**6. The big debate on DDT as anti-malaria tool**

In 1955, the WHO commenced a program to eradicate malaria worldwide, relying largely on DDT. The program was initially very 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 (Harrison, 1978). However, widespread agricultural use led to resistant insect populations. In many areas, early victories partially or completely reversed, and in some cases rates of transmission even increased (Chapin & Wasserstrom,1981). The program was successful in eliminating malaria only in areas with "high socio-economic status, well-organized health‐ care systems, and relatively less intensive or seasonal malaria transmission" (Sadasivaiah et al., 2007). In tropical regions, DDT was less effective due to the continuous life cycle of mos‐ quitoes and poor infrastructure. It was not applied at all in sub-Saharan Africa due to these perceived difficulties.

Moreover, the adverse health effects of DDT versus the health gains in terms of malaria pre‐ vention 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. The WHO is con‐ ducting a re-evaluation of health risks of DDT, but progress has been slow (PAN, 2012). Nevertheless, in 2006 it approved the use of DDT, particularly indoor residual spraying of walls, in areas endemic for malaria for health-related reasons (WHO, 2006a; WHO, 2006b), although it also carefully drew up major guidelines (WHO 2000). Currently, DDT represents one the main stays to achieve goals of Global Eradication Program launched in 2007 by the Bill and Melinda Gates Foundation, the World Health Organization (WHO) and the Roll Back Malaria association (Roberts & Enserink, 2007; Greenwood, 2008; Khadjavi et al., 2010; Prato et al., 2012). However, in the recent years the possible effects of DDT on human health have been a hot topic of discussion inside malaria research community, as certified by the large number of available publications and intense correspondence among scientists (e.g., Blair et al., 2009; Burton, 2009; van den Berg, 2009; Tren & Roberts, 2010; Bouwman et al., 2011; Tren & Roberts, 2011). The debate is heavily polarized, and three main viewpoints can be identified, as suggested by Bouwman et al. (Bouwman et al., 2011): anti-DDT, centrist-DDT, and pro-DDT.

#### **6.1. Anti-DDT point of view**

diga, 2001) and up to 15 years in temperate soils (Ritter et al., 1995). The half-life of each

The global risk of adverse effects to human health and the environment has led the inter‐ national community to mandate the UN Environment Programme (UNEP) to convene an intergovernmental negotiating committee (INC) for a POPs Convention to phase out pro‐ duction and use (UNEP, 1997a; UNEP, 1997b). As a result of these environmental con‐ cerns, the use of DDT was increasingly restricted or banned in most developed countries

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 cur‐ rently 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.g., when mud blocks of abandoned houses are dissolved in the rain). Even today, DDT remains so widespread in the environment that it is likely that exposure to it is unavoidable. While exposure in the industrialised world has fallen dramatically, exposure remains high in some

DDT is very fat-soluble and could therefore be found in fatty foods such as meat and diary products. Even in countries across North America and Northern Europe, where its use has been banned for over a decade DDT residues are still often found in food. This is because of environmental persistence, illegal use, or importation of contaminated food from regions

In 1955, the WHO commenced a program to eradicate malaria worldwide, relying largely on DDT. The program was initially very 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 (Harrison, 1978). However, widespread agricultural use led to resistant insect populations. In many areas, early victories partially or completely reversed, and in some cases rates of transmission even increased (Chapin & Wasserstrom,1981). The program was successful in eliminating malaria only in areas with "high socio-economic status, well-organized health‐ care systems, and relatively less intensive or seasonal malaria transmission" (Sadasivaiah et al., 2007). In tropical regions, DDT was less effective due to the continuous life cycle of mos‐ quitoes and poor infrastructure. It was not applied at all in sub-Saharan Africa due to these

Moreover, the adverse health effects of DDT versus the health gains in terms of malaria pre‐ vention 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. The WHO is con‐

developing countries where DDT continues to be used in vector control.

**6. The big debate on DDT as anti-malaria tool**

of its metabolic products is similar or longer.

340 Insecticides - Development of Safer and More Effective Technologies

after 1970.

where DDT is still used.

perceived difficulties.

DDT opponents usually claim for DDT elimination because of environmental and health concerns. However, Tren & Roberts (Tren & Roberts, 2011) pointed that the "activist groups currently promote an anti-DDT agenda routinely hyping supposed human health and envi‐ ronmental harm from DDT and ignoring studies that find no association between DDT and such harm". As an example, Tren & Roberts mentioned the Biovision's "Stop DDT" project engaged to achieve a world-wide ban on DDT (Biovision, 2011), which apparently was con‐ nected to the Secretariat of the Stockholm Convention's promotion of an arbitrary deadline for cessation of DDT production by 2020 (United Nations Environment Programme, 2007). Another representative example of a recent anti-DDT action is given by a court case occur‐ red in Uganda (Lewis, 2008): a petition filed in Kampala's High Court accused the Ugandan government of not following DDT spraying guidelines, whether those of the WHO or those of Uganda's National Environment Management Authority. In that case, it appears evident that the big matter was not DDT itself as a molecule, but its incorrect use. In this context, a major point questioned by anti-DDT scientists is that also IRS workers are highly exposed to DDT, since prescribed personal protection procedures and safe practices are not always fol‐ lowed, because of uncomfortable working conditions. Not wearing masks or gloves and fre‐ quent wiping of sweaty faces with the same cloth increases dermal and inhalation uptake leading to very high exposure (Bowman et al., 2011). Indeed, DDT serum levels in IRS work‐ ers in South Africa were high compared with the general population living in DDT-sprayed houses (Bouwman et al., 1991). On the other hand, Bimenya et al. (Bimeneya et al., 2010) did not found any DDT increase in serum of Ugandan DDT applicators over an entire spray sea‐ son, stating that effective exposure reduction is possible when protective clothing is used and strict adherence to WHO guidelines (WHO, 2000) is observed. Nevertheless, the WHO's review of human health aspects of DDT use in IRS concluded that "for households where IRS is undertaken, there was a wide range of DDT and DDE serum levels between studies. Generally, these levels are below potential levels of concern for populations" (WHO, 2011b), and none of the thousands of studies conducted to find possible human health effects of DDT satisfied even the most basic epidemiological criteria to prove a cause-and-effect rela‐ tionship (Tren & Roberts, 2011).

**7. Studies on DDT toxicity**

**7.1. Animals**

fects on animal and human health will be reviewed.

may be typically encountered in humans.

decreases the toxicity of DDT to fish (PAN, 2012).

bald eagles from the North American Great Lakes (PAN, 1996).

Despite the concerns of DDT opponents (see par. 6.1), to date there is no consistent evidence that DDT or its metabolite DDE can be toxic for humans. Indeed, despite the large number of studies performed in this context, results are highly contradicting, probably due to differ‐ ent analytical conditions and approaches used by different researchers. On the other hand, DDT toxic effects on animals have been demonstrated quite convincingly. This should be taken in account in the context of general environmental issues (par. 5.5) which led to DDT ban in malaria-free countries. In the following sub-sections, current knowledge on DDT ef‐

DDT as Anti-Malaria Tool: The Bull in the China Shop or the Elephant in the Room?

http://dx.doi.org/10.5772/53241

343

Due to its lipophilicity, DDT readily binds with fatty tissue in any living organism, and be‐ cause of its chemical stability, bioconcentrates and biomagnifies with accumulation of DDT through the food chain, in particular in predatory animals at the top of the ecological pyra‐ mid (Jensen et al., 1969). By the mid 1950s, experimental studies on animals have demon‐ strated chronic effects on the nervous system, liver, kidneys, and immune systems in experimental animals attributable to DDT and DDE (Turusov et al., 2002), and it quickly be‐ came apparent that this could extend to the broader environment (Ramade, 1987). However, dose levels at which effects were observed are at very much higher levels than those which

DDT is highly toxic to fish. The 96-hour LC50 (the concentration at which 50% of a test pop‐ ulation die) ranges from 1.5 mg/litre for the largemouth bass to 56 mg/litre for guppy. Small‐ er fish are more susceptible than larger ones of the same species. An increase in temperature

DDT and its metabolites can lower the reproductive rate of birds by causing eggshell thin‐ ning which leads to egg breakage, causing embryo deaths. Sensitivity to DDT varies consid‐ erably according to species. Predatory birds and fish-eating birds at the top of the food chain are the most sensitive. The thickness of eggshells in peregrine falcons was found to have de‐ creased dramatically following the pesticide's introduction (Ratcliffe, 1970), likely due to hormonal effects and changes in calcium metabolism (Peakall, 1969). Colonies of brown peli‐ cans in southern California plummeted from 3000 breeding pairs in 1960 to only 300 pairs and 5 viable chicks in 1969. In the US, the bald eagle nearly became extinct because of envi‐ ronmental exposure to DDT. According to research by the World Wildlife Fund and the US EPA, birds in remote locations can be affected by DDT contamination. Albatross in the Mid‐ way islands of the mid-Pacific Ocean show classic signs of exposure to OCs chemicals, in‐ cluding deformed embryos, eggshell thinning and a 3% reduction in nest productivity. Researchers found levels of DDT in adults, chicks and eggs nearly as high as levels found in

#### **6.2. Centrist-DDT point of view**

According to Bouwman et al. (Bouwman et al., 2011), "the centrist-DDT point of view adopts an approach that pragmatically accepts the current need for DDT to combat malaria transmission using indoor residual spraying (IRS) but at the same time recognizes the risks inherent in using a toxic chemical in the immediate residential environment of millions of people". Thus, scientists sharing a centrist-DDT point of view such as Bouwman and collea‐ gues suggest caution in using DDT because of insufficient investigation whether DDT is safe or not; however, they do recognize its undoubted benefits in areas endemic for malaria and its major role as a life-saving tool. In this context, DDT-centrists call for alternative chemi‐ cals, products, and strategies, eventually in order to terminate in the future any use of DDT in IRS for malaria control. As it will be discussed in paragraph 6, some vector control meth‐ ods are already available as alternatives to DDT. Two of these, the use of alternative insecti‐ cides in IRS and the use of insecticide-treated bed nets (ITNs), are mainstreamed because of their proven impact on the malaria burden; other alternatives are receiving limited attention to date, but may play an important role in the future (van den Berg, 2009).

#### **6.3. Pro-DDT point of view**

DDT supporters consider DDT safe to use in IRS when applied correctly, and promote DDT to be used for IRS in malaria control where it is still effective. In their perspective, in a riskbenefit comparison, the eventual toxic effects of DDT would be far less than those caused by malaria (Africa Fighting Malaria, 2010; Roberts et al., 1997). Apparently, this is the point of view of WHO itself, since it approved in 2006 the use of DDT, particularly indoor residual spraying of walls, in areas endemic for malaria for health-related reasons (WHO, 2006a; WHO, 2006b), although it also carefully drew up major guidelines (WHO 2000). Moreover, several national malaria control programs and ministers of health repeatedly proclaimed the importance of DDT for disease control programs in countries with high incidence of malar‐ ia. These include Namibia and the Southern African Development Community (SADC), which recently reasserted that DDT is a major tool for malaria vector control and announced their intention to produce DDT locally (SADC, 2011). Similarly, the 35 heads of state of the countries members of the African Leaders Malaria Alliance (ALMA) recently endorsed use of DDT in indoor residual spraying (IRS) (ALMA 2010). As a matter of fact, as a conse‐ quence of the global eradication program recently launched by charity foundations, which invested relevant amounts of money in DDT-based vector control (Roberts & Enserink, 2007; Greenwood, 2008; Khadjavi et al., 2010; Prato et al., 2012), in 2010 World Health Organiza‐ tion (WHO) officially registered - for the first time in the last decade - a decline in estimated malaria cases and deaths, with 655.000 deaths counted among more than 200 million clinical cases worldwide (WHO 2011a).
