African health campaigners have accused western aid donors of deliberately ignoring an effective anti-malaria tool.
By Richard Black
BBC science correspondent
They told the BBC World Service Earth Files programme that some international donors were refusing to fund projects that use the chemical DDT for mosquito control.
Regulations are in place to control the chemical's use
The campaigners say the UN agency Roll Back Malaria is also ignoring the clear benefits of spraying DDT inside people's homes.
DDT is one of 12 substances deemed to be environmentally damaging that will be banned shortly under a new treaty.
The global treaty is called Pops, short for Persistent Organic Pollutants, and comes into force in 12 months' time.
Concern over DDT, and a number of the other chemicals covered by Pops, stems largely from Rachel Carson's famous book Silent Spring, published 40 years ago
Silent Spring documented the damage which indiscriminate agricultural use of a new generation of pesticides and herbicides, including DDT, was doing to North American wildlife.
But in a number of countries, including South Africa, Ethiopia, Madagascar and Swaziland, DDT is the principal method of controlling malaria.
It is sprayed on to the inside walls of houses, and is a once-a-year operation.
"South Africa has a long-standing history of indoor residual house spraying," the deputy director of South Africa's National Malaria Programme, Devanand Moonasar, told Earth Files.
"We've been using it now since the early 1920s, and we're using it with a great deal of success."
Dr Moonasar says much care is taken to ensure no DDT leaks into water or the ground.
"We're very careful as to how we're implementing DDT in South Africa; we have training for the malaria spray operators on how to apply DDT, but more especially how to use DDT in a controlled way to ensure none goes into the environment."
Back and forth
When the Earth Files team visited a spraying team operating in Limpopo province, we saw these precautions for ourselves.
Insecticides including DDT are stored in a padlocked brick building, and a supervisor keeps a register of stocks and supplies.
Sprayers are not allowed to pour liquid containing DDT, including water which they have washed their equipment with, on to the ground.
THE POPS 'DIRTY DOZEN'
Polychlorinated Biphenyls (PCBs)
Eight years ago South Africa switched from DDT to a different type of insecticide called pyrethroids, regarded as more environmentally benign.
But within four years, mosquitoes became resistant, and the annual number of malaria cases rose tenfold.
DDT was re-introduced, and cases have fallen again.
This paralleled the experience of Madagascar, which suffered an epidemic of malaria in the late 1980s, brought on by the curtailment of DDT spraying programmes - only curbed again by its re-introduction.
These experiences led a number of African countries to negotiate a special exemption in the Pops treaty permitting them to use DDT for malaria control.
They received crucial support from an unexpected quarter - South Africa's Endangered Wildlife Trust.
"Although I personally hate the compound, there was no alternative," the Trust's chairman, Gerhard Verdoorn, said.
"If we had said to them 'No, you can't use DDT', I'm quite convinced that we might have lost a couple of thousand people with malaria.
The culprit: Mosquitoes spread the disease parasite
"So we had to make a move to bring back the compound under a very strictly controlled situation."
Verdoorn's group helps run the training programmes for sprayers, and says if there is any evidence of DDT being diverted for other purposes - sold on the black market for agricultural use - they will withdraw their support.
Experts interviewed by the BBC said that black markets had been found in India and Ethiopia.
Gerhard Verdoorn believes there is no conclusive evidence that DDT used in indoor residual spraying has any significant environmental impact.
The quantities used are tiny in comparison with the agricultural programmes of the 1960s.
Apart from its well-documented environmental impacts, DDT is widely regarded as a threat to human health - a potent poison and a carcinogen. But the scientific evidence presents a rather different picture.
Professor Len Ritter, from Guelph University, is executive director of the Canadian Network of Toxicology Centres, which compiled a major report on DDT and related substances for the United Nations.
"I hate to say conclusively yes or no because these matters are always subject to interpretation; but I would say on the totality of the weight of the evidence, I could not conclude that DDT poses a significant risk of cancer," he told Earth Files.
Malaria is a major problem in sub-Saharan Africa
Professor Ritter's report came to a similar conclusion regarding the other suggested harmful effects of DDT - as a disrupter of the human immune system, of hormone levels, as a cause of birth defects.
On whether DDT is acutely poisonous to humans, the eminent British scientist Kenneth Mellanby writes in his book The DDT Story: "I myself, when lecturing about DDT during the years immediately after World War II, frequently consumed a substantial pinch of DDT, to the consternation of the audience, but with no apparent harm to myself, either then or during the next 40 years."
In the west, though, DDT continues to be seen as a pariah chemical.
Environmental groups like Greenpeace lobby for the Pops exemption to end in just a few years' time. Dr Paul Johnston is principal scientist in the Greenpeace Research Laboratories at the UK's Exeter University.
"The interests of all people need to be considered," he told Earth Files.
"There are very large issues relating to how it behaves in the global environment.
"It only partially breaks down into secondary products, and DDT and these metabolites are transported very long distances and can be localised in other environments where they can cause problems, particularly in the very cold environment of the Arctic."
Though DDT has been found in Arctic wildlife, despite never having been deployed in the polar region, it is impossible to tell whether it came from use in agriculture or in disease prevention.
Though South Africa is rich enough to fund its own malaria control programme, many other poorer African nations are not; they are heavily dependent on western aid.
According to Richard Tren, director of the pressure group Africa Fighting Malaria, western donors, conscious of their domestic reputations, will not support malaria programmes based on DDT spraying.
"The reason that DDT is not used in the US and Europe is because they don't have malaria," he told Earth Files.
DDT is sprayed inside homes on the walls
"They did use DDT, and they got rid of malaria. Not a single donor agency will support the use of DDT or any other insecticide in indoor residual spraying, and that's a real problem because these agencies will only support the use of insecticide-treated nets."
The belief that western agencies will not support DDT-based malaria projects is widely held among people close to the issue in South Africa.
Documents seen by Earth Files support their case.
The Swedish aid agency Sida has a procurement policy expressly prohibiting the use of its funds for buying DDT.
It is difficult to establish exactly which agency funds which programmes in which countries, as many health projects cover several disease areas, and much aid is channelled through international bodies such as the Global Fund to Fight Aids, TB and Malaria.
However, the British government's Department for International Development funds 13 malaria-only projects in eight African countries; none of them uses DDT.
The US aid agency USAid was unable to supply such data, but told the BBC: "For most countries with USAid support for malaria control in sub-Saharan Africa, indoor residual spraying has not been judged to be the most effective use of US government funds."
Perhaps the most damaging allegation is that United Nations organisations are ignoring the opportunities offered by spraying.
A few months ago the UN agency Roll Back Malaria produced a draft document called Scaling Up For Sustainable Impact which set out a suggested strategy for the next four years.
One group of leading experts sent back a lengthy critique.
"We consider that the dismissive paragraph about indoor residual spraying is seriously flawed.
"Reviews of the literature of major indoor residual spraying trials in tropical Africa in the 1950s to the 1970s showed that they had better impact than any of the recent insecticide-treated bednet trials - eg, halving of all-cause infant mortality."
Roll Back Malaria says it has now prepared a revised edition which addresses some of these criticisms.
Issue of choice
Nevertheless its senior advisor Dr Thomas Teuscher concedes it may have downplayed the impact of indoor residual spraying in its public pronouncements.
"The use of indoor residual spraying clearly has equal weight as all the others," he said.
"You could argue it is not as visible; it is maybe a matter of words and not of content, a matter as to how it is put to the public and explained.
Roll Back Malaria was instrumental in setting up the Abuja Declaration, a major commitment to halve the burden of malaria across Africa by the year 2010, which was signed four years ago by African leaders.
The declaration sets interim targets which should be reached by 2005:
These targets do not include preventing malaria through indoor residual spraying.
- 60% of pregnant women and children under five should sleep under an insecticide-treated bednet
- 60% of pregnant women should receive intermittent preventive treatment (ie drugs to prevent infection)
- 60% of those suffering from malaria shall have prompt access to effective and affordable treatment within 24 hours.
The reasons why spraying is not mentioned are unclear; the accusation is, though, that western environmental concerns are denying African countries a free choice in how they tackle malaria.