Feature Story

Finding alternatives to DDT

May 1, 2016

DDT accumulates in animal tissue and thus magnifies as it works its way up the food chain. Its impact is particularly severe on predatory bird species such as eagles, pelicans, and falcons, as it weakens their eggshells, causing them to crack prematurely. Widespread use of DDT led to a significant decline in the abundance of these and other bird species wherever it was used.

In May, 2001, as delegates gathered in Stockholm for final negotiations on an international treaty to rid the world of a class of particularly harmful and persistent chemicals, they faced a tough choice regarding perhaps the best known of them all.

Dichloro-Diphenyl-Trichloroethane or DDT, has been infamous as an environmental hazard since the 1960s, when scientists identified it as a severe health and environmental threat. DDT accumulates in animal tissue and thus magnifies as it works its way up the food chain. Its impact is particularly severe on predatory bird species such as eagles, pelicans, and falcons, as it weakens their eggshells, causing them to crack prematurely. Widespread use of DDT led to a significant decline in the abundance of these and other bird species wherever it was used.

Since countries began banning the use of DDT in the 1970s, many of those species have made great comebacks. In that sense, the campaign against DDT has been one of the most spectacular environmental successes of the past half-century. On that basis alone, a casual observer might have predicted that DDT would be on the top of the list of chemicals banned under the Stockholm Convention.

In fact, negotiators faced a rather more complex choice. While few people dispute the harmful effects of DDT on the environment, it also fills one important purpose: It is extremely effective in killing or repelling mosquitoes, and hence has long been a key weapon in the fight against malaria. So when the Stockholm Convention compiled the list of chemicals to be eliminated immediately, DDT was not among them. Instead, DDT was on a second list of chemicals that the Parties to the Convention agreed to restrict as much as possible, but with exceptions for acceptable purposes such as malaria control.

The challenge then was to find ways to control malaria that did not include the use of DDT. The need for a substitute to be at least as effective as DDT is clear: Malaria continues to be endemic in the developing world, causing more than one million deaths every year. According to the World Health Organization (WHO), nearly half of the world’s population is at risk of malaria. In Mexico and Central America nearly 109 million people live in areas that are environmentally favorable to the transmission of the disease, and 35 percent of them are at high risk. Because of the ongoing failure to develop a truly effective anti-malaria vaccine, the major public health intervention remains focused on controlling the mosquito vector of the parasite that causes the disease.

During the last decade, Mexico and other Central American countries have gradually discontinued DDT sprayings for mosquito control. But even in countries that no longer use DDT it remains relatively inexpensive and effective, so there continues to be the risk that a sudden outbreak in malaria would force government agencies to begin using DDT again unless there were other proven options.

Developing DDT-free methods of controlling malaria has a double benefit. It removes a persistent organic pollutant (POP) from the environment and has a significant impact on public health. The links between these steps and a vibrant, sustainable economy are clear: As long as POPs remain in the soil and water they pose short- and long-term threats to the ability of people to contribute to their communities economically and socially, and threaten wild species locally and around the world.

In an effort to speed the development of alternative methods to DDT, in 2004 the GEF funded nearly US$7.5 million for a regional project through UNEP and the World Health Organization to prevent reintroduction of DDT for malaria control. The program promoted new techniques for controlling mosquitoes and implemented a coordinated regional program to improve national capacities. The WHO builds its approach for controlling vector-born disease, called Integrated Vector Management, on the recognition that controlling the disease requires cooperation across health, agricultural, and environmental sectors, and depends in large part on the involvement and empowerment of local communities.

With Integrated Vector Management as the framework, the GEF/WHO project worked with 202 communities of 50 municipalities in eight countries — Mexico, Guatemala, Belize, El Salvador, Honduras, Nicaragua, Costa Rica, and Panama. The work covered close to 160,000 people directly and an estimated 6.8 million indirectly representing nearly 30 percent of those in the highly affected areas.

In the Talamanca region of Costa Rica, for example, residents of this largely rural area undertook a variety of efforts to control mosquitoes and the spread of malaria. These included clearing stream banks of vegetation that can harbor mosquito larvae, draining stagnant water from ditches and water channels, cleaning houses and patios to remove any potential breeding sites, whitewashing houses with lime as an insecticide, and experimenting with plants that repel mosquitoes, such as the neem tree, an Indian native. Native fish species and bacteria that eat mosquito larvae were also released into local streams.

Other strategies tested in Talamanca and elsewhere included bed nets and mesh screens on windows and doors. People in rural communities also learned how to recognize the signs of malaria and the importance of rapid and thorough treatment of suspected cases, as this can significantly reduce the risk of transmission. Community participation thus became a central axis of the malaria control activities.

The project transformed towns into healthy communities — clean, without rubbish or weeds in the open areas, with neat and tidy houses and yards. In Guatemala, community leaders say that the “clean houses” strategy had other positive impacts as well, such as reduction in vector born diseases like dengue and scabies, reduction of common house fly, the improvement of community safety (because it is possible to see intruders from a longer distance), basic environmental sanitation, and improvement of the streets.

Communities that worked with the project are now able to respond effectively to new challenges. The floods that occurred in Panama, Guatemala and Costa Rica in 2008 and 2009, for example, were followed by a strong reaction of the community, as they worked to eliminate mosquito breeding sites and refugees, cleaned houses and patios, and actively searched for patients with fever. That community engagement enabled the prevention of malaria outbreaks without the use of insecticides.

Overall, the project achieved a 63 percent reduction in malaria cases and a more than 86 percent decrease in cases linked with Plasmodium falciparum, the malarial parasite that causes the most severe kind of infection and the highest death rate globally. For instance, there was a reduction from 2,439 people with malaria in 2004 to 914 in 2007, surpassing the goal of reducing malaria morbidity 50 percent by 2015, according to the Millennium Development Goals. In Guatemala, places for watering farm animals and cattle called “aguadas” saw the frequency of malaria cases in the community drop from once every month to once every three months. Several communities registered zero malaria cases in 2007 and 2008. In Panama in 2008, 90 percent of the controlled localities registered zero local transmission (autochthonous) cases of malaria.

The project has demonstrated that it is possible to control or even eliminate malaria with environmentally friendly methods and without the use of persistent insecticides, and that such an approach is cost effective, highly replicable, and sustainable. The main conditions are the combination of control strategies, the intersectorial approach and community participation. The strategies needed for this kind of intervention, such as the control of mosquito breeding sites, cleaning houses and patios are easily adopted by the communities. They also contribute to the empowerment of the communities and to the change of the understanding about their participation in malaria control.

Building coalitions across the agricultural, health and environmental sectors and with the general population is essential to reducing the use of DDT. Such coalitions are in fact essential to implementing the Stockholm Convention in general, not simply in relation to DDT.

The success of DDT-free control methods had a catalytic role across the region. There was an extension of the interventions to other neighboring localities and municipalities due to an initiative of the community leaders and health workers. In Mexico, Guatemala, Nicaragua and Honduras, the replication was very extensive — Guatemala alone has extended to control methods to 600 towns.

The most important outcome, however, may not be the local or regional impact of the project, but the adoption of DDT-free control methods at even broader scales. The GEF, WHO, and UNEP are now using a similar approach in some 40 countries in Africa, the Eastern Mediterranean, and Central Asia. The aim of the new projects, a major initiative of the GEF and UNEP, with close to US$40 million funding, is to achieve a 30 percent cut in the application of DDT world-wide by 2014 and its total phase-out by the early 2020s, if not sooner, while staying on track to meet the malaria targets set by WHO.

The new projects underline the determination of the international community to combat malaria while realizing a low, indeed zero DDT world. The efforts by the GEF, UNEP, and WHO are catalyzing innovative solutions and sustainable choices to meet vital health and environmental aspirations. By offering solid evidence for the effectiveness of combinations of locally-adapted, cost-effective and sustainable vector-control methods, these efforts are facilitating a sustainable transition away from DDT. The dividends from these investments will mean a cleaner, safer and sustainable environment for future generations.