DDT

Chemical structure:

DDT is created by the reaction of trichloromethanal with chlorobenzene (C₆H₅Cl). Trade or other names for DDT include Anofex, Cesarex, Chlorophenothane, Dedelo, p,p'-DDT, Dichlorodiphenyltrichloroethane, Dinocide, Didimac, Digmar, ENT 1506, Genitox, Guesapon, Guesarol, Gexarex, Gyron, Hildit, Ixodex, Kopsol, Neocid, OMS 16, Micro DDT 75, Pentachlorin, Rukseam, R50 and Zerdane.

DDT is persistent in the environment, with a reported half life of between 2-15 years and is immobile in most soils. Routes of loss and degradation include runoff, volatilization, photolysis and biodegradation (aerobic and anaerobic). These processes generally occur only very slowly. Breakdown products in the soil environment are DDE (1,1-dichloro-2,2-bis(p-dichlorodiphenyl)ethylene) and DDD (1,1-dichloro-2,2-bis(p-chlorophenyl)ethane), which are also highly persistent and have similar chemical and physical properties.

History

It was first synthesized in 1873, and its insecticidal properties were discovered by the Swiss scientist Paul Hermann Müller[?] in 1942 who was awarded the 1948 Nobel Prize in Physiology and Medicine for his efforts. DDT is the best known of a number of chlorine-containing pesticides used in the 1940s and 1950s. It was extensively used during World War II among Allied troops and certain civilian populations to control insect typhus and malaria vectors; entire cities in Italy were dusted to control the typhus carried by lice. DDT was then extensively used as an agricultural insecticide after 1945. In the 1950s doses of DDT and other insecticides had to be doubled or trebled as resistant insect strains developed, and evidence began to grow that the chemical was concentrated in the food chain. The compound is stable and concentrates in fatty tissue, reaching dangerous levels in carnivores high in the food chain. It is also excreted in milk.

The banning of DDT

In 1962 Rachel Carson's book Silent Spring was published. The book argued that pesticides, and especially DDT, were poisoning both wildlife and the environment and also endangering human health. The book received little support from the mainstream scientific community. Nonetheless, the public reaction to Silent Spring launched the modern environmental movement, and DDT became a prime target of the growing anti-chemical and anti-pesticide movements during the 1960s.

DDT was first banned from use in Norway and Sweden in 1970, and the United Kingdom in 1984. The EPA's first administrator, William Ruckelshaus[?], defying his science advisors, announced a ban in 1972 on virtually all uses of DDT in America, where it is classified in EPA Toxicity Class II. It is still used in other (primarily tropical) countries where mosquito-borne malaria is a larger health problem than DDT's potential toxicity.

DDT is an organochlorine. Some organochlorines have been shown to have weak estrogenic activity, that is, they are chemically similar enough to estrogen to trigger hormonal responses in contaminated animals. This sort of activity has been observed in DDT in laboratory studies involving mouse and rat test subjects, but available epidemiological evidence does not indicate that these effects have occurred in humans as a result of DDT exposure.

Studies of alligators in Florida swamps have found extensive oestrogenation due to high levels of DDT exposure. Many male crocodiles in the area have deformed genitalia and feminised bodily features, while their eggs are showing high rates of infertility and abnormal fetal development. Some researchers believe that this is echoed in the human population. Fertility studies in Scandanavia (not entirely sure which country), where DDT was widely used to control pests, have found that the average male sperm count has dropped by almost 50% since DDT started to be used, while there is an increased rate of certain cancers of the reproductive organs compared to former years.

Support for using DDT

Controversy remains in some scientific circles over DDT's actual toxicity, however. Some scientists have protested that the laboratory animal studies done in 1969 (and which led to the banning of DDT in much of the developed world) which showed that DDT caused an increase in liver cancer was inconsistent with observations in the wild, given that DDT had been used widely during the preceding three decades with no increase in liver cancer in any of the human populations among whom it had been sprayed. When the World Health Organization investigated the 1969 mouse study, they found that both experimental and control groups had developed a surprising number of tumors. Further investigation revealed that the food fed to both groups were moldy and contained aflatoxin, a carcinogen. When the tests were repeated using uncontaminated foods, neither group developed abnormal numbers of tumors. Since DDT remains one of the most effective pesticides available to combat the spread of malaria in tropical countries, and is also one of the great spectres of the environmentalist movement, this debate is likely to remain vigorously argued for the forseeable future.

In 2001, after a five-year ban led to more than a ten-fold increase in malaria cases, South Africa permitted its use again. Uganda is considering using it as well, although it fears the loss of aid from international agencies who want DDT to remain banned.

The World Health Organization estimates that 2.5 million people die of malaria each year: mostly African children. According to the U.N. World Health Organization (WHO), malaria kills one child under the age of 5 every 30 seconds.

Dr. Elizabeth Whelan, the president of the American Council on Science and Health[?] (a nominally independent organization which receives funding from the chemical industry) claims that 60 million or more lives "have been needlessly lost since the ban on DDT took effect. ... It's a real tragedy that DDT has been so demonized over the years by activist organizations such as Environmental Defense and the regulatory bodies that they have duped." [1] (http://www.washtimes.com/commentary/20021017-7408114.htm)

See also: Opposing view on the ACSH (http://www.prwatch.org/improp/acsh), ACSH homepage (http://www.acsh.org)