Cecil Adams,
Thanks for your efforts to address the very complex issue of DDT and malaria control in your column, “Was Rachel Carson a Fraud and is DDT Actually Safe for Humans?” (December 13, 2002.
I think you reach an appropriate conclusion that DDT has saved millions of lives and remains an important tool for malaria control, but as you reach that conclusion you convey a misleading impression that DDT is going to be banned under the Stockholm Convention on persistent organic pollutants (POPs).
The most important point that you didn’t share with your readers is that the POPs convention clearly and unambiguously allows the current continued use of DDT for malaria control. The treaty addresses DDT in a section separate from the sections on the other pollutants. The treaty basically allows any country that determines that it needs to use DDT to use it. All a country has to do is sign up on DDT Register maintained by the treaty Secretariat and to keep the Secretariat and the World Health Organization informed (every three years) on the amount of DDT used and its continuing need, if any.
The treaty does state a goal of “reducing and ultimately eliminating the use of DDT.” But there’s no end date for its use. Countries are encouraged to promote research and development on safe alternatives, with the objective of encouraging overall improvement of disease control so that countries will no longer have a need for DDT.
The issue of alternatives to DDT also deserves somewhat expanded treatment. You correctly note that DDT is not a panacea, and yes, there is uncertainty about the effectiveness and cost of alternatives. But it is also the case that countries such as Mexico, the Philippines and Vietnam have successfully moved away from reliance on DDT. There’s a new project now getting underway in several Central American countries, with funds provided as a result of the POPs treaty, to help those countries determine if they can follow a similar path.
The issue of DDT’s toxicity also is a little more complex that you let on. DDT was historically viewed as safe because it didn’t appear acutely toxic. But there’s growing recognition that doses of DDT and chemicals like it that may be safe for adults are not necessarily safe for the “next generation” of humans—those in the womb. The leading study on this point was published by Dr. Matthew Longnecker from the U.S. National Institute of Environmental Health Sciences in 2001 in “The Lancet.” He and his colleagues linked in utero exposure to DDT in the womb to small-for-gestational age and pre-term babies.
In a related vein, another NIEHS scientist, Dr. Walter Rogan, published two separate but corroborating studies (of women in North Carolina and Mexico) that found that higher levels of DDT in the women’s breast milk was associated with shorter duration of lactation. Dr. Rogan has pointed out that the duration of lactation periods is significant in many parts of the world because of reliance on breast milk to feed infants. Dr. Rogan has speculated that this is due to the estrogenic activity of DDE.
Your point on eggshell thinning also deserves elaboration. Yes, there is scientific uncertainty about the exact mechanisms by which DDT and its metabolites thin eggshells, but this shouldn’t be confused with the substantial scientific evidence, recited in National Academy of Sciences reports and elsewhere, making the link between DDT and eggshell thinning. It’s worth remembering that the link between tobacco smoke and lung cancer was made many decades before scientists figured out the mechanism of action.
The court that upheld EPA Administrator Ruckelshaus’ ban on DDT for agricultural use thirty years ago found substantial evidence in the record to support the decision. The court did not give special weight to the contrary views of the EPA judge, who it noted was a coal mining accident specialist. When making his decision, Ruckelshaus also emphasized that EPA’s proceedings never involved the use of DDT for health programs in other countries. He observed that “EPA will not presume to regulate the felt necessities of other countries.”
The POPs convention’s treatment of DDT—banning it for agricultural use but maintaining it for public health use—substantially mirrors the decision that EPA Administrator Ruckelshaus made thirty years ago. Premature or underweight birth, or premature deprivation of breast milk, are additional burdens on the precarious health of those born into poverty… The POPs treaty reflects the aspiration that we ought to aim for protecting infants and children from malaria without compromising their health in other ways.
Richard Liroff
World Wildlife Fund