This new tide of chemicals represents a drastic change in public and environmental health. Instead of infectious diseases like smallpox or cholera, we are concerned with those potentially harmful things in our environment – like radiation and chemicals – that we have introduced into the world ourselves. They have the power to render the world uninhabitable, “silent and birdless.”
Carson’s contributions to our modern understanding of environmental health cannot be underestimated. She provided an early platform for the idea that, in this new era, the greatest threats to human health were the toxins created by humans themselves. This is a warning to the public, whose awareness of the dangers of radiation should be extended to dangerous pesticides.
Because of the hard to see, unpredictable, and delayed effects of absorbing small amounts of pesticides over time, it can be easy to ignore the problem. Humans seem programmed to shrug off disasters in the distant future, concerned only with those effects that can be seen immediately. Still, we are vulnerable in the same way the robins were, as part of an interdependent system that scientists call ecology. Whenever some part of this ecology is disrupted, its potential negative effects on the other parts are difficult to predict.
The difficulty of prioritizing future threats is one that must be overcome by reliance on the precautionary principle. The best way to understand the danger is to look at what pesticides have already done to the natural, inescapably interconnected systems of which we are a part – this has been Carson’s goal since the beginning of the book.
The human body itself contains a delicate ecology, where cause and effect are difficult to pin down – doctors are hard pressed to understand exactly what symptoms are a result of what lifestyle choices or genetic predispositions. It is therefore difficult to know when or how an insecticide might leave its mark on your system. Many pesticides are stored in fatty tissue and can accumulate over years, only to be unleashed in a stressful situation when fat is burned to release energy. British experimenters, who used their own bodies as test subjects, found that a small, direct exposure to DDT caused tremors and aching for an entire year.
By comparing the systems within the human body to the natural ecosystems she has already examined, Carson brings the awareness of relationship and dependency to a human level. Her health warning is deliberately frightening, and a main feature of her argument continues to be that so much is unknown or poorly understood, that it seems to make sense to slow down and conduct more research. The evidence we have is enough to know that the danger is real.
The liver is a vital part of this body ecology, and the first line of defense against poisons. Anything that could disrupt the liver, then, would greatly increase our vulnerability to environmental toxins. Methoxychlor, for example, is absorbed 100x faster when found in combination with another chemical that handicaps the liver.
Just as she has demonstrated the potentially disastrous effects of chemicals that interact and are transformed by their environments in the wild, Carson here relates this danger to human health by showing how certain chemicals can cripple natural defenses.
Sensitivity to synthetic pesticides varies from person to person, and seems also to vary depending on previous exposures to a given chemical. With each renewed contact, symptoms can return or worsen with exposure to smaller doses. Moreover, unlike in laboratories, no chemical in real life is ever encountered alone, and, as we saw with the discussion of polluted streams and waterways, the effects of the interaction between them are largely unstudied.
Given the prevalence of chemical residues, which Carson has already outlined in the previous chapter, we are all vulnerable to these prolonged exposures – this is another point in favor of rethinking the current idea about tolerable levels of chemical residue on food. The interconnected, messy, complex world is just too difficult to simulate in a laboratory setting, where these limits are established.
Pesticides’ effects on the nervous system are long lasting and little understood. During prohibition, a bootlegged alcohol substitute called Jamaican Ginger included a chemical in the family of organic phosphates. 15,000 people developed a crippling paralysis as a result of drinking this particular moonshine. The same type of paralysis was seen again when pesticides came into use two decades later. In clinical work from the University of Melbourne, pesticides were subsequently linked to mental disease as well – “a heavy price to pay for the temporary destruction of a few insects.”
As with her reference to the Borgias, Carson makes use of an infamous event from history to illustrate the poisonous nature of pesticides. Is it not strange, given the storied harm of these substances, that they should be allowed to invade our present and future so easily? Learning from the example of history should suggest that caution and research are required before undertaking such a risk.