DDT reintroduction for malaria control: the cost-benefi t debate for public health Reintrodução do DDT para combate à malária: uma discussão de custo-benefício para a saúde pública

DDT is a persistent insecticide that was widely used in the world from the 1940s until the 70s, when it was banned in the United States and other countries. Most of its toxic effects are not observed in the acute forms, but particularly after chronic exposure. These long-term issues include reproductive effects, varying according to the time of life in which the individuals were exposed. The aims of the current study were to review the principal toxicological effects of DDT on reproduction, stratifying by physiological periods of exposure, and based on the magnitude of these effects, to discuss the cost-benefit relationship of reintroducing DDT with the specifically defined vector control criteria. DDT; Pesticide Exposure; Malaria Introduction The impact of pesticides on human health has received worldwide attention from the scientific community, especially in developing countries, where the use of these compounds has increased rapidly. Their evaluation requires knowledge and a clear view of the relative importance and magnitude of each of the contamination routes 1. Pesticides appeared in Brazil in the 1960s and 1970s as a scientific solution for pest control in crops and livestock 2. Earlier, in the 1940s, some substances with insectidal properties had already been used to control certain endemic diseases like malaria and schistosomiasis 3. A first class of pesticides that was widely used in public health consisted of the organochlorines, among which the most widely known example is dichlorodiphenyltrichloroethane, or DDT. A previous publication 4 described the discovery of the insecticidal power of DDT, the first synthetic organic insecticide, launching the era of the organochlorine pesticides. Beginning with DDT, a growing number of pesticides emerged. During World War II, and DDT was widely used by the U.S. Army in campaigns in various regions of the world, after which its use became widespread 5. Despite the benefits, the indiscriminate use of this class of substances led to serious ecological problems. It is now estimated that nearly all living beings, both plant and animal, are contaminated by organochlorine insecticides 4. REVISÃO REVIEW Guimarães RM et al. 2836 Cad. Saúde Pública, Rio de Janeiro, 23(12):2835-2844, dez, 2007 Concern over the use of DDT began in the 1960s, when the famous book Silent Spring by Rachel Carlson 6 described a series of harmful effects on the environment and wildlife resulting from pesticide use. The author specifically emphasized the effect of DDT in weakening the eggshells of the American eagle (Haliaetus leucocephalus), contributing to a sharp decline in this species. In addition, due to its high persistence in the environment and numerous reports of resistant insect species, DDT was gradually replaced with other substances in many developed countries. In Brazil, DDT was banned from agricultural use in 1985. In 1997, the Fundação Nacional de Saúde [FUNASA; National Health Foundation] also banned its use for vector control. Finally, since 1998 there has been a total ban on DDT for any use in Brazil 3. However, in some countries with endemic malaria areas, DDT is still widely used. Since economic interests often clash with the need for environmental protection, DDT is still produced and exported in large amounts by countries that have already banned its use in their own territories 7. A well-known case of the use of DDT that generated known environmental impacts was Cidade dos Meninos in Rio de Janeiro, where an old Ministry of Health insecticide factory that had been closed down in the 1950s released large amount of insecticides into the air, particularly hexachlorocyclohexane (HCH) and DDT 3. DDT exerts its action on the physical makeup and health of humans, in addition to contaminating the environment and animal populations. Thus, understanding DDT’s mechanisms of action is crucial for evaluating the impact of such contamination on human health. We currently have a considerable body of knowledge on the multiple toxic effects of DDT 8. Particularly in the last 15 years, great attention has focused on this insecticide’s possible estrogenic and anti-androgenic effects and how such interference with the endocrine system’s homeostasis represents a mechanism of action that explains part of the compound’s toxic effects 7. Furthermore, DDT byproducts have been linked to infertility, miscarriage, and breast cancer, and such effects are modulated according to the stage of life in which the individual was exposed. Beyond this accumulated knowledge, there is an impasse in the scientific community on the reintroduction of DDT in countries where endemic diseases whose vectors can be eliminated by DDT are demanding its renewed use. They base their argument on a cost-benefit discourse, given the high mortality rates from vector-borne diseases like malaria and yellow fever. A recent article 8 reviewed the main characteristics of this organochlorine and some aspects of its use in leishmaniasis and malaria vector control. Considering the compound’s description and one of the possible groups of outcomes in humans, namely its endocrine-modulating and reproductive effects, the current article has the following objective: to review the main toxic effects of DDT related to the reproductive system’s biochemical and physiological mechanisms, according to the specific period of life in which the individual is exposed; based on the magnitude of these effects, to discuss the cost-benefit relationship involved in the possible reintroduction of DDT with specifically defined vector control criteria. The first part of the article reviews some key aspects of DDT toxicology, after which we list some studies that have examined the relationship between DDT exposure and selected outcomes; finally, the discussion develops and presents arguments for and against the reintroduction of DDT as a vector control pesticide. Chemical properties of DDT DDT (dichlorodiphenyltrichloroethane) is a synthetic insecticide belonging to the organochlorine chemical class. DDT also has several metabolites, emphasizing DDE and DDD. Both DDE and DDD are byproducts of DDT. All the isomers are solid, white, odorless, and tasteless substances, with the empirical formula C14H9Cl5 9,10. DDT’s persistence is due to its great chemical and physical stability and its slow and partial biodegradation 5. Since DDT possesses optical isomerism, the commercial product is a mixture of two isomers (op’DDT, some 23%, and pp’DDT, some 77%) obtained as a compound with a high degree of purity through the reaction of a chlorobenzol molecule with a chloral hydrate molecule in the presence of sulfuric acid 10.