Dr. Judith Weis is a Professor of Biological Sciences at Rutgers University, Newark Campus. She received her bachelor’s degree from Cornell University, and MS and PhD from New York University.
- Toxicological Profile of DDTfrom the Agency for Toxic Substances & Disease Registry
- Chemistry Basics of DDT
- DDT Ban Takes Effect-Press Release from EPA in 1972
- Toxic materials in the food chain
- An Introduction to DDT
- Rachel Carson’s Silent Spring
DDT is the abbreviation for the chemical 1,1,1-trichloro-2,2-bis-(p-chlorophenyl) ethane. DDT is used as an insecticide. It has the appearance of colorless needles or of a white to slightly off-white powder. It is insoluble in water and is slightly soluble in alcohol. Since it had not been shown to be particularly lethal to humans, it was used extensively in Word War II to reduce and manage mosquito populations and to control malaria for the protection of U.S. troops. Also, it was used on civilian populations in Europe to prevent the spread of lice and the diseases they carried. DDT became popular as the first modern pesticide, hailed as a miraculous advance in pest control. Its developer, Paul Müller of Switzerland, won the Nobel Prize in 1948). Peak usage in the U.S. occurred in 1962 when about 80 million kilograms of DDT were used of about 82 million kilograms produced. Although it is no longer used in the U.S., it is still used in some countries to control mosquitoes that may carry malaria.
The chemical compound DDT is referred to as an organochlorine or a chlorinated hydrocarbon. That is, it is a carbon-based chemical with hydrogen and chlorine atoms attached to the carbon atoms. Organochlorines are relatively insoluble in water; but they are highly soluble in fats or lipids. They are often referred to as lipophilic or fat-loving chemicals. Due to their lipophilic character they bioaccumulate in fat. Additionally, organochlorines tend to be very persistant in soils and sediments. A key study done in 1967 in an estuary on Long Island Sound showed a biomagnification factor for DDT of more than 200,000 times.
Most agricultural chemicals were not used directly in aquatic environments, but entered them through run-off from land. DDT was sprayed, however, extensively in salt marshes to control biting flies and mosquitoes. In the late 1940s and 1950s DDT was considered a panacea, as it could be applied as a powdered dust on the water in relatively small amounts per acre and could keep killing mosquito larvae for many months with a single application. It is a wide spectrum insecticide that could be used to kill all kinds of insects; but it was not very toxic to humans.
DT enjoyed great success until the development of chemically-induced resistance by mosquitoes. Resistance developed in insect populations because all of the insects exposed to DDT were not killed by the chemical. A few resistant individuals remained, they bred, and their offspring proved more resistant to the effects of DDT—this is evolution at work. In following applications, more DDT was sprayed. Eventually, the insects became so resistant that it became impractical to try to control them with DDT. This necessitated substitutions with other chemicals, to which the insects eventually became resistant. Pesticide—and antibiotic—resistance remains a serious problem.
Generally through the action of microorganisms, most DDT breaks down slowly into DDE(1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene)and DDD (1,1-dichloro-2,2-bis(p-chlorophenyl)ethane). DDD was also manufactured and used as an insecticide, but to a much lesser extent than DDT. DDE has no commercial use, but is commonly detected along with DDT at concentrations in the environment that often exceed those measured for DDT.