DDT is one of the most
controversial chemical compounds in recent history. It has proven effectiveness
as an insecticide, but its potent toxicity isn't limited to insects. Banned by
many countries including the United States, DDT is nonetheless still used
legally or illegally in some places.
DDT, also known as dichloro-diphenyl-trichloroethane, belongs to a class of
pesticides known as organ chlorides. A synthetic chemical compound that must be
made in a laboratory (it doesn't occur in nature), DDT is a colorless,
crystalline solid. DDT can't be dissolved in water; it is, however, easily
dissolved in organic solvents, fats or oils. As a result of its tendency to
dissolve in fats, DDT can build up in the fatty tissues of animals that are
exposed to it. This accumulated build-up is known as bio accumulation, and DDT
is described by the EPA as a persistent, bio accumulative toxin. Because of this
bio accumulation, DDT remains in the food chain, moving from crayfish, frogs,
and fish into the bodies of animals that eat them. Therefore, DDT levels are
often highest in the bodies of animals near the top of the food chain, notably
in predatory birds like eagles, hawks, pelicans, condors and other meat-eating
birds.
People are most likely to be exposed to DDT from foods, including meat, fish,
and dairy products. DDT can be absorbed by eating, breathing, or touching
products contaminated with DDT. In the body, DDT is converted into several
breakdown products called metabolites, including the metabolite
dichloro-diphenyl-trichloroethane (DDE). DDT and DDE are stored in the body’s
fatty tissues. In pregnant women, DDT and DDE can be passed to the fetus. Both
chemicals are found in breast milk, resulting in exposure to nursing infants.
How DDT Affects People’s Health Human health effects from DDT at low
environmental doses are unknown. Following exposure to high doses, human
symptoms can include vomiting, tremors or shakiness, and seizures. Laboratory
animal studies showed effects on the liver and reproduction.
The U.S. Department of Agriculture, the federal agency with responsibility for
regulating pesticides before the formation of the U.S. Environmental Protection
Agency in 1970, began regulatory actions in the late 1950s and 1960s to prohibit
many of DDT's uses because of mounting evidence of the pesticide's declining
benefits and environmental and toxicological effects. The publication in 1962 of
Rachel Carson's Silent Spring stimulated widespread public concern over the
dangers of improper pesticide use and the need for better pesticide controls.
In 1972, EPA issued a cancellation order for DDT based on its adverse
environmental effects, such as those to wildlife, as well as its potential human
health risks. Since then, studies have continued, and a relationship between DDT
exposure and reproductive effects in humans is suspected, based on studies in
animals. In addition, some animals exposed to DDT in studies developed liver
tumors. As a result, today, DDT is classified as a probable human carcinogen by
U.S. and international authorities. DDT is known to be very persistent in the
environment, will accumulate in fatty tissues, and can travel long distances in
the upper atmosphere.
In September 2006, the World Health Organization (WHO) declared its support for
the indoor use of DDT in African countries where malaria remains a major health
problem, citing that benefits of the pesticide outweigh the health and
environmental risks. The WHO position is consistent with the Stockholm
Convention on POPs, which bans DDT for all uses except for malaria control.