My take on DDT
My posts regarding the third-hand junk science on DDT presented by Christopher Pearson have provoked an interesting debate, which leads me to want to clarify my position on the issue. You can find relevant references in my previous posts and the comments threads. Here are the conclusions I have drawn:
The ban on the agricultural use of DDT, beginning in the US in 1972, and much reviled by junk scientists, was fully justified, for several reasons.
- DDT has well-established adverse environmental effects, particularly on predatory birds
- DDT persists and accumulates in human body tissues, which is an undesirable property for any potential toxin. There is strong, but not conclusive evidence of health risks to humans arising from this
- DDT has broad-spectrum effects, killing beneficial as well as harmful insects, and is highly persistent
- Indiscriminate agricultural use of DDT promotes the development of resistance, reducing or eliminating the usefulness of DDT in its most beneficial use, as an antimalarial
The early success of DDT as an antimalarial in countries such as India and Sri Lanka was not sustained, but this had little or nothing to do with the 1972 ban. The main problems were the development of resistance and the lack of sustained funding. Resistance problems also reduced the effectiveness of antimalarial drugs and there was little commercial interest in the development of new ones.
The use of DDT as an antimalarial, sprayed on house walls or insecticidal nets was not banned in 1972, and never has been. The majority of junk science diatribes, including Pearson, state or imply the contrary, either through ignorance (almost certainly the case for Pearson) or malice.
Between about 1995 and 2000, debate over DDT was intensified because environmental groups wanted a complete phaseout of DDT as part of the UN convention on persistent organochlorine pollution (POP). Environmental groups argued that there were safer, and equally effective alternatives, such as pyrethroids and pressed developing countries to adopt these methods. In some cases, for example in South-East Asia, this worked fairly well. In other cases, such as South Africa, the alternative methods failed or funding was inadequate and it was necessary to return to DDT. During the debate leading up to the POP convention, rhetoric on both sides was heightened, tending to obscure agreement on the basic points that the only legitimate use of DDT was antimalarial and that replacement of DDT was contingent on the provision of affordable and effective alternatives, funded by rich countires. Quoted out of context, some of the arguments on the pro-DDT side have been used by junk science writers to back up their attacks on the 1972 ban. There are some instances in which environmental pressure led to ill-advised decisions to abandon DDT. But far more damage to the viability of DDT as an antimalarial was done by its use as a broad-spectrum agricultural insecticide – the very policy defended by junk science writers.
The current position is that, in at least some poor countries (particularly those where there has been no history of extensive spraying and therefore no buildup of resistance) there is no affordable and effective alternative to using DDT spray on house walls. As long as this remains the case, DDT use should be continued. Where there is a more expensive, but equally effective, alternative, the cost should be borne by rich countries, since the benefits of reduced DDT in the environment are global.