08 February 2008 16:09 [Source: ICB]
DDT has found itself in the doghouse since the 1960s - bad news for the world's poor in the fight against malaria
Ivan Lerner/New York
ONCE HIGHLY regarded, the insecticide dichloro-diphenyl-trichloroethane (DDT) was transformed by overuse into a substance that is now almost universally feared and reviled.
But what of malaria, the other bad guy. An infection of Plasmodium parasites, which are spread by the bite of Anopheles mosquitoes, nearly all malaria control strategies target either the parasite or the mosquito in some way.
DDT was one of the stars of World War II, used in wiping out malaria, typhus and other insect-delivered diseases on the battlefield and in nearby cities. DDT was first synthesized in 1874, but in 1939 Paul Muller of Geigy Pharmaceutical (the predecessor to Novartis) discovered the chemical's insecticidal behavior: it killed all the bugs it was tested on. For this, Muller won the 1948 Nobel Prize in medicine.
Today, according to the Stone Mountain, Georgia-based Malaria Foundation International (MFI), malaria is responsible for about 500m clinical cases of disease and about 2.7m deaths a year, mostly those of children under five and pregnant women.
But the increasing rate of malaria and other insect-borne tropical diseases in Africa, South America and other parts of the Third World has made several groups, especially the Geneva-based World Health Organization (WHO), take a new look at DDT's beneficial properties. But resistance from environmental groups is strong, and more than 40 years of public vilification of DDT does not help.
DDT is important to malaria control because in addition to the toxicity from prolonged physical contact, it is also a contact irritant that causes mosquitoes to exit a house quickly after making contact with DDT treated surfaces, says Donald Roberts, professor emeritus at the Bethesda, Maryland-based Uniformed Services University of the Health Sciences.
"DDT is a unique chemical," says Roberts. "No other WHO approved insecticide has this profile of chemical actions."
There are effective DDT replacements, says Roberts, but these alternative chemicals are often more expensive and generally have shorter spans of residual life - meaning the chemical must be sprayed more frequently, adding to overall cost.
The WHO estimates that Malathion, the cheapest alternative to DDT, costs more than twice as much as DDT and must be sprayed twice as often. Another mosquito-fighting chemical, deltamethrin, is over three times as expensive as DDT, and propoxur, although also highly effective, costs 23 times as much.
Too much of a good thing
After World War II, the agriculture industry clamored for DDT and hereby the problems began.
Although largely credited for pounding in the first nail to DDT's coffin, Carson wrote that her complaint with the insecticide was with how the agricultural industry was abusing it through overuse, spraying practically everything.
In Carson's book, she writes: "Practical advice should be 'spray as little as you possibly can,' rather than, 'spray to the limit of your capacity.'"
DDT is a persistent organic compound where traces have been found up to 12 years later in areas where it had been used. The very worst publicity befell DDT when it was linked to the thinning of eggshells - and potential extinction, said environmentalists - of the US's national bird, the bald eagle. The ban on DDT is regarded as one of the reasons for the reemergence of the bald eagle in nearby areas of the US.
The agricultural use of DDT in the US was banned in 1972. The UK banned DDT in 1984, and India in 1989. The 2001 Stockholm Convention, with 98 nations signing, restricted DDT use to vector control.
But a major consequence of DDT's ban, says Roberts, has been the reemergence of major diseases like malaria and dengue fever. He notes that in Brazil during the 1970s there was almost no risk of dengue fever and for many years, less than 100,000 cases of malaria were diagnosed throughout the country.
After the ban, though, these diseases returned. In 2007, Brazil recorded almost 500,000 dengue cases, deaths from dengue hemorrhagic fever and "hundreds of thousands" of malaria cases, says Roberts.
But these changes are only the fault of a lack of DDT, says Roberts, who credits anti-insecticide activism as well. "Advocacy groups have orchestrated a worldwide campaign and used fear tactics to achieve their goal of stopping all public health uses of insecticides." These groups, he adds, "are willing to sacrifice [people] in order to advance their vision of a chemical free environment."
AND THEN THERE WERE TWO
Once made by several companies, including Montrose Chemical, Merck, Velsicol and Dow Chemical, DDT production in the US in 1962 was around 85,000 tonnes/year, but by 1971, production dropped to 2,000 tonnes/year.
Currently, DDT is made only in India and China, with the New Delhi-based Hindustan Insecticides Ltd. (HIL), which is considered the largest producer in the world with an estimated 1,344 tonnes/year of DDT capacity.
With the renewed interest towards DDT as a tool to fight malaria, the company has ventured into exporting DDT primarily to African nations.
There are two DDT manufacturers in China, with a total annual output of about 4,000 tons, according to China's State Environmental Protection Administration's pollution control department.
PEOPLE, PESTS AND POISON
The WHO says that indoor spraying of DDT can reduce malaria transmission by up to 90%.
WHO's regional director for Africa, Dr Luis Gomes Sambo, says: "The WHO position on indoor-residual spraying is that countries have the right to choose the products to use...DDT being one of them," if there are no other alternatives possible.
Uganda has received the thumb's up from WHO, despite protests from anti-DDT groups, and began indoor residual spraying in February. Meanwhile, the Republic of Malawi plans to start using DDT again by the end of the year.
Often an impoverished nation must rely on donor funds for its health budget, and then it has to play by the donors' rules. In the past - most recently in 2002 - when Uganda had attempted a DDT-based mosquito repellent program, it was dropped after the threat of economic sanctions against the African nation's fruit and fish exports.
Although DDT has been characterized as being possibly carcinogenic, there is still much debate, controversy and contrasting information on the subject. The MFI states that any unknown risk "must be balanced against the public health benefits."
According to WHO, roughly 40% of the global population is at risk of malaria, and most at risk are the poorest nations. The disease causes a 1.3%/year loss in economic growth in countries with intense transmissions. A long-term answer for a sustainable fight against this disease has yet to be found.
For the latest chemical news, data and analysis that directly impacts your business sign up for a free trial to ICIS news - the breaking online news service for the global chemical industry.
Get the facts and analysis behind the headlines from our market leading weekly magazine: sign up to a free trial to ICIS Chemical Business.
Sample issue >>
My Account/Renew >>
Register for online access >>
|ICIS Top 100 Chemical Companies|
|Download the listing here >>|