In our last commentary we said there was no evidence to support the claim that DDT was responsible for the decline in the number of bald eagles, peregrine falcons and brown pelicans. Vice President Gore included this claim in his 1992 book, and he recently repeated it when he spoke at the home of Rachel Carson, who blamed the decline on thin egg shells caused by DDT. Dr. J. Gordon Edwards, a distinguished biologist and entomologist, has spent many years exposing the lies told about DDT by well-meaning but misinformed people like Rachel Carson and Al Gore. This report is based on a paper he wrote 20 years ago.

Edwards cited several studies, beginning with one on bald eagles conducted by the U.S. Fish and Wildlife Service in Alaska. Captive eagles fed large doses of DDT for a prolonged period of time did not lay eggs with thin shells. Another study found that pheasant eggs with 349 parts per million of DDT hatched just as well as those with little or no DDT. A 1970 study of bald eagle eggshells from Wisconsin, Florida and Maine found that the thinnest shells were from Florida and the thickest shells were from Wisconsin. The Florida eggs had the least amount of DDT and the Wisconsin eggs had the most.

In 1969, D.J. Jefferies found that captive finches in England that were fed large doses of DDT laid eggs with shells that were seven percent thicker. In 1968, Hickey and Anderson reported in Science that the shells of red-tailed hawks increased in thickness by six percent in the first ten years after DDT was introduced. R.K. Tucker found that large doses of DDT fed to quail produced no thinning of their shells.

These scientific studies showed that the effect of DDT on egg shells was, if anything, the opposite of what is now widely accepted as true. Dr. Edwards has explained that thin egg shells are caused by the presence of mercury, lead, PCBs or sulfur compounds in the food. They can also be caused by a shortage of calcium in the diet. They can even be caused by stress. Edwards charges that some scientists created stressful situations at the same time they were experimenting with feeding birds large doses of DDT. They then attributed the thinning to the DDT, not to stress or other factors.

He says that there were many studies that simply failed to distinguish between DDT and chemicals in the environment that mimic DDT. He cites two scientists who led much of the fight against DDT who later admitted that there were serious errors in their analyses that blamed DDT for thinning of egg shells and declines in bird populations. Some of the analyses even reported finding DDT in organisms that had died and been placed in sealed containers before DDT was discovered.

Edwards charges that the news media accepted these erroneous reports without question and that many scientists who led the anti-DDT campaign have been slow to admit that it was based on badly flawed science. DDT saved millions of lives by killing the mosquitoes that spread malaria. Malaria was nearly wiped out in many countries, but tragically it has made a comeback in the tropics because we have pressured those governments to ban its use.

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