In September , American biologist Rachel Carson published a book called Silent Spring which chronicled in detail the environmental and health risks posed by the use of DDT. The compound had been viewed as a boon by many as it was incredibly effective against hundreds of different types of insects, as opposed to the previously used compounds which specifically target just a few insects. However, Carson also pointed out that several animals and birds died in large numbers as the result of DDT poisoning.
There was mass outcry following the release of her book which led to the chemical being banned for the first time in by the US Environment Protection Agency EPA. It was here that many nations came to the decision to ban DDT use. However, they did add that developing countries, which largely relied on DDT for controlling mosquito populations, would be permitted to use the compound only for the purpose of controlling vector-borne diseases.
In August , India banned 18 pesticides. The committee's review completely vindicating her findings. One of the new EPA's first acts was to ban DDT, due to both concerns about harm to the environment and the potential for harm to human health. There was also evidence linking DDT with severe declines in bald eagle populations due to thinning eggshells. Since DDT was banned in the U.
Recently, Carson's work has again been targeted by conservative groups. Capitalizing on the iconic status of DDT, these groups are promoting widespread use of the chemical for malaria control as part of a broader effort to manufacture doubt about the dangers of pesticides, and to promote their anti-regulatory, free market agenda while attempting to undermine and roll back the environmental movement's legacy.
Many DDT promoters are also in the business of denying climate change. Please click here to see any active alerts.
DDT dichloro-diphenyl-trichloroethane was developed as the first of the modern synthetic insecticides in the s. It was initially used with great effect to combat malaria, typhus, and the other insect-borne human diseases among both military and civilian populations. It also was effective for insect control in crop and livestock production, institutions, homes, and gardens.
DDT's quick success as a pesticide and broad use in the United States and other countries led to the development of resistance by many insect pest species. The U. Department of Agriculture, the federal agency with responsibility for regulating pesticides before the formation of the U. New insecticides are not expected in the short term.
Nonchemical methods are potentially important, but their effectiveness at program level needs urgent study. To reduce reliance on DDT, support is needed for integrated and multipartner strategies of vector control and for the continued development of new technologies. Integrated vector management provides a framework for developing and implementing effective technologies and strategies as sustainable alternatives to reliance on DDT.
DDT is used in indoor spraying for control of vectors of malaria and visceral leishmaniasis. In negotiations that led to the treaty, there was concern that a sudden ban on DDT use could adversely affect the malaria burden.
Thus, DDT was permitted to be produced and used for the purpose of controlling disease vectors in accordance with recommendations and guidelines of the World Health Organization WHO and when locally safe, effective, and affordable alternatives are not available WHO a.
Malaria is a complex parasitic disease confined mostly to tropical areas and transmitted by mosquitoes of the genus Anopheles. Malaria-endemic countries are faced with a high cost of prevention and treatment of the disease.
Vector control is an essential component of malaria control programs. The WHO has reaffirmed the importance of vector control through indoor residual spraying IRS as one of the primary interventions for reducing or interrupting malaria transmission in countries in both stable and unstable transmission zones.
The course of action promoted by the WHO has been to retain DDT as part of the arsenal of insecticides available for IRS globally, to be able to manage insecticide resistance until suitable alternatives are available WHO a.
The use of DDT for IRS is recommended only where the intervention is appropriate and effective in the local epidemiologic situation. In this review, I present the current situation regarding the use of DDT for vector control, covering aspects of production, use, legislation, cost-effectiveness, health effects, environmental effects, insecticide resistance, monitoring, and evaluation. I provide an outline of alternative methods, strategies, and new developments; discuss cost-effectiveness, current implementation, barriers, and gaps in implementing the alternatives; and present possible solutions to reduce reliance on DDT.
Contemporary information on the production and use of DDT was obtained from a formal questionnaires by the Stockholm Convention Secretariat, completed by national authorities; b documents published by the Stockholm Convention; c direct communications with national authorities; and d information available from project proposals submitted to the Global Environment Facility Information has been supplemented with data presented by country delegates at workshops in the context of the Stockholm Convention.
I obtained information on side effects, insecticide resistance, cost-effectiveness, and alternatives from literature searches. I used the search engine Scopus to retrieve studies related to DDT and malaria, with vector control as additional search term.
Because of the breadth of the subject matter, only the most relevant studies were selected, and reviews were prioritized. Old literature was accessed electronically, or hard copies were obtained from libraries. Information on human exposure and health effects was based on reviews published over the past 5 years and supplemented with recent studies on exposure due to indoor spraying.
By far the largest amounts are produced in India for the purpose of disease vector control. The remainder was meant for malaria control and was exported.
India and China both export DDT to countries in Africa, either as technical product or as a formulation, for the purpose of vector control. South Africa exports some of its formulated product to other countries in Africa.
Annual global production and use of DDT in 10 3 kg active ingredient in , , and Abbreviations: Dc: Direct communication with national authorities; NA, not available; Pd: project proposals submitted to the Global Environment Facility; Qu: questionnaire on DDT by the Secretariat of the Stockholm Convention completed by national autorities; SC: documents published by the Secretariat; Ws: workshop presentations by country delegates in the context of the Stockholm Convention. An estimated 5, metric tons of DDT active ingredient was used for disease vector control in Table 1.
India is by far the largest consumer of DDT, but in use was down one-fourth from the level. With the possible exception of the Dominican Republic, there is no reported use of DDT for disease vector control from the Americas.
Use in Ecuador, Mexico, and Venezuela was phased out in China has reported that no DDT has been used for disease vector control since , and future use is reserved only for malaria outbreaks. IRS programs are currently expanding in Africa, the main driver being the U. Pilot programs on IRS have been initiated in some African countries, and several other countries are considering reintroducing the intervention.
There is a paucity of data on DDT supplies. The available information indicates that large amounts of DDT are stored in many countries, but most of the stock is outdated or of unknown quality. Moreover, the transfer of DDT stock between countries is not always documented or reported, and this poses a problem in tracking quantities of the chemical and establishing the quality of DDT being used.
A major multistakeholder effort is needed for the cleanup of outdated DDT stock, for example, through the Africa Stockpiles Programme Curtis and Olsen Many countries that use DDT have inadequate legislation or lack capacity to implement or enforce regulations on pesticide management. Funding agencies aiding in the purchase of DDT should be obligated to provide financial assistance to ensure that regulations and monitoring capacity are in place to support proper management of DDT from the cradle to the grave, for example, by involving the environmental sector.
No published data exist on cost-effectiveness in terms of cost per disability-adjusted life-year averted by IRS using DDT. Statements of high cost-effectiveness of DDT have been based on the positive experience from the malaria eradication era Mabaso et al. Both the effectiveness and costs of DDT are dependent on local settings and merit careful consideration in relation to alternative products or methods. However, information is lacking on the potential variability in residual action of insecticides, including DDT e.
Direct costs of IRS are the procurement and transport of insecticide, training of staff, operations, awareness-raising of communities, safety measures, monitoring of efficacy and insecticide resistance, monitoring of adverse effects on health and the environment, and storage and disposal.
This comparison will further change with the availability of new formulations of pyrethroids that have increased residual activity. Moreover, incorporating the cost of safety measures in the application of DDT will significantly change its comparative cost advantage.
Apart from the direct costs, it is essential that the unintended costs of DDT or alternative insecticides to human health and the environment are included in the cost assessment.
In addition, contamination of food crops with DDT could negatively affect food export Anonymous A comprehensive cost assessment of DDT versus its alternatives should include the potential costs of atmospheric transport and chronic health effects. The results will be crucial in future decision making on vector management strategies for prevention of malaria.
High levels of human exposure to DDT among those living in sprayed houses, most of whom are living under conditions of poverty and often with high levels of immune impairment, have been found in recent studies in South Africa and Mexico Aneck-Hahn et al.
The simultaneous presence of, and possible interaction between, DDT, dichlorodiphenyldichloroethylene DDE , and pyrethroids in human tissue is another area of concern Bouwman et al. In North America, rather high levels of exposure have been recorded in biological samples collected near the time of peak use during the s Eskenazi et al. Exposure of the fetus and young child occurs through the placenta and through lactation Bouwman et al. DDT accumulates in fatty tissue and is slowly released.
A monitoring system is needed for the assessment of trends in exposure to DDT, allowing for the attribution of effects to IRS locally; in this regard, human milk is considered an important media to be monitored Malisch and van Leeuwen Studies on health effects of DDT have focused mostly on subjects in North America and Europe, who have generally been exposed to levels lower than those reported from areas with IRS.
As an indication, however, initial work suggests that nonoccupational exposure through IRS is associated with impaired semen quality in men Aneck-Hahn et al. Health effects of DDT and DDE most commonly suggested by studies in North America and Europe are early pregnancy loss, fertility loss, leukemia, pancreatic cancer, neurodevelopmental deficits, diabetes, and breast cancer Beard ; Chen and Rogan ; Cox et al.
In many cases the results have not been consistent between studies, but nevertheless these accumulating reports bear much concern, particularly in relation to chronic effects. Breast cancer has been most rigorously studied; even though the majority of results showed no causative association with DDT exposure Brody et al. In addition, experimental studies on animals have demonstrated neurotoxic, carcinogenic, immunotoxic, and reproductive effects attributable to DDT and DDE Turusov et al.
The adverse health effects of DDT versus the health gains in terms of malaria prevention require more attention. For example, a gain in infant survival resulting from malaria control could be partly offset by an increase in preterm birth and decreased lactation, both of which are high risk factors for infant mortality in developing countries.
As a persistent molecule, DDT has low to very low rates of metabolism and disposition, depending on ambient temperatures. It is degraded slowly into its main metabolic products, DDE and dichlorodiphenyldichloroethane DDD , which have similar physicochemical properties but differ in biological activity. DDT is emitted through volatilization and runoff. It is more volatile in warmer than in colder parts of the world, which through long-range atmospheric transport results in a net deposition and thus gradual accumulation at high latitudes and altitudes Harrad Loss through runoff is low because DDT has a strong affinity for organic matter in soils and aquatic sediment but is virtually insoluble in water.
Half-lives of DDT have been reported in the range of 3—7 months in tropical soils Varca and Magallona ; Wandiga and up to 15 years in temperate soils Ritter et al. The half-life of each of its metabolic products is similar or longer. DDT readily binds with fatty tissue in any living organism, and because of its stability, bioconcentrates and biomagnifies with increasing trophic level in food chains Kelly et al.
Studies have shown that DDT is highly toxic to insects, shrimp, and fish Fisk et al. DDT and its metabolic products present in the global environment have originated mostly from its previous large-scale use in agriculture and domestic hygiene. Because DDT is currently allowed only for indoor spraying for disease vector control, its use is much smaller than in the past.
Nevertheless, DDT sprayed indoors may end up in the environment e. As the number and size of programs that use DDT for indoor spraying increase, insecticide resistance is a matter of growing concern. Unless due attention is paid to the role of insecticide resistance in the breakdown of the malaria eradication campaign of the s, resistance may once again undermine malaria control Busvine In the past, the use of DDT in agriculture was considered a major cause of DDT resistance in malaria vectors, as many vectors breed in agricultural environments Mouchet At present, DDT resistance is thought to be triggered further by the use of synthetic pyrethroids Diabate et al.
This is due to a mechanism of cross-resistance between pyrethroids and DDT, the so-called sodium channel mutation affecting neuronal signal transmission, which is governed by the kdr knock-down resistance gene Martinez-Torres et al. Vectors with the kdr gene are resistant to both groups of insecticides, and this has serious consequences for malaria vector control, because pyrethroids and DDT are the two main groups of chemicals used.
The kdr gene is being reported from an increasing number of countries; thus, even in countries without a history of DDT use, resistance to DDT is emerging in populations of malaria vectors WHO The main African vector, Anopheles gambiae s. Further, there is recent evidence of resistance in A. Multiple resistance to DDT and other insecticides in the major vector Anopheles culicifacies is present in many parts of the country Dash et al.
Resistance has also been reported in Anopheles sinensis from China Cui et al. Resistance does not necessarily result in failure to control disease. However, the repellent and irritant properties of DDT also have the potential to reduce transmission of disease and relieve the selective pressure for toxic resistance Grieco et al.
This is an area requiring more research. An important lesson learned from the experience with oncocerciasis river blindness , another vector-borne disease, is that the development and spread of insecticide resistance is much slower when vector populations are under effective control Guillet P, personal communication , suggesting that suppressing vector proliferation helps prevent or delay the development of resistance.
Effective monitoring and decision support systems can enable insecticide resistance to be detected at an early stage, which should lead to the implementation of changes in insecticide policy Sharp et al. However, the choice of unrelated insecticides remains limited Nauen Even an intelligent insecticide resistance management strategy using rotations, mosaics, or mixtures may not prevent resistance development Hemingway et al.
A number of vector control methods are available as alternatives to DDT. Two of these, the use of alternative insecticides in IRS and the use of insecticide-treated bed nets ITNs , are mainstreamed because of their proven impact on the malaria burden.
Other available alternatives are receiving limited attention in contemporary malaria control efforts, but have an important role to play. Table 2 summarizes alternative methods. Alternatives to DDT should pose less risk to human health and the environment and be supported with monitoring data. Alternative methods for malaria vector control, indicating the targeted vector stage, the potential risk, and required resources and delivery mechanisms.
IRS with insecticides is an effective method of malaria control. Its strength lies in its effect on shortening the life span of adult mosquitoes near their human targets, which has a critical impact on malaria transmission MacDonald However, there is limited information on effectiveness and operational feasibility of IRS in African countries with highly endemic malaria, some of which recently reintroduced IRS or plan to do so.
Twelve insecticides belonging to four chemical classes are recommended for IRS in vector control, which collectively address only three modes of toxic action Nauen Pyrethroids are the most cost-effective alternatives to DDT in malaria control except where pyrethroid resistance occurs Walker There are two new developments with regard to IRS.
Second, new formulations of existing insecticides with prolonged residual activity are being developed as alternatives to DDT Hemingway et al. Two slow-release formulations of pyrethroids are already available on the market. The insecticide enhances the protective effect for the person under the net, but also has a beneficial effect on the community at large Hawley et al. ITNs have been shown convincingly to cause substantial reductions in all-cause child mortality, under both experimental Lengeler and operational conditions Armstrong Schellenberg et al.
0コメント