C151- Codes A8, D13

Dichlorodiphenyltrichloroethane

DDT also known as Dichlorodiphenyltrichloroethane, was one of the most widely used pesticidesworldwide. Established in 1939 as an insecticide, and during World War II; DDT was used to combat diseases such as typhus and malaria among both military and civilian populations. After the war, it was continuously used by farmers as a pesticide to protect their; crops, livestock production, institutions, homes, and gardens. In the 1970s, scientists and communities expressed their concerns towards the safety of DDT and this powerful chemical production was suspended. However, DDT remains one of the most important and well-known chemical compounds to the society.

Physical and Chemical Properties

The scientific name for DDTis 1,1,1-trichloro-2,2-bis-(p-chlorophenyl) ethane. The chemical formula for DDT is C14H9Cl5. For every DDT molecule, there are 14 carbon atoms, 9 hydrogen atoms, and 5 chlorine atoms.

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DDT appears as a white crystalline powder and posesses the smell of table salt. DDT’s chemical structure is similar to the insecticide methoxychlor and acaricide. DDT is a substituted molecule. At the carbon atom attached to the benzylic carbon atom, all three hydrogen’s are replaced by chlorine atoms, which on the other hand, two of the three hydrogen atoms are replaced by a benzene ring. Each ring contains a chlorine atom at the para- position. (This is should be written more specifically because the carbon next to a benzene ring is called a “benzylic carbon atom”)

The large concern right about DDT is due to its long lasting chemical impact upon the environment. The reason for its chemical stability in the environment is because of its low solubility in water- this is a very unique about DDT. It is mostly insoluble in water, whereas highly soluble in most organics solvents, oils and fats. Due to its chemical structure not being soluble in water, DDT has the ability to stay within the environment. In contrast, DDT is very soluble in fats, meaning organisms with high fat content are easily susceptible to DDT poisoning.

DDT is not a naturally occurring compound, but is synthesized through the reaction of chloral (CCl3CHO) with chlorobenzene (C6H5Cl) in the presence of sulfuric acidcatalyst.

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Many organisms metabolize DDT by the elimination of HCl (a hydrogen atom is removed from one ethane carbon and a chlorine atom from the other, therefore creating a derivative of ethane called DDE, dicholorodiphenyldichloroethene. DDE is a metabolite of DDT. (Should explain what metabolite means) The chemical DDE is also produced slowly in the environment by the degradation of DDT under alkaline conditions, and by the DDT-resistance insects that detoxify DDT by this transformation.

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DDT’s persistence within the environment makes it become the ideal insecticide. Its persistence is due to its low vapor pressure, slow rate of evaporation, insolubility in water, and low light and chemical reactivity in the environment.

Humans beings always have a form of DDT stored within the body. Most traces of DDT within the human body are eliminated slowly by degradation over large period’s time. Most of the DDT stored in our bodies is actually the DDE that was present in the food that we eat, having been previously been converted from DDE. DDE is stored in our bodies through our fat.

Biochemical effects of DDT

All cells possess plasma membrane that separated the inside and outside of the cell. The cell membranes are composed of lipids. This membrane will allow certain substances that can enter the body such as oxygen, nutrients, and DDT, which is lipid soluble. The plasma membranes opens up to become porous to allows multiple ions to pass through.

For a nerve cell, the concentrations of Na+ and K+ inside and outside of a cell are especially important, because they help determine when the nerve cell will fire its signals. After DDT gets into the plasma membrane, concentrations unbalanced of sodium and potassium ions are permeable. The muscles contraction and relaxation can no longer function normally. Thus, when an organism is poisoned with DDT, it dies by either convulsions (random, uncontrolled contraction of the muscles) or paralysis (complete loss of muscle control).

History and Uses

DDT was first synthesized in 1874 by OthmarZeidler, an Austrian chemist. In 1934, Wolfgang von Leuthold filed a patent for the ability to kill insects of a "multiple chlorinated aliphatic or fat-aromatic alcohols with at least one trichloromethane group. In 1939, Swiss scientist Paul Hermann Müller established the pesticide properties of DDT and was awarded the Nobel Prize in Physiology and Medicine for his work.

Because of all these uses for DDT, the United States used a lot of it during the mid-1900s. At one point, the US was producing 220 million pounds of DDT a year. By the 1970s, we began to get worried about DDT's environmental and health effects. So finally in June of 1972, the US Environmental Protection Agency cancelled all use of DDT on crops. Only limited use of the chemical is allowed in emergency case of disease control.

Environmental impacts

DDT in the environment can come from atmospheric deposition, soil and sediment runoff and improper use and disposal. DDT is persistent in the environment and can be deposited into environmental reservoirs through runoff. Depending on conditions, its half-life in soil can range from 22 days to 30 years. DDT can degrade by volatilization, photolysis and aerobic and anaerobicbiodegradation. In water environment, due to the hydrophobic properties, DDT tend to be absorbed by aquatic organisms, only a little amount is available in the water. Its breakdown products and metabolites, DDE and DDD, are also highly persistent and have similar chemical and physical properties. Because of its lipophilic properties, DDT and its derivative tend to accumulate in the body fat of organisms and remain in the food chain for a long duration.

  • Microorganisms

Even small amounts of DDT can affect small microorganisms. This is especially true for microorganisms that live in the water such as algae, and plankton, because the aquatic environment can bring more DDT in contact with these organisms.Although affected by DDT, the microorganisms persist, by absorbing the DDT within themselves.

  • Invertebrates

Terrestrial Invertebratesare not affected very much by DDT and have a high tolerance to DDT. However, they retain a lot of the DDT in their bodies. This accumulation poses a threat to predators that eat these organisms. In contrast, aquatic invertebrates are sensitive to DDT. When in contact with DDT, they are subject to reproductive/development impairment and nervous system disorders.

  • Birds

DDT, through its metabolite DDE, caused eggshell thinning and resulted in severe population declines in multiple North American and European bird species. Eggshell thinning lowers the reproductive rate of certain bird species by causing egg breakage and embryo deaths.Some bird species affected by DDT are osprey, eagles, pelicans, falcons and hawks.

  • Humans

In the early to mid 1950s, DDT became one of the most widely used pesticides. At this time it was currently not known as a hazard to people’s health. The reason was that it is difficult for DDT to be absorbed through human skin. Eventually, it was realized that some DDT was able to accumulate in our bodies. In the 1960's, concern arose about the widespread use of DDT and its effects on humans. A study in 1968 showed that Americans were consuming an average of 0.025 milligrams of DDT per day.

Even though DDT has been banned since 1972, DDT can remain the environment for up to 15 years. Human can be affected by DDT by eating contaminated fish and shellfish, eating imported food directly exposed to DDT, and eating crops grown in contaminated soil. Infants may be exposed to DDT through the mother’s breast milk.

When DDT is introduced into the human bodies, it is stored primarily in such fatty organs as the adrenals, testes, and thyroid. DDT is also stored in smaller concentrations in the liver and kidneys. The concentration of DDT is especially high in human breast milk since breast milk is the production of body fat where DDT accumulates the most.

The amount of DDT that can be tolerated depends on the body weight. At concentration above 236 mg per kg of body weight, DDT can lead to death. Lower concentration at of 6-10 mg/kg leads to such symptoms as headache, nausea, vomiting, confusion, and tremors.

Researchers have proved that DDT is a probable human carcinogen. More recent evidence from epidemiological studies indicates that DDT causes cancers of the liver, pancreas and breast. There is mixed evidence that it contributes to leukemia, lymphoma and testicular cancer.DDT can also damage the liver, temporarily damage the nervous system, reduces reproductive success, and damage the reproductive system.

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