If we narrow our focus, we can see the effects of pesticides on the workings of individual cells. Recent medical research shows that energy production via cellular oxidation happens on a cellular level to fuel the body. A prizewinning roster of scientists have over the last quarter century been gradually uncovering the secrets of this beautiful mechanism, which Carson refers to as “one of the wonders of the living world.”
From the macro scale of entire ecosystems, Carson has narrowed her focus first to the human body and now to the functioning of individual cells. This is part of her project of education, as she gives a popular voice to the work of scientists around the world. That pesticides could affect our bodies on even this cellular level is another reason for treating them with extreme caution.
ATP and ADP, the body’s units of energy, are produced in minute structures called mitochondria within each cell. After ATP is used as energy, it loses a group of atoms called a phosphate and becomes ADP. This ADP is then recharged in turn by a process called “coupled phosphorylation,” in a carefully coordinated string of enzyme reactions. Radiation and synthetic chemicals both have the frightening power to uncouple this fundamental process, causing the body to burn itself out. This uncoupling power, which Carson calls “the crowbar to wreck the wheels of oxidation,” is present in many pesticides.
Again comparing the well-known effects of radiation to those of pesticides, Carson explains that even the process that is perhaps most fundamental to life, the production of energy in cells, is in fact another instance of the ‘complex system’ carefully calibrated by nature. Here, too, pesticides have the power to disrupt a careful balance, and the body is not designed to combat them, since their development has been so rapid compared to the pace of evolution.
The disruption of the oxidation process has an effect on fertility that is visible in eggs and other germ cells in animals – this might explain the sterility that has been observed in birds after exposure to DDT. If pesticides prevent ADP from coupling with a new phosphate group, respiration continues but no energy is created, so that the body uses power without creating any. Because ATP is “the universal currency of energy,” the driving energy force in life everywhere, its disruption in other species is a sign that humans can also be affected. We are not immune.
By linking this examination of the process by which cells produce energy to sterility in birds, Carson is driving home her point that humans are vulnerable to the same harm that we see affecting the natural world. ATP, the energy unit at the core of this process, is universal, and so its effects in other species will be mirrored in humans – just as it was with the sprayers, early in the book, who were paralyzed by a new malarial spray.
Carson returns to the plight of the birds, recalling the sterile blue robin eggs and the larger, white eagle eggs, “cold and lifeless.” Observations of DDT levels in unhatched bird eggs have shown unsafe concentrations, which according to scientists’ understanding of the oxidation process outlined above would have disrupted the proper production of ATP and crippled development of fledglings.
The problem of sterility is a chief factor in the decline of these emblematic bird species, and this understanding of the cellular energy production process offers one explanation – again suggesting that the same sterility could strike humans with the right level of exposure to DDT.
Humanity’s “genetic heritage” is also under threat, in a way that mirrors the problems of radiation, which can cause mutations that are passed down over generations. Cell division, or mitosis—the process by which one cell divides into two—is another universal process in the natural world that is affected by radiation and by mutagens, including common pesticides. Mitosis involves a careful alignment of chromosomes, which are the structures made up of DNA, so that all the genetic information is split evenly between two daughter cells. This process may be 1000 million years old, and is part of what has allowed life to flourish.
Equally alarming are the effects of pesticides on cell division, another process that is universal across the world of living creatures, meaning that disruptions in one species – of fish, for example, who often suffer mutations from their chemical environments – could be mirrored in humans. The danger of mutations is associated with nuclear radiation – which was a huge topic at the time that Silent Spring was published, coming in the midst of the Cold War and just a few decades of the dropping of the atomic bombs. Carson captures the urgency of the pesticide issue by making it clear that pesticides, in their dangerously rapid development, pose a similar threat to nuclear radiation in the way they affect cells.
Anything that disrupts the accuracy of this age-old process could change the course of evolution and cause disease in individuals of a species. Although the study of human chromosomes is in its infancy, we can see the effects of pesticides on cell division in other species of plant and animal, and predict their results in humans. Chromosome abnormalities like those we see in animals as a result of pesticide exposure are known to cause many issues in humans, including hereditary disease, sterility, and cancer.
Evolution is often thought of as the ultimate, abstract safety mechanism on a species wide level – it allows populations, on a longer time scale, to adapt to changing environments or new diseases. Crippled by a lack of time, however, and now attacked directly in the process of cell division, evolution may not be able to protect humanity any longer. That humans can now influence this process on such a scale is shocking enough – are we arrogant enough to assume that we know better than this ancient system at the heart of life?
Far too little is known about the effects of pesticides on cell division, but it is clear that disruptions in chromosome replication are responsible for a wide range of mental and physical illnesses. These dangers are widely discussed with regard to radiation, but the potential for chemicals to cause mutations is underappreciated and has not been sufficiently studied. It seems absurd, argues Carson, to continue exposing ourselves to such a potentially dangerous cocktail of chemicals for so little benefit.
If exposure to pesticides can cause mental and physical illness – and Carson has provided ample evidence that it may – then are we not responsible as a nation, or even as a species, for halting the advance of these dangerous chemicals? Carson makes the case that a basic level of caution is needed to prevent a future in which man creates his own downfall by continuing down his current path.