DDT is an important chemical to look at in its global use today for pesticide eradication in the war against Malaria. Here is an exerpt from an ethics paper on its use in Malaria control.

The history of DDT is extremely complex and politically connected. The chemical was developed in 1939 by Paul Muller who received the Nobel Prize for its invention as an insecticide.[1] It was used in World War II to combat typhus and malaria and was hailed as a miracle cure to diseases that previously had no such relief. In the United States the use of DDT as an agricultural pesticide was prevalent throughout the 1950s and 1960s. In Rachel Carson’s revolutionary book Silent Spring the indiscriminate overuse in all methods of agriculture is described: “Yet only a year after expressing satisfaction with the state of affairs (gypsy moth), its (New England) Plant Pest Control division embarked on a program calling for blanket spraying of several million acres a year.”[2] The book brought to light many environmental and health concerns that surrounded what was at the time considered “so universally used that in most minds the product takes on the harmless aspect of familiar.”[3]

Much of the science that Carson raised in her book was not common knowledge when it was published. Further investigation was prompted, and she is attributed in part to helping spark the Green Revolution in the United States during the 1960’s and 1970’s. DDT is a persistent organic pollutant that does not readily break down in the environment, so many of its environmental impacts are not noticed immediately. Before DDT is incorporated into fatty tissue it is metabolized and a new inactive form known as DDE is created.[4] This is what can be measured in fat tissue in humans, and the ranges vary greatly. Today the average North American has a concentration of 3 parts per million (ppm), while workers in insecticide plants in the 1960s had concentrations up to 648 ppm.[5]^,[6]

DDT is dangerous because of its ability to bio-magnify. It is fat soluble and does not readily get released as waste. As one animal absorbs it, for example a fish through its gills, it stays there until another animal eats it that then absorbs all of it. The larger fish then absorbs all of the DDE in every little fish it eats which is then passed on up the food chain becoming more and more concentrated in the fat of each animal. For birds this is important because once a certain concentration is reached the DDE inhibits calcium absorption, and the eggshells are then too thin to support the parent birds. In the United States the decline of the Bald Eagle population was highly correlated to DDE concentrations. For every 16 micro grams of DDE in the birds there was a fifteen percent shell thinning associated.[7]

The harm from bio-magnification is important not only where the chemical is sprayed but also globally because DDT has the ability to travel in the atmosphere. Because the chemical has a low volatility level a small percentage of it evaporates and then travels to as far as the artic where it is cold enough to condense.[8] Here the chemical can be bio-magnified in the food chain and reach humans and animals on the other side of the planet from where the chemical was sprayed. With the integration of DDE in organisms the effects are often long term and difficult to study. The most important aspect of the chemical impact is its overall harm to biodiversity. There is no way to know what organism it will harm or how, but regardless there are problems that arrive from the indiscriminate killing of organisms.

The human health risks of DDT are also complex. DDE and DDT are hormone-disrupting chemicals that can lead to immunological, developmental, and reproductive problems. There have been many studies done on humans trying to directly correlate prolonged DDT exposure to acute problems but like all carcinogens it is hard to create direct correlations to prolonged exposure because of the lack of study controls. In Tzaneen, Limpopo Province, South Africa a study was done that showed a direct correlation between DDT exposure and decreased semen count.[9] In New York City breast cancer was strongly associated with DDE concentrations.[10] Although the direct mechanisms to causing cancer and other problems are not specifically known it is accepted that long term exposure to DDT is harmful to human health.

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[1] Baird, Colin., Cann, Michael. 2005. Environmental Chemistry Third Edition. W. H. Freeman and Company, New York, NY. 435.

[2]Carson, Rachel. 1962. Silent Spring. Houghton Mifflin Company, New York, NY. 20.

[3] Carson, 20.

[4] Baird C, 450.

[5] Baird C, 445.

[6] Carson, 22.

[7] Wiemeyer, Stanley N., Bunck, Christine M., Stafford, Charles J. 1993. “Environmental contaminants in bald eagle eggs 1980–84—and further interpretations of relationships to productivity and shell thickness.” Archives of Environmental Contamination and Toxicology. Vol. 24(2): 316 February. 316.

[8] Baird C, 414.

[9] Dalvis, Mohamed., Myers, Jonathan., Thompson, Mary Lou., Robins, Thomas., Dyerd, Silke., Riebow, John., Molekwa, Josef., Jeebhay, Mohamed., Millar, Robert., Krugerg, Phillip. 2004. “The long-term effects of DDT exposure on semen, fertility, and sexual function of malaria vector-control workers in Limpopo Province, South Africa.” Environmental Research Vol. 96(1):1-8 September.

[10] Wolff, Mary., Toniolo, Paolo., Lee, Eric., Rivera, Marilyn., Dubin, Neil. 1993. “Blood Levels of Organochlorine Residues and Risk of Breast Cancer.” Journal of the National Cancer Institute. Vol. 85(8): 648-652, April.