DDT: Weighing the Benefits and Risks

Transcription

1 Jerald Varona Chem 151 James Whitesell 14 March 2014 DDT: Weighing the Benefits and Risks DDT, dichlorodiphenyltrichloroethane, was heralded as a savior during the World War II era and post-wwii era after effectively saving millions of lives from insect-borne diseases such as typhus and malaria. The use of DDT was also appropriated to act as an insecticide in crop and livestock production. Despite DDT's great success in eradicating insect-borne diseases in various countries, including the United States, its negative effects on the environment and potential toxicity to wildlife and humans led to its banning in the United States in Figure 1: Structure of DDT DDT, C 14 H 9 Cl 5, was originally synthesized in the late 19 th century. However in 1939, a Swiss Chemist, Paul Muller stumbled upon DDT's insecticidal qualities when searching for an insecticide against clothes moths. Muller discovered it by spraying a small amount of DDT into a cage with one fly in it. After some time, the fly slowly died and soon DDT tests were performed successfully on other insects known to spread diseases. Muller eventually received the Nobel Prize in Physiology and Medicine in 1948 for his work with the pesticide and the control of vector diseases. [1] During World War II, Muller's work with DDT was applied and it soon became an important and efficient means of controlling and preventing the insect-borne diseases typhus and malaria, which are transmitted through lice and mosquitoes, respectively. DDT was first used by the Allied Forces by mixing DDT with an inert powder and dusting troops and refugees to prevent lice-borne typhus. Dusting stations were set up in the camps and within a couple weeks the Forces had dusted millions of citizens and successfully fought a typhus epidemic from occurring. [1] The use of DDT as an insecticide proved to be a great success in a short period of time and eventually was administered on a large scale to flush out the disease in various countries.

2 Figure 2: Allied Force soldier dusting civilian with DDT using a DDT-hand spraying equipment. Not long after DDT's success against the typhus epidemic, the pesticide was appropriated to the control and prevention of malaria. Previously, malaria had been controlled by indoor residual spraying (IRS) of various insecticides on the feeding grounds of the mosquito, usually the walls of a house, in order to intoxicate them. Before DDT, various insecticides were used for the spraying but in comparison, were not as effective, labor-intensive, and less potent than DDT. The insecticides needed to be sprayed about every 2 weeks in the walls of houses. [1] DDT, on the other hand, has a longer half-life and was more cost-efficient since it only needed to be sprayed every six months. The longer half-life is attributed to the hydrophobic nature of DDT, giving way to a low solubility in water and high solubility in fats. This meant that DDT does not dissolve in water well, but it dissolves in the fat of organisms well. [3] Therefore, DDT was an effective choice for indoor residual spraying and also for insecticidal uses in agriculture since it remained in the environment for longer periods of time. This greater time span allowed a malaria control unit to cover more ground, spray more houses and ultimately, protect more people. In the United States, DDT was utilized in two different manners: an indoor residual insecticide and a larvacide. The latter acted as an insecticide that attacked and targeted the larval stage of the mosquito. [7] The results were immensely successful and virtually eradicated the disease within years, and DDT was soon utilized successfully overseas in Europe, and in some African and South American countries. After DDT was administered in India alone, between 1953 and 1957, the percentage of morbidity went from 10.8% to 5.3% of the total poupulation and malarial deaths became almost nonexistent. [1] With all of the success of DDT, came a growing amount of backlash due to the efforts of Rachel Carson in 1962 and her book, Silent Spring. Carson exposed the destructive effects certain pesticides, DDT included, had on the health of wildlife and the environment. The health defects were primarily found in birds of prey species in North America and Europe by altering their reproductive systems. Carson argued that the spraying of DDT for disease control had caused the eggshells of these birds to

3 become thinner, which lead to breakage and embryo death. Naturally, these health defects caused a depletion in population of birds species such as the bald eagle, brown pelican, and peregrine falcon to name a few. Because of the declining population of birds species, Carson aptly named her book, Silent Spring, referring to a quiet spring season without the chirping of birds. The toxicity of DDT was not exclusive to aviary species but also aquatic species and is a possible carcinogen to humans, however the evidence is equivocal. Several studies have been made in order to determine possible carcinogenic effects on humans. However, some studies have found a causal relationship between DDT exposure and reproductive defects; while other studies have not shown significant evidence that DDT is harmful to humans. [2] The dangers of DDT to wildlife and potentially human life can be attributed to the fact that DDT bioaccumulates and is fat soluble. Therefore, when an organism consumes something contaminated with DDT, the chemical tends to store within the organism's fat and continues to build up if more DDT-contaminated food is consumed. Due to its lipophilic nature, DDT is resistant to metabolism and is not broken down well in organisms. When another animal preys on the DDTconsuming animal, the predator obtains the prey's burden of DDT. As this process continues, it leads to biomagnification which refers to an increased concentrations of DDT in the higher links of the food chain. [4] Figure 3: Biomagnification of DDT in the food chain As a result of Carson's Silent Spring and studies showing the detrimental effects DDT had on the environment and wildlife, a growing environmentalist movement against the use of pesticides and chemicals came to the forefront. Due to pressure from environmental groups, in 1971, the Environmental Protection Agency (EPA) held hearings investigating the risk of DDT use. Although some studies were done and showed no significant evidence that DDT was a cancer threat, and that it was relatively benign, there was still doubt. However, in terms of the environment, the evidence was

4 much stronger as detailed in Silent Spring. In 1972, the EPA issued the cancellation and delisting of DDT in the United States based on the environmental risks and potential carcinogenic factors in humans. [2] Although DDT was canceled, the use of DDT was still allowed for public health under certain conditions, such as the control of malaria if an outbreak were to occur. Other countries, however, have the choice to use the chemical or not. In 1996, the Stockholm Convention was held by the United Nations Environment Program where global bans and restrictions were made against persistant organic pollutants (POPs), which includes DDT. There was an exemption in the Convention for the use of DDT only to control mosquitoes that are vectors for malaria. In 2006, The World Health Organization (WHO) issued support for the use of DDT as an indoor residual spray in African countries who suffered from the effects of malaria. Following the support of DDT used to combat malaria by the WHO, an increasing amount of debate against the use of DDT as an indoor residual spray chemical has arisen particularly in African countries where malaria has continued to kill millions. The debate is polarized and is seen differently by different groups of people. Some believe that DDT should not be used and want to eliminate any production or use of DDT because of the environmental and health risks. Others see DDT as a safe and logical chemical to use as an indoor residual spray in order to control malaria. The debate is centered around the fact that DDT has been an effective means to control vector diseases such as malaria, but studies have also shown that it is a risk to the health of the environment and potentially humans. Those who are pro-ddt would rather save millions of lives and risk endangering the environment and risk mutations or consequences in human health. On the other hand, those against DDT believe that as a result of indoor residual spraying of DDT on the walls inside houses, individuals of that household will be effectively exposed to DDT. Those who are anti-ddt firmly believe that as a result of being exposed heavily to DDT, the individuals are susceptible to severe health risks. Although these health risks are not full proven, recent studies from have shown correlations between DDT exposure and effects on sperm quality, diabetes, hormone levels in blood, and others. [5] Recently in 2013, delegates of African countries once again brought this debate over DDT to light amidst the growing mortality and morbidity rates from malaria. African officials reached the decision to adopt DDT as the primary means to eradicate the insect-borne disease from their malariastricken countries. The same controversies and fears over the use of DDT were discussed, but ultimately African officials saw its benefits to outweigh the risks. One official went on the say that if DDT was not used then it would be like a death sentence to their constituents. In order to regulate, officials ordered DDT to only be used indoors on ceilings and walls and with food covered and put away. South Africa, for example, has used DDT under WHO's regulations. In 1996, the country switched to alternative pesticides for malaria control but saw a large increase in malaria incidence, and eventually switched back to DDT in addition to new drugs to successfully control the disease. [6] Once its insecticidal properties were discovered, DDT quickly became a gift to countries that were suffering from insect-borne diseases, especially malaria. But just quickly as it rose to fame, DDT soon became the center of controversy as the environmental and health defects of DDT were uncovered. It is a prime example of the potential danger of high usages of chemicals in the environment and the source of fear among anti-pesticide and anti-chemicals advocates. The choice between risking the possible harm that would be inflicted by the use of DDT or saving millions of lives is one notion that will constantly be associated with DDT. Until studies can fully support evidence that DDT is a harmful chemical and carcinogen to humans; or until a more efficient and non-toxic insecticide is found will the debates end. But until that happens, it is up to the people of these countries to regulate the usage of DDT as a means to combat malaria.

5 Works Cited 1. Bates, Roger. The Rise, Fall, Rise, and Imminent Fall of DDT The Environmental Protection Agency. DDT A Brief History McGinn, Anne Platt. World Watch Magazine. May/June 2002, Volume 15, No Bouwman, Hindrik; Berg, Henk van den; Kylin, Henrik. DDT and Malaria Prevention: Addressing the Paradox Ovuorie, Tobore. African Countries Adopt Controversial Deadly Chemical, DDT, for Malaria Treatment Larvicide