Effect of DDT to This Environment
Pesticides became a bad forebode in agriculture since mid-twentieth century. In agriculture, pesticides are an important element to control the major vector-borne diseases such as malaria and visceral leishmaniasis. There are 4 major groups of pesticides: insecticides, rodenticides, herbicides and fungicides. Although pesticides are vital to protect the crop and also human health in the whole world, but due to their detrimental effects on natural ecosystems more deaths are cause by the pesticide poisoning than infectious diseases. Hence, we should focus more on the short and long term harms of pesticides on the environment. Most of the pesticides are highly toxic and will have immediate adverse effects on human health and also wildlife. Besides that, pesticides which spray on the plant at ground will easily contaminate the soil, water and air. The chronic consequences cause by pesticide including neurotoxic, carcinogenic, immunotoxic, hormonal and reproductive effects. One of the highly problematic pesticides is the insecticide dichlorodiphenlytrichoroethane also known as DDT.
1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane is the scientific name of DDT and the chemical formula is C14H9Cl5. DDT is build up by 14 carbon, 9 hydrogen and 5 chlorine atoms (Figure 1).
Figure 1. Molecular structure of DDT.
In its nature form, DDT is crystalline powder with odorless to slightly fragrant in white color. The melting point is at 108.5ËšC, and boiling point at 185ËšC. DDT is highly insoluble in water but is soluble in most organic solvents. This molecule is lipophilic and partitions readily into the fat of all living organisms. Biomagnification and bioaccumulation in the food web make this molecule become more negative impact to the organisms. When the DDT break down the product will be 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane (DDD or TDE) and 1,1-dichloro-2,2bis(4-chlorophenyl)ethylene)(DDE). These two compounds are actually also present everywhere in the environment and are more persistent than the parent compound (Ritter, Solomon, & Forget, 1996).
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DDT is an organochlorine insecticide and is considered a persistent organic pollutant (POP) (PAN Germany for PAN International, 2009). According to Turusov et al. (2002), in year 1874, DDT was first synthesized but until year 1943 its insecticidal properties just discovered and in 1943 large-scale industrial production are started. DDT is contributed to worldwide use and widely accepted by people because of its low price and effectiveness to control malaria and typhus during and immediately after World War II. In order to control the agriculture and forest pests, much more DDT was used after 1945. About 400,000 tons of DDTs were used yearly in this world at 1960s, and 70 – 80% was used for agriculture (Turusov et al., 2002). DDT is a persistent, widespread environmental contaminant that causes significant anatomical, behavioral abnormalities and physiological in humans and also wildlife (Iwaniuk, et al., 2006). In January 1970, the first country – Sweden had banned the use of DDT. In the same year, the former Union of Soviet Socialist Republics (U.S.S.R) was prohibited all DDT and DDT-based products for use as pesticides because of their destruction and persistence effect by bioaccumulation and the carcinogenicity. The production and use of DDT in agriculture were banned too in 1981, but the use for public health purposed was still allowed. In year 1972, most uses of DDT were banned in other countries. The use of DDT has been banned in 34 countries and severely restricted in 34 other countries. Argentina, Australia, Bulgaria, Canada, Colombia, Cyprus, Ethiopia, Finland, Hong Kong, Japan, Mozambique, Lebanon, Switzerland, Norway, and USA are the countries that have banned DDT. The countries that have severely restricted its use include Thailand, Israel, Panama, Kenya, Mexico, Belize, India, Ecuador and the EU (Ritter, Solomon, & Forget, 1996).
DDT is not very strong toxic like most of the organochlorine insecticides, but this chemical is widely use and spread (Ritter, Solomon, & Forget, 1996). In Turusov et al. (2001) study showed that the process of biodegradation of this chemical is very slow and it will persists for a long time in the environment. DDT will likely to accumulate in the food chain and in the tissues of living organisms. When expose to DDT and digest it, this molecule will store in all the tissues, especially in fat. Bioaccumulation occurred by accumulate the DDT from small concentration to high concentration in the food web. Due to it widespread, uncontrolled, and intensive use, this chemical has resulted in worldwide pollution. In the body of all birds and fishes analyzed in the study of Turusov et al. (2001), DDT residues are found even in those living in desert areas or in the depths of the oceans.
Human are most likely to be exposed to DDT from the food they eat. Almost all the meat, fish, and dairy products are contaminating with DDT. Hence, by eating, breathing or touching the products which contaminated with DDT, this chemical will easily absorbed into our body. After ingested, DDT will convert into several breakdown products called metabolites that included DDE and stored in the fatty tissues. For the pregnant women, DDT and DDE can be passed to the fetus by breast feeding (Centers for Disease Control and Preventation, 2009). If human expose to high concentration of DDT, the symptoms like vomiting, tremors or shakiness, and seizures will occur. Besides that, DDT also considered a possible human carcinogen.
Birds usually played a major role in creating awareness of pollution problems. Birds are most probably believed to expose to DDT by ingestion (Enrlich, et al. 1988). The pesticide can be swallowing by the birds directly or the birds eat the contaminated prey. Besides that, they may also ingest pesticide residues off feathers while preening, or they may drink or bathe in contaminated water. When the birds expose to aerially spread DDT, the chemical will absorbed through the skin or inhaled into the body (Edwards, 2004). DDT and DDE are persistent as they tend to concentrate as they move through the food chain (Figure 2). In the marine communities, the contaminated planktons are eaten by small fishes, and then bigger fishes will consume small fishes. DDTs are passing from a small concentration in planktons to bigger fish. DDT will store in the fatty acid of fishes, when fish-eating birds consume the fish, all the bio accumulated DDT will pass into the bird’s body. Most of the DDT from numerous fishes ends up in the body of few birds. Bioaccumulation of DDT in birds high on food chains occurs not only because there is usually reduced biomass at each step in those chains, but also because predatory birds tend to live a long time. DDT take in only a little per day, but when they keep most of what they get and they live many days (Deinlein, n.d.).
Figure 2. Bioaccumulation of DDT.
DDT with high concentration does not usually kill the bird outright. However, DDT and its relatives will alter the bird’s calcium metabolism in a way that results in thin eggshells (Edwards, 2004). Since the eggshells are too thin and are unable to support the weight of the embryo of bird, heavily DDT-infested Brown Pelicans and Bald Eagles tend to find omelets in their nests. DDT resulted in the decimation of the Brown Pelican populations in much of North America and the extermination the Peregrine Falcon in the eastern United States and southeastern Canada. Shell-thinning caused lesser declines in populations of Golden and Bald Eagles and White Pelicans, among others (Enrlich, et al. 1988). Fortunately, the scientists are able to figure out the cause of the breeding failures in time, and the use of DDT was banned almost completely in the US at 1972.
The Arctic, polar bears also become one of the victims of DDT. Chemical pollutants are carried towards the Arctic Ocean by the great continental rivers of Russia and Canada. DDT that in the sea are wafted northwards by the currents. Even the DDT molecule in the air will be carry by winds to the Arctic, where they condense in the cold and fall to the ground in snow or hail. The most direct and effective way to bring DDT that will cause an effect to polar bear and its offspring is biomagnification. DDTs are biomagnify as they move up the food chain from the small plankton to polar bear. As polar bear is the carnivores, it accumulates the most concentrated amounts of them. Before the hibernation, polar bear will consume large amount of fish to store as fat. DDT which accumulates in the fish will then store in the fatty tissues. When the polar bear start to use the fat during hibernation, DDT is being release and causes the death. In addition, DDT will also reduce the polar bear capacity to bread and lower their immune system (Polar bears: Walking on thin ice, 2006).
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The available epidemiologic and scientific data indicate that the presence and persistence of DDT and its metabolites worldwide are still problems of great relevance to public health. It has been debated at the United Nations Environment Program whether DDT should have been totally banned together with 11 other persistent organic pollutants. However, the total ban of DDT was sharply criticized in South Africa. This is because, a temporary total ban on the use of DDT for indoor spraying resulted in a sudden increase in malaria. Now, 11 countries in Africa, 7 in Asia, and 5 in Latin America still use DDT for vector disease control (Turusov et al., 2002). There is a general consensus that limited and strictly controlled use of DDT should be allowed for public health purposes, in particular where other effective, safe, and affordable alternatives are not available, and the benefits are clearly far superior to possible risks. In conclusion, to solve the problem of DDT an efficient pesticides that do not have the negative properties of DDT and its metabolites should be sought with the goal of replacing DDT completely.
Centers for Disease Control and Preventation (CDC), (2009). Retrieved from http://www.cdc.gov/biomonitoring/pdf/DDT_FactSheet.pdf
Deinlein, M. (n.d.). Smithsonian Migratory Bird Center. When it comes to pesticides, birds are sitting ducks. Retrieved from http://nationalzoo.si.edu/scbi/migratorybirds/fact_sheets/fxsht8.pdf
Edwards, J. G. (2004). DDT: A case study in scientific fraud. Journal of American Physicians and Surgeons, 9, 3, 83-88.
Ehrlich, P. R., Dobkin, D. S., & Wheye, D. (1988). DDT and birds. Retrieved from https://web.stanford.edu/group/stanfordbirds/text/essays/DDT_and_Birds.html
Iwaniuk, A. N., Koperski, D. T., Cheng, K. M., Elliott, J. E., Smith, L. K., …, Wylie, D. R. W. (2006). The effects of environmental exposure to DDT on the brain of a songbird: Changes in structures associated with mating and song. Behavioural BrainResearch, 173, 1-10.
Polar bears: Walking on thin ice. (2006). Retrieved from http://www.independent.co.uk/environment/polar-bears-walking-on-thin-ice-523207.html
Ritter, L., Solomon, K. R., & Forget, J. (1996). Persistent organic pollutants. Retrieved from http://www.chem.unep.ch/pops/ritter/en/ritteren.pdf
Turusov, V., Rakitsky, V. & Tomatis, L. (2002). DIchlorodiphenytrichloroethane (DDT): Ubiquity, persistence, and risks. Environmental Health Perspectives, 110, 2, 125-128.
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