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DDT (from its original chemical name, '''D'''ichloro-'''D'''iphenyl-'''T'''richloroethane) is one of the best known synthetic , and soon its production and use skyrocketed. ''Environmental Health Criteria 9: DDT and its derivatives'' , World Health Organization, 1979. In 1962, Houghton Mifflin published '' Silent Spring '' by American biologist Rachel Carson . 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.1 The book resulted in a large public outcry that eventually led to DDT being banned in the US, and its publication was one of the signature events in the birth of the Environmental Movement . 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. 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. Can the Bald Eagle Still Soar After It Is Delisted , Eric Stokstad, ''Science'', 316(5832):1689-1690, 2007. PROPERTIES AND CHEMISTRY DDT is an Organochlorine insecticide, similar to the pesticides Dicofol and Methoxychlor . It is a highly Hydrophobic , colorless, Crystal line solid with a weak, chemical Odor . It is nearly Insoluble in Water but has a good solubility in most Organic Solvent s, Fat s, and Oil s. DDT does not occur naturally, and is producted by the reaction of Chloral (C2HCl3O) 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 the 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. Environmental Health Criteria 9: DDT and its derivatives Word Health Organization, 1979. DDT is moderately toxic, with a rat LD50 of 113 mg/kg, and has potent insecticidal properties; it kills by opening Sodium Ion Channel s in insect Neuron s, 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. Insect Resistance on the Move 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 DDT was first synthesized in 1874 by Othmar Zeidler , 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. Use in the 1940s and 1950s DDT is the best-known of a number of chlorine-containing Pesticide s 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 insect Typhus and malaria Vector s (nearly eliminating typhus as a result). 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 Midge s in Great Britain, and was used extensively as an agricultural insecticide after 1945. DDT contributed to the final eradication of malaria in Europe and North America, although malaria had already been eliminated from much of the developed world in the early 20th century through the use of a range of public health measures and generally increasing health and living standards. "Malaria's decline in the United States and Europe in the late 1800s was due mainly to draining swamps and removing mill ponds". Even in countries without these advances, it was critical in their eradication of the disease. "Malaria was eradicated from Brazil and Egypt , largely due to extensive DDT spraying."http://www.malariasite.com/malaria/history_control.htm 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.G. Chapin & R. Wasserstrom, "Agricultural production and malaria resurgence in Central America and India," ''Nature,'' 293:181-185, (1981). 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 ''s impregnated with insecticides. ''Health risks and benefits of bis(4-chlorophenyl)-1,1,1-trichloroethane (DDT)'' WJ Rogan and A Chen, ''The Lancet'' 366:763-773, 2005. 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 , NY. 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 Hoyt. 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 school teacher, Art Cooley, meanwhile was observing the decline of Osprey s 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, and DDT was replaced in most antimalarial uses by less Persistent , and more expensive, alternative insecticides. 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 Stockholm Convention , ratified in 2001 and effective as of 17 May 2004 , outlawed several Persistent Organic Pollutant s, 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. {Link without Title} 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. 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.3 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 km&2, the required amount is roughly equal to the amount of DDT that might previously have been used to spray 4 km&2 of cotton during a single growing season.4 U.S. ban In 1962, Rachel Carson 's book '' Silent Spring '' was published. The book argued that Pesticide s, especially 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 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 .5 The ban and Carson's book have subsequently been vigorously criticized by a tiny group of pro-DDT advocates, including Steven Milloy, Roger Bate and Richard Tren , whose critiques draw on the work of the late San Jose State University entomologist J. Gordon Edwards , a witness at the hearings who stated that there was no evidence to substantiate the claims that DDT posed a threat to human health. They report that, at the end of the hearings, 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 Mark Commission s) that had come to the opposite conclusion. Milloy and Edwards claimed that Ruckelshaus did not actually attend any of the EPA commission's hearings, and (citing unnamed aides) that he did not read any transcripts of the hearings. However, generally administrative law under both the Administrative Procedures Act and the EPA's own rules suggest the EPA director should not attend such hearings since the director would be in a position of taking administrative appeals; similar to the way the Supreme Court justices do not attend criminal arraignment hearings or criminal trials, Ruckelshaus's not attending the hearings is no problem legally. Ruckelshaus overturned Sweeney's ruling, arguing 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." Ruckelshaus's action was contested by DDT manufacturers in court; had Ruckelshaus acted without sound reason, under administrative law the courts should have overturned his ruling. The court cases were decided in EPA's favor, and appeals got no traction, suggesting that Ruckelshaus's actions were solidly based on science. Recent changes In September 2006, the World Health Organization announced that DDT will be used as one of the three main tools against Malaria . WHO is hence recommending indoor residual spraying (IRS) in epidemic areas, as well as in places with constant and high malaria transmission.6 The USAID subsequently announced that it would fund the use of DDT.http://www.abc.net.au/news/newsitems/200608/s1703488.htm. A new study by the ''Public Library of Science'' (PloS) has confirmed that "DDT Highly Effective Against Resistant Mosquitoes". Researchers stated that "59% of DDT-resistant Aedes aegypti mosquitoes, carriers of human diseases like dengue and urban yellow fever, avoided huts sprayed with DDT" and that treating huts with DDT deterred 73% of mosquitoes from entering[http://www.medicalnewstoday.com/articles/79127.php DDT Highly Effective Against Resistant Mosquitoes . ENVIRONMENTAL IMPACT DDT is a . DDT and its metabolic products DDE and DDD in 2005, 85% had detectable levels of DDE.USDA, ''Pesticide Data Program Annual Summary Calendar Year 2005'', November 2006. DDT is a , 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
Chronic
Cancer
Breast cancer Several studies have looked for associations between breast cancer and DDT exposure. These studies have generally measured DDT or DDE blood levels at the time of breast cancer diagnosis or after and "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.,'' 2007, in press. These studies have been extensively reviewed:
Recently, a study in ''Environmental Health Perspectives'' found a strong correlation 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. (Most 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 correlation 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. Exposure to DDT is linked to cancer , Douglas Fischer, ''Contra Costa Times,'' August 8th, 2007. Developmental and reproductive toxicity DDT and its breakdown product DDE, like other organochlorines, have been shown to have Xenoestrogen ic activity; meaning it is chemically similar enough to estrogen to trigger hormonal responses in contaminated animals. This hormonal-mimicking activity has been observed when DDT is used in laboratory studies involving Mice and Rat s as test Subjects , and available Epidemiological evidence indicates that these effects may be occurring in humans as a result of DDT exposure.
:''Although DDT is generally not toxic to human beings and was banned mainly for ecological reasons, subsequent research has shown that exposure to DDT at amounts that would be needed in malaria control might cause preterm birth and early weaning, abrogating the benefit of reducing infant mortality from malaria...DDT might be useful in controlling malaria, but the evidence of its adverse effects on human health needs appropriate research on whether it achieves a favourable balance of risk versus benefit. :''Future perspectives: Although acute toxic effects are scarce, toxicological evidence shows endocrine-disrupting properties; human data also indicate possible disruption in semen quality, menstruation, gestational length, and duration of lactation. The research focus on human reproduction and development seems to be appropriate. DDT could be an effective public-health intervention that is cheap, longlasting, and effective. However, various toxic-effects that would be difficult to detect without specific study might exist and could result in substantial morbidity or mortality. Responsible use of DDT should include research programmes that would detect the most plausible forms of toxic effects as well as the documentation of benefits attributable specifically to DDT. Although this viewpoint amounts to a platitude if applied to malaria research in Africa, the research question here could be sufficiently focused and compelling, so that governments and funding agencies recognise the need to include research on all infant mortality when DDT is to be used. ''
DDT USE AGAINST MALARIA , 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 microbe itself to the drugs traditionally used to treat the illness19 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. 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. {Link without Title} 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. 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."23}} According to the Cato Institute , after South Africa stopped using DDT in 1996, the incidence of malaria in KwaZulu Natal province rose from 8,000 cases with 20 deaths in 1996, to 42,000 cases with 340 deaths in 2000. Today, after the reintroduction of DDT and new drug therapies, the number of deaths from malaria in the region is less than 50 per year. South Africa could afford and did try newer alternatives to DDT, but they proved less effective. Uganda also began permitting the use of DDT in anti-malarial efforts, despite a threat that its agricultural exports to Europe could be banned if they were contaminated with DDT.24 The Ugandan government has stated that it cannot achieve its development goals without first eliminating malaria. The GDP shows a striking correlation between malaria and poverty, where malaria is estimated to reduce per capita growth by 1.3 percent per annum.25 Malaria cases increased in South America after countries in that continent stopped using DDT. 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 has brought devastating outbreaks of Dengue Fever , Dengue Hemorrhagic Fever , and a renewed threat of urban Yellow Fever .26 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. Indeed, 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 {Link without Title} six or seven years."27 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."28 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.29 Parasitology journal articles confirm that malarial vector mosquitoes have become resistant to DDT and HCH in most parts of India.30 Nevertheless, DDT is still manufactured and used in India.31 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."32 Advocates for continuing use of DDT against malaria state that "Limited use of DDT for public health has continued to be effective in areas where it is used inside homes. As DDT's chief property is repellency, mosquitoes often avoid the DDT treated homes altogether. In so doing, they avoid the exposure that promotes resistance as well. DDT resistance exists in West Africa and in other malarial areas, such as India. Isolated occurrences of DDT resistance have occurred in South Africa, and South Africa continues to monitor for resistance. As the various Departments of Health that use it carefully control DDT use, it is unlikely that resistance will emerge as a major problem."http://www.fightingmalaria.org/faq.aspx#will%20mosquitos%20develop%20resistance Studies of malaria-vector mosquitoes trapped while exiting windows in KwaZulu-Natal Province , South Africa found susceptibility to 4% DDT (the WHO susceptibility standard), in 63% of the samples, compared to the average of 86.5% in the same species caught in the open. The authors concluded that "Finding DDT resistance in the vector ''An. arabiensis'', close to the area where we previously reported pyrethroid-resistance in the vector ''An. funestus'' Giles, indicates an urgent need to develop a strategy of insecticide resistance management for the malaria control programmes of southern Africa." '' K. Anopheles arabiensis and An. quadriannulatus resistance to DDT in South Africa '', Hargreaves, R. H. Hunt, B. D. Brooke, J. Mthembu, M. M. Weeto, T. S. Awolola, M. Coetzee, 2003, Medical and Veterinary Entomology 17 (4), 417–422. doi:10.1111/j.1365-2915.2003.00460.x The avoidance of DDT-sprayed walls by mosquitoes, while sometimes touted as a beneficial aspect of DDT , in fact is detrimental to the actual eradication of the disease. Unlike other insecticides such as pyrethroids, DDT requires a long period of contact before mosquitoes pick up a lethal dose; however its irritant property makes them fly off before this occurs. "For these reasons, when comparisons have been made, better malaria control has generally been achieved with pyrethroids than with DDT." Residents' resistance to use of DDT Many residents resist spraying of DDT for various reasons. For instance, the smell lingers, '' In Malaria War, South Africa Turns To Pesticide Long Banned in the West '', Roger Thurow, , Tropical Medicine & International Health 9 (8), 846–856. doi:10.1111/j.1365-3156.2004.01263.x '' Malaria and the DDT Story '' While that stain makes it easier to check whether the room has been sprayed it causes some villagers to avoid spraying of their homes '' South Africa’s War against Malaria Lessons for the Developing World '', Richard Tren and Roger Bate, Cato Institute or to resurface the wall, which eliminates the residual insecticidal effect of the spraying. "Pyrethroids such as deltamethrin and lambdacyhalothrin are … much more acceptable to householders because they leave no visible deposit on walls… therefore rates of refusal of spraying by householders are lower with pyrethroids than with DDT." In addition, DDT is not suitable for this type of spraying in Western-style Plaster ed or painted walls, only traditional dwellings with unpainted walls made of mud, sticks, Dung , thatch, Clay , or cement.As rural areas of South Africa become more prosperous, there is a shift towards Western style housing, leaving fewer homes suitable for DDT spraying, and necessitating the use of alternative insecticides. Other villagers object to DDT spraying because it does not kill Cockroach es or Bedbug s; rather, it excites such pests making them more active, so that often use of another insecticide is additionally required. Pyrethroids such as deltamethrin and lambdacyhalothrin, on the other hand, are more acceptable to residents because they kill these nuisance insects as well as mosquitoes. As a result, says Dr. Avertino Barreto , chief of Infectious Disease control in Mozambique , resistance to DDT spraying is "homegrown", not due to "pressure from environmentalists". "They only want us to use DDT on poor, rural black people," he says. "So whoever suggests DDT use, I say, 'Fine, I'll start spraying in your house first.' " In areas where resistance from the residents prevents a high percentage of the homes being effectively sprayed, it reduces the "chance of reaching a level of coverage at which the vectorial capacity of the mosquito population will be lowered to a point at which malaria transmission will be interrupted." Human exposure associated with DDT spraying for disease vectors In the low income areas where malaria eradication is necessary, it is almost impossible to ensure that DDT intended for disease prevention does not get diverted to use on crops, on a totally unregulated basis. "The consequent insecticidal residues in crops at levels unacceptable for the export trade have been an important factor in recent bans of DDT for malaria control in several tropical countries". Adding to this problem is a lack of skilled personnel and supervision. Evidence for exposure to DDT is seen in South Africa http://whqlibdoc.who.int/bulletin/1990/Vol68-No6/bulletin_1990_68(6)_761-768.pdf http://whqlibdoc.who.int/bulletin/1994/Vol72-No6/bulletin_1994_72(6)_921-930.pdf, where in contrast to areas where DDT use has ceased (even where it was used heavily), in areas where DDT is currently in use ostensibly in small amounts for malaria prevention only, DDT levels in men and women were significantly higher than the allowable daily intake . , 70:241-250 These levels have been associated with neurological abnormalities in babies ingesting relatively large quantities of DDT in their milk although toxicity via this mode of intake has not been proved. Criticism of restrictions on DDT use There are claims that restrictions on the use of DDT in vector control have resulted in substantial numbers of unnecessary deaths due to , author of ''Eco-Imperialism: Green Power, Black Death'', argues that the epidemic of malaria in Africa not only takes the lives of 2 million people a year, but leaves those who survive malaria unable to contribute to the economy while sick and more vulnerable to subsequent diseases that might kill them. These arguments have been called "outrageous" by former WHO scientist Socrates Litsios. May Berenbaum, a professor of entomology at the University of Illinois at Urbana-Champaign, says that "to blame environmentalists who oppose DDT for more deaths than Hitler is worse than irresponsible." Rachel Carson's birthday bashing , Kirsten Weir, Salon.com, June 29, 2007, accessed July 1, 2007. Restrictions on DDT use for vector control were imposed by various national governments, donor countries and international aid agencies, in response to pressure from environmentalists. It has been suggested that DDT treatments were used long enough to eliminate insect-borne diseases in the West, but now that it is only needed in poorer nations in Africa, Asia and elsewhere, it has been banned or otherwise restricted. Some environmental groups have been strongly criticized for trying to ban all use of DDT. According to ban and stated: "Environmentalists in rich, developed countries gain nothing from DDT, and thus small risks felt at home loom larger than health benefits for the poor tropics. More than 200 environmental groups, including Greenpeace, Physicians for Social Responsibility and the World Wildlife Fund, actively condemn DDT for being "a current source of significant injury to...humans."http://www.nature.com/nm/journal/v6/n7/abs/nm0700_729.html Criticisms of a ban on DDT often refer specifically to the 1972 US ban (with the implication that this constituted a worldwide ban), while ignoring that DDT has not been banned for public health use in most areas of the world where malaria is endemic.Dr Alan Lymbery and Professor Andrew Thompson, letter in the ''The Australian'', February 2, 2004. {Link without Title} Reference is also often made to Rachel Carson 's ''Silent Spring'' even though she never pushed for a ban on DDT. In fact, she devoted a page of the book to consideration of the relationship between DDT and malarial mosquitoes, with cognizance of the development of resistance in the mosquito, concluding: It is more sensible in some cases to take a small amount of damage in preference to having none for a time but paying for it in the long run by losing the very means of fighting the advice given in Holland by Dr Briejer in his capacity as director of the Plant Protection Service . Practical advice should be "Spray as little as you possibly can" rather than "Spray to the limit of your capacity." However, the fact that DDT is not formally banned in developing nations does not necessarily mean that those nations have the option to use it. Developing nations are typically heavily dependent on aid from agencies that made the aid contingent upon non-usage of DDT. The ''British Medical Journal'' of March 11, 2000, reports that the use of DDT in Mozambique "was stopped several decades ago, because 80% of the country's health budget came from donor funds, and donors refused to allow the use of DDT." {Link without Title} Many African nations have been dissuaded from to using DDT in part because the European Union has said that their agricultural exports may not be accepted if spraying was "widespread."34 According to the maintains that USAID and some other international donor organizations have refused to fund public health DDT programs.35 Similarly, Roger Bate of AFM asserts that many countries have been coming under pressure from international health and environment agencies to give up DDT or face losing aid grants, and that Belize and Bolivia have gone on record to say that they gave in to pressure on this issue from the US Agency for International Development.36 USAID's Kent R. Hill states that the agency has been misrepresented: |
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