“Spring straining” (DDT)

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DDT is short for a 31-lettered, synthetic insecticide created during the Great Depression. Its initial use was to kill disease vectors such as mosquitoes, lice, and tsetse flies. It was so effective and beneficial that discoverer Paul Hermann Müller received the Nobel Prize for Medicine.

Subsequently it was used in agriculture to protect crops from a variety of pests, and again proved efficient at doing so. But in the late 1950s, detractors raised the alarm about possible health effects on people and animals. The main concern was that DDT was causing eggshell thinning that resulted in the death of embryonic birds.  

Following the 1962 release of Rachel Carson’s Silent Spring, DDT’s use was prohibited in many countries. While the ban has been cited by some as helping bird populations recover, others have characterized it as overzealous. Those in the latter camp consider its alleged detrimental effects to have been exaggerated. They further note that DDT has the sizable benefit of saving Third World lives through malaria reduction.

We now know that eggshell thinning can be caused by lead, oil, phosphorus, calcium deficiency, and dehydration. Stress can also be a factor for captive birds undergoing testing. While DDT could also be to blame, Skeptoid’s Brian Dunning wrote that several studies in the 1970s and ‘80s failed to correlate even high levels of the insecticide with thinning. To be fair, other studies reached a different conclusion, one that was consistent with what Carson suggested. After perusing the studies and examining the issue, Dunning wrote, “My conclusion based on a review is that there probably is a correlation, but it’s not a strong one; and at best it’s only one of many causes. Whether DDT is used or not would probably not have a large impact on bird populations.”

Further, Silent Spring focused mostly on bald eagles, a species that was already experiencing a significant decline because of habitat loss and over-hunting.  The Bald Eagle Protection Act and the bird’s placement on the endangered species list in 1967 spurred its successful comeback. Attributing this to a DDT ban is likely a correlation/causation error.

And even if a DDT ban has benefited bird populations, those in the Third World are dying because of it since the insecticide remains one of the most effective pesticides at fighting malaria. Although DDT remains legal for insecticide use where widespread malaria exists, money for combating mosquitoes often comes from wealthy donors in the West.  Those donors sometimes stipulate that DDT not be used, leaving recipient nations with less efficient options. That contributes to such results as 407,000 Africans dying from malaria in 2016, compared to zero killed by DDT.

 

  

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