DDT (from its
trivial nameIn chemistry and biology, a trivial name is a non-systematic name or non-scientific name. That is, the name is not recognised according to the rules of any formal system of nomenclature. Many trivial names continue to be used because their sanctioned equivalents are considered too cumbersome...
,
dichloro
diphenyl
trichloroethane) is one of the most well-known synthetic
pesticideA pesticide is a substance or mixture of substances used to kill a pest.A pesticide is any substance or mixture of substance intended for:- preventing, destroying, repelling or mitigating any pest....
s. 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 second half of
World War IIWorld War II, or the Second World War , was a global military conflict which involved a majority of the world's nations, including all great powers, organized into two opposing military alliances: the Allies and the Axis...
, it was used with great effect to control
mosquitoMosquito is a common insect in the family Culicidae...
es spreading
malariaMalaria is a vector-borne infectious disease caused by a eukaryotic protist of the genus Plasmodium. It is widespread in tropical and subtropical regions, including parts of the Americas, Asia, and Africa. Each year, there are approximately 350–500 million cases of malaria, killing between one and...
and lice transmitting
typhusEpidemic typhus is a form of typhus so named because the disease often causes epidemics following wars and natural disasters...
among civilians and troops, resulting in dramatic reductions in the incidence of both diseases. The Swiss chemist
Paul Hermann MüllerPaul Hermann Müller also known as Pauly Mueller was a Swiss chemist and Nobel laureate. In 1948 he received the Nobel Prize in Physiology or Medicine for his 1939 discovery of insecticidal qualities and use of DDT in the control of vector diseases such as malaria and yellow fever...
was awarded the
Nobel Prize in Physiology or MedicineThe Nobel Prize in Physiology or Medicine is awarded once a year by the Swedish Karolinska Institute. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895, awarded for outstanding contributions in Physics, Chemistry, Literature, Peace, and Physiology or Medicine...
in 1948 "for his discovery of the high efficiency of DDT as a contact poison against several
arthropodAn arthropod is an invertebrate that has an exoskeleton , a segmented body, and jointed attachments called appendages. Arthropods are animals belonging to the Phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s." After the war, DDT was made available for use as an agricultural
insecticideAn insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
, and soon its production and use skyrocketed.
In 1962,
Silent SpringSilent Spring is a book written by Rachel Carson and published by Houghton Mifflin in September 1962. The book is widely credited with helping launch the environmental movement....
by American biologist
Rachel CarsonRachel Louise Carson was an American marine biologist and nature writer whose writings are credited with advancing the global environmental movement....
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
cancerCancer is a class of diseases in which a group of cells display uncontrolled growth , invasion , and sometimes metastasis...
and that their agricultural use was a threat to wildlife, particularly birds. Its publication was one of the signature events in the birth of the
environmental movementEnvironmentalism is a broad philosophy and social movement regarding concerns for environmental conservation and improvement of the state of the environment...
.
Silent Spring resulted in a large public outcry that eventually led to most uses of DDT being banned in the US in 1972. DDT was subsequently banned for agricultural use worldwide under the
Stockholm ConventionStockholm Convention on Persistent Organic Pollutants is an international environmental treaty that aims to eliminate or restrict the production and use of persistent organic pollutants .- History :...
, but its limited use in disease vector
controlFor vector control of induction motors, see Vector_control_Vector control is any method to limit or eradicate the mammals, birds, arthropods, or insects which transmit disease pathogens....
continues to this day and remains controversial.
Along with the passage of the
Endangered Species ActThe Endangered Species Act of 1973 is the most wide-ranging of the dozens of United States environmental laws passed in the 1970s...
, the US ban on DDT is cited by scientists as a major factor in the comeback of the
bald eagleThe Bald Eagle is a bird of prey found in North America that is most recognizable as the national bird and symbol of the United States of America. This sea eagle has two known sub-species and forms a species pair with the White-tailed Eagle. Its range includes most of Canada and Alaska, all of the...
, the National bird of the United States, from near-
extinctionIn biology and ecology, extinction is the end of an organism or group of taxa. The moment of extinction is generally considered to be the death of the last individual of that species...
in the contiguous US.
Properties and chemistry
DDT is an organochlorine, similar in structure to the insecticide
methoxychlorMethoxychlor is a synthetic organochlorine used as an insecticide.-Usage:The use of methoxychlor has been banned in the United States and the European Union....
and the acaricide
dicofolDicofol is an organochlorine pesticide that is chemically related to DDT. Dicofol is a miticide that is very effective against red spider mite....
. It is a highly hydrophobic, colorless,
crystalA crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is crystallography...
line solid with a weak, chemical
odorAn odor or odour is caused by one or more volatilized chemical compounds, generally at a very low concentration, that humans or other animals perceive by the sense of olfaction. Odors are also called smells, which can refer to both pleasant and unpleasant odors...
. It is nearly insoluble in water but has a good solubility in most
organicOrganic chemistry is a discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation of chemical compounds that contain carbon...
solventA solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution.The most common solvent in everyday life is water. Most other commonly-used solvents are organic chemicals. These are called organic solvents...
s,
fatFats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. Chemically, fats are generally triesters of glycerol and fatty acids. Fats may be either solid or liquid at normal room temperature, depending on their structure and composition...
s, and oils. DDT does not occur naturally, but is produced by the reaction of chloral (CCl
3CHO) with
chlorobenzeneChlorobenzene is an aromatic organic compound with the chemical formula C
6H
5Cl. This colorless, flammable liquid is a common solvent and a widely used intermediate in the manufacture of other chemicals.-Uses:...
(C
6H
5Cl) in the presence of
sulfuric acidSulfuric acid, , is a strong mineral acid. It is soluble in water at all concentrations. Sulfuric acid has many applications, and is one of the top products of the chemical industry. World production in 2001 was 165 million tonnes, with an approximate value of US$8 billion...
, which acts as a catalyst. Trade names that DDT has been marketed under include Anofex, Cezarex, Chlorophenothane, Clofenotane, Dicophane, Dinocide, Gesarol, Guesapon, Guesarol, Gyron, Ixodex, Neocid, Neocidol, and Zerdane.
Isomers and related compounds
Commercial DDT is actually a mixture of several closely related compounds. The major component (77%) is the
pArene substitution patterns are part of organic chemistry IUPAC nomenclature and pinpoint the position of substituents other than hydrogen in relation to each other on an aromatic hydrocarbon.- Ortho, meta, and para substitution :...
,
p isomerIn chemistry, isomers are compounds with the same molecular formula but different structural formulas. The word is derived from the Greek ισομερης, isomerès; isos = "equal", méros = "part"....
which is pictured at the top of this article. The
o,
p' isomer (pictured to the right) is also present in significant amounts (15%).
DichlorodiphenyldichloroethyleneDichlorodiphenyldichloroethylene is the full name of DDE. This compound is formed by the loss of hydrogen chloride of DDT , of which it is one of the more common breakdown products. DDE is fat soluble which tends to build up in the fat of animals...
(DDE) and
dichlorodiphenyldichloroethaneDichlorodiphenyldichloroethane is an organochlorine insecticide that is slightly irritating to the skin. DDD is a metabolite of DDT. DDD is colorless and crystalline; it is closely related chemically and is similar in properties to DDT, but it is considered to be less toxic to animals than is DDT...
(DDD) make up the balance. DDE and DDD are also the major metabolites and breakdown products of DDT in the environment. The term "
total DDT" is often used to refer to the sum of all DDT related compounds (
p, p-DDT,
o, p-DDT, DDE, and DDD) in a sample.
Production and use statistics
From 1950 to 1980, when DDT was extensively used in agriculture—more than 40,000 tonnes were used each year worldwide—and it has been estimated that a total of 1.8 million tonnes of DDT have been produced globally since the 1940s. In the U.S., where it was manufactured by Ciba,
Montrose Chemical CompanyAfter World War II, Montrose Chemical Corporation of California, 20201 S. Normandie Ave., Torrance, California began producing Dichloro-Diphenyl-Trichloroethane , the new “wonder pesticide.” Their waste disposal system funneled the plant’s processed waste into the county sewer system and ultimately...
, Pennwalt and
Velsicol Chemical CorporationVelsicol Chemical Corporation is a Rosemont, Illinois based chemical company founded in 1931 that specializes in plasticizers. It has approximately 450 employees and is owned by the private equity firm Arsenal Capital....
, production peaked in 1963 at 82,000 tonnes per year. More than 600,000 tonnes (1.35 billion lbs) were applied in the U.S. before the 1972 ban, with usage peaking in 1959 with about 36,000 tonnes applied that year.
Today, 4-5,000 tonnes of DDT are used each year for the control of malaria and
visceral leishmaniasisVisceral leishmaniasis , also known as kala-azar, black fever, and Dumdum fever, is the most severe form of leishmaniasis. Leishmaniasis is a disease caused by protozoan parasites of the Leishmania genus. It is the second-largest parasitic killer in the world , responsible for an estimated 500,000...
, with
IndiaIndia, officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the south, the Arabian Sea on the west, and the Bay of Bengal...
being the largest consumer. India,
ChinaChina is a cultural region, an ancient civilization, and, depending on perspective, a national or multinational entity extending over a large area in East Asia....
, and
North KoreaNorth Korea, officially the Democratic People's Republic of Korea , is a state in East Asia, occupying the northern half of the Korean Peninsula. Its capital and largest city is Pyongyang. The Korean Demilitarized Zone serves as the buffer area between North Korea and South Korea...
are the only countries still producing and exporting it, and production is reportedly on the rise.
Mechanism of action
In insects, it has potent insecticidal properties, where it kills by opening
sodium ion channelSodium channels are integral membrane proteins that form ion channels, conducting sodium ions through a cell's plasma membrane. They are classified according to the trigger that opens the channel for such ions, i.e...
s in the
neuronA neuron is an excitable cell in the nervous system that processes and transmits information by electrochemical signaling. Neurons are the core components of the brain, the vertebrate spinal cord, the invertebrate ventral nerve cord, and the peripheral nerves...
s, causing them to fire spontaneously leading to spasms and eventual death. Insects with certain mutations in their sodium channel gene are resistant to DDT and other similar insecticides. DDT resistance is also conferred by up-regulation of genes expressing cytochrome P450 in some insect species.
In humans, however, it may affect health through genotoxicity or endocrine disruption.
See Effects on human health below
History
First synthesized in 1874 by
Othmar ZeidlerOthmar Zeidler was a German Austrian chemist.As a doctoral student at University of Strasbourg, Zeidler is credited with first synthesis of the insecticide Dichloro Diphenyl Trichloroethane or DDT in 1874, He worked with Adolf von Baeyer at Straßburg.-References:* at www.cdc.gov...
, DDT's insecticidal properties were not discovered until 1939 by the
SwissThe Swiss are citizens of the Swiss Confederation, natives of Switzerland. The demonym derives from the toponym of Schwyz and has been in widespread use to refer to the Old Swiss Confederacy since the 16th century....
scientist
Paul Hermann MüllerPaul Hermann Müller also known as Pauly Mueller was a Swiss chemist and Nobel laureate. In 1948 he received the Nobel Prize in Physiology or Medicine for his 1939 discovery of insecticidal qualities and use of DDT in the control of vector diseases such as malaria and yellow fever...
, who was awarded the 1948
Nobel PrizeThe Nobel Prize is a Sweden-based international monetary prize. The award was established by the 1895 will and estate of Swedish chemist and inventor Alfred Nobel. It was first awarded in Physics, Chemistry, Physiology or Medicine, Literature, and Peace in 1901...
in Physiology and Medicine for his efforts.
Use in the 1940s and 1950s
DDT is the best-known of a number of
chlorineChlorine Chlorine Chlorine ( , from the Greek word 'χλωρóς' (khlôros, meaning 'pale green'), is the chemical element with atomic number 17 and symbol Cl. It is a halogen, found in the periodic table in group 17 (formerly VII, VIIa, or VIIb). As the chloride ion, which is part of common salt and...
-containing pesticides used in the 1940s and 1950s. With
pyrethrumPyrethrum refers to several Old World plants of the genus Chrysanthemum which are cultivated as ornamentals for their showy flower heads. It is also the name of a natural insecticide made from the dried flower heads of C. cinerariifolium and C. coccineum...
in short supply, DDT was used extensively during World War II by the
AlliesThe Allies of World War II were the countries that opposed the Axis powers during the Second World War . The involvement of the Allies in World War II was either natural and inevitable they were invaded or under the direct threat of invasion by the Axis or compelled by concerns that the Axis powers...
to control the insect vectors of typhus—nearly eliminating the disease in many parts of Europe. In the South Pacific, it was sprayed aerially for malaria control with spectacular effects. While DDT's chemical and insecticide properties were important factors in these victories, advances in application equipment coupled with a high degree of organization and sufficient manpower were also crucial elements in the success of these wartime spray programs. In 1945, it was made available to farmers as an agricultural insecticide.
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. One CDC physician involved in the United States' DDT spraying campaign said of the effort that "we kicked a dying dog." But in countries without these advances, it was critical in their eradication of the disease.
In 1955, the
World Health OrganizationThe World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health...
commenced a program to eradicate malaria worldwide, relying largely on DDT. The program was initially highly successful, eliminating the disease in "Taiwan, much of the Caribbean, the Balkans, parts of northern Africa, the northern region of Australia, and a large swath of the South Pacific" and dramatically reducing mortality in Sri Lanka and India. However 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. 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".
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 falciparumPlasmodium falciparum is a protozoan parasite, one of the species of Plasmodium that cause malaria in humans. It is transmitted by the female...
. 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
bednetA mosquito net offers protection against mosquitos, flies, and other insects, and thus against diseases such as malaria. Its fine, see-through, mesh construction stops many insects from biting and disturbing the person using the net...
s impregnated with insecticides and other interventions.
Silent Spring and the U.S. ban
As early as the 1940s, scientists in the U.S. had begun expressing concern over possible hazards associated with DDT, and in the 1950s the government began tightening some of the regulations governing its use. However, these early events received little attention, and it was not until 1957, when the
New York Times reported an unsuccessful struggle to restrict DDT use in
Nassau County, New YorkNassau County is a suburban county in the New York Metropolitan Area east of New York City in the U.S. state of New York. As of the 2000 census, the population was 1,334,544...
, that the issue came to the attention of the popular naturalist-author,
Rachel CarsonRachel Louise Carson was an American marine biologist and nature writer whose writings are credited with advancing the global environmental movement....
.
William ShawnWilliam Shawn was an American magazine editor who edited The New Yorker from 1952 until 1987.-Education and Early Life:...
, editor of
The New YorkerThe New Yorker is an American magazine of reportage, commentary, criticism, essays, fiction, satire, cartoons, and poetry published by Condé Nast Publications...
, urged her to write a piece on the subject, which developed into her famous book
Silent SpringSilent Spring is a book written by Rachel Carson and published by Houghton Mifflin in September 1962. The book is widely credited with helping launch the environmental movement....
, published in 1962. The book argued that
pesticideA pesticide is a substance or mixture of substances used to kill a pest.A pesticide is any substance or mixture of substance intended for:- preventing, destroying, repelling or mitigating any pest....
s, including DDT, were poisoning both wildlife and the environment and were also endangering human health.
Silent Spring was a best seller, and public reaction to it launched the modern
environmental movementEnvironmentalism is a broad philosophy and social movement regarding concerns for environmental conservation and improvement of the state of the environment...
in the United States. The year after it appeared,
President KennedyJohn Fitzgerald "Jack" Kennedy , often referred to by his initials JFK, was the 35th President of the United States, serving from 1961 until his assassination in 1963....
ordered his Science Advisory Committee to investigate Carson's claims. The report the committee issued "add[ed] up to a fairly thorough-going vindication of Rachel Carson’s Silent Spring thesis," in the words of the journal
ScienceScience is the academic journal of the American Association for the Advancement of Science and is considered one of the world's most prestigious scientific journals. The peer-reviewed journal, first published in 1880 is circulated weekly and has a print subscriber base of around 130,000...
, and recommended a phaseout of "persistent toxic pesticides". DDT became a prime target of the growing anti-chemical and anti-pesticide movements, and in 1967 a group of scientists and lawyers founded the
Environmental Defense FundEnvironmental Defense Fund or EDF is a US-based nonprofit environmental advocacy group. The group is known for its work on issues including global warming, ecosystem restoration, oceans, and human health...
(EDF) with the specific goal of winning a ban on DDT.
Victor YannaconeVictor Yannacone is a controversial, pioneering environmental attorney, who played leading roles in successful campaigns to ban DDT in the U.S. and expose the effects of Agent Orange on Vietnam vets.-DDT:...
, Charles Wurster, Art Cooley and others associated with inception of EDF had all witnessed bird kills or declines in bird populations and suspected that DDT was the cause. In their campaign against the chemical, EDF petitioned the government for a ban and filed a series of lawsuits. Around this time, toxicologist
David PeakallDavid Beaumont Peakall was an internationally recognised toxicologist. His research into the effects of DDE and DDT on eggshells contributed to the ban on DDT in the US. He proved that the chemicals caused thinning of eggshells, leading to a reduction in the population of various bird species...
was measuring
DDEDichlorodiphenyldichloroethylene is the full name of DDE. This compound is formed by the loss of hydrogen chloride of DDT , of which it is one of the more common breakdown products. DDE is fat soluble which tends to build up in the fat of animals...
levels in the eggs of peregrine falcons and
California condorThe California Condor is a North American species of bird in the New World vulture family Cathartidae and the largest North American land bird. Currently, this condor inhabits only the Grand Canyon area, Zion National Park, and western coastal mountains of California and northern Baja California...
s and finding that increased levels corresponded with thinner shells.
In response to an EDF suit, the U.S. District Court of Appeals in 1971 ordered the
EPAThe U.S. Environmental Protection Agency is an agency of the federal government of the United States charged to regulate chemicals and protect human health by safeguarding the natural environment: air, water, and land...
to begin the de-registration procedure for DDT. After an initial six-month review process,
William RuckelshausWilliam Doyle Ruckelshaus is an American attorney and civil servant. He served as the first head of the Environmental Protection Agency in 1970, was subsequently acting Director of the Federal Bureau of Investigation, and then Deputy Attorney General of the United States...
, the Agency's first
AdministratorThe Administrator of the Environmental Protection Agency is the head of the United States federal government's Environmental Protection Agency, and is thus responsible for enforcing the nation's Clean Air and Clean Water Acts, as well as numerous other environmental statutes...
rejected an immediate suspension of DDT's registration, 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 AgricultureThe United States Department of Agriculture is the United States federal executive department responsible for developing and executing U.S. federal government policy on farming, agriculture, and food...
, 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 then 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 the cancellation of most uses of DDT—an exemption allowed for public health uses under some conditions. Immediately after the cancellation was announced, both EDF and the DDT manufactures filed suit against the EPA, with the industry seeking to overturn the ban, and EDF seeking a comprehensive ban. The cases were consolidated, and in 1973 the U.S. Court of Appeals for the District of Columbia ruled that the EPA had acted properly in banning DDT.
The U.S. DDT ban took place amid a climate of growing public mistrust of industry, with the
Surgeon GeneralThe Surgeon General of the United States is the operational head of the Public Health Service Commissioned Corps and thus the leading spokesman on matters of public health in the federal government...
issuing a report on
smokingSmoking is a practice where a substance, most commonly tobacco, is burned and the smoke tasted or inhaled. This is primarily practised as a route of administration for recreational drug use, as combustion releases the active substances in drugs such as nicotine and makes them available for...
in 1964, the
Cuyahoga RiverThe Cuyahoga River is located in Northeast Ohio in the United States. Outside of Ohio, the river is most famous for being "the river that caught fire", helping to spur the environmental movement in the late 1960s...
catching fire in 1969, the fiasco surrounding the use of
diethylstilbestrolDiethylstilbestrol is a drug, an orally active synthetic nonsteroidal estrogen that was first synthesized in 1938. In 1971 it was found to be a teratogen when given to pregnant women.-Synthesis:...
(DES), and the well-publicized decline in the
bald eagleThe Bald Eagle is a bird of prey found in North America that is most recognizable as the national bird and symbol of the United States of America. This sea eagle has two known sub-species and forms a species pair with the White-tailed Eagle. Its range includes most of Canada and Alaska, all of the...
population.
Some uses of DDT continued under the public health exemption. For example, in June 1979, the California Department of Health Services was permitted to use DDT to suppress flea vectors of
bubonic plaguePlague is a deadly infectious disease caused by the enterobacteria Yersinia pestis . Plague is a zoonotic, primarily carried by rodents and spread to humans via fleas. Plague is notorious throughout history, due to the unrivaled scale of death and devastation it brought...
. DDT also continued to be produced in the US for foreign markets until as late as 1985, when over 300 tonnes were exported.
Restrictions on usage
In the 1970s and 1980s, agricultural use of DDT was banned in most developed countries. DDT was first banned in
HungaryHungary , in English officially the Republic of Hungary , is a landlocked country in the Carpathian Basin of Central Europe, bordered by Austria, Slovakia, Ukraine, Romania, Serbia, Croatia, and Slovenia. Its capital is Budapest. Hungary is a member of OECD, NATO, EU, V4 and is a Schengen state...
in 1968 then in
NorwayNorway , officially the Kingdom of Norway, is a country in Northern Europe occupying the western portion of the Scandinavian Peninsula, as well as Jan Mayen and the Arctic archipelago of Svalbard under the Spitsbergen Treaty...
and
SwedenSweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe...
in 1970 and the US in 1972, but was not banned in the
United KingdomThe United Kingdom of Great Britain and Northern Ireland is a sovereign state located off the northwestern coast of continental Europe. It is an island country, spanning an archipelago including Great Britain, the northeastern part of Ireland, and many small islands...
until 1984. The use of DDT in vector control has not been banned, but it has been largely replaced by less persistent alternative insecticides.
The
Stockholm ConventionStockholm Convention on Persistent Organic Pollutants is an international environmental treaty that aims to eliminate or restrict the production and use of persistent organic pollutants .- History :...
, which entered into force in 2004, outlawed several
persistent organic pollutantPersistent organic pollutants are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes...
s, and restricted the use of DDT to vector control. The Convention has been ratified by more than 160 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, the public health use of DDT was exempted from the ban until alternatives are developed. The Malaria Foundation International states that "The outcome of the treaty is arguably better than the status quo going into the negotiations…For the first time, there is now an insecticide which is restricted to
vector controlFor vector control of induction motors, see Vector_control_Vector control is any method to limit or eradicate the mammals, birds, arthropods, or insects which transmit disease pathogens....
only, meaning that the selection of resistant mosquitoes will be slower than before."
Despite the worldwide ban on agricultural use of DDT, its use in this context continues in India North Korea, and possibly elsewhere.
Today, about 4-5,000 tonnes of DDT are used each year for vector control. In this context, DDT is applied to the inside walls of homes to kill or repel mosquitos entering the home. This intervention, called
indoor residual sprayingIndoor residual spraying or IRS is the process of spraying the inside of dwellings with an insecticide to kill mosquitoes that spread malaria. A dilute solution of insecticide is sprayed on the inside walls of certain types of dwellings—those with walls made from porous materials such as mud or...
(IRS), greatly reduces environmental damage compared to the earlier widespread use of DDT in agriculture. It also reduces the risk of resistance to DDT. This use only requires a small fraction of that previously used in agriculture; for example, the amount of DDT that might have been used on 40 hectares (100 acres) of cotton during a typical growing season in the U.S. is estimated to be enough to treat roughly 1,700 homes.
Environmental impact
DDT is a
persistent organic pollutantPersistent organic pollutants are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes...
that is extremely hydrophobic and strongly absorbed by soils. Depending on conditions, its soil half life can range from 22 days to 30 years. Routes of loss and degradation include runoff, volatilization, photolysis and aerobic and anaerobic
biodegradationBiodegradation is the material breakdown of chemicals by a physiological environment. The term is often used in relation to ecology, waste management and environmental remediation . Organic material can be degraded aerobically with oxygen, or anaerobically, without oxygen...
. When applied to aquatic ecosystems it is quickly absorbed by organisms and by soil or it evaporates, leaving little DDT dissolved in the water itself. Its breakdown products and metabolites, DDE and DDD, are also highly persistent and have similar chemical and physical properties. These products together are known as "total DDT". DDT and its breakdown products are transported from warmer regions of the world to the
ArcticThe Arctic is the region around the Earth's North Pole, opposite the Antarctic region around the South Pole. The Arctic includes the Arctic Ocean and parts of Canada, Greenland , Russia, the United States , Iceland, Norway, Sweden and Finland.The word Arctic comes from the Greek αρκτικός , "near...
by the phenomenon of
global distillationGlobal distillation or the grasshopper effect is the geochemical process by which certain chemicals, most notably persistent organic pollutants , are transported from warmer to colder regions of the Earth, particularly the Poles and mountain tops...
, where they then accumulate in the region's food web.
DDT, DDE, and DDD
magnifyBiomagnification, also known as bioamplification or biological magnification, is the increase in concentration of a substance, such as the pesticide DDT, that occurs in a food chain as a consequence of:...
through the
food chainFood chains describe the eating relationships between species within an ecosystem or a particular living place. Many types of food chains or webs are applicable depending on habitat or environmental factors...
, with
apex predatorApex predators is a predator that has virtually no predators of its own, residing at the top of its food chain...
s such as raptors having a higher concentration of the chemicals than other animals sharing the same environment. They are very lipophilic and are stored mainly in body fat. DDT and DDE are very resistant to metabolism; in humans their half-lives are 6 and up to 10 years, respectively. In the United States, these chemicals were detected in almost all human blood samples tested by the Centers for Disease Control in 2005, though their levels have sharply declined since most uses were banned in the US. Estimated dietary intake has also declined, despite it still being commonly detected in food samples tested by the FDA.
Marine algae (
seaweedSeaweedSeaweed has antioxidents. Is a loose colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...
s) have been shown to act as
bioremediationBioremediation can be defined as any process that uses microorganisms, fungi, green plants or their enzymes to return the natural environment altered by contaminants to its original condition. Bioremediation may be employed to attack specific soil contaminants, such as degradation of chlorinated...
agents and can reduce the toxicity of soil contaminated by DDT by up to 80% within six weeks.
Effects on wildlife and eggshell thinning
DDT is toxic to a wide range of animals in addition to insects. It is highly toxic to aquatic life, including
crayfishCrayfish, crawfish, or crawdads — members of the superfamilies Astacoidea and Parastacoidea — are freshwater crustaceans resembling small lobsters, to which they are related...
,
daphnidsDaphnia are small, planktonic crustaceans, between 0.2 and 5 mm in length. Daphnia are members of the order Cladocera, and are one of the several small aquatic crustaceans commonly called water fleas because of their saltatory swimming style...
,
sea shrimpShrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
and many species of
fishA fish is any aquatic vertebrate animal that is typically ectothermic , covered with scales, and equipped with two sets of paired fins and several unpaired fins...
. It is less toxic to mammals but cats are very susceptible, and in several instances cat populations were significantly depleted in malaria control operations that used DDT, often leading to explosive growth in rodent populations. DDT may be moderately toxic to some
amphibianAmphibians , such as frogs, toads, salamanders, newts, and caecilians, are ectothermic animals that metamorphose from a juvenile water-breathing form, to an adult air-breathing form. Though amphibians typically have four limbs, the Caecilians are notable for being limbless. Unlike other land...
species, especially in the larval stages. Most famously, it is a reproductive toxicant for certain birds species, and it is a major reason for the decline of the
bald eagleThe Bald Eagle is a bird of prey found in North America that is most recognizable as the national bird and symbol of the United States of America. This sea eagle has two known sub-species and forms a species pair with the White-tailed Eagle. Its range includes most of Canada and Alaska, all of the...
,
brown pelicanThe Brown Pelican is the smallest of the eight species of pelican, although it is a large bird in nearly every other regard...
peregrine falconThe Peregrine Falcon , also known simply as the Peregrine, and historically as the "Duck Hawk" in North America, is a cosmopolitan bird of prey in the family Falconidae. It is a large, crow-sized falcon, with a blue-gray back, barred white underparts, and a black head and "moustache"...
, and
ospreyThe Osprey , sometimes known as the sea hawk, is a diurnal, fish-eating bird of prey. It is a large raptor, reaching 60 centimetres in length with a 1.8 metre wingspan...
. Birds of prey,
waterfowlWaterfowl are certain wildfowl of the order Anseriformes, especially members of the family Anatidae, which includes ducks, geese, and swans.They are strong swimmers with medium to large bodies. They have historically been an important food source, and continue to be hunted as game, or raised as...
, and
song birdsA passerine is a bird of the order Passeriformes, which includes more than half of all bird species. Sometimes known as perching birds or, less accurately, as songbirds, the passerines form one of the most diverse terrestrial vertebrate orders:...
are more susceptible to eggshell thinning than chickens and
related speciesGalliformes are an order of birds containing turkeys, grouse, chickens, quails, and pheasants. More than 250 living species are found worldwide. Common names are gamefowl or gamebirds, landfowl, gallinaceous birds or galliforms...
, and DDE appears to be more potent than DDT.
The biological mechanism for the thinning is not entirely known, but it is believed that p,p'-DDE impairs the shell gland's ability to excrete
calcium carbonateCalcium carbonate is a chemical compound with the chemical formula CaCO
3. It is a common substance found in rock in all parts of the world, and is the main component of shells of marine organisms, snails, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural...
onto the developing egg. There is also evidence that o,p'-DDT disrupts the development of the female reproductive tract, thereby impairing the quality of the eggshells produced by the bird once it matures. Multiple mechanisms may be at work, or different mechanisms may operate in different species. Some studies have shown that although DDE levels have fallen dramatically, eggshell thickness remains 10–12 percent thinner than before DDT was first used.
Effects on human health
Potential mechanisms of DDT on humans are genotoxicity and
endocrine disruptionEndocrine disruptors are exogenous substances that act like hormones in the endocrine system and disrupt the physiologic function of endogenous hormones. They are sometimes also referred to as hormonally active agents or endocrine disrupting chemicals/compounds ...
. DDT may have direct genotoxicity, but may also induce enzymes that produce other genotoxic intermediates and
DNA adductA DNA adduct is a piece of DNA covalently bonded to a chemical. This has shown to be the start of a cancerous cell, or carcinogenesis. DNA adducts in scientific experiments are used as biomarkers and as such are themselves measured to reflect quantitatively, for comparison, the amount of cancer in...
s. It is an endocrine disruptor; The DDT metabolite
DDEDichlorodiphenyldichloroethylene is the full name of DDE. This compound is formed by the loss of hydrogen chloride of DDT , of which it is one of the more common breakdown products. DDE is fat soluble which tends to build up in the fat of animals...
acts as an
antiandrogenAn antiandrogen, or androgen antagonist, is any of a group of hormone receptor antagonist compounds that are capable of preventing or inhibiting the biologic effects of androgens, male sex hormones, on normally responsive tissues in the body...
(but not as an
estrogenEstrogens are a group of steroid compounds, named for their importance in the estrous cycle, and functioning as the primary female sex hormone, their name comes from estrus/oistros + gen/gonos = to generate.Estrogens are used as part of some oral contraceptives, in estrogen replacement...
). o,p'-DDT, a minor component in commercial DDT has weak estrogenic activity. However, p,p'-DDT, the main component of DDT, has little or no androgenic or estrogenic activity.
Acute toxicity
DDT is classified as "moderately toxic" by the United States National Toxicology Program (NTP) and "moderately hazardous" by WHO, based on the rat oral
LD50In toxicology, the median lethal dose, LD50 , LC50 or LCt50 of a toxic substance or radiation is the dose required to kill half the members of a tested population...
of 113 mg/kg. DDT has on rare occasions been administered orally as a treatment for
barbiturateBarbiturates are drugs that act as central nervous system depressants, and, by virtue of this, they produce a wide spectrum of effects, from mild sedation to total anesthesia. They are also effective as anxiolytics, hypnotics and as anticonvulsants. They have addiction potential, both physical and...
poisoning.
Diabetes
Organochlorine compounds, generally, and DDT and DDE, specifically, have been linked to diabetes. A number of studies from the US and Sweden have found that the prevalence of the disease in a population increases with serum DDT or DDE levels.
Developmental and reproductive toxicity
DDT and DDE, like other organochlorines, have been shown to have
xenoestrogenEstrogens are a group of steroid compounds, named for their importance in the estrous cycle, and functioning as the primary female sex hormone, their name comes from estrus/oistros + gen/gonos = to generate.Estrogens are used as part of some oral contraceptives, in estrogen replacement...
ic activity, meaning they are chemically similar enough to estrogens to trigger hormonal responses in animals. This
endocrine disruptingEndocrine disruptors are exogenous substances that act like hormones in the endocrine system and disrupt the physiologic function of endogenous hormones. They are sometimes also referred to as hormonally active agents or endocrine disrupting chemicals/compounds ...
activity has been observed toxicological studies involving
miceA mouse is a small mammal belonging to the order of rodents. The best known mouse species is the common house mouse . It is also a popular pet. The American white-footed mouse and the deer mouse also sometimes live in houses. In some places, certain kinds of field mice are also common...
and
ratRats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus...
s, and available epidemiological evidence indicates that these effects may be occurring in humans as a result of DDT exposure. There is therefore concern that DDT may cause developmental and reproductive toxicity.
- A review article in The Lancet
The Lancet is a peer-reviewed general medical journal, published weekly.One of the world's best-known and most respected general medical journals, with editorial offices in London and New York, The Lancet was founded in 1823 by Thomas Wakley, who named it after the surgical instrument called a...
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-disruptingEndocrine disruptors are exogenous substances that act like hormones in the endocrine system and disrupt the physiologic function of endogenous hormones. They are sometimes also referred to as hormonally active agents or endocrine disrupting chemicals/compounds ...
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
Lactation describes the secretion of milk from the mammary glands, the process of providing that milk to the young, and the period of time that a mother lactates to feed her young. The process occurs in all female mammals, and in humans it is commonly referred to as breastfeeding or nursing...
. Some 21st century researchers argue that these effects may cause increases in infant deaths in areas where DDT is used for malaria control, and thus offset any benefit derived from its anti-malarial effects. A 2008 study, however, failed to confirm the association between exposure and difficulty breastfeeding.
- 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
The University of California, Berkeley is a public research university located in Berkeley, California, United States. The oldest of the ten major campuses affiliated with the University of California, Berkeley offers some 300 undergraduate and graduate degree programs in a wide range of disciplines...
suggests children who have been exposed to DDT while in the womb have a greater chance of experiencing development problems, and other studies have found that even low levels of DDT or DDE in umbilical cordIn placental mammals, the umbilical cord is the connecting cord from the developing embryo or fetus to the placenta...
serum at birth are associated with decreased attention at infancy and decreased cognitive skills at 4 years of age. Similarly, Mexican researchers have demonstrated a link between DDE exposure in the first trimester of pregnancy and retarded psychomotorPsychomotor can refer to:* Psychomotor learning* Psychomotor retardation* Psychomotor agitation...
development.
- A 2007 study documented decreases in semen
Semen is an organic fluid, also known as seminal fluid, that usually contains spermatozoa. It is secreted by the gonads and other sexual organs of male or hermaphroditic animals and can fertilize female ova...
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. The same researchers reported similar results in 2006 from a study of men in Mexico. 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."
- Several studies have examined the association between time to pregnancy (TTP) and levels of DDT or DDE in the blood of pregnant women. These studies have generally found that high exposure levels do not increase TTP. There is some evidence that the daughters of highly exposed women may have more difficulty getting pregnant (i.e. increased TTP).
- DDT exposure is associated with early pregnancy loss, a type of miscarriage
Miscarriage or spontaneous abortion is the spontaneous end of a pregnancy at a stage where the embryo or fetus is incapable of surviving, generally defined in humans at prior to 20 weeks of gestation...
. 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." 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 findings are relevant to the debate about DDT and malaria control.
- A case-control study of congenital hypothyroidism
Congenital hypothyroidism is a condition of thyroid hormone deficiency present at birth. Approximately 1 in 4000 newborn infants has a severe deficiency of thyroid function, while even more have mild or partial degrees. If untreated for several months after birth, severe congenital hypothyroidism...
in Japan concluded that in utero DDT exposure may affect thyroidThe thyroid is one of the largest endocrine glands in the body. This gland is found in the neck inferior to the thyroid cartilage and at approximately the same level as the cricoid cartilage...
hormone levels and "play an important role in the incidence and/or causation of cretinismCretinism is a condition of severely stunted physical and mental growth due to untreated congenital deficiency of thyroid hormones or from prolonged nutritional deficiency of iodine.-Etymology and use of cretin:...
." Other studies have also found the DDT or DDE interfere with proper thyroid function.
Other
Occupational exposure to DDT (either as a farmer or a malaria control worker) has been linked to:
- Neurological problems
- Asthma
Asthma is a predisposition to chronic inflammation of the lungs in which the airways are reversibly narrowed. Asthma affects 7% of the population of the United States, and 300 million worldwide...
Carcinogenicity
DDT is suspected to cause cancer. The NTP classifies it as "reasonably anticipated to be a human
carcinogenA carcinogen is any substance, radionuclide or radiation that is an agent directly involved in the promotion of cancer or in the increase of its propagation. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes...
", and the EPA classifies DDT, DDE, and DDD as a class B2 "probable" human carcinogens. The
International Agency for Research on CancerThe International Agency for Research on Cancer is an intergovernmental agency forming part of the World Health Organisation of the United Nations....
classifies it is as a "possible" human carcinogen. These evaluations are based mainly on the results of animal studies.
There is epidemiological evidence (i.e. studies in humans) that DDT causes cancer of the:
- Liver
Hepatic tumors are tumors or growths on or in the liver . These growths can be benign or malignant...
- Pancreas
Pancreatic cancer is a malignant neoplasm of the pancreas. Each year in the United States, about 42,470 individuals are diagnosed with this condition and 35,240 die from the disease. The prognosis is generally poor; less than 5 percent of those diagnosed are still alive five years after diagnosis...
- Breast
Breast cancer is a cancer that starts in the breast, usually in the inner lining of the milk ducts or lobules. There are different types of breast cancer, with different stages , aggressiveness, and genetic makeup. With best treatment, 10-year disease-free survival varies from 98% to 10%...
(see below)
There is mixed evidence that it contributes cancer of the:
- Blood
Leukemia is a cancer of the blood or bone marrow and is characterized by an abnormal proliferation of blood cells, usually white blood cells . Leukemia is a broad term covering a spectrum of diseases...
(i.e. Leukemia)
- Testis
Testicular cancer is cancer that develops in the testicles, a part of the male reproductive system.In the United States, between 7,500 and 8,000 diagnoses of testicular cancer are made each year. Over his lifetime, a man's risk of testicular cancer is roughly 1 in 250 . It is most common among...
- Lymphatic system
The Non-Hodgkin lymphomas are a diverse group of hematologic cancers which encompass any lymphoma other than Hodgkin's Lymphoma.Lymphoma is a type of cancer derived from lymphocytes, a type of white blood cell. Many subtypes of non-Hodgkin lymphoma have been described...
(i.e. non-Hodgkin Lymphoma)
In contrast, epidemiological studies suggest that DDT/DDE
does not cause cancers of the:
- Plasma
Multiple myeloma , also known as MM, myeloma, plasma cell myeloma, or as Kahler's disease is a cancer of the white blood cells known as plasma cells. A type of B cell, plasma cells are a crucial part of the immune system responsible for the production of antibodies in humans and other vertebrates...
, (i.e. multiple myeloma)
- Prostate
Prostate cancer is a form of cancer that develops in the prostate, a gland in the male reproductive system. The cancer cells may metastasize from the prostate to other parts of the body, particularly the bones and lymph nodes. Prostate cancer may cause pain, difficulty in urinating, problems...
- Endometrium
Endometrial cancer refers to several types of malignancy which arise from the endometrium, or lining of the uterus. Endometrial cancers are the most common gynecologic cancers in the United States, with over 35,000 women diagnosed each year in the U.S...
- Rectum
Colorectal cancer, also called colon cancer or large bowel cancer, includes cancerous growths in the colon, rectum and appendix. With 655,000 deaths worldwide per year, it is the third most common form of cancer and the third leading cause of cancer-related death in the Western world. Many...
- Lung
Lung cancer is a disease of uncontrolled cell growth in tissues of the lung. This growth may lead to metastasis, which is the invasion of adjacent tissue and infiltration beyond the lungs. The vast majority of primary lung cancers are carcinomas of the lung, derived from epithelial cells...
- Bladder
Bladder cancer refers to any of several types of malignant growths of the urinary bladder. It is a disease in which abnormal cells multiply without control in the bladder. The bladder is a hollow, muscular organ that stores urine; it is located in the pelvis...
- Stomach
Stomach or gastric cancer can develop in any part of the stomach and may spread throughout the stomach and to other organs; particularly the esophagus, lungs and the liver. Stomach cancer causes about 800,000 deaths worldwide per year.-Epidemiology:...
Breast cancer
The question if DDT or DDE are
risk factors of breast cancerRisk factors of breast cancer belongs in the field of epidemiology of breast cancer.Breast cancer, like other forms of cancer, is considered to result from multiple environmental and hereditary risk factors....
has been the subject of numerous investigations. While individual studies have come to conflicting conclusions, the most recent reviews of all the evidence conclude that exposure to DDT before puberty increases the risk of breast cancer later in life. Until recently, almost all studies measured DDT or DDE blood levels at the time of breast cancer diagnosis or after. This study design has been criticized, since the levels of DDT or DDE at diagnosis do not necessarily correspond to the levels present in a woman's body at the time when her cancer first started. Such studies have thus yielded conflicting results and taken as a whole "do not support the hypothesis that exposure to DDT is an important risk factor for breast cancer." The studies of this design have been extensively reviewed.
In contrast to these studies, a study published in 2007 found a strong association between exposure to specifically the
p,p-isomer of DDT early in life and breast cancer later in life. Unlike previous studies, this was
prospective cohort studyA prospective cohort study is a cohort study that follows over time a group of similar individuals who differ with respect to certain factors under study, in order to determine how these factors affect rates of a certain outcome...
in which blood samples were collected from young mothers in the 1960s while DDT was still in use, and their breast cancer status was then monitored. 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 third who were exposed most to
p, p-DDT had a fivefold increase in breast cancer incidence over the least exposed third, after correcting for the protective effect of
o,p-DDT. These results are supported by animal studies.
DDT use against malaria
MalariaMalaria is a vector-borne infectious disease caused by a eukaryotic protist of the genus Plasmodium. It is widespread in tropical and subtropical regions, including parts of the Americas, Asia, and Africa. Each year, there are approximately 350–500 million cases of malaria, killing between one and...
remains a major public health challenge in many parts of the world. The
World Health OrganizationThe World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health...
(WHO) estimates that there are 250 million cases every year, resulting in almost 1 million deaths. About 90% of these deaths occur in
AfricaAfrica is the world's second-largest and second most-populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area. With a billion people in 61 territories, it accounts for about 14.8% of the...
, and mostly to children under the age of 5. Spraying DDT is one of many public health interventions currently used to fight the disease. Its use in this context has been called everything from a "miracle weapon [that is] like Kryptonite to the mosquitoes," to "toxic colonialism."
Before the advent of DDT, aggressive campaigns to eliminate mosquito breeding grounds by drainage or poisoning with
Paris greenParis Green is a common name for copper acetoarsenite, or C.I. Pigment Green 21, an extremely toxic blue green chemical with four main uses: pigment, animal poison , insecticide, and blue colorant for fireworks...
or
pyrethrumPyrethrum refers to several Old World plants of the genus Chrysanthemum which are cultivated as ornamentals for their showy flower heads. It is also the name of a natural insecticide made from the dried flower heads of C. cinerariifolium and C. coccineum...
were used, sometimes successfully, to fight the disease. In many parts of the world, rising standards of living resulted in the elimination of malaria as a collateral benefit of the introduction of window screens and improved sanitation. Today, a variety of interventions are used, and usually many are used simultaneously. These include the use of antimalarial drugs to prevent or treat malaria infections; improvements in public health infrastructure to quickly diagnose, sequester, and treat infected individuals; the distribution of
bednetsA mosquito net offers protection against mosquitos, flies, and other insects, and thus against diseases such as malaria. Its fine, see-through, mesh construction stops many insects from biting and disturbing the person using the net...
and other methods intended to keep mosquitoes from biting humans; and
vector controlFor vector control of induction motors, see Vector_control_Vector control is any method to limit or eradicate the mammals, birds, arthropods, or insects which transmit disease pathogens....
strategies. These include larvaciding with appropriate insecticides, ecological controls such as draining mosquito breeding grounds or introducing fish to eat larva, and
indoor residual sprayingIndoor residual spraying or IRS is the process of spraying the inside of dwellings with an insecticide to kill mosquitoes that spread malaria. A dilute solution of insecticide is sprayed on the inside walls of certain types of dwellings—those with walls made from porous materials such as mud or...
(IRS) with insecticides. IRS involves the treatment of all interior walls and ceilings with insecticides, and is particularly effective against mosquitoes, since many species will rest on an indoor wall before or after feeding. DDT is one of 12 insecticides approved by the WHO for IRS, and the contemporary DDT debate revolves around how much of a role the chemical should play in this mix of strategies.
The WHO's anti-malaria campaign of the 1950s and 1960s relied heavily on DDT and initially the results were promising, though short lived. Experts tie the resurgence of malaria to numerous factors, including poor leadership, management, and funding of malaria control programs; poverty; civil unrest; and increased
irrigationIrrigation is an artificial application of water to the soil. It is usually used to assist in growing crops in dry areas and during periods of inadequate rainfall...
. The evolution of resistance of the malaria parasite to the drugs traditionally used to treat the disease (e.g.
chloroquineChloroquine is a 4-aminoquinoline drug used in the treatment or prevention of malaria.-Uses:* It has long been used in the treatment or prevention of malaria. After the malaria parasite Plasmodium falciparum started to develop widespread resistance to chloroquine, new potential utilisations of...
) and evolution of resistance of mosquitoes to insecticides have greatly exacerbated the situation. Resistance of mosquitoes to DDT was largely fueled by its often unrestricted use in agriculture. This, coupled with the awareness that DDT may be harmful both to humans and the environment led many governments to restrict or curtail the use of DDT in vector control.
Once the mainstay of anti-malaria campaigns, as of 2006 only 13 countries were still using DDT, including India and some southern African states, though the number is expected to rise.
Overall effectiveness of DDT against malaria
When it was first introduced in World War II, DDT was very effective in reducing malaria morbidity and
mortalityMortality rate is a measure of the number of deaths in some population, scaled to the size of that population, per unit time. Mortality rate is typically expressed in units of deaths per 1000 individuals per year; thus, a mortality rate of 9.5 in a population of 100,000 would mean 950 deaths per...
. The WHO's anti-malaria campaign, which consisted mostly of spraying DDT, was initially very successful as well. For example, in
Sri LankaSri Lanka , officially the Democratic Socialist Republic of Sri Lanka , is an island country in South Asia, located about off the southern coast of India...
, the program reduced cases from about 3 million per year before spraying to just 29 in 1964. Thereafter the program was halted to save money, and malaria rebounded to 600,000 cases in 1968 and the first quarter of 1969. The country resumed DDT spraying, but it was largely ineffective because mosquitoes had acquired resistance to the chemical in the interim, presumably because of its continued use in agriculture. The program was forced to switch to
malathionMalathion is an organophosphate parasympathomimetic which binds irreversibly to cholinesterase. Malathion is an insecticide of relatively low human toxicity....
, which though more expensive, proved effective.
Today, DDT remains on the WHO's list of insecticides recommended for IRS. Since the appointment of
Arata Kochiis a Japanese physician and public health expert, who is the director of the World Health Organization's malaria program. He had previously been director of its tuberculosis programs for ten years.-External links:...
as head of its anti-malaria division, WHO's policy has shifted from recommending IRS only in areas of seasonal or episodic transmission of malaria, to also advocating it in areas of continuous, intense transmission. The WHO has none-the-less affirmed its commitment to eventually phasing DDT out, aiming "to achieve a 30% cut in the application of DDT world-wide by 2014 and its total phase-out by the early 2020s if not sooner" while simultaneously combating malaria. The WHO plans to implement alternatives to DDT to achieve this goal.
South Africa is one country that continues to use DDT under WHO guidelines. In 1996, the country switched to alternative insecticides and malaria incidence increased dramatically. Returning to DDT and introducing new drugs brought malaria back under control. According to DDT advocate Donald Roberts, malaria cases increased in
South AmericaSouth America is the southern continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere...
after countries in that continent stopped using DDT. Research data shows a significantly strong negative relationship between DDT residual house sprayings and malaria rates. In a research from 1993 to 1995, Ecuador increased its use of DDT and resulted in a 61% reduction in malaria rates, while each of the other countries that gradually decreased its DDT use had large increase in malaria rates.
Mosquito resistance to DDT
The evolution of resistance to DDT in mosquitoes has greatly reduced its effectiveness in many parts of the world, and current WHO guidelines require that before the chemical is used in an area, susceptibility of local mosquitoes to DDT must be confirmed. The appearance of DDT-resistance is largely due to its use in agriculture, where it was used in much greater amounts than the relatively small quantities used for disease prevention. According to one study that attempted to quantify the lives saved by banning agricultural uses of DDT and thereby slowing the spread of resistance, "it can be estimated that at current rates each kilo of insecticide added to the environment will generate 105 new cases of malaria."
Resistance was noted early in spray campaigns, with Paul Russell, a former head of the
AlliedThe Allies of World War II were the countries that opposed the Axis powers during the Second World War . The involvement of the Allies in World War II was either natural and inevitable they were invaded or under the direct threat of invasion by the Axis or compelled by concerns that the Axis powers...
Anti-Malaria campaign, observing in 1956 that eradication programs had to be wary of relying on DDT for too long as "resistance has appeared [after] six or seven years." DDT has lost much of its effectiveness in many parts of the world including Sri Lanka,
PakistanPakistan , officially the Islamic Republic of Pakistan, is a country located at the crossroads of South Asia, the Middle East, and Central Asia...
,
TurkeyTurkey , known officially as the Republic of Turkey
, is a Eurasian country that stretches across the Anatolian peninsula in Western Asia and Thrace in the Balkan region of southeastern Europe...
and
Central AmericaManagua
Guatemala City
San Salvador
San Pedro Sula
Panama City
San José, Costa Rica
Santa Ana, El Salvador
León
San Miguel|-|}...
, and it has largely been replaced by
organophosphateAn organophosphate is the general name for esters of phosphoric acid. Phosphates are probably the most pervasive organophosphorus compounds. Many of the most important biochemicals are organophosphates, including DNA and RNA as well as many cofactors that are essential for life...
or
carbamateCarbamates, or urethanes, are a group of organic compounds sharing a common functional group with the general structure R1-O-NR2-R3. Carbamates are esters of carbamic acid, NH2COOH, an unstable compound with R1 = R2 = R3 = H...
insecticides,
e.g. malathion or
bendiocarbBendiocarb is an acutely toxic carbamate insecticide used in public health and agriculture and is effective against a wide range of nuisance and disease vector insects...
.
In many parts of
IndiaIndia, officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the south, the Arabian Sea on the west, and the Bay of Bengal...
, DDT has largely lost its effectiveness. Agricultural uses were banned in 1989, and its use for anti-malarial purposes has been declining. Its use in urban areas has been halted completely. Nevertheless, DDT is still manufactured and used in the country, and one study had concluded 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."
Studies of malaria-vector mosquitoes in KwaZulu-Natal Province,
South AfricaThe Republic of South Africa is a country located at the southern tip of Africa, with a coastline on the Atlantic and Indian Oceans. To the north lie Namibia, Botswana and Zimbabwe, to the east are Mozambique and Swaziland, while Lesotho is an independent country surrounded by South Africa.Modern...
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."
It has been argued that DDT can still be effective against resistant mosquitoes, and that the avoidance of DDT-sprayed walls by mosquitoes is an additional benefit of the chemical. For example, a 2007 study reported that DDT-resistant mosquitoes still avoided DDT-treated huts. The researchers argued that DDT was the best pesticide for use in IRS (even though it did not afford the most protection from mosquitoes out of the three test chemicals) because the others pesticides worked primarily by killing or irritating mosquitoes—modes of action the authors presume mosquitoes will develop resistance to. Others have argued that the avoidance of DDT sprayed walls by mosquitoes 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." 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."
Residents' resistance to use of DDT
For IRS to be effective, at least 80% of homes and barns in an area must be sprayed, and if enough residents refuse spraying, the effectiveness of the whole program can be jeopardized. Many residents resist DDT spraying for various reasons. For instance, the smell lingers, it stains on the walls, and it sometime fails to kill—or even exacerbates problems with—other insect pests.
The use of
pyrethroidA pyrethroid is a synthetic chemical compound similar to the natural chemical pyrethrins produced by the flowers of pyrethrums . Pyrethroids now constitute a major proportion of the synthetic insecticide market and are common in commercial products such as household insecticides...
insecticides (e.g.
deltamethrinDeltamethrin is a pyrethroid ester insecticide.-Usage:Deltamethrin products are among some of the most popular and widely used insecticides in the world and have become very popular with pest control operators and individuals in the United States in the past five years. This material is a member of...
and
lambda-cyhalothrinLambda-cyhalothrin is a pyrethroid insecticide which is a highly active isomer of cyhalothrin. Brand names include 'Karate', 'Kung-fu' and 'Matador' ; in the USA, 'Triazide' and 'Hot Shot' are used in the Home Landsape and Garden markets...
) can overcome some of these issues, and meets with less resistance than DDT.
Human exposure associated with DDT spraying
People living in areas where DDT is used for IRS have high levels of the chemical and its breakdown products in their bodies. Compared to contemporaries living in countries where DDT is not used,
South AfricaThe Republic of South Africa is a country located at the southern tip of Africa, with a coastline on the Atlantic and Indian Oceans. To the north lie Namibia, Botswana and Zimbabwe, to the east are Mozambique and Swaziland, while Lesotho is an independent country surrounded by South Africa.Modern...
ns living in sprayed homes have levels that are several orders of magnitude greater.
Breast milkHuman breast milk refers to the milk produced by a mother to feed her baby. It provides the primary source of nutrition for newborns before they are able to eat and digest other foods; older infants and toddlers may continue to be breastfed...
from regions where DDT is used for malaria control contains enough DDT to greatly exceed the allowable daily intake of breast feeding infants. These levels have been associated with neurological abnormalities in babies ingesting relatively large quantities of DDT in their milk.
Most studies of DDT's health effects on human have been conducted in developed countries where DDT is not used and exposure is relatively low. Many experts are therefore concerned about the health consequences of its use in IRS, as this results in very high exposure. They urge that alternatives been used instead. Epidemiologist Brenda Eskenazi argues that "We know DDT can save lives by repelling and killing disease-spreading mosquitoes. But evidence suggests that people living in areas where DDT is used are exposed to very high levels of the pesticide. The only published studies on health effects conducted in these populations have shown profound effects on male fertility. Clearly, more research is needed on the health of populations where indoor residual spraying is occurring, but in the meantime, DDT should really be the last resort against malaria rather than the first line of defense."
Illegal diversion of DDT from the public health sector to agriculture is also a concern, as it is almost impossible to prevent, and its subsequent use on crops is totally unregulated. For example, DDT use is wide spread in Indian agriculture, particularly
mangoMangoes belong to the genus Mangifera, consisting of numerous species of tropical fruiting trees in the flowering plant family Anacardiaceae. The mango is indigenous to the Indian Subcontinent...
production, and is reportedly used by librarians in the country to protect books. Another example is in Ethiopia, where DDT intended for malaria control is reportedly being used in coffee production. "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.
Criticism of restrictions on DDT use
Critics claim that restrictions on the use of DDT in vector control have resulted in substantial numbers of unnecessary deaths due to malaria. Estimates for the number of these deaths range from hundreds of thousands, according to Nicholas Kristof, to much higher figures. Robert Gwadz of the
National Institutes of HealthThe National Institutes of Health is an agency of the United States Department of Health and Human Services and is the primary agency of the United States government responsible for biomedical and health-related research. It consists of 27 separate institutes and centers which includes the Office...
said in 2007 that "The ban on DDT may have killed 20 million children." These arguments have been called "outrageous" by former WHO scientist Socrates Litsios, and May Berenbaum, an entomologist at the University of Illinois, says that "to blame environmentalists who oppose DDT for more deaths than Hitler is worse than irresponsible." Investigative journalist Adam Sarvana characterizes this notion as a "myth" promoted principally by
Roger BateRoger Bate is an economist who has held a variety of positions in free market, libertarian, and conservative think tanks and lobby groups promoting anti-regulatory, pro-business causes. His current work focuses on U.S. and international aid policy, performance of aid organizations, and health...
of the pro-DDT advocacy group
Africa Fighting MalariaAfrica Fighting Malaria is an NGO based in Washington DC and South Africa which states it "seeks to educate people about the scourge of Malaria and the political economy of malaria control"...
(AFM) in service of his anti-regulatory,
free marketA free market describes a market without economic intervention and regulation by government except to regulate against force or fraud. The terminology is used by economists and in popular culture. A free market requires protection of property rights, but no regulation, no subsidization, no single...
ideology.
Criticisms of a "ban" on DDT often specifically reference the 1972 US ban (with the erroneous implication that this constituted a worldwide ban and prohibited use of DDT in vector control). Reference is often made to
Rachel CarsonRachel Louise Carson was an American marine biologist and nature writer whose writings are credited with advancing the global environmental movement....
's
Silent Spring even though she never pushed for a ban on DDT.
John QuigginJohn Quiggin is an Australian economist and professor at the University of Queensland. Quiggin studied at the Australian National University, obtaining bachelor's degrees in Arts and Economics in 1978 and 1980 respectively, and completing a master's degree in Economics in 1984. Quiggin was awarded...
and Tim Lambert have written that "the most striking feature of the claim against Carson is the ease with which it can be refuted." Carson actually devoted a page of her book to considering the relationship between DDT and malaria, warning of the
evolutionIn biology, evolution is change in the genetic material of a population of organisms from one generation to the next. Though changes produced in any one generation are normally small, differences accumulate with each generation and can, over time, cause substantial changes in the population, a...
of DDT resistance in mosquitoes and 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 [is 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."
According to
Amir AttaranAmir Attaran is a Canadian lawyer, immunologist, and law professor.Currently, Attaran is Associate Professor of Law and Population Health and the holder of the Canada Research Chair in Law, Population Health and Global Development Policy at the University of Ottawa.- Early life and education...
and Roger Bate, many environmental groups fought against the public health exception of DDT in the 2001
Stockholm ConventionStockholm Convention on Persistent Organic Pollutants is an international environmental treaty that aims to eliminate or restrict the production and use of persistent organic pollutants .- History :...
, over the objections of third world governments and many malaria researchers. Attaran strongly objected to an outright ban, writing, "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..."
It has also been argued that donor governments and agencies have refused to fund DDT spraying, or made aid contingent upon not using DDT. According a report in the
British Medical Journal, use of DDT in
MozambiqueMozambique, officially the Republic of Mozambique , is a country in southeastern Africa bordered by the Indian Ocean to the east, Tanzania to the north, Malawi and Zambia to the northwest, Zimbabwe to the west and Swaziland and South Africa to the southwest. It was explored by Vasco da Gama in 1498...
"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." Roger Bate asserts that "many countries have been coming under pressure from international health and environment agencies to give up DDT or face losing aid grants: Belize and Bolivia are on record admitting they gave in to pressure on this issue from [USAID]."
The
United States Agency for International DevelopmentThe United States Agency for International Development is the United States federal government organization responsible for most non-military foreign aid...
(USAID) has been the focus of much criticism. While the agency is currently funding the use of DDT in some African countries, in the past it has not. When
John StosselJohn F. Stossel is a consumer reporter, investigative journalist, author, libertarian columnist, and former co-anchor for the ABC News show 20/20. Stossel began his journalism career as a researcher for KGW-TV and later became a consumer reporter at WCBS-TV in New York City before joining ABC News...
accused USAID of not funding DDT because it wasn't "politically correct," Anne Peterson, the agency's assistant administrator for global health, replied that "I believe that the strategies we are using are as effective as spraying with DDT … So, politically correct or not, I am very confident that what we are doing is the right strategy." USAID's Kent R. Hill states that the agency has been misrepresented: "USAID strongly supports spraying as a preventative measure for malaria and will support the use of DDT when it is scientifically sound and warranted." With regard to decision to start funding the use of the chemical, the Agency's website states that "USAID has never had a 'policy' as such either 'for' or 'against' DDT for IRS. The real change in the past two years [2006/07] has been a new interest and emphasis on the use of IRS in general—with DDT or any other insecticide—as an effective malaria prevention strategy in tropical Africa." The website further explains that in many cases alternative malaria control measures were judged to be more cost-effective that DDT spraying, and so were funded instead.
DDT versus other insecticides
Advocates of increased use of DDT in IRS claim that alternative insecticides are more expensive, more toxic, or not as effective. As discussed above, susceptibility of mosquitoes to DDT varies geographically and the same is true for alternative insecticides, so its effectiveness vis-a-vis other chemicals varies. With regard to toxicity and cost-effectiveness versus other insecticides, actual data is lacking. The relative costs of employing various insecticides vary by location and ease of access, the habits of the particular mosquitoes prevalent in each area, the degrees of resistance to various pesticides exhibited by the mosquitoes, and the habits and compliance of the population, among other factors. Furthermore, the choice of insecticide has little impact on the overall cost of a round of spraying, since insecticide costs are only a fraction total budget for an IRS campaign. However to be effective, IRS needs to be maintained throughout the malaria season, and DDT lasts longer than alternative insecticides, so needs to be applied less frequently.
OrganophosphateAn organophosphate is the general name for esters of phosphoric acid. Phosphates are probably the most pervasive organophosphorus compounds. Many of the most important biochemicals are organophosphates, including DNA and RNA as well as many cofactors that are essential for life...
and
carbamateCarbamates, or urethanes, are a group of organic compounds sharing a common functional group with the general structure R1-O-NR2-R3. Carbamates are esters of carbamic acid, NH2COOH, an unstable compound with R1 = R2 = R3 = H...
insecticides,
e.g. malathionMalathion is an organophosphate parasympathomimetic which binds irreversibly to cholinesterase. Malathion is an insecticide of relatively low human toxicity....
and
bendiocarbBendiocarb is an acutely toxic carbamate insecticide used in public health and agriculture and is effective against a wide range of nuisance and disease vector insects...
, respectively, are more expensive than DDT per kilogram and are applied at roughly the same dosage.
PyrethroidA pyrethroid is a synthetic chemical compound similar to the natural chemical pyrethrins produced by the flowers of pyrethrums . Pyrethroids now constitute a major proportion of the synthetic insecticide market and are common in commercial products such as household insecticides...
s such as
deltamethrinDeltamethrin is a pyrethroid ester insecticide.-Usage:Deltamethrin products are among some of the most popular and widely used insecticides in the world and have become very popular with pest control operators and individuals in the United States in the past five years. This material is a member of...
are also more expensive than DDT, but are applied more sparingly (0.02-0.3 g/m
2 vs 1-2 g/m
2), so the net cost per house is about the same per 6 months.
DDT versus non-chemical vector control
Before DDT, malaria was successfully eradicated or curtailed in several tropical areas by removing or poisoning the breeding grounds of the mosquitoes or the aquatic habitats of the larva stages, for example by filling or applying oil to places with standing water. These methods have seen little application in Africa for more than half a century.
The relative effectiveness of IRS (with DDT or alternative insecticides) versus other malaria control techniques (e.g. bednets or prompt access to anti-malarial drugs) varies greatly and is highly dependent on local conditions.
A study by the World Health Organization released in January 2008 found that mass distribution of insecticide-treated mosquito nets and artemisinin based drugs cut malaria deaths in half in Rwanda and Ethiopia, countries with very high malaria burdens. IRS with DDT was determined to not have played an important role in the reduction of mortality.
VietnamVietnam , officially the Socialist Republic of Vietnam , is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea to the east...
is an example of a country that has seen a continued decline in malaria cases after switching in 1991 from a poorly funded DDT-based campaign to a program based on prompt treatment, bednets, and the use of pyrethroid group insecticides. Deaths from malaria dropped by 97%.
In Mexico, the use of a range of effective and affordable chemical and non-chemical strategies against malaria has been so successful that the Mexican DDT manufacturing plant ceased production voluntarily, due to lack of demand. Furthermore, while the increased numbers of malaria victims since DDT usage fell out of favor would, at first glance, suggest a 1:1 correlation, many other factors are known to have contributed to the rise in cases.
A review of fourteen studies on the subject in sub-Saharan Africa, covering insecticide-treated nets, residual spraying, chemoprophylaxis for children, chemoprophylaxis or intermittent treatment for pregnant women, a hypothetical vaccine, and changing the first line drug for treatment, found decision making limited by the gross lack of information on the costs and effects of many interventions, the very small number of cost-effectiveness analyses available, the lack of evidence on the costs and effects of packages of measures, and the problems in generalizing or comparing studies that relate to specific settings and use different methodologies and outcome measures. The two cost-effectiveness estimates of DDT residual spraying examined were not found to provide an accurate estimate of the cost-effectiveness of DDT spraying; furthermore, the resulting estimates may not be good predictors of cost-effectiveness in current programs.
However, a study in Thailand found the cost per malaria case prevented of DDT spraying ($1.87 US) to be 21% greater than the cost per case prevented of lambdacyhalothrin-treated nets ($1.54 US), at very least casting some doubt on the unexamined assumption that DDT was the most cost-effective measure to use in all cases. The director of Mexico's malaria control program finds similar results, declaring that it is 25% cheaper for Mexico to spray a house with synthetic pyrethroids than with DDT. However, another study in South Africa found generally lower costs for DDT spraying than for impregnated nets.
A more comprehensive approach to measuring cost-effectiveness or efficacy of malarial control would not only measure the cost in dollars of the project, as well as the number of people saved, but would also take into account the negative aspects of insecticide use on human health and ecological damage. One preliminary study regarding the effect of DDT found that it is likely the detriment to human health approaches or exceeds the beneficial reductions in malarial cases, except perhaps in malarial epidemic situations. It is similar to the earlier mentioned study regarding estimated theoretical infant mortality caused by DDT and subject to the criticism also mentioned earlier.
A study in the Solomon Islands found that "although impregnated bed nets cannot entirely replace DDT spraying without substantial increase in incidence, their use permits reduced DDT spraying."
A comparison of four successful programs against malaria in Brazil, India, Eritrea, and Vietnam does not endorse any single strategy but instead states "Common success factors included conducive country conditions, a targeted technical approach using a package of effective tools, data-driven decision-making, active leadership at all levels of government, involvement of communities, decentralized implementation and control of finances, skilled technical and managerial capacity at national and sub-national levels, hands-on technical and programmatic support from partner agencies, and sufficient and flexible financing."
DDT resistant mosquitoes have generally proved susceptible to pyrethroids. Thus far, pyrethroid resistance in
Anopheles has not been a major problem.
See also
- DDT in Australia
-DDT:Dichloro-Diphenyl-Trichloroethane) was a widely used synthetic pesticide before its used was banned in many countries. It is a persistent organic pollutant with a half life of 2-15 years.-History:...
- DDT in New Zealand
The use of DDT in New Zealand was banned in 1989 due to negative environmental impacts.-DDT:DDT is an organochlorine insecticide that does not occur naturally. It is a persistent organic pollutant with a half life of 2-15 years...
- DDT in the United States
The use of DDT in the United States is banned, except for a limited exemption for public health uses. The ban is due in a large part to Rachael Carson's book Silent Spring.-Initial concerns about DDT:...
- Mickey Slim
The Mickey Slim was a drink that had short-lived popularity in the United States in the 1940s and 1950s. According to the The Dedalus Book of Absinthe by Phil Baker, it was made by combining gin with a pinch of DDT , an insecticide that would later be banned in most countries; consumers of this...
External links
Toxicity
Environmental impact
Politics and DDT
Malaria and DDT