During the course of a normal day, people face varieties of different risks. Some risks are known and others are faced with a degree of uncertainty. One of the risks or potential hazards that most people encounter perhaps every moment in a day is their exposure to a variety of chemicals. In most cases people make an informed decision to avoid the substances that are known to be harmful. Problems arise when the public is perhaps unwittingly exposed to a substance where the acute or cumulative affects of exposure may be dangerous.
In the United States, a change occurred in 1962 that many consider the start of the environmental movement. Rachel Carlson, a former marine biologist with the US Wildlife Fisheries, wrote a book called "Silent Spring" This one book was the start of or the catalyst for the modern environmental movement. This book aroused public consciousness and influenced subsequent environmental legislation for years to come including the ban on DDT in the United States and many other countries (Lewis, 1985).
What is DDT (Dichlorodiphenyltrichloroethane)
DDT ((Dichlorodiphenyltrichloroethane) is the first of the chlorinated organic insecticide, was originally discovered in 1873. In 1939 that chemist Paul Muller discovered the effectiveness of DDT as an insecticide and was subsequently awarded the Nobel Prize in medicine and physiology in 1948(ASTDR, 2002).
Worldwide use of DDT in the late 1940’s increased tremendously because of its effectiveness against the mosquito and lice; thereby eradicating diseases like malaria and typhus. It was relatively inexpensive and had a low toxicity to mammals compared with other insecticides. The World Health Organization estimates approximately 25 million lives were saved because of the use of DDT. By the 1950’s it was widely used throughout the United States, especially in the mosquito prone areas of the south. Today, some areas with prime real estate and multi-million dollar homes were once endemic with malaria and only made habitable through the application of DDT (WHO, 2005).
The Controversy
In the early 1960’s, it was discovered that DDT was toxic to fish. Residues were found to remain in the food chain for long periods of time due to its bioaccumulation in the liver and adipose tissue of animals. This led to a 1969 research study that demonstrated an increased incidence of liver tumors and leukemia in laboratory mice (ASTDR, 2002).
Degradation of the substance was also found to be very slow with residual amounts found in soil samples up to 15 years after application. Wildlife researchers (Ames, 1966) linked the exposure to DDT to the habitat decline of the osprey and peregrine falcon due to increased fragility and thickness of their eggs. By 1972, responding to the public outcry, the U.S. Department of Agriculture began to phase out the use of DDT.
The problem with these studies is that they have never been duplicated. A hallmark and perhaps the most important tenet of the scientific method is not only must a hypothesis be testable, but that it must be reproducible. In "DDT: Epidemiological Evidence" researchers demonstrated that cancer correlations between DDT and population levels were not reproducible. Samples taken from areas where high concentrations of DDT were ubiquitous and where trace amounts were found in human blood, urine and feces, there was no corresponding increase in cancer rates in the population. It concludes that the insecticide did not have a significant impact on human cancer patterns and therefore is unlikely to be an important carcinogen for man at previous exposure levels, (Higginson, 1985). Similarly in "Pesticides and breast cancer risk: a review of DDT, DDE, and Dieldrin", while acknowledging that DDT and its metabolites are persistent organic pollutants, the offer could find no demonstrable evidence that DDT was implicated in an increased risk of breast cancer (Snedaker, 2001). Subsequent analysis of five US studies carried did not provide evidence to support a role of DDE (a byproduct of DDT) with increased cancer risks (Laden, Collman, Iwamoto, et al, 2001).
Endemic Malaria and the African Dilemma
The African countries have a unique moral and economic dilemma that is faced by few other nations. Will current and future governmental leaders use DDT to combat the malaria endemic?
The World Health Organization and the US Centers for Disease Control reports that between 1.5-2.5 million people die of malaria or malaria attributed illnesses, annually. Nearly 90% of these deaths occur in tropical Africa with 18% of all deaths occurring in children under the age of 5 (WHO, 2005). There simply is no other disease, in any part of the world that can generate these types of statistics.
Complicating the decision are the economic variables. In a global economy, if governments revert back to the use of DDT, there is a risk that exported products could be banned. Economic figures indicate that countries in Europe imported greater than 10 billion dollars in agricultural products (UN, 2009). Domestically, treating victims continues to strain the budgets of most African governments. Governments often rely on aid from groups such as USAID, the World Health Organization and other Non Governmental Organizations. Most of these agencies are opposed to using DDT for malaria prevention. Without this funding to support DDT spraying, these nations cannot afford it and are forced to adopt less cost effective measures.
Some governments have continued to use it in the face of malaria related deaths. In South Africa's DDT spraying program, malaria rates were cut by 80 percent in 18 months with no demonstrated harmful environmental effects. Other successes in Mozambique, Zambia, Madagascar and Swaziland were attainable with malaria rates cut by more than 75 percent within two years.
Is DDT the panacea or the magic bullet that will forever remove the scourge of malaria from the world? Probably not, but it remains an overlooked and underutilized tool in an arsenal that has been depleted by regulations forced by incomplete evidence or the emotional reaction of some environmentalists.
References:
Ames, P. (1966). DDT Residues in the eggs of the Osprey in the Northeastern United States and their relation to nesting success. Journal of Applied Ecology, 3, 87-97
ASTDR (2002) Agency for Toxic Substances and Disease Registry: DDT, DDE and DDD in Division of Toxicology FAQ
Higgionson, J. (1985). DDT: Epidemiological Evidence. IARC: International Agency for Research on Cancer, 65, 107-117
Laden, F., Collman, G., & Iwamoto, K. (2001). 1,1-Dichloro-2,2-bis(p-chlorophenyl)ethylene and Polychlorinated Biphenyls and Breast Cancer: Combined Analysis of Five U.S. Studies. Journal of the National Cancer Institute, 93(10), 768-775
Snedeker, S. (2001). Pesticides and breast cancer risk: a review of DDT, DDE, and dieldrin. Enivironmental Health Perspectives, 3, 35-47.
The US Environmental Protection Agency. (1985). History: The Birth of the EPA. In J. Clark (Ed.), EPA Journal, Washington, DC
Thurow, R. (2001) In Malaria War, South Africa turns to pesticide long banned in the West in Wall Street Journal
Turusov, V, Rakitsky, V, & Tomatis, L. (2002). Dichlorodiphenyltrichloroethane (DDT): ubiquity, persistence, and risks. Environmental Health Perspectives, 110(2), 125-128.
United Nations. (2009). United Nations Commodity Trade Statistics Database. In UN Commtrade. New York, New York.
World Health Organization, (2005) The WHO Recommended Classification of Pesticides by Hazard and Guidelines to Classification.
