The Role of Chemistry in History

Introduction / DDT molecule / Malaria / World War II

Environmental Problems / Insect Resistance / Begin Using Again?  /  References

• Over 1 million people die from Malaria each year
• Much of Europe and the America’s were malarial until the early 1950s
• Most people associate the disease with developing and tropical countries but it was only recently been eradicated
• Two ways to fight the disease:
• 1. Use drugs such as quinine to treat already infected patients
• 2. Try to destroy the carriers of the disease: anopheles mosquito

• In 1944, DDT was proposed as a way to eradicate Malaria after the success of killing mosquitoes and protecting soldiers during WWII
• It was first used again in Italy.  Spraying began in 1945 and by 1948 and after spraying half a million pounds over 135,000 miles, the malarial death in Italy was zero.
• After this success the World Health Organization (WHO) began to implement malaria control programmes in several countries.

• Example of the successes of DDT in Malaria eradication:
• South America shortly after the first spray in 1946, the number of Malaria cases dropped 1/3 from what it was in 1942.
• Sri Lanka began spraying in 1946 as well. In 10 years the number of cases of Malaria was cut from 3 million to 7300 and had eliminated ALL Malaria related deaths. And by 1964 the number of cases was just 29.
• In India it was estimated that around 75 million contracted the disease each year and about 800,000 people died. Through the use of DDT the number of contracted malaria cases dropped from 75 million in 1951 to 50,000 in 1961.
• Malaria was successfully eradicated from 10 countries (4 in Europe and 6 in Americas and Carribean)
• In 1951:
  • it was discovered that the anophelines mosquitoes in Greece came back to spraying sites within days
• In 1953:
  • it was clinically proven that the anepheles mosquito was physiologically resistant to DDT 
• In 1956 the Malaria rates began to rise again because of:
• The successes many countries stopped the intensive spraying because they thought that they had effectively stopped the spread of the disease.
• And because of the developing resistance to the pesticide.
• The World Health Organization decided to blast these countries with DDT where Malaria was increasing to hopefully kill the mosquitoes before they had the chance to develop the resistance. But many third world countries where this treatment was needed didn’t have the capabilities for such a blast.
• Slowly the Eradication campaign turned into control and in sub-saharan Africa it was reduced to a Containment Campaign.
• Then in 1962 Rachel Carson published Silent Spring and the environmental battle on DDT began and it was subsequently banned by the U.S. in 1972.

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Introduction / DDT molecule / Malaria / World War II

Environmental Problems / Insect Resistance / Begin Using Again?  /  Resources

• In recent years (since 2001) DDT has started to make a comeback and the enivronmental issues (as discussed in the environmental section) and resistance has been re-investigated.

• Donald Roberts, entomologist at te Uniformed Services of the Health Sciences in Bethesda, Maryland, conducted experiments in the Amazon basin to investigate resistance

  • he chose two huts side-by-side and sprayed one of them and not the other

  • he discovered that even if the mosquitoes were resistant to the DDT it was effective in repelling the mosquitoes

  • So it still could protect humans even if the DDT was not actually killing the mosquito

• Based off the statistics that show that it was the agricultural use of DDT that had an effect on the environment and not the small amount that was used for protection against malaria, DDT has begun to be used again for malaria control.

  • South Africa began using it again and the malaria cases have fallen 65 percent from 2005 to 2007 and the deaths from malaria have dropped 73 percent

• Hopefully with this new positive outlook on DDT it will be available to help future generations fight the spread of malaria.

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Introduction / DDT molecule / Malaria / World War II

Environmental Problems / Insect Resistance / BeginUsing Again?  /  References

There are a few theories as to how certain insects became resistant:

1. Large amounts of a chemical trigger an ‘ancestral response’

• biological response mechanism to natural toxins
• the insects that trigger this mechanism were able to develop a resistance and survive–natural selection

2. Resistance could result from behavioral changes

• the insect learns not to land on certain areas that have the insecticide so they are not genetically resistant but the insecticide is not as efficient.

3. In areas where there is extensive spraying of insecticides the number of resistant mosquitoes increases. Because it speeds up natural selection by “selecting” the mosquitoes that carry the resistant gene and killing the majority of mosquitoes that don’t have the resistant gene.

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Introduction / DDT molecule / Malaria / World War II

Environmental Problems / Insect Resistance / BeginUsing Again?  /  References

• In Silent Spring, Rachel Carson claimed that DDT was responsible for:

  • the decline in the bird population because of thinning of eggshells

  • the decline of the fish population

• However, a study conducted in 1998 in Great Britain suggests that eggshells were thinning about 47 years before DDT even became available

  • Rhys E. Green, of the Edinburgh office of the Royal Society for the Protection of Birds, speculated that the initial cause of the thinning was due to the beginning of industrialization because the polluntants that were released into the air may have contributed to a reduction in calcium which is needed for eggshells

• Another study concurred with Carson and stated that DDT also accumulates in the tissues of animals which induce reproductive and neurological defects in birds and fish

• And yet another study claimed that DDT also builds up in cows milk and can cause severe impairment in calves.

• No matter what problems DDT may or may not cause the environment there has been evidence to suggest that it was only the massive agricultural use of DDT and not the malarial use that caused the environmental problems.

  • statistics gathered by Roberts, Laughlin, Hsheih, and Legters (see reference section):

    • more than 765 kilograms of DDT might be used to treat 100 acres during a growing season

    • that same amount is sufficient enough to treat more than 1,692 houses or approximately 8460 persons (assuming there are 4-5 persons per house)

• It has also been discovered that the appearance of resistant mosquitoes coincides with locations where DDT was used for agricultural purposes.

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Introduction / DDT molecule / Malaria / World War II

Environmental Problems / Insect Resistance / BeginUsing Again?  /  References

• Disease is a major factor in deciding the outcome of war:

• Examples:

• American Revolution: both sides suffered losses from scurvy, cerebrospinal fever, yellow fever, typhus, and malaria.

• Spanish-American War: More of our troops in Cuba and the Caribbean were killed because of yellow fever and malaria than from the Spanish.

• Out of all the major wars we have fought only in World War II, when extensive use of DDT to kill mosquitoes and protect the troops from disease, were the total number of deaths from disease lower than from wounds.
• Certain insects are carriers of disease such as:
  • Mosquitoes-malaria, dengue, yellow fever
  • Lice-typhus
  • Flies-dysentery
• At the beginning of WWII the Army’s medical department laid out a plan of protection for the troops against insects that carry these diseases. The plan included:
  • pyrethrum spray
  • protective clothing
  • screens and nets
  • rotenone powder
• But the Japanese monopolized the source of rotenone and the pyrethrum crop in Africa was destroyed.
• Because of this the troops in Guadalcanal, New Guinea, and Northern Africa fell ill due to Malaria. DDT was needed badly.
• By May 1943, DDT powder was deemed safe and effective by the Bureau of Entomology and Plant Quarantine and was distributed to troops to douse their clothing with to protect them from lice.
• In December 1943, the U.S. army invaded and occupied the city of Naples, Italy where typhus was prevelant. The army set up dusting stations around the city and civilians would come and soldiers would douse them with DDT powder.
• By March 1944: 2, 250,000 people were doused and the typhus epidemic in Italy was stopped. Also no American soldier contracted typhus in Italy.
•  Also, as the Allied Forces in 1944 began to fight the Germans along two fronts: one through Northern France and the other through Southern Italy.
• To slow down the Allied troops advance through Italy, the Germans breached the dikes in southern and central Italy which had been in place to dry up the land and protect it from the anophelines mosquitoes, carriers of malaria.  With the re-flooding of the land the mosquitoes came back.  The Allied Forces sprayed the DDT and were able to continue their advance through Italy.
• Overall, the amazing effect of DDT on insect eradication proved useful in times of war to protect soldiers from contracting those diseases carried by insects and help them to stay healthy and continue to fight.
• If the Allied Forces had not obtained DDT the troops would most likely have perished in Italy due to malaria and Germany could very well have ended up winning the war.

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Introduction / DDT molecule / Malaria / World War II

Environmental Problems / Insect Resistance / Begin Using Again?  /  References

DDT was first synthesized by Othmar Zeidler from Strasbourg, Austria in 1874. He was a chemistry student testing various compounds to get material for his doctorate. He recorded the synthesis of DDT in 6 lines in a journal and then forgot about it. It was synthesized again in 1938 by a Swiss chemist named Paul Muller of Basle. He discovered the unique properties that DDT had and realized the importance of such an insecticide. In 1939, Switzerland was having problems importing chemicals due to the beginning of the war and the German invasion of Poland. The Colorado potato beetle struck their potato crop and DDT was first put to the test. It completely destroyed the beetle and save the crop. Then in 1942 the Geigy Company, a Swiss Dye House that owned the patent, offered it to the American Army. After a year long intense investigation and study of the compound by the Bureau of Entomology and Plant Quarantine, DDT was given to the Army to protect against insects found abroad that carried disease.

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Introduction / DDT molecule / Malaria / World War II

Environmental Problems / Insect Resistance / Begin Using Again?  /  References

DichloroDiphenylTrichloroethane or DDT is comprised of:

• A chloral hydrate molecule [CCl₃CH(OH)₂] as the center “stem”
  • this molecule has sleep producing properties and is known as “knockout drops” in night clubs.

  

• The two ends of the molecule are Monochlorobenzene (C₆H₅Cl)
  • basically a benzene ring with a chlorine atom interchanged with a hydrogen

• The monochlorobenzene attaches to the OH group of the chloral hydrate molecule and water is released.

• It is a unique insecticide in that it kills both types of insects
  • 2 types:
    • 1. insects that chew plants
      • these insects are killed with the stomach poison aspect of DDT when they ingest the plant.
    • 2. insects that puncture plants and suck out juice
      • these insects are killed as soon as they come in contact with the plant.
• It also has a “residual effect” so the effects last for a long time without the need for the area to be resprayed. It can be effective 6 months or more.
• DDT is not water soluable so it needed to either be dissolved in kerosene, made into an emulsion, or the grains were chemically coated to make a wettable powder.
• Because of its insolubility it is not metabolized quickly in animals. The half life is 8 years, so it takes an animal 8 years to digest half of its total intake of the molecule.

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