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From Wikipedia, the free encyclopedia
Resistance has greatly reduced DDT's effectiveness. WHO guidelines require that absence of resistance must be confirmed before using the chemical. Resistance is largely due to agricultural use, in much greater quantities than required for disease prevention. According to one study that attempted to quantify the lives saved by banning agricultural use and thereby slowing the spread of resistance, "it can be estimated that at current rates each kilo of insecticide added to the environment will generate 105 new cases of malaria."
Resistance was noted early in spray campaigns. Paul Russell, a former head of the Allied Anti-Malaria campaign, observed in 1956 that "resistance has appeared [after] six or seven years." DDT has lost much of its effectiveness in Sri Lanka, Pakistan, Turkey and Central America, and it has largely been replaced by organophosphate or carbamate insecticides, e.g. malathion or bendiocarb.
In many parts of India, DDT has also largely lost its effectiveness. Agricultural uses were banned in 1989, and its anti-malarial use has been declining. Urban use has halted completely. Nevertheless, DDT is still manufactured and used, and one study had concluded that "DDT is still a viable insecticide in indoor residual spraying owing to its effectivity in well supervised spray operation and high excito-repellency factor."
DDT can still be effective against resistant mosquitoes, and the avoidance of DDT-sprayed walls by mosquitoes is an additional benefit of the chemical. For example, a 2007 study reported that resistant mosquitoes avoided treated huts. The researchers argued that DDT was the best pesticide for use in IRS (even though it did not afford the most protection from mosquitoes out of the three test chemicals) because the others pesticides worked primarily by killing or irritating mosquitoes—encouraging the development of resistance to these agents. Others argue that the avoidance behavior slows the eradication of the disease. Unlike other insecticides such as pyrethroids, DDT requires long exposure to accumulate a lethal dose; however its irritant property shortens contact periods. "For these reasons, when comparisons have been made, better malaria control has generally been achieved with pyrethroids than with DDT." In India, with its outdoor sleeping habits and frequent night duties, "the excito-repellent effect of DDT, often reported useful in other countries, actually promotes outdoor transmission."
People living in areas where DDT is used for IRS have high levels of the chemical and its breakdown products in their bodies. Compared to contemporaries living where DDT is not used, South Africans living in sprayed homes have levels that are several orders of magnitude greater. Breast milk in regions where DDT is used against malaria greatly exceeds the allowable standards for breast-feeding infants. These levels are associated with neurological abnormalities in babies.
Most studies of DDT's human health effects have been conducted in developed countries where DDT is not used and exposure is relatively low. Many experts urge that alternatives be used instead of IRS. Epidemiologist Brenda Eskenazi argues, "We know DDT can save lives by repelling and killing disease-spreading mosquitoes. But evidence suggests that people living in areas where DDT is used are exposed to very high levels of the pesticide. The only published studies on health effects conducted in these populations have shown profound effects on male fertility. Clearly, more research is needed on the health of populations where indoor residual spraying is occurring, but in the meantime, DDT should really be the last resort against malaria rather than the first line of defense."
Illegal diversion to agriculture is also a concern, as it is almost impossible to prevent, and its subsequent use on crops is uncontrolled. For example, DDT use is widespread in Indian agriculture, particularly mango production, and is reportedly used by librarians to protect books. Other example include Ethiopia, where DDT intended for malaria control is reportedly being used in coffee production, and Ghana where it is used for fishing." The residues in crops at levels unacceptable for export have been an important factor in recent bans in several tropical countries. Adding to this problem is a lack of skilled personnel and supervision.
Criticism of restrictions on DDT use
Critics claim that restricting DDT in vector control have caused unnecessary deaths due to malaria. Estimates range from hundreds of thousands, to millions. Robert Gwadz of the National Institutes of Health said in 2007, "The ban on DDT may have killed 20 million children." These arguments have been dismissed as "outrageous" by former WHO scientist Socrates Litsios. May Berenbaum, University of Illinois entomologist, says, "to blame environmentalists who oppose DDT for more deaths than Hitler is worse than irresponsible." Investigative journalist Adam Sarvana and others characterize this notion as a "myth" promoted principally by Roger Bate of the pro-DDT advocacy group Africa Fighting Malaria (AFM).
Criticisms of a DDT "ban" often specifically reference the 1972 US ban (with the erroneous implication that this constituted a worldwide ban and prohibited use of DDT in vector control). Reference is often made to Rachel Carson's Silent Spring even though she never pushed for a ban on DDT. John Quiggin and Tim Lambert wrote, "the most striking feature of the claim against Carson is the ease with which it can be refuted." Carson actually devoted a page of her book to considering the relationship between DDT and malaria, warning of the evolution of DDT resistance in mosquitoes and concluding:
It is more sensible in some cases to take a small amount of damage in preference to having none for a time but paying for it in the long run by losing the very means of fighting [is the advice given in Holland by Dr Briejer in his capacity as director of the Plant Protection Service]. Practical advice should be "Spray as little as you possibly can" rather than "Spray to the limit of your capacity."
It has also been alleged that donor governments and agencies have refused to fund DDT spraying, or made aid contingent upon not using DDT. According to a report in the British Medical Journal, use of DDT in Mozambique "was stopped several decades ago, because 80% of the country's health budget came from donor funds, and donors refused to allow the use of DDT." Roger Bate asserts, "many countries have been coming under pressure from international health and environment agencies to give up DDT or face losing aid grants: Belize and Bolivia are on record admitting they gave in to pressure on this issue from [USAID]."
The United States Agency for International Development (USAID) has been the focus of much criticism. While the agency is currently funding the use of DDT in some African countries, in the past it did not. When John Stossel accused USAID of not funding DDT because it wasn't "politically correct," Anne Peterson, the agency's assistant administrator for global health, replied that "I believe that the strategies we are using are as effective as spraying with DDT ... So, politically correct or not, I am very confident that what we are doing is the right strategy." USAID's Kent R. Hill states that the agency has been misrepresented: "USAID strongly supports spraying as a preventative measure for malaria and will support the use of DDT when it is scientifically sound and warranted." The Agency's website states that "USAID has never had a 'policy' as such either 'for' or 'against' DDT for IRS. The real change in the past two years [2006/07] has been a new interest and emphasis on the use of IRS in general—with DDT or any other insecticide—as an effective malaria prevention strategy in tropical Africa." The website further explains that in many cases alternative malaria control measures were judged to be more cost-effective that DDT spraying, and so were funded instead.
"The modern conservative is engaged in one of man's oldest exercises in moral philosophy;
that is, the search for a superior moral justification for selfishness."
-- John Kenneth Galbraith