What Is DDT? Environmental Impact and Current Uses

DDT is a synthetic insecticide belonging to a class of chemicals called organochlorides.  Also known as dichloro-diphenyl-trichloroethane, it is one of the most effective yet controversial synthetic insecticides ever developed. While incredibly effective at controlling mosquitoes, it also has devastating environmental impacts. Today, DDT is banned in much of the world, but it is still used to control malaria in some areas where the benefits might outweigh the risks.

What Is DDT and Why Was It Banned?

DDT was first synthesized in 1874, however, it wasn’t until 1939 that scientist Paul Müller discovered its effectiveness as an insecticide. Müller was awarded the Nobel Prize in 1948 for his discovery and DDT use became fairly widespread. 

DDT was initially used by the military during World War II to control malaria, typhus, body lice, and bubonic plague. It was sprayed on the interior walls of houses and even carried in small cans by soldiers for personal insect protection. DDT aerosol bombs became an easy way to control disease in the field.

After the war, DDT use continued to soar. In 1945, DDT was released for commercial sale and became widely used for insect control in crop and livestock production, institutions, homes, and gardens. In the early 1950s, due to its success in decreasing mosquito populations, the World Health Organization launched the Global Malaria Eradication Program.

DDT was so widely used because it was effective, relatively inexpensive to manufacture, and lasted a long time in the environment. An estimated 5,000 metric tons of DDT were used for disease vector control in 2005, although current levels of DDT production and storage are often difficult to track.

While initially DDT was an incredibly effective insecticide, its widespread use quickly led to the development of resistance by many insect pest species. Since the introduction of DDT for mosquito control in 1946, DDT resistance at various levels has been reported from more than 50 species of anopheline mosquitoes, including many that spread malaria. After decades of use, evidence of the pesticide's declining benefits and suspected environmental and toxicological effects were becoming causes for concern.

Risk to Humans

Human exposure to DDT occurs primarily through inhalation after spraying or ingestion from food sources. Once in the body, DDT collects primarily in fat tissue and remains there for quite some time. According to a study on DDT persistence, it would take between 10 and 20 years for DDT to disappear from an individual if exposure would totally cease, but its primary metabolite, DDE, would possibly persist throughout the lifespan of the individual.

Being at the top of the food chain, humans ingest DDT from food crops that were sprayed with it in the field. In addition, DDT accumulates in the fat of fish and mammals who were also exposed to DDT in the environment. That DDT is then passed up the food chain.

This long-term bioaccumulation, as it is called, means that over time, levels of DDT are highest in humans and larger predatory animals, especially meat-eating birds like eagles, hawks, condors, etc. 

While the EPA lists DDT as a class B carcinogen; this classification comes mainly as a result of animal studies as opposed to human studies. According to the Environmental Protection Agency, class B carcinogens are those that show some evidence of causing cancer in humans but at present it is far from conclusive.

There is currently no evidence in humans that DDT causes cancer or reproductive problems; however, workers exposed to large concentrations during application have reported a variety of neurological effects. DDT exposure side effects such as vomiting, tremors or shakiness, and seizures have been reported.

Environmental Impact of DDT

The persistence of DDT in the environment, one of its most useful insecticidal properties, was also one of its most concerning in regards to its environmental impact.  

Scientists began voicing concerns about the environmental effects of DDT as early as the 1940s; however, it wasn’t until Rachel Carson wrote the book “Silent Spring” in 1962 that widespread public concern began to grow. 

In her book, Carson detailed how a single drop of DDT applied to crops lingered for weeks and months, even after a rainfall. And as an insecticide, it was incredibly efficient, killing not only mosquitoes but a host of other insects as well. Considered a general insecticide, DDT kills everything from beetles and lice to fleas and houseflies.  For insect-eating birds, this poses a significant problem. "Silent Spring" detailed the reduction in some songbird populations as a possible result of widespread insecticide use. 

In addition, long-term buildup of DDT in meat-eating birds like the bald eagle resulted in reproductive complications as well. High concentrations of DDT in these birds caused thinning of their eggshells and breeding failure. As a direct result of eggshell thinning, these eggs were easily broken, causing a significant population decline. The work Carson did in highlighting the dangers of DDT is often called the beginning of the modern environmental movement.

As public concern grew, numerous environmental organizations joined the fight. In 1967, the Environmental Defense Fund, the National Audubon Society, the National Wildlife Federation, the Izaak Walton League, and other environmental groups joined the movement to restrict the use of DDT through legal action at both the local and federal levels. Due to the initiation of numerous court proceedings regarding the use of DDT, on October 21, 1972, the Federal Environmental Pesticides Control Act was enacted.

As a result of growing environmental concerns, numerous countries around the world came together as part of the United Nations Environment Programme to restrict the usage of a broad selection of persistent organic pollutants (POPs), a group that includes DDT. This treaty is known as the Stockholm Convention on POPs, which only allowed use of DDT for controlling malaria.

Current Uses

Many people mistakenly assume that DDT is no longer in use. However, the Stockholm Convention on POPs did not ban its use entirely.

Currently, numerous countries around the globe, from Africa to China, either use DDT to fight malaria or have reserved the right to do so in the future. 

The use of DDT continues to be a controversial topic even today. Malaria is a significant risk to human health in many areas of the world. While some areas have had good results controlling mosquito populations with other insecticides, others have been unsuccessful. 

DDT and Malaria

Malaria is a serious and sometimes fatal disease caused by parasite-infected mosquitoes when they feed on humans. According to the Centers for Disease Control, in 2020 an estimated 241 million cases of malaria occurred worldwide and 627,000 people died, mostly children in the African Region.

While malaria is found in many countries, it is most commonly diagnosed in sub-Saharan Africa and South Asia.

Many countries where malaria is common have switched from DDT to other insecticides, however, not all of these attempts have been successful. In areas where malaria is undeterred by other insecticides, DDT may be the only way to control mosquito populations and reduce fatalities from malarial disease. 

Cost, ease of use, species of mosquito, and chemical resistance all play a part in a country’s decision on which insecticide to choose, however, the final factor is whether or not the chosen product works to reduce disease. 

One concern regarding the use of DDT in certain areas of the world is that no country exists in isolation. When sprayed outdoors, DDT does not stay in a localized area. Traces of DDT have been recovered from dust known to have drifted over 600 miles and in water melted from Antarctic snow. From the soil your food grows in, to the rain falling in your backyard, DDT is still detectable today in microscopic amounts.