Current Perspectives On A Global Ban Of DDT - Essay Example

Current Perspectives On A Global Ban Of DDT Dichlorodiphenltrichloroethane, better known as DDT, was the first pesticide to be applied to the systematic environmental control of insects (Barnhoorn et al. 22). The Swiss scientist Paul Muller was the discoverer of the insecticidal properties of this organochlorine chemical in 1942 and was awarded the Nobel Prize for his efforts. DDT is actually a mixture of isomeric forms of organochlorine. It acts as a nerve poison that paralyzes and kills insects; unfortunately, its neurotoxic effects are experienced by many other forms of life if exposed to this pesticide in the context of its environmental application (Prüss-Ustün,  Bonjour, and Corvalán 47). Much research has been carried out to determine precisely its effects on the nervous system; however, its physiological mode of action is not yet well understood (Barnhoorn et al. 23-26). The first important use of DDT occurred shortly after its discovery, during World War II, when it was used to control an outbreak of typhus in military troops, which is transmitted by infected lice (Beier et al. S14). Its most widespread environmental applications, however, have been its use in agriculture and in an effort to destroy the species of mosquitoes that are the vectors for the transmission of the malarial parasite to humans Prüss-Ustün, Bonjour, and  Corvalán 49) Despite the accumulated evidence that DDT has serious toxic effects on the environment and in humans, its use continues in certain areas of the world, especially in many counties of Africa. From 1950-1980 DDT was used as a pesticide for agricultural purposes such 40,000 tons were dispersed into the environment each year (Beier et al. S19-20). The Stockholm Convention banned the agricultural use of this pesticide. Today, it is estimated that 4-5,000 tons of DDT are used each year to control the spread of malaria and leishmanias. India is the largest consumer worldwide. India, China and North Korea are the only countries that continue to manufacture DDT. Moreover, the use of DDT as an agricultural pesticide has continued in India and North Korea (Beier et al. 24-27). The use of DDT to control the spread of malaria in tropical areas of the world in the 1960s and 1970s resulted in the rapid decline of this disease; however, its use was limited in areas of the world where the incidence of malaria is high, including sub-Saharan Africa (Beier et al. S22). Since then, areas of high malarial incidence have adopted the extensive use of DDT to control the spread of this disease. The use of DDT in the developing nations of the world where the incidence of malaria is high has engendered controversy, as the use of DDT has been banned in many parts of the world as the potential long-term dangers associated with the use of this pesticide have become widely appreciated. DDT is characterized as a moderately hazardous chemical by the World Health Organization (WHO) (Beier et al. S17). It primarily affects the central and peripheral nervous systems where it acts as a neurotoxin. In addition, DDT affects the functions of the liver, the primary site of chemical detoxification in the body. Acute exposures to moderate levels of DDT are associated with nausea, diarrhea and liver toxicity. High dose acute DDT exposure affects the nervous system directly, causing tremors and convulsions (Barnhoorn et al. 29-31). Acute exposure to DDT is rare, except among industrial workers. More commonly, the effects of chronic exposure to low levels of DDT are observed. In experimental animals, chronic DDT exposure affects the nervous system, kidneys, liver and the immune system. Moreover, important effects of chronic DDT exposure on the reproductive system have been noted in tests on experimental animals. These effects are believed to be mediated by DDT interactions with endocrine hormones associated with reproductive activity (Korrick et al. 491). It has been difficult to quantify the effects of long term, chronic exposure to DDT in humans. Animal studies in mice have also demonstrated that DDT exposure may cause teratogenic effects on fetal development, affecting nervous system functions including learning. Epidemiological studies generally have not identified significant physiological effects in humans in areas where DDT has been used as an environmental pesticide (Korrick et al. 491). Because DDT is a fat-soluble chemical, it is stored in adipose tissue in animals and humans. DDT stored in fat tissue will remain there unless the tissue is metabolized by the body. This produces cumulative exposure effects as continual uptake of DDT in the body from environmental sources increases the net amount of DDT accumulation in the body over time. DDT stored in fat tissue will remain there unless the tissue is metabolized by the body (Korrick et al. 492). Animal studies have shown that DDT stored in adipose tissue can cross the placenta, suggesting the possibility of teratogenic effects in the unborn. The amount of DDT stored in adipose tissue increases with age and is found at three-fold higher levels in African Americans than in Caucasians, for reasons that are unclear (Korrick et al. 492). Potential links to cancer from DDT exposure have been extensively researched using experimental animal models. Some studies have produced data indicating that DDT exposure is associated with liver and lung tumors. Based on these findings, the US Health and Human Services Department has issued advisories stating that DDT is a likely human carcinogen, although no direct evidence has been cited (Korrick et al. 495). In contrast, the US Environmental Protection Agency has called DDT a “probable” human carcinogen. The US National Cancer Institute has produced studies showing that high levels of DDT in the bloodstream are associated with an increased incidence of breast cancer in areas of the US where DDT has been widely used as an environmental pesticide. In this clinical case study, called the New York University Women’s Health Study, researchers studied 14,290 women and selected 58 women with breast cancer and 171 matched controls for assessment of the relationship between circulating levels of DDT and breast cancer. The studies showed that women with elevated DDT levels were four times more likely to develop breast cancer than women whose DDT levels were low (Korrick et al. 494). A case study in Zimbabwe showed that women with elevated levels of DDT in their blood and body tissues secreted DDT in their breast milk at levels capable of producing neural effects in infants (Korrick et al. 496). Another important case study on the effects of DDT exposure in humans was a 2006 study carried out by University of California at Berkeley, that provided evidence that children exposed to DDT in the womb may experience developmental defects and that even low levels may affect cognitive ability. DDT may also be associated with early pregnancy loss, based on the results of a case study in China (Korrick et al, 494-496). Many research studies suggest that the continued use of DDT over the past 25 years has threatened the existence of wildlife species and presents an important human health concern that must be addressed (Barnhoorn et al. 21). DDT persists for long periods of time in the environment; its half-life may range between 2-15 years (Barnhoorn et al. 25). Its environmental effects can be devastating. DDT is a major source of wildlife contamination and death in areas where it has been used extensively (Prüss-Ustün, Bonjour, and Corvalán 60). Fish are extremely sensitive to its effects and bird species may be threatened due to the effects of DDT on eggshells, such that it causes their thinning and breakage affecting reproduction of many bird species. The bald eagle was threatened with extinction in the US during the years when DDT was used as an environmental pesticide. Among other bird species threatened by environmental exposure are brown pelican, peregrine falcon, and the osprey (Barnhoorn et al. 32). The environmental effects of DDT exposure may be experienced at long distances from the primary site of application. DDT travels beyond its site of application by air and water currents and spreads from warmer to colder areas of the globe by a mechanism called global distillation (Barnhoorn et al. 35). DDT is very resistant to breakdown in colder climates, enhancing its cumulative effects. DDT has been found in the arctic ice and in remote islands of the Pacific, suggesting that no area of the world is immune to the effects of this toxic chemical. Due to the cumulative storage of DDT in body tissues, DDT is found in milk, dairy products and meat from animals in areas where DDT has been used as an environmental pesticide and is concentrated in the food web (Barnhoorn et al. 43). The long term cumulative effects of exposure are demonstrated by the fact that DDT residues continue to be found in meat and dairy products in the US and Northern Europe despite the fact that DDT has not been used as an environmental pesticide in these areas of the world for decades! In the UK, the Working Party of Pesticide residues (WPPR) has found DDT residues in dairy products, fish, and other meats (Barnhoorn et al. 44). The Acceptable Daily Intake (ADI) of DDT has been calculated for many countries. The World Health Organization (WHO) has accumulated evidence showing that the consumption of DDT contaminated foods is higher in developing nations that in industrialized countries and exceeds the ADI in many of these countries (Barnhoorn et al. 45). Ever since the publication of Silent Spring, by Rachel Carson in 1962, there has been a major public outcry to ban the use of this toxic chemical which poses a threat to the survival of life on this planet. Many environmentalists deplore the continued use of DDT by developing nations and the failure of the global community to enforce an international prohibition against its use (Barnhoorn et al. 30). The United Nations has played an important role in this debate. While banning the use of this pesticide for agricultural purposes, the organization has been reticent to impose this restriction on the use of DDT as a means to control the spread of vectorial borne disease (Rogier et al. 177). The current exemptions on the worldwide ban on the use of DDT established by the UN in 2001 involve many developing nations in parts of the world where malaria is endemic as it remains one of the best weapons against this disease, despite the occurrence of resistance in mosquito populations that limits the overall effectiveness of this approach. Currently, malaria has one of the highest mortality rates of any disease worldwide, with 880,000 deaths reported annually (Beier et al. S4). DDT continues to be used to control the spread of malaria in many countries of Africa, Asia, India and South America. Approximately 250 million cases of malaria are recorded each year; 90% of estimated 1 million deaths each year occur in Africa, where it is a major cause of infant and early childhood mortality. Many public health officials believe that the use of DDT is justified based on these statistics and the absence of alternative deminstrated effective means of mosquito control (Beier et al S7). The most common current application of DDT is “Indoor Residual Spraying” (IRS) to control the indoor mosquito population in homes. DDT is a recommended agent by the WHO for IRS mosquito control (Beier et al. S8). In 1996, South Africa attempted to use alternatives to DDT for mosquito control and experienced a dramatic upsurge in the incidence of malaria (Beier et al. S11). Critics of the DDT ban initiative feel that the restricted use of this chemical is currently responsible for the deaths of over one million children froim malaria. In the absence of comparably effective alternatives, many nations where this disease is endemic would rather risk the long term environmental and human health risks associated with this pesticide than risk a higher incidence of malaria, whose devastating consequences to human life are immediately manifest (Rogier et al. 179). Many counties have felt that they have no choice but to use this pesticide to control the mosquito population, in the absence of any perceived reasonable alternative approaches to controlling the spread of this disease. Moreover, supporters of the use of this pesticide argue that the amount of DDT used for disease control is a small fraction of that used for agricultural purposes, which is a mitigating factor in terms of its potential environmental and heath effects (Beier et al. S4). This use of a pesticide with known toxic properties must be balanced against the threat that its disuse may provoke an increased incidence of life-threatening disease in malaria-stricken regions of the world. In mid-2009, the United Nations presented a global initiative to eradicate the use of DDT by 2020 (Rogier et al. 177). The stated goal of this effort is to achieve a 30% reduction in the global use of DDT by 2014, with the complete elimination of its use by 2020. This initiative is sponsored by the UN Environment Program (UNEP), the World health Organization (WHO) and the Global Environmental Facility, and is expected to cost $40 million. This directive was primarily aimed at sub-Saharan countries of Africa, South America and Asia, all of which continue to use DDT as a way of dealing with endemic malaria, which continues to plague this region of the world (Rogier et al. 178). The UN goal is to establish ten programs that would include 40 African nations, the Eastern Mediterranean and Central Asia with the goal of implementing technologies to control malaria that do not involve the use of DDT. A preliminary pilot project established by the UN in Mexico and Central America demonstrated that the incidence of malaria could be controlled with measures that did not include the use of this dangerous pesticide (Rogier et al. 180). The alternative approaches to DDT that were implemented in Mexico and central America included the use of mosquito screens over beds in family homes, elimination of stagnant water where the mosquitoes breed and other simple measures to protect against mosquito bites were successful in reducing the incidence of malaria by 63%, a very impressive statistic (Rogier et al. 182). Additional environmental approaches with a targeted long range effect on controlling the mosquito population in these areas involved planting trees such as oak and neem that act as natural repellents and also by introducing species of fish and other microbes that that are natural predators of the mosquito. Based on this successful intervention, the program will be implemented in other areas of the world where malaria is endemic and DDT continues to be used in a sometimes desperate effort to control this often fatal disease that is spread by several species of the Anopheles mosquito (Rogier et al. 184). The application of new approaches to vector control and increased research funding to develop an effective vaccine for malaria would go a long way to achieve a global cessation of the use of this pesticide. Works Cited Barnhoorn, I. E. J., M. S. Bornman, C. Jansen van Rensburg, and H. Bouwman. “DDT residues in water, sediment, domestic and indigenous biota from a currently DDT-sprayed area." Chemosphere (September 2009) 21-45. Beier, John, Joseph Keating, John Githure, Michael Macdonald, Daniel Impoinvil, and Robert Novak. "Integrated vector management for malaria control." Malaria Journal 7 (2008): S4-30. Korrick, S. A., C. Chen, A. I. Damokosh, J. Ni, X. Liu, S. I. Cho, L. Altshul, L. Ryan, and X. Xu. "Association of DDT with spontaneous abortion: a case-control study.." Annals of epidemiology 11 (October 2001): 491-496. Prüss-Ustün, A., S. Bonjour, and C. Corvalán. "The impact of the environment on health by country: a meta-synthesis." Environmental health : a global access science source 7 (2008): 47-68. Rogier, C., M. C. Henry, M. Rowland, P. Carnevale, F. Chandre, V. Corbel, C. Curtis, J. M. Hougard, and WHOPES, WHO Pesticide Evaluation Scheme. "[Guidelines for phase III evaluation of vector control methods against malaria]." Médecine tropicale : revue du Corps de santé colonial 69 (April 2009): 173-184. Read More