On a Farther Shore: The Life and Legacy of Rachel Carson, Author of Silent Spring by William Souder

Author:William Souder [Souder, William]
Language: eng
Format: epub, azw3
Tags: Biography & Autobiography, Nature, Environmental Conservation & Protection, Women, Environmentalists & Naturalists
ISBN: 9780307462220
Publisher: Crown
Published: 2012-09-04T00:00:00+00:00

The “safety” of a pesticide is a relative question, as the toxicity of any substance depends on the dose and the route of exposure. Calling a compound an “insecticide” identifies its purpose and suggests that its effects are specific to the targeted pests. But, in fact, scientists had determined only that insects could be killed with doses of DDT that didn’t seem harmful to people, and, for all anybody knew, enough DDT would kill a person in the same way it killed a bug. Because all life on earth evolved from common ancestors, all living things share certain biological features. The most obvious is DNA, which is present in all living organisms—other than some viruses—and which performs the same function in all of them. A specific sequence of DNA—a gene—makes RNA, which makes the same protein whether it’s in a mouse or a whale. And the more alike two organisms are, the more their respective genomes resemble each other. A human and a chimpanzee have genomes that are 96 percent identical. Above the molecular level, many biological processes are also “conserved” among different species.

One such feature is the transmission of electrical signals along nerve cells, or neurons. These impulses, powered by the rapid movement of ions across the cell membrane, carry sensory information and control muscle movements. In certain types of neurons these messages must cross gaps—as happens at the juncture between a neuron and a muscle—and this is accomplished by chemical chaperones called neurotransmitters. Once the impulse has been delivered across such a juncture, specialized enzymes neutralize the neurotransmitter and restore the chemical balance in the gap.

During the early development of the organochlorine and organophosphate insecticides, such cellular processes were incompletely understood. But because these poisons caused twitching and rigidity and convulsions it was thought that they must in some way interfere with nerve impulses, possibly by disrupting the actions of neurotransmitters or by interfering with the flow of ions across the neuron’s cell membrane. Either could lead to the repeated firing and intermittent paralysis of muscle cells. Which is exactly what was observed in the case of insects poisoned by DDT or other insecticides. The ultimate cause of death following such “general uncoordinated activity” was believed to be “metabolic exhaustion.”

After their initial studies, researchers started to wonder whether pesticides, especially the fat-soluble organochlorines, could build up in the body of someone repeatedly exposed to them—and if such a bioaccumulation did occur, what would be the effects of the increasing body burdens of pesticides? But it would be years before scientists would learn that special proteins, embedded in the membranes of cells or deep within their nuclei, act as hormone receptors—and that these receptors can make mistakes, binding to pesticides or their by-products as if they were hormones and thereby initiating willy-nilly, out-of-control cellular responses that can lead to disease and reproductive issues.

Putting aside the long-term health hazards arising from pesticide exposure—cancer and birth defects, for example—fatal or serious human “intoxications” by organochlorine insecticides were thought to be rare,

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