 7.3 Environmental impact 7.4 Politics and DDT 7.5 Malaria and DDT 7.6 Chemical

Properties and chemistry

DDT is an organochlorine insecticide, similar to the pesticides dicofol and methoxychlor. It is a highly hydrophobic, colorless, crystalline solid with a weak, chemical odor. It is nearly insoluble in water but has a good solubility in most organic solvents, fats, and oils.

DDT does not occur naturally, and is produced by the reaction of chloral (CCl₃CHO) with chlorobenzene (C₆H₅Cl) in the presence of a sulfuric acid catalyst. The major product of this reaction is the p,p isomer pictured in this article, but the o,p isomer (in which one of the chlorine atoms is shifted around the aryl group) is also generated in significant amounts. Commercial DDT is actually a mixture of several closely related compounds, with p,p-DDT generally comprising 77% of the formulation, o,p-DDT 15%, and related compounds making up the balance. The major metabolites and breakdown products of DDT in the environment are dichlorodiphenyldichloroethylene (DDE) which produced by the dehydrohalogenation of DDT, and dichlorodiphenyldichloroethane (DDD). Both DDE and DDD are found in small amounts in commercial DDT samples.

DDT is moderately toxic, with a rat LD₅₀ of 113 mg/kg,World Health Organization, The WHO Recommended Classification of Pesticides by Hazard, 2005. and has potent insecticidal properties; it kills by opening sodium ion channels in insect neurons, causing the neuron to fire spontaneously. This leads to spasms and eventual death. Insects with certain mutations in their sodium channel gene may be resistant to DDT and other similar insecticides. DDT resistance is also conferred by up-regulation of genes expressing cytochrome P450 in some insect species.Denholm I, Devine GJ, Williamson MS (2002). "Evolutionary genetics. Insecticide resistance on the move". Science 297 (5590): 2222–3. doi:10.1126/science.1077266. PMID 12351778. 

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.

History

Commercial product containing 5% DDT

First synthesized in 1874 by Othmar Zeidler,Othmar Zeidler (1874). "Verbindungen von Chloral mit Brom- und Chlorbenzol". Berichte der deutschen chemischen Gesellschaft 7 (2): 1180 - 1181. doi:10.1002/cber.18740070278.  DDT\'s 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.

Use in the 1940s and 1950s

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 in Europe and the Pacific as well as certain civilian populations to control the insect vectors for typhus and malaria (nearly eliminating typhus as a result). 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, and was used extensively as an agricultural insecticide after 1945.

DDT played a small role in the final elimination of malaria in Europe and North America, as malaria had already been eliminated from much of the developed world before the advent of DDT through the use of a range of public health measures and generally increasing health and living standards.Bad Blood, Kim Larsen, OnEarth, Winter 2008. One CDC physician involved in the United States\' DDT spraying campaign said of the effort that "we kicked a dying dog."Shah, Sonia “Don’t Blame Environmentalists for Malaria,” The Nation. April 2006. But in countries without these advances, it was critical in their eradication of the disease.

In 1955, the World Health Organization commenced a program to eradicate malaria worldwide, relying largely on DDT. Though this program was initially highly successful worldwide (reducing mortality rates from 192 per 100,000 to a low of 7 per 100,000),http://blumberg-serv.bio.uci.edu/past%20teaching/bio2B-sp2005/DDT-Amy.ppt resistance soon emerged in many insect populations as a consequence of widespread agricultural use of DDT. In many areas, early victories against malaria were partially or completely reversed, and in some cases rates of transmission even increased.Chapin G, Wasserstrom R (1981). "Agricultural production and malaria resurgence in Central America and India". Nature 293 (5829): 181–5. doi:10.1038/293181a0. PMID 7278974.  The program was successful in eliminating malaria only in areas with "high socio-economic status, well-organized healthcare systems, and relatively less intensive or seasonal malaria transmission".Sadasivaiah, Shobha; Tozan, Yesim & Breman, Joel G. (2007), "Dichlorodiphenyltrichloroethane (DDT) for Indoor Residual Spraying in Africa: How Can It Be Used for Malaria Control?", Am. J. Trop. Med. Hyg. 77 (Suppl 6): 249–263, <http://www.ajtmh.org/cgi/content/full/77/6_Suppl/249>

DDT was less effective in tropical regions due to the continuous life cycle of mosquitoes and poor infrastructure. It was not pursued at all in sub-Saharan Africa due to these perceived difficulties, with the result that mortality rates in the area 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. The goal of eradication was abandoned in 1969, and attention was focused on controlling and treating the disease. Spraying programs (especially using DDT) were curtailed due to concerns over safety and environmental effects, as well as problems in administrative, managerial and financial implementation, but mostly because mosquitoes were developing resistance to DDT. Efforts were shifted from spraying to the use of bednets impregnated with insecticides.Rogan WJ, Chen A (2005). "Health risks and benefits of bis(4-chlorophenyl)-1,1,1-trichloroethane (DDT)". Lancet 366 (9487): 763–73. doi:10.1016/S0140-6736(05)67182-6. PMID 16125595. 

Concerns about environmental effects

Concerns about DDT\'s environmental effects grew out of direct personal observations, usually involving a marked reduction in bird life, later supplemented by scientific investigation. The first recorded group effort against the chemical involved several citizens, including one or more scientists, in Nassau County, New York. Their unsuccessful struggle to have DDT regulated was reported in the New York Times in 1957, and thereby came to the attention of the popular naturalist-author, Rachel Carson. New Yorker editor William Shawn urged her to write a piece on the subject, which developed into Silent Spring, her famous 1962 bestseller.Lear, Linda (1997). Rachel Carson: Witness for Nature. New York: Henry Hoyten. Despite the uproar surrounding Silent Spring, DDT remained in use.

A few years later, Carol Yannacone witnessed a fish kill at Yaphank Ponds following spraying by the Suffolk County Mosquito Control Commission. She convinced her husband Victor Yannacone, an attorney, to sue; their suit resulted in a local ban on DDT. Charles Wurster, a professor at nearby State University of New York at Stony Brook, had earlier noticed that the use of DDT on elms in New Hampshire killed birds without saving trees.Inventive Minds - Newsday.com A Bellport school teacher, Art Cooley, meanwhile was observing the decline of ospreys and other large birds around the Carmans River, and he too correctly suspected a DDT connection—the specific effect being extremely thin and fragile shells that prevent reproduction. The Yannacones joined forces with Wurster and Cooley to form the EDF in 1967, and launched a wider campaign against DDT. David Peakall measured DDE levels in peregrine eggs collected in Alaska from 1969 to 1973, and showed a strong inverse relationship between DDE content and eggshell thickness. The chemical industry claimed that shell thinning occurred too rapidly after the introduction of DDT in 1946 for DDT to be the cause. Peakall filled blown peregrine eggs collected from the critical period with solvent and measured DDE in the extracted lipids. DDE was present in sufficient concentrations to account for significant eggshell thinning in 1946 in Great Britain and as early as 1948 in California. Later, he would apply similar methods to California Condor eggshell fragments as evidence that this species was extremely sensitive to DDE. The efforts of this group of people eventually led to the US ban, and a spectacular recovery in once-endangered osprey and eagle populations.

Restrictions on usage

In the 1970s and 1980s, agricultural use of DDT was banned in most developed countries. DDT was first banned in Norway and Sweden in 1970 and the US in 1972, but was not banned in the United Kingdom until 1984. The use of DDT in vector control has not been banned, but it has been largely replaced by less persistent, and more expensive, alternative insecticides.

The Stockholm Convention, ratified in 2001 and effective as of 17 May 2004, outlawed several persistent organic pollutants, and restricted the use of DDT to vector control. The Convention was signed by 98 countries and is endorsed by most environmental groups. Recognizing that a total elimination of DDT use in many malaria-prone countries is currently unfeasible because there are few affordable or effective alternatives for controlling malaria, the public health use of DDT was exempted from the ban until such alternatives are developed. Regular updates on the continued need to use DDT and on global DDT production and use is available from the Stockholm Convention. [1] Malaria Foundation International states:

The outcome of the treaty is arguably better than the status quo going into the negotiations over two years ago. For the first time, there is now an insecticide which is restricted to vector control only, meaning that the selection of resistant mosquitoes will be slower than before.MFI second page. Malaria Foundation International. Retrieved on 2006-03-15.

As of 2006, DDT continues to be used in other (primarily tropical) countries where mosquito-borne malaria and typhus are serious health problems. Use of DDT in public health to control mosquitoes is primarily done inside buildings and through inclusion in household products and selective spraying; this greatly reduces environmental damage compared to the earlier widespread use of DDT in agriculture. It also reduces the risk of resistance to DDT.Is DDT still effective and needed in malaria control?. Malaria Foundation International. Retrieved on 2006-03-15. This use only requires a small fraction of that previously used in agriculture; for the whole country of Guyana, covering an area of 215,000 km², the required amount is roughly equal to the amount of DDT that might previously have been used to spray 4 km² of cotton during a single growing season.Roberts, Donald R.; Larry L. Laughlin, Paul Hsheih, and Llewellyn J. Legters (July-September 1997). "DDT, global strategies, and a malaria control crisis in South America". Emerging Infectious Diseases 3 (3): 295-302. PMID 9284373. 

U.S. ban

In 1962, Rachel Carson\'s book Silent Spring was published. The book argued that pesticides, including DDT, were poisoning both wildlife and the environment and were also endangering human health. Public reaction to Silent Spring launched the modern environmental movement in the United States, and DDT became a prime target of the growing anti-chemical and anti-pesticide movements during the latter 1960s.

During the late 1960s, pressure grew within the United States to effect a ban on DDT. In January 1971, the U.S. District Court of Appeals ordered William Ruckelshaus, the EPA\'s first Administrator, to begin the de-registration procedure for DDT. Initially, after a six-month review process, Ruckelshaus rejected an outright ban, citing studies from the EPA\'s internal staff stating 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 entomologists 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. In the summer of 1972, Ruckelshaus announced a ban on most uses of DDT in the U.S., where it was classified as an EPA Toxicity Class II substance. An exemption was allowed for public health uses under some conditions, but it appears that this exemption has never been invoked. Despite the domestic ban on its use, DDT continued to be produced in the US for foreign markets until as late as 1985, when over 300,000 kg were exported.Toxicological Profile: for DDT, DDE, and DDE. Chapter Five: Production, Import, Use, and Disposal. Agency for Toxic Substances and Disease Registry, September 2002.

The 1970s ban in the U.S. took place amid a climate of public mistrust of the scientific and industrial community, following such fiascoes as Agent Orange and use of the hormone diethylstilbestrol (DES). In addition, the placement of the bald eagle on the endangered species list was also a strong factor leading to its being banned in the United States. The overuse of DDT was found to be a major factor in the bald eagle population decline, a point confirmed in later studies and in the dramatic recovery of the eagle once DDT concentrations in their food were reduced—though the claim is disputed by latter-day DDT advocates including Steven Milloy.Milloy, S. J. (2006). Bald Eagle-DDT Myth Still Flying High. Retrieved on 2006-07-10.

Environmental impact

DDT is a persistent organic pollutant with a half life of 2-15 years, and is immobile in most soils. Its half life is 56 days in lake water and approximately 28 days in river water. 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.Toxicological Profile for DDT, DDE, and DDD; Chapter 6. ASTDR 2002 These products together are known as total DDT.

DDT and its metabolic products DDE and DDD magnify through the food chain, with apex predators such as raptors having a higher concentration of the chemicals, stored mainly in body fat, than other animals sharing the same environment. In the United States, human blood and fat tissue samples collected in the early 1970s showed detectable levels in all samples. A later study of blood samples collected in the latter half of the 1970s (after the U.S. DDT ban) showed that blood levels were declining further, but DDT or metabolites were still seen in a very high proportion of the samples. Biomonitoring conducted by the CDC as recently as 2002 shows that more than half of subjects tested had detectable levels of DDT or metabolites in their blood,National Report on Exposure to Environmental Chemicals. Centers for Disease Control and Prevention 2005. and of the 700+ milk samples tested by the USDA in 2005, 85% had detectable levels of DDE.USDA, Pesticide Data Program Annual Summary Calendar Year 2005, November 2006.

DDT is a toxicant across a certain range of phyla. In particular, DDT is a major reason for the decline of the bald eagle in the 1950s and 1960shttp://www.fws.gov/endangered/i/b/msab0h.html as well as the peregrine falcon. DDT and its breakdown products are toxic to embryos and can disrupt calcium absorption, thereby impairing eggshell quality.Toxicity Profiles, Ecological Risk Assessment | Region 5 Superfund | US EPA Studies in the 1960s and 1970s failed to find a mechanism for the hypothesized thinning.Milloy, S. J. (2006). Bald Eagle-DDT Myth Still Flying High. Retrieved on 2006-07-10. However, more recent studies in the 1990s and 2000s have laid the blame at the feet of DDE.Guillette, Louis J., Jr. (2006). Endocrine Disrupting Contaminants. Retrieved on 2007-02-02.Lundholm, C.E. (1997). "DDE-Induced eggshell thinning in birds". Comp Biochem Physiol C Pharmacol Toxicol Endocrinol (118).  Some studies have shown that although DDE levels have fallen dramatically, eggshell thickness remains 10–12 percent thinner than before DDT was first used.Division of Environmental Quality DDT is also highly toxic to aquatic life, including crayfish, daphnids, sea shrimp and many species of fish. DDT may be moderately toxic to some amphibian species, especially in the larval stages. In addition to acute toxic effects, DDT may bioaccumulate significantly in fish and other aquatic species, leading to long-term exposure to high concentrations.

Effects on human health

The effects of DDT on human health are disputed since studies have yielded conflicting results.

Toxicity

Acute

• DDT is classified as "moderately toxic" by the US National Toxicological Program and "moderately hazardous" by WHO.Pesticideinfo.org It is not considered to be acutely toxic, and in fact it has been applied directly to clothes or used in soap.World Health Organization (1997). Vector Control - Methods for Use by Individuals and Communities. Lice. Retrieved on 2006-03-15. Indeed, DDT has on rare occasions been administered orally as a treatment for barbiturate poisoning.Rappolt, RT (1973). "Use of oral DDT in three human barbiturate intoxications: hepatic enzyme induction by reciprocal detoxicants". Clin Toxicol 6 (2): 147-51. PMID 4715198. 

Chronic

• Occupational exposure to DDT was associated with reduced verbal attention, visuomotor speed, sequencing, and with increased neuropsychological and psychiatric symptoms in a dose-response pattern (ie, per year of DDT application) in retired workers aged 55–70 years in Costa Rica. DDT or DDE concentrations were not determined in this study.van Wendel de Joode B, Wesseling C, Kromhout H, Monge P, Garcia M, Mergler D (2001). "Chronic nervous-system effects of long-term occupational exposure to DDT". Lancet 357 (9261): 1014-6. doi:10.1016/S0140-6736(00)04249-5. PMID 11293598. 
• In one 1969 study, 24 cynomolgus monkeys and rhesus monkeys fed up to 16 mg/kg/day of DDT for 130 months were compared to a control group of 17 monkeys. Six animals in the dosed group died, and the study demonstrated "clear evidence of hepatic and CNS toxicity following long-term DDT administration." Although the exposed group developed two malignancies and three benign tumors, compared to zero in the control group, statistically this is still "inconclusive with respect to a carcinogenic effect of DDT in nonhuman primates."Takayama S, Sieber SM, Dalgard DW, Thorgeirsson UP, Adamson RH (1999). "Effects of long-term oral administration of DDT on nonhuman primates". Journal of Cancer Research and Clinical Oncology 125 (3-4): 219-25. doi:10.1007/s004320050266. PMID 10235477. 
• In an early study, humans voluntarily ingested 35 mg of DDT daily for about two years, and were then tracked for several years afterward. Although there was "suggestive evidence of adverse liver effects", no other adverse effects were observed.CUETO C Jr, DURHAM WF, HAYES WJ Jr (1956). "The effect of known repeated oral doses of chlorophenothane (DDT) in man". J Am Med Assoc 162 (9): 890-7. PMID 13366680. 
• Farmers exposed to DDT occupationally have an increased incidence of non-allergic asthma. Anthony J Brown, Pesticide Exposure Linked to Asthma, Scientific American, Sept 17, 2007.
• Organochlorine compounds in general and DDE specifically have been linked to diabetes.Jones, Oliver AH; Maguire, Mahon L & Griffin, Julian L (January 26, 2008), "Environmental pollution and diabetes: a neglected association", The Lancet 371: 287-288, <http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6T1B-4RNK38J-B-1&_cdi=4886&_user=4420&_orig=browse&_coverDate=02%2F01%2F2008&_sk=996280390&view=c&wchp=dGLbVtb-zSkzS&md5=49ceb153cf41f91572ac41664bcf057e&ie=/sdarticle.pdf> A study of Native Americans exposed to DDE primarily from eating contaminated fish found that elevated blood DDE levels were associated with an increased incidence of diabetes. These results are consistent with previous studies on diabetes incidence and organochlorine exposure. Codru, Neculai, "Diabetes in Relation to Serum Levels of Polychlorinated Biphenyls and Chlorinated Pesticides in Adult Native Americans", Environmental Health Perspectives 115: 1442-1447, <http://www.ehponline.org/members/2007/10315/10315.pdf> A recent study of Mexican Americans yielded similar results. Cox, Shanna & et al, "Prevalence of Self-Reported Diabetes and Exposure to Organochlorine Pesticides among Mexican Americans: Hispanic Health and Nutrition Examination Survey, 1982–1984", Environmental Health Perspectives 115: 1747–1752, <http://www.ehponline.org/members/2007/10258/10258.pdf>

Cancer

• The EPA, in 1987 , classified DDT as class B2, a probable human carcinogen based on "Observation of tumors (generally of the liver) in seven studies in various mouse strains and three studies in rats. DDT is structurally similar to other probable carcinogens, such as DDD and DDE." Regarding the human carcinogenicity data, they stated "The existing epidemiological data are inadequate. Autopsy studies relating tissue levels of DDT to cancer incidence have yielded conflicting results." US EPA (1987). Integrated Risk Information System p, p\'-Dichlorodiphenyltrichloroethane (DDT) (CASRN 50-29-3) __II.A.1. Weight-of-Evidence Characterization. Retrieved on 2006-04-18.
• A study of malaria workers who handled DDT occupationally found an elevated risk of cancers of the liver and biliary tract. Another study has found a correlation between DDE and liver cancer in white men, but not for women or black men. An association between DDT exposure and pancreatic cancer has been demonstrated in a few studies, but other studies have found no association. Several studies have looked for associations between DDT and multiple myeloma, and testicular, prostate, endometrial, and colorectal cancers, but none conclusively demonstrated any association.
• A Canadian study from 2007 found a positive association between DDE and non-Hodgkin Lymphoma.Spinelli, John J. & et al. (2007 Dec 15), "Organochlorines and risk of non-Hodgkin lymphoma", Int. J. Cancer 121 (12): 2767-75, PMID 17722095, doi:10.1002/ijc.23005, <http://www3.interscience.wiley.com/cgi-bin/abstract/115807299/ABSTRACT>

Breast cancer

Several studies have looked for associations between breast cancer and DDT exposure. Almost all studies have measured DDT or DDE blood levels at the time of breast cancer diagnosis or after. While individual studies have yielded conflicting results, taken as a whole, the studies of this design "do not support the hypothesis that exposure to DDT is an important risk factor for breast cancer."DDT and Breast Cancer in Young Women: New Data on the Significance of Age at Exposure, Barbara A. Cohn, Mary S. Wolff, et al., Environ. Health Perspect., 115:1406–1414 (2007). These types of studies have been extensively reviewed:

• In 2007, the journal Cancer published a review of all of the epidemiological studies on breast cancer and DDT and DDE published between 2000 and 2006. The authors state that "Positive findings for well-controlled studies in the early 1990s of associations between breast cancer risk and the insecticide DDT, its breakdown product DDE, and PCBs prompted additional study. Snedeker reviewed studies of DDT/DDE and dieldrin, concluding that existing research strategies provided conflicting and mostly negative evidence…Updating the picture to 2006 provides…essentially unchanged conclusions for DDT/DDE…[I]n light of these findings, additional study of incident breast cancer in association with biological measures of DDE/DDT levels near the time of diagnosis is not a promising avenue."Green Brody, Julia et al. (2007). "Environmental pollutants and breast cancer". Cancer. 

• A 2005 review in The Lancet, states that "In a study in 1993, 37 breast cancer patients had higher serum DDE concentrations (11.8 μg/L) than controls (7.7 μg/L), and results from several subsequent studies supported such an association. However, large epidemiological studies and subsequent pooled and meta-analyses failed to confirm the association."

• A 2004 meta-analysis of studies on the association of p,p\'-DDE and breast cancer concluded that "Overall, these results should be regarded as a strong evidence to discard the putative relationship between p,p\'-DDE and breast cancer risk. Nevertheless, the exposure to DDT during critical periods of human development—from conception to adolescence—and individual variations in metabolizing enzymes of DDT or its derivatives are still important areas to be researched in regard to breast cancer development in adulthood.DDE Burden and Breast Cancer Risk: A Meta-Analysis of the Epidemiologic Evidence. Malaquías López-Cervantes, Luisa Torres-Sánchez, Aurelio Tobías, and Lizbeth López-Carrillo, EHP, 112(2): 207-214, 2004.

A new study in Environmental Health Perspectives found a strong association between exposure to the p,p-isomer of DDT early in life and breast cancer later in life. Exposure to the o,p\'-isomer was negatively correlated with breast cancer (i.e. a protective effect was observed), and no association was observed for DDE. Unlike the studies discussed in the reviews cited above, this was prospective study in which blood samples were collected from young California mothers in the 1960s while DDT was still in use, and their breast cancer status was then tracked. (As discussed above, previous studies measured exposure more recently, long after DDT was banned in the US.) In addition to suggesting that exposure to the p,p-isomer of DDT is the more significant risk factor of breast cancer, the study also suggests that the timing of exposure is critical. For the subset of women born more than 14 years prior to the introduction of DDT into US agriculture, there was no association between DDT levels and breast cancer. However, for women born more recently—and thus exposed earlier in life—the most p,p-DDT exposed third of women had a fivefold increase in breast cancer incidence over the least exposed third, after correcting for the protective effect of o,p-DDT.News media articles about this study: (a) Exposure to DDT is linked to cancer, Douglas Fischer, Contra Costa Times, August 8th, 2007. (b) Study suggests DDT, breast cancer link, Marla Cone, LA Times, September 30th, 2007.

Developmental and reproductive toxicity

DDT and its breakdown product DDE, like other organochlorines, have been shown to have xenoestrogenic activity; meaning they are chemically similar enough to estrogens to trigger hormonal responses in animals. This endocrine disrupting activity has been observed when DDT is used in laboratory studies involving mice and rats as test subjects, and available epidemiological evidence indicates that these effects may be occurring in humans as a result of DDT exposure. In areas where DDT is used for malaria control, infants can be exposed via breastmilk in levels that exceed the W.H.O\'s acceptable daily intake value for DDT.Bouwman H, Sereda B, Meinhardt HM (2006). "Simultaneous presence of DDT and pyrethroid residues in human breast milk from a malaria endemic area in South Africa". Environ. Pollut. 144 (3): 902–17. doi:10.1016/j.envpol.2006.02.002. PMID 16564119.  Ntow WJ, Tagoe LM, Drechsel P, Kelderman P, Gijzen HJ, Nyarko E (2008). "Accumulation of persistent organochlorine contaminants in milk and serum of farmers from Ghana". Environ. Res. 106 (1): 17–26. doi:10.1016/j.envres.2007.05.020. PMID 17931619. 

• A review article in The Lancet concludes that, "research has shown that exposure to DDT at amounts that would be needed in malaria control might cause preterm birth and early weaning … toxicological evidence shows endocrine-disrupting properties; human data also indicate possible disruption in semen quality, menstruation, gestational length, and duration of lactation."
• Human epidemiological studies suggest that DDT exposure is a risk factor for premature birth and low birth weight, and may harm a mother\'s ability to breast feed.Rogan WJ, Ragan NB (2003). "Evidence of effects of environmental chemicals on the endocrine system in children". Pediatrics 112 (1 Pt 2): 247–52. PMID 12837917.  Some researchers argue that these effects may cause increases infant deaths in areas where DDT is used for malaria control, and thus offset any benefit derived from its anti-malarial effects.Chen A, Rogan WJ (2003). "Nonmalarial infant deaths and DDT use for malaria control". Emerging Infect. Dis. 9 (8): 960–4. PMID 12967494. Roberts D, Curtis C, Tren R, Sharp B, Shiff C, Bate R (2004). "Malaria control and public health". Emerging Infect. Dis. 10 (6): 1170–1; author reply 1171–2. PMID 15224677. Chen A, Rogan WJ. Malaria control and public health (replies). Emerging Infectious Disease, 10(6):1171-1172, June 2004 A recent study, however, failed to confirm the association between exposure and difficulty breastfeeding.Cupul-Uicab, LA; et al. (2008). "DDE, a Degradation Product of DDT, and Duration of Lactation in a Highly Exposed Area of Mexico". Environ. Health Perspect. 116 (2): 179-183. 
• Several recent studies demonstrate a link between in utero exposure to DDT or DDE and developmental neurotoxicity in humans. For example, a 2006 study conducted by the University of California, Berkeley suggests children who have been exposed to DDT while in the womb have a greater chance of experiencing development problems,BBC (2006). DDT \'link\' to slow child progress. Retrieved on 2006-07-05. and another study from the same year found that even low-level concentrations of DDT in serum from the umbilical cord at birth were associated with a decrease in cognitive skills at 4 years of age.Ribas-Fitó N, Torrent M, Carrizo D, et al (2006). "In utero exposure to background concentrations of DDT and cognitive functioning among preschoolers". Am. J. Epidemiol. 164 (10): 955–62. doi:10.1093/aje/kwj299. PMID 16968864.  Similarly, Mexican researchers have demonstrated a link between DDE exposure in the first trimester of pregnancy and retarded psychomotor development.Torres-Sánchez L, Rothenberg SJ, Schnaas L, et al (2007). "In utero p,p\'-DDE exposure and infant neurodevelopment: a perinatal cohort in Mexico". Environ. Health Perspect. 115 (3): 435–9. doi:10.1289/ehp.9566. PMID 17431495. 
• A 2007 study documented decreases in semen quality among South African men from communities where DDT is used to combat endemic malaria. The researchers found statistically significant correlations between increased levels of DDT or DDE in blood plasma and decreases in several measures of semen quality including ejaculate volume, certain motility parameters, and sperm count.Aneck-Hahn NH, Schulenburg GW, Bornman MS, Farias P, de Jager C (2007). "Impaired semen quality associated with environmental DDT exposure in young men living in a malaria area in the Limpopo Province, South Africa". J. Androl. 28 (3): 423–34. doi:10.2164/jandrol.106.001701. PMID 17192596.  The same researchers reported similar results in 2006 from a study of men in Mexico.De Jager C, Farias P, Barraza-Villarreal A, et al (2006). "Reduced seminal parameters associated with environmental DDT exposure and p,p\'-DDE concentrations in men in Chiapas, Mexico: a cross-sectional study". J. Androl. 27 (1): 16–27. doi:10.2164/jandrol.05121. PMID 16400073.  A review of earlier studies noted that "Studies of populations with a much lower exposure than that seen in current malaria-endemic areas have shown only weak, inconsistent associations between DDE and testosterone amounts, semen quality, and sperm DNA damage."
• One recent study suggests that women exposed to DDT while in the womb have more difficulty getting pregnant as adults than non-exposed women. On the other hand, prenatal DDE exposure increased the probability of pregnancy.Cohn BA, Cirillo PM, Wolff MS, et al (2003). "DDT and DDE exposure in mothers and time to pregnancy in daughters". Lancet 361 (9376): 2205–6. doi:10.1016/S0140-6736(03)13776-2. PMID 12842376. 
• DDT exposure is associated with early pregnancy loss, a type of miscarriage. A prospective cohort study of Chinese textile workers found "a positive, monotonic, exposure-response association between preconception serum total DDT and the risk of subsequent early pregnancy losses." Venners SA, Korrick S, Xu X, et al (2005). "Preconception serum DDT and pregnancy loss: a prospective study using a biomarker of pregnancy". Am. J. Epidemiol. 162 (8): 709–16. doi:10.1093/aje/kwi275. PMID 16120699.  The median serum DDE level of study group was lower than that typically observed in women living in homes sprayed with DDT, suggesting that these finding are relevant to the debate about DDT and malaria control. Longnecker MP (2005). "Invited Commentary: Why DDT matters now". Am. J. Epidemiol. 162 (8): 726–8. doi:10.1093/aje/kwi277. PMID 16120697. 

DDT use against malaria

The World Health Organization estimates there are between 300 million and 500 million cases of malaria every year, resulting in more than 1 million deaths,2005 WHO World Marlaria Report (see bottom of page) with about 90% of these deaths occurring in Africa, mostly to children under the age of 5.

Most prior use of DDT was in agriculture, but the controlled use of DDT continues to this day for the purposes of public health. Current use for disease control requires only a small fraction of the amounts previously used in agriculture, and at these levels the pesticide is much less likely to cause environmental problems. Residual house spraying involves the treatment of all interior walls and ceilings with insecticide, and is particularly effective against mosquitoes, which favour indoor resting before or after feeding. Advocated as the mainstay of malaria eradication programmes in the late 1950s and 1960s, DDT remains a major component of control programmes in southern African states, though many countries have abandoned or curtailed their spraying activities. South Africa, Swaziland, Mozambique and Ecuador are examples of countries that have very successfully reduced malaria infestations with DDT.

Indeed, the problems facing health officials in their fight against malaria neither begin nor end with DDT. Experts tie the spread of malaria to numerous factors, including the resistance of the malaria parasite itself to the drugs traditionally used to treat the illnessNorton, Jim. The DDT Ban Myth. Info-pollution.com. Retrieved on 2006-03-15. and a chronic lack of funds in the countries worst hit by malaria.

The growth of resistance to DDT and the fear that DDT may be harmful both to humans and the environment led the U.N., donor countries, and various national governments to restrict or curtail the use of DDT in vector control. At the same time, use of DDT as an agricultural insecticide was often unrestricted, and restrictions were often evaded, especially in developing countries where malaria is rife, so that resistance continued to grow.

A commentary on the current state of global malaria control was published in the May 2007 issue of the Journal of the American Medical Association. The authors identify "3 critical factors that are currently absent or in too short supply" for making progress in the fight against malaria: "leadership, management, and money," while making no mention of restrictions limiting the use of DDT. They also single out resistance of the malaria parasite to chloroquine as the cause of increasing malaria mortality in sub-Saharan Africa, not restrictions on DDT.Feachem RG, Sabot OJ (2007). "Global malaria control in the 21st century: a historic but fleeting opportunity". JAMA 297 (20): 2281–4. doi:10.1001/jama.297.20.2281. PMID 17519417. 

Today there is debate among professionals working on malaria control concerning the appropriate role of DDT. The range of disagreement is relatively narrow: Few believe either that large scale spraying should be resumed or that the use of DDT should be abandoned altogether. The debate focuses on the relative merits of DDT and alternative pesticides as well as complementary use of interior wall spraying, insecticide-treated bed-nets, and other mosquito control techniques.

Since the appointment of Arata Kochi as head of its anti-malaria division, the WHO has shifted its position in this controversy, from primary reliance on bed-nets to a policy more favorable to DDT. Until an announcement made on 16 September 2006, the policy had recommended indoor spraying of insecticides in areas of seasonal or episodic transmission of malaria, but a new policy also advocates it where continuous, intense transmission of the disease causes the most deaths.WHO | WHO gives indoor use of DDT a clean bill of health for controlling malaria In 2007, the WHO clarified its position, saying it is "very much concerned with health consequences from use of DDT" and reaffirmed its commitment to phasing out the use of DDT.http://www.yubanet.com/artman/publish/article_56180.shtml

Overall effectiveness of DDT against malaria

In the period from 1934-1955 there were 1.5 million cases of malaria in Sri Lanka, resulting in 80,000 deaths. After the country invested in an extensive anti-mosquito program with DDT, there were only 17 cases reported in 1963. Thereafter the program was halted, and malaria in Sri Lanka rebounded to 600,000 cases in 1968 and the first quarter of 1969. Although the country resumed spraying with DDT, many of the local mosquitoes had acquired resistance to DDT in the interim, presumably because of the continued use of DDT for crop protection, so the program was not nearly as effective as it had been before. Switching to the more-expensive malathion in 1977 reduced the malaria infection rate to 3,000 by 2004. A recent study notes, "DDT and Malathion are no longer recommended since An. culicifacies and An. subpictus has been found resistant."Briët, Olivier JT; Gawrie NL Galappaththy, Flemming Konradsen, Priyanie H Amerasinghe and Felix P Amerasinghe (2005). "Maps of the Sri Lanka malaria situation preceding the tsunami and key aspects to be considered in the emergency phase and beyond". Malaria Journal 4: 8. doi:10.1186/1475-2875-4-8. PMID 15676073. 

A 2004 editorial in the British Medical Journal argues that the campaign against malaria is failing, that funding of malaria control should therefore be increased, and that use of DDT should be considered since DDT has "a remarkable safety record when used in small quantities for indoor spraying in endemic regions."Yamey, Gavin (8 May 2004). "Roll Back Malaria: a failing global health campaign". BMJ 328: 1086-1087. doi:10.1136/bmj.328.7448.1086. PMID 15130956. 

One insecticide supply company states on its website:

DDT is still one of the first and most commonly used insecticides for residual spraying, because of its low cost, high effectiveness, persistence and relative safety to humans. [...] In the past several years, we supplied DDT 75% WDP to Madagascar, Ethiopia, Eritrea, Sudan, South Africa, Namibia, Solomon Island, Papua New Guinea, Algeria, Thailand, and Myanmar for Malaria Control project, and won a good reputation from WHO and relevant countries\' government.Yorkool Chemical - Manufacturer/Supplier of DDT, pyrethroid, and microbial insecticides for Malaria Control. Retrieved on 2006-03-15.

According to DDT advocate Donald Roberts, malaria cases increased in South America after countries in that continent stopped using DDT. Other mosquito-borne diseases are also on the rise. Roger Bate claims that 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 has brought devastating outbreaks of dengue fever, dengue hemorrhagic fever, and a renewed threat of urban yellow fever.Bate, Roger (24 April 2001). Without DDT, malaria bites back. spiked-online.com. Retrieved on 2006-03-15.

Mosquito resistance to DDT

Although the publication of Silent Spring undoubtedly influenced the U.S. ban on DDT in 1972, the reduced usage of DDT in malaria eradication began the decade before because of the emergence of DDT-resistant mosquitoes. Paul Russell, a former head of the Allied Anti-Malaria campaign, observed that eradication programs had to be wary of relying on DDT for too long as "resistance has appeared [after] six or seven years."Garrett, L (1994). The Coming Plague: Newly Emerging Diseases in a World Out of Balance. Penguin Books, UK. 

In some areas DDT has lost much of its effectiveness, especially in areas such as India where outdoor transmission is the predominant form. According to one article by V.P. Sharma, "The declining effectiveness of DDT is a result of several factors which frequently operate in tandem. The first and the most important factor is vector resistance to DDT. All populations of the main vector, An. culicifacies have become resistant to DDT." In India, with its outdoor sleeping habits and frequent night duties, "the excito-repellent effect of DDT, often reported useful in other countries, actually promotes outdoor transmission."Sharma, V. P. (10 Devember 2003). "DDT: The fallen angel". Current Science 85 (11): 1532-1537. 

Due to this DDT resistance, in Sri Lanka, parts of India, Pakistan, Turkey and Central America, DDT has already been replaced by organophosphate or carbamate insecticides, e.g. malathion or bendiocarb. Control of Malaria Vectors in Africa and Asia C.F.Curtis

According to a pesticide industry newsletter, DDT is obsolete for malarial prevention in India not only owing to concerns over its toxicity, but because it has largely lost its effectiveness. Use of DDT for agricultural purposes was banned in India in 1989, and its use for anti-malarial purposes has been declining. Use of DDT in urban areas of India has halted completely. Food supplies and eggshells of large predator birds still show high DDT levels.Agarwal, Ravi (May 2001). "No Future in DDT: A case study of India". Pesticide Safety News.  Parasitology journal articles confirm that malarial vector mosquitoes have become resistant to DDT and HCH in most parts of India.Sharma, V.P. (1999). "Current scenario of malaria in India". Parassitologia 41 (1-3): 349-53. PMID 10697882.  Nevertheless, DDT is still manufactured and used in India.Art Fisher, Mark Walker, Pam Powell. DDT and DDE: Sources of Exposure and How to Avoid Them (PDF). Retrieved on 2006-03-15. One study concludes "The overall results of the study revealed that DDT is still a viable insecticide in indoor residual spraying owing to its effectivity in well supervised spray operation and high excito-repellency factor." http://www.mrcindia.org/journal/422054.pdf

The initial appearance of this resistance was largely due to the much greater quantity of DDT which had been used for agricultural spraying, rather than the relatively insignificant amounts used for disease prevention. According to one study which attempted to quantify the lives saved due to banning agricultural use of DDT and thereby slowing the spread of DDT resistance: "Correlating the use of DDT in El Salvador with renewed malaria transmission, it can be estimated that at current rates each kilo of insecticide added to the environment will generate 105 new cases of malaria."

Advocates for continuing use of DDT against malaria state that "Limited us