11. The Precautionary Principle: Silent Spring’s Toxic Legacy

Larry Katzenstein

The publication of Rachel Carson’s Silent Spring in 1962 triggered repercussions that resonate to this day—from creating the modern environmental movement to spawning federal laws governing air and water quality, protection of endangered species, worker safety, and much more. But a crucially important “contribution” of Silent Spring has gone largely unrecognized: it gave birth to the “precautionary principle,” a philosophy for regulating chemicals and technologies and arguably one of the late-20th century’s more pernicious doctrines.

The Extended Shadow

By general consensus, Silent Spring led President Richard Nixon in 1970 to establish the Environmental Protection Agency, charged with regulating the pesticides and herbicides that Rachel Carson criticized for endangering the environment and human health. On its website, EPA had this to say about the book that led to its creation:

Silent Spring played in the history of environmentalism roughly the same role that Uncle Tom’s Cabin played in the abolitionist movement. In fact, EPA today may be said without exaggeration to be the extended shadow of Rachel Carson.¹

The precautionary principle in many ways can be considered the “extended shadow” of Silent Spring. In this chapter, I’ll make the case that Silent Spring—thanks to the precautionary principle it created— continues to bias public policy and attitudes against new products and technologies because of the dangers they allegedly pose to the environment and public health. I’ll offer evidence that the spirit of this 50-year-old book continues to animate calls for “precautionary” measures.

Defining the Precautionary Principle

The precautionary principle is a strategy for coping with scientific uncertainty. Its proponents contend that governments should prohibit or restrict technologies or activities “when they are suspected of posing some harm to human health or the environment, even if the probability and magnitude of such harm has not been demonstrated scientifically.”² And it requires that “the main burden of providing evidence for safety” rests on “the proposers of a new technology or activity”³ rather than on government regulators or society.

The precautionary principle embodies familiar and commonsensical ideas such as “better safe than sorry” and “look before you leap.” At first blush, the societal response that is called for—plan ahead to avoid threats that damage the environment or human health— seems reasonable. But as this chapter will show, the precautionary principle on closer scrutiny is far from benign. Jonathan Adler has nicely summarized the dangers of this doctrine:

More and more, environmental policy incorporates the “precautionary principle,” which calls upon governments to impose regulatory measures based upon the barest potential of environmental harm. If a chemical substance might be causing harm, it should be controlled or eliminated. If a new technological innovation could have unknown environmental effects, it should not be permitted. The precautionary principle may appeal to common-sense notions of safety, but its application will not produce a safer, cleaner world. Quite the opposite. The incorporation of the precautionary principle in environmental, health, and safety regulation is itself a threat to environmental protection and optimal safeguards for public health.⁴

As Adler suggests, the precautionary principle is not just an abstract concept floating in the intellectual ether. Indeed, the principle is written into international environmental declarations and agreements such as the Rio Declaration on Environment and Development, the United Nations Framework Convention on Climate Change, and the Convention on Biological Diversity. In Europe, where it holds particular sway, “the precautionary principle is now written into law,”⁵ and “has emerged as a critical component of the new European approach to risk regulation.”⁶ The European Union’s resistance to genetically modified foods and hormone-treated beef and its activist role in opposing global warming are clear expressions of the principle.

Coming up with a definitive definition of the precautionary principle is difficult: A 1999 study found 19 formulations of the precautionary principle expressed in international treaties, laws, and academic writings.⁷ In choosing the iteration of the principle that best exemplifies its precautionary spirit, I defer to Indur Goklany, author of the acclaimed book The Precautionary Principle: A Critical Appraisal of Environmental Risk Assessment. He has written that “a popular and reasonably good definition” of the precautionary principle appears in the so-called Wingspread Declaration,⁸ which emerged from the Wingspread Conference on the Precautionary Principle—a three-day meeting held in January 1998 in Racine, Wisconsin.⁹

The statement announcing the conference called its 31 participants “treaty negotiators, activists, scholars and scientists from the United States, Canada and Europe.”¹⁰ But the attendees have also been described as “a panel of activists with an agenda.”¹¹

Following are key sections from the Wingspread Consensus Statement on the Precautionary Principle. I have italicized the sentence expressing the principle itself.

The release and use of toxic substances, the exploitation of resources, and physical alterations of the environment have had substantial unintended consequences affecting human health and the environment. . . . We believe there is compelling evidence that damage to humans and the worldwide environment is of such magnitude and seriousness that new principles for conducting human activities are necessary. . . . Corporations, government entities, organizations, communities, scientists, and other individuals must adopt a precautionary approach to all human endeavors. Therefore, it is necessary to implement the Precautionary Principle:

When an activity raises threats of harm to human health or the environment, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically.

In this context the proponent of an activity, rather than the public, should bear the burden of proof.

Theoretically, the precautionary principle protects the public health and the environment by curbing the threats posed by newer technologies such as genetically modified foods or nuclear energy. But applications of the precautionary principle can actually cause more harm to health and the environment rather than less.

A Brief Digression: My Personal Brush with Precaution

Before describing Silent Spring’s role in creating the precautionary principle, it may be instructive to describe my own evolution—from a disciple of the precautionary principle to a dissenter—during my career at Consumer Reports, where I worked as a health and environment writer from 1978 to 1990.

My first major article for the magazine was the cover story for the August 1979 issue, entitled “Are Hair Dyes Safe?” After a six-month investigation, I concluded that the answer was a resounding no. Hyping hypothetical risks in the best tradition of the precautionary principle, I wrote that “the problem consumers face is that the NCI [National Cancer Institute] has tested only a minority of the coal-tar dyes now used in hair dyes. Many of those not yet tested could prove just as hazardous as some of those already tested.”¹²

In December 1986, I learned that the National Association of Science Writers’ holiday party in New York City would be preceded by a talk on food irradiation. I had never heard of the technology, but judging from its name, I was sure I could turn it into another fear-inducing cover story for Consumer Reports. Instead, the talk turned around my career and my life.

The speaker, food irradiation consultant George Giddings, discussed irradiation’s proven ability to rid food of pathogenic bacteria and—if widely used on raw meat and poultry—to prevent thousands of deaths and hundreds of thousands of cases of foodborne illness due to E. coli, salmonella, listeria, and other microbes each year.

Giddings also reviewed the risks raised by irradiation’s opponents— from their prediction that thousands of dangerous irradiators would spring up around the country to their claims that irradiating food produces toxic residues that could cause serious health effects, including cancer—and explained why those risks were vanishingly small or nonexistent.

After the talk, I knew that I had a good story, but not the one I’d expected. This story would inform readers about the life-saving benefits of food irradiation and debunk the irresponsible allegations of its opponents. Such an article, I was sure, could help win national acceptance for food irradiation and would further Consumer Reports’ goal of protecting the public’s health. I lobbied my editors for a year and a half and finally got the go-ahead. But soon the food irradiation article I’d fought so hard for hit a roadblock in the form of the precautionary principle.

Rhoda Karpatkin, executive director of Consumers Union of the United States (the publisher of Consumer Reports) at the time, was also serving then as president of the International Organization of Consumers Unions. IOCU (now known as Consumers International) is a federation based in The Hague, Netherlands, consisting of Consumers Union and 164 other consumer organizations from 63 countries.

Europe in the 1980s was already under the sway of the precautionary principle, and European-based organizations such as IOCU were by no means immune. IOCU had issued two resolutions calling for a worldwide moratorium on food irradiation. In the best tradition of the precautionary principle, IOCU’s major objection to food irradiation was that it “has not yet been proved sufficiently safe.”¹³ Ms. Karpatkin was clearly not pleased at the prospect of a pro–food irradiation article appearing in Consumer Reports during her stint as IOCU president. Before I could even start on the article, she walked into the editor’s office and—as I was later informed— told him, “I don’t want Katzenstein writing that article on food irradiation.”

Disappointed and disgusted, I immediately began looking for another job. I left Consumer Reports and became medical editor at American Health magazine, where I finally did get to write “my” article. “Food Irradiation: The Story behind the Scare” appeared in the December 1992 issue of American Health¹⁴ and was later condensed in Reader’s Digest.¹⁵ Consumer Reports got around to writing about food irradiation in 2003.¹⁶ Not surprisingly, the article was decidedly negative, calling for “further tests of chemical byproducts created by meat irradiation.” Another victory for precaution, another defeat for public health.

Tracing the Precautionary Principle’s Origin

The premise of this chapter—that Silent Spring gave birth to the precautionary principle—first of all requires that the book preceded the principle, and here there is good consensus. Articles dealing with the history of the precautionary principle trace its creation to the late 1960s, several years after Silent Spring’s publication in 1962. There is also agreement that the earliest versions of the precautionary principle were formulated in Germany and Sweden in response to local environmental concerns.

The first legal use of the term is said to be the 1969 Swedish Environmental Protection Act, which required Swedish industries to demonstrate the safety of their products to regulators instead of regulators having to prove harm.¹⁷ At around the same time, the German government was developing its environmental policy on the basis of Vorsorgeprinzip, a concept that has been translated as “foresight planning.”¹⁸ The Vorsorgeprinzip concept influenced legislation approved in the 1970s to prevent acid rain from damaging German forests.

One reason that Europe is credited with the precautionary principle is that the principle arguably is better entrenched there than elsewhere in the world. Versions of the precautionary principle have been written into important European laws, including the 1992 Fifth Environmental Action Program and the 1992 Maastricht Treaty.¹⁹

Despite these codifications in European law and the roles of Germany and Sweden in articulating the principle around 1969, I contend that “credit” for the precautionary principle’s conception rightfully belongs to an event that occurred several years earlier: the publication of Silent Spring. Those who claim the precautionary principle as a European creation, promulgated in response to European concerns, fail to appreciate the tremendous impact that resulted from Silent Spring’s publication, not only in the United States but internationally.

In his introduction to the 1994 edition of Silent Spring, then Vice President Al Gore noted that the book “achieved enormous popularity and broad public support” and “planted the seeds of a new activism that has grown into one of the great popular forces of all time”—the environmental movement. “Without this book,” Gore wrote, “the environmental movement might have been long delayed or never have developed at all.”²⁰

The following passage, from Rachel Carson: The Environmental Movement, by John Henricksson, powerfully describes Silent Spring’s success in planting those “seeds of a new activism” among interest groups that would eventually “blossom” into the modern environmental movement:

Ad hoc groups—groups organized for one specific purpose— have opposed the building of nuclear power plants, the dumping of toxic wastes into rivers, and the systematic poisoning of coyotes in the West or wolves in Alaska.

All of these groups profoundly mistrust the idea of progress through new technology. They take Silent Spring as their bible. Rachel Carson had described one environmental issue with such clarity and precision that they could use it as a model for other issues. . . . Their own battles were extensions of the one that she had fought. . . .²¹

Among the battles listed as being inspired by Silent Spring is “the battle against acid rain”—the concern that led Germany (as noted above) to pass one of the earliest instances of legislation incorporating the precautionary principle.²²

Other supporting evidence for the book’s impact and influence include the following:

• After its publication, Silent Spring not only spent weeks atop the U.S. best seller list but also became an international best seller that has been described as “one of the most influential books in the modern world.”²³

• The New York Times included Silent Spring on its list of the 20th century’s 100 most important books;²⁴ and in 1992, a panel of distinguished Americans selected Silent Spring as the most influential book of the previous 50 years.²⁵

• Silent Spring was translated into 22 languages.²⁶

• In the United States Silent Spring’s popularity spurred enactment of key federal laws that embody aspects of precautionary regulation: the National Environmental Policy Act; the Clean Air Act; the Clean Water Act; the Federal Insecticide, Fungicide and Rodenticide Act; the Safe Drinking Water Act; the Environmental Pesticides Control Act; the Toxic Substances Control Act;²⁷ and the Endangered Species Act.²⁸

Thus, it is not difficult to imagine that Silent Spring—one of the most notable books of the 20th century—inspired the Europeans who articulated the earliest iterations of the precautionary principle as well as the authors of the many versions that followed.

Silent Spring’s Long Reach

Somewhat more direct evidence that Silent Spring reached across the Atlantic Ocean to create the precautionary principle comes from a book on risk assessment of chemicals, published in the Netherlands in 2007. Chapter 12, “The Management of Industrial Chemicals in the EU,”²⁹ recounts the history of Europe’s long-awaited chemical policy: a law known as REACH (Registration, Evaluation, Authorization, and restriction of Chemicals). Enacted in 2005, REACH created a single system for evaluating all EU industrial chemicals and was designed to “ensure a high level of protection of human health and the environment.”

In laying out the key developments culminating in REACH, Chapter 12 cites both Silent Spring and the precautionary principle. The introductory section contains the following passage:

The use and releases of chemicals increased enormously in the 20th century. It has become apparent that this increase was not without “cost” to health and the environment, particularly in the industrialized countries. This was clearly illustrated by Rachel Carson in the early 1960s, whose book Silent Spring described the disastrous effects of the wide scale use of pesticides on fish, birds and ecosystems.

The need to establish legally binding frameworks for the control of chemicals was soon recognized and started in the 1960’s. . . . [T]he focus was on the hazards of chemicals, i.e., the inherent or intrinsic properties of chemicals having the potential to cause adverse effects.

After citing the need for an EU chemicals policy that will “ensure a high level of protection of human health and the environment,” the chapter continues:

Fundamental to achieving these objectives is the precautionary principle. Whenever reliable scientific evidence is available that a substance may have an adverse impact on human health and the environment but there is still scientific uncertainty about the precise nature or the magnitude of the potential damage, decision-making must be based on precaution in order to prevent damage to human health and the environment.”³⁰

Comparing the Book and the Principle

Of course, the best evidence of all that Silent Spring was mother to the precautionary principle comes from the many similarities between the beliefs expressed in Silent Spring and those espoused in the principle itself. The remainder of this chapter will examine several of the key similarities between the two.

Only Man-Made Risks are Important

The precautionary principle made its formal international debut in 1982.³¹ That year, the United Nations World Charter for Nature declared that when “potential adverse effects [from activities likely to pose significant risks to nature] are not fully understood, the activities should not proceed.”³² In that UN world charter and in its later appearances, the precautionary principle has always been invoked for the purpose of curtailing man’s activities or products made by man. Those wielding the principle clearly regard naturally occurring risks as undeserving of a precautionary approach and dismiss them as undeserving of consideration—for being inevitable, irrelevant, or, almost by definition, less important than man-made risks.

The precautionary principle’s “blind spot” regarding natural risks may actually help to explain its allure, according to legal scholar Cass Sunstein, who currently is on leave from Harvard Law School while he directs the White House Office of Information and Regulatory Affairs. Sunstein, whose extensive writings on the precautionary principle include his 2005 book, Laws of Fear: Beyond the Precautionary Principle, described the principle’s allure in a 2008 op-ed piece:

[W]hy does the precautionary principle seem so appealing? Part of the answer is psychological. Particularly powerful is the belief that nature is benevolent and harmonious. Studies show that people overestimate the carcinogenic risk from pesticides and underestimate the risks of natural carcinogens. People also believe that nature implies safety, so much that they will prefer natural water to processed water even if the two are chemically identical. Most people believe that natural chemicals are safer than man-made chemicals. Most toxicologists disagree.

The truth is that nature is often a realm of destruction, illness, killing, and death. Human activity is not necessarily or systematically more destructive than what nature does.³³

The precautionary principle’s willful disregard for naturally occurring risks springs right from the pages of Silent Spring. The book regales readers about risks posed by some 40 man-made hazards, from aldrin to urethane, yet says practically nothing about naturally occurring toxins. Naturally occurring toxins are mentioned primarily to contrast their apparent safety with the risks posed by synthetic chemicals:

In being man-made—by ingenious laboratory manipulation of the molecules, substituting atoms, altering their arrangement, [insecticides created in the laboratory during and after World War II] differ sharply from the simpler insecticides of prewar days. These were derived from naturally occurring minerals and plant products—compounds of arsenic, copper, lead, manganese, zinc, and other minerals, pyrethrum from the dried flowers of chrysanthemums, nicotine sulphate from some of the relatives of tobacco, and rotenone from leguminous plants of the East Indies.³⁴

In their 1996 book, Bruce Ames and Lois Swirsky Gold, University of California at Berkeley toxicologists, commented on Carson’s obsession with man-made risks. In words that echo Sunstein’s critique of the precautionary principle and its underestimation of risks from natural carcinogens, Ames and Gold wrote:

Rachel Carson’s fundamental misconception [in Silent Spring] was: “For the first time in the history of the world, every human being is now subjected to contact with dangerous chemicals, from the moment of conception until death.” She was wrong. The vast bulk of the chemicals to which humans are exposed are natural, and for every chemical some amount is dangerous. Carson thus lacked perspective about the wide variety of naturally occurring chemicals to which all people are exposed and did not address the fact that, outside the workplace, exposures to synthetic pollutants are extremely low relative to the natural background. . . . Since the vast proportion of human exposures are to naturally occurring chemicals, while the vast proportion of chemicals tested for carcinogenicity are synthetic, there is an imbalance in data and perception about chemicals and cancer.³⁵

Accentuate the Negative

One of the most remarkable things about Silent Spring is how few of its words are devoted to saying anything positive about the many pesticides, herbicides, and other chemicals it discusses— an omission acknowledged by one of Carson’s biographers: “Carson was not always neutral in her use of sources and . . . she was sometimes driven by moral fervor more than by scientific evidence. Indeed, her use of evidence was selective, and she made no attempt to catalogue the benefits of pesticides. . . .”³⁶

The precautionary principle is similarly characterized by refusal to recognize any benefits offered by the chemicals or technologies that it would restrict—one of the main reasons that Sunstein has dubbed it “The Paralyzing Principle.” In his article by the same name, Sunstein wrote that “the most serious problem with the Precautionary Principle is that it offers no guidance” because “risks of one kind or another are on all sides of regulatory choices.”³⁷

In elaborating, Sunstein discusses five controversial topics that have attracted precautionary attention: strong controls on arsenic in drinking water, genetic engineering of food, global warming, threats to marine mammals posed by naval exercises, and nuclear power. Reflexively invoking the precautionary principle, he warns, could lead to “substitute risks in the form of hazards that materialize, or are increased, as a result of regulation.” Nuclear power provides a good illustration of this conundrum, Sunstein notes:

Many people fear nuclear power on the ground that nuclear power plants raise various health and safety issues, including some possibility of catastrophe. But if a nation does not rely on nuclear power, it is likely to rely on fossil fuels, and in particular on coal-power plants. Such plants create risks of their own, including risks associated with global warming.³⁸

“What guidance does the Precautionary Principle provide [in dealing with those five controversies]?” Sunstein asks. “It is tempting to say that the principle calls for strong controls on [them]. In all of those cases, there is a possibility of serious harms, and no authoritative scientific evidence suggests that the possibility is close to zero.”

He then suggests asking “a more fundamental question”:

Is more stringent regulation really compelled by the Precautionary Principle? The answer is that it is not. In most of the cases above, it should be easy to see that in its own way, stringent regulation would actually run afoul of the Precautionary Principle [and its goal of protecting people against risks to their safety and health]. The simplest reason is that such regulation might well deprive society of significant benefits, and for that reason produce risks and even deaths that would otherwise not occur.³⁹

“Safe” Exposure is Impossible

In an apparent effort to portray Carson as having rationally assessed pesticides in Silent Spring, her biographers invariably emphasize that she did not favor outlawing them. For example, in the first nine pages of her 2005 book, Priscilla Coit Murphy states three times that Silent Spring did not call for a pesticide ban. The third iteration reads as follows:

With respect to the conduct of the debate [over Silent Spring’s scientific validity], even more important [than her list of principal sources of information in an appendix] is the fact that Carson explicitly declined to prescribe total abstinence from pesticides. Early on, in the second chapter, she makes the following statement: “It is not my contention that chemical insecticides must never be used. I do contend that we have put poisonous and biologically potent chemicals indiscriminately into the hands of persons largely or wholly ignorant of their potentials for harm.” Many of her critics chose to ignore that disclaimer, however. . . .⁴⁰ [Emphasis added.]

True, Carson did say that she wasn’t calling for a ban on pesticide use. But on other pages of her book, she makes a claim that, as a practical matter, would clearly require a ban: that no level of pesticide exposure can be considered safe. Carson articulated that belief in “One in Every Four,” Silent Spring’s “cancer” chapter. “One in every four” refers to the proportion of Americans who allegedly will develop cancer sometime during their lives.⁴¹ She makes the case that “dangerous chemicals” have “entered the environment of everyone—even of children as yet unborn,” and that it is “hardly surprising, therefore, that we are now aware of an alarming increase in malignant disease.”⁴²

Carson presented her “no safe dose” argument twice in this chapter. The first mention occurs in the context of man’s exposure to many different chemicals at once: “Human exposures to cancer-producing chemicals (including pesticides) are uncontrolled and they are multiple,” she writes and goes on to note, “It is quite possible that no one of these exposures alone would be sufficient to precipitate malignancy—yet any single supposedly ‘safe dose’ may be enough to tip the scales that are already loaded with other ‘safe doses.’”⁴³

In the next paragraph, she describes yet another malignant scenario, this one involving synergistic interactions among toxins:

Or again the harm may be done by two or more different carcinogens acting together, so that there is a summation of their effects. The individual exposed to DDT, for example, is almost certain to be exposed to other liver-damaging hydrocarbons, which are so widely used as solvents, paint removers, degreasing agents, dry-cleaning fluids, and anesthetics. What then can be a “safe dose” of DDT?⁴⁴

Carson’s motive for putting “safe dose” in quotation marks was the subject of an interesting analysis by Randy Harris who writes that they were Carson’s way of emphasizing that any exposure to DDT should be considered hazardous:

If someone asks you what a “safe dose” of DDT is, as Carson just has, you know right away that the words in quotation marks are not hers. She is disavowing them. She has brought them in from elsewhere and bagged them in pairs of raised commas, one pair inverted, so you will know that someone else—someone without enough knowledge, or someone with duplicitous intentions—has used them in a way that is misleading and dangerous. The words are not hers, but you have no trouble recognizing that she has a belief about them or that the belief concerns their veracity. The quotation marks deliver a truth judgment, a negative truth judgment, on the material they flank. There is no safe dose of DDT, Carson says with her quotation marks, and you shouldn’t believe anyone who tells you there is.⁴⁵

Then, on the following page, Carson expands on her “no exposure is safe” argument by raising the possibility that chemicals not known to cause cancer could possibly enhance the potency of carcinogens:

Water pollution experts throughout the United States are concerned by the fact that detergents are now a troublesome and practically universal contaminant of public water supplies. There is no practical way to remove them by treatment. Few detergents are known to be carcinogenic, but in an indirect way they may promote cancer by acting on the lining of the digestive tract, changing the tissues so that they may more easily absorb dangerous chemicals, thereby aggravating their effect. But who can foresee and control this action? In the kaleidoscope of shifting conditions, what dose of a carcinogen can be “safe” except a zero dose?⁴⁶

The chemophobia spawned by Silent Spring is now inscribed in the precautionary principle, which calls for assurances of safety before new chemicals or technologies can be marketed. As Adler notes in his critique of the precautionary principle, proving safety requires proving a negative (“no harm”)—something that is scientifically impossible to do:

The scientific process can test the robustness of a given hypothesis—substance X will cause cancer or substance Y disrupts amphibian production—but it cannot prove that a given substance is risk-free. Substance X might not cause rodent tumors, but it could always cause something else. For this reason, scientists fear that the Precautionary Principle could “block the development of any technology if there is the slightest theoretical possibility of harm.”⁴⁷

Meanwhile, environmental and consumer extremists who espouse the precautionary principle have fanned the public’s Silent Spring–induced fear that we’re in the midst of a chemical-induced cancer epidemic and that zero is the only safe dose of chemical exposure. As C. F. Wilkinson, writing in Silent Spring Revisited, noted:

What society will not tolerate is the possibility, no matter how remote, that long-term, low-level exposure to pesticides and other chemicals might ultimately lead to sinister chronic effects such as cancer, mutagenesis, or birth defects, which are generally considered the ultimate insults to human health. Public fears in this area have been greatly heightened in recent years by a vocal group of toxicological apocalyptics who claim that up to 90% of current human cancers can be attributed directly to pesticides and other synthetic chemicals.⁴⁸

These “toxicological apocalyptics”—Public Citizen, the Center for Science in the Public Interest, Greenpeace, and other environmental and consumer groups—whip up fear over cancer to attract media attention and scare up contributions. In their obsession with highlighting cancer risks, the apocalyptics make demands for adhering to the precautionary principle that can border on the ludicrous.

I encountered my favorite example of precautionary zealotry while researching my article on food irradiation for American Health. It involved an anti-nuclear group called Food & Water, which led the opposition to food irradiation during the 1980s and 1990s. Food & Water insisted that irradiating food creates dangerous “unique radiolytic products,” or URPs, capable of causing “cancer and birth defects.” URPs, it turned out, were entirely hypothetical—as is often the case with the “risks” that precautionary proponents inveigh against. When I asked Michael Colby, Food & Water’s national director, to name an URP, his reply was somewhat tortured: “No one has identified them,” he said. “We know they exist; they just haven’t been identified.”⁴⁹

Carson’s concept of zero-dose exposure has become the rallying cry of precautionary advocates. For example, Dr. Samuel Epstein, a well-known adherent, has declared that “no safe level or thresholds are recognized for chemicals inducing carcinogenic, teratogenic, or mutagenic effects.”⁵⁰ Equally important, the concept has been adopted by several of America’s most important regulatory agencies.

In the realm of chemical regulation, zero-doze exposure now goes by the name “linear, no-threshold theory,” which presumes that the dose-response curve extends linearly to the origin (at least for low-level exposures) and that there are no thresholds below which exposure to a given carcinogen can be considered safe. During the 1970s, the Consumer Product Safety Commission, EPA, FDA, and Occupational Safety and Health Administration “all adopted no-threshold models on the grounds that, given the uncertainties inherent in animal studies [which provide much of the data used in constructing dose-response curves], it was prudent to assume low-dose linearity.”⁵¹ (Emphasis added.)

In a 2000 op-ed piece, Kenneth Smith addressed the controversy over the proposed repository for spent nuclear fuel in Nevada, lamenting Carson’s influence in foisting the no-threshold theory on EPA. Smith noted that industry, consistent with recommendations from the National Academy of Sciences, said it was sufficient to limit annual radiation exposure levels to “the dose one would receive on five coast-to-coast, round-trip plane trips across the United States.” EPA, however, was “insisting on limiting exposure to the equivalent of three trips and possibly even lower.” After noting that this contest between five and three coast-to-coast trips “is precisely the kind of regulatory regime with which Rachel Carson cursed the United States,” Smith wrote:

Ms. Carson based her influential “novel,” Silent Spring, on the fiction that exposure to disappearingly small amounts of man-made chemicals and radiation might poison man and everything else on the globe. The author was a biologist, not an expert in cancer research, and almost four decades later there is still no scientific basis for her warnings. But in the name of protecting the public, regulators now rely on her theory that there is no threshold below which exposure to alleged carcinogens is safe.⁵²

Despite what seems to be a growing scientific consensus that safe thresholds for carcinogens do exist, today’s EPA seems even more closely wedded to Rachel Carson and the precautionary principle than it was 10 years ago, when Smith wrote his piece.

The Dioxin Saga

That message is clearly conveyed by Jon Hamilton’s 2010 National Public Radio segment about what to do with the many sites around the country where soil is contaminated with low levels of dioxin, “considered one of the world’s most dangerous chemicals.” Hamilton recounts that in December 1982, the people of Times Beach, Missouri, were ordered to abandon their town forever because EPA had found high levels of dioxin in the soil—the result of dioxin-contaminated waste oil spread on roads years earlier to keep down the dust. Hamilton notes that in ordering the evacuation, federal officials “had taken a drastic step—one that was based more on a hunch than on definitive science”:

They knew the chemical came from industrial processes, including chlorine bleaching at paper mills, pesticide production, and waste incineration. And they knew high doses caused liver tumors in rodents. So federal officials took a cautious approach. They decided residential soil should contain less than one part per billion of dioxin. In some areas of Times Beach, levels were 100 times that high. As a result, the empty town became one of the nation’s first Superfund sites.⁵³

A few years later, EPA’s attention shifted from the high dioxin levels of Times Beach to the very low levels that the agency was finding in many other places, from sources such as the burning of backyard trash—findings that created challenges for the agency. Hamilton quotes Joshua Cohen, deputy director of the Center for the Evaluation of Value and Risk in Health at Tufts University and a member of a committee assembled by the National Academy of Sciences to review EPA’s assessment of risks from dioxin: “The problem,” said Cohen, “is that there is no ideal study that directly answers the question: Does dioxin cause cancer at typical everyday exposure levels, and, if so, how big a risk does it pose?”⁵⁴ EPA scientists decided to extrapolate cancer risk from studies of workers who had been exposed to high levels of dioxin. So for exposure levels one-tenth as high as those experienced by workers, EPA would assume that the risk is one-tenth as large. As a result, says Hamilton, every bit of dioxin-contaminated soil in the country would pose a risk.⁵⁵

Cohen and many other scientists outside EPA argue that this is the wrong approach for evaluating dioxin and some other chemicals. According to Hamilton, “They say that because of the way these chemicals behave in the body, there’s a threshold below which the risk of cancer disappears. If that’s true, and these scientists are correct, there would be no reason to worry about exposure in most places.” In 2006, Cohen and other members of the National Academy of Sciences committee supported experts who were asking EPA to reconsider its no-threshold position for dioxin risk. But in late 2009, the agency proposed making the acceptable level of dioxin in soil even lower. And in May of 2010, EPA scientists issued their latest rejection of the threshold approach to cancer risk.⁵⁶

EPA’s stance contrasts sharply with European regulators and the World Health Organization, who decided a decade ago that dioxin does have a safe threshold. As a result, they accept exposure levels that are much higher than EPA’s proposed standard.

Most experts on the precautionary principle regard it as being more deeply entrenched in Europe than in the United States. They might be both surprised and distressed to see EPA regulators pursuing dioxin with far more zeal than even their European counterparts have shown.

A World of Unintended Consequences

If anything can be said to be the raison d’etre of the precautionary principle, it is the need to avoid the unintended consequences of new chemicals and technologies—a sentiment spelled out in the first sentence of the Wingspread Consensus Statement on the Precautionary Principle:

The release and use of toxic substances, the exploitation of resources, and physical alterations of the environment have had substantial unintended consequences affecting human health and the environment.⁵⁷

This basic premise—that tampering with nature can have unforeseen and tragic results—seems clearly to have been inspired by Silent Spring, a book whose working title was Man against Nature.⁵⁸ In the book’s first few pages, Carson calls environmental pollution “the central problem of our age”:

Along with the possibility of the extinction of mankind by nuclear war, the central problem of our age has . . . become the contamination of man’s total environment with such substances of incredible potential for harm—substances that accumulate in the tissues of plants and animals and even penetrate the germ cells to shatter or alter the very material of heredity upon which the shape of the future depends.

Some would-be architects of our future look toward a time when it will be possible to alter the human germ plasma by design. But we may easily be doing so now by inadvertence, for many chemicals, like radiation, bring about gene mutations. It is ironic to think that man might determine his own future by something so seemingly trivial as the choice of an insect spray.⁵⁹ [Emphasis added.]

The remainder of the nearly 300 pages in Silent Spring consists largely of a litany of anecdotes—cases of environmental depredations trotted out one after the other to illustrate what Carson calls “a new kind of havoc”:

As man proceeds toward his announced goal of the conquest of nature, he has written a depressing record of destruction, directed not only against the earth he inhabits but against the life that shares it with him. The history of the recent centuries has its black passages—the slaughter of the buffalo on the western plains, the massacre of the shorebirds by the market gunners, the near-extermination of the egrets for their plumage. Now, to these and others like them, we are adding a new chapter and a new kind of havoc—the direct killing of birds, mammals, fishes, and indeed practically every form of wildlife by chemical insecticides indiscriminately sprayed on the land.

Under the philosophy that now seems to guide our destinies, nothing must get in the way of the man with the spray gun.⁶⁰

And so, for example, readers of Chapter 6, “Earth’s Green Mantle,” are regaled with this vivid anecdote:

The spraying [to clear roadside brush] is not only improperly planned but studded with abuses such as these. In a southern New England town one contractor finished his work with some chemical remaining in his tank. He discharged this along woodland roadsides where no spraying had been authorized. As a result the community lost the blue and golden beauty of its autumn roads where asters and goldenrod would have made a display worth traveling far to see.⁶¹

Chapter 8, “And No Birds Sing,” cites more than 40 cases in which birds allegedly succumbed to man-made poisons, including the following:

During the winter of 1957–1958, Dr. Wallace saw no chickadees or nuthatches at his home feeding station for the first time in many years. Three nuthatches he found later provided a sorry little step-by-step lesson in cause and effect: one was feeding on an elm, another was found dying of typical DDT symptoms, the third was dead. The dying nuthatch was later found to have 226 parts per million of DDT in its tissues.⁶²

Silent Spring’s anecdotes, of course, are not limited to instances of environmental damage. In Chapter 14, “One in Every Four,” Carson trots out numerous cases, such as the following, in which exposure to DDT and other toxic chemicals allegedly caused serious health problems:

Such word-famous institutions as the Mayo Clinic admit hundreds of victims of these diseases of the blood-forming organs [that is, leukemia]. Dr. Malcolm Hargraves and his associates in the Hematology Department at the Mayo Clinic report that almost without exception these patients have had a history of exposure to various toxic chemicals, including sprays which contain DDT, chlordane, benzene, lindane, and petroleum distillates.⁶³

When Unintended Consequences Undermine a principle

The great irony, of course, is that deployment of the precautionary principle can itself lead to damaging consequences. Frank Cross has described this “dark side”:

The truly fatal flaw of the precautionary principle . . . is the unsupported presumption that an action [that is, a regulatory action] aimed at public health protection cannot possibly have negative effects on public health. Yet these unanticipated adverse effects are demonstrably common. . . . Because the precautionary principle counsels for action against even those uncertain hazards that might be nonexistent, the presence of real adverse health effects consequent to that action means that regulation will often cause more health harm than good.⁶⁴

In arguing that the precautionary principle can backfire badly— endangering instead of safeguarding the environment and public health—Cross cites some instructive examples:

• The 1984 ban on the fumigant ethylene dibromide resulted in increased public exposure to aflatoxin, a mold-produced food contaminant estimated to be 1,000 times more carcinogenic than ethylene dibromide.

• Greenpeace campaigned in the early 1990s for a ban on all uses of chlorine, in part because chlorination of drinking water forms small amounts of carcinogenic trihalomethanes. Peru responded to the chlorine scare by halting the chlorination of many of the country’s water supplies. That decision—made in an effort to prevent “a handful of purely speculative cancer cases”—caused one of Latin America’s worst cholera epidemics, when more than 1.3 million people contracted cholera and at least 11,000 died from the infection.⁶⁵

Most ironic of all, however, Cross cites the precautionary bungle whose unintended consequences may have caused more deaths than any other. That was the 1972 decision by EPA Administrator William Ruckleshaus to ban the use of DDT, the pesticide at the scientific and emotional center of Silent Spring itself:

Countries around the globe had used DDT to eradicate or at least control insect-borne diseases, particularly malaria. These countries followed U.S. action in prohibiting or restricting the use of DDT. At the time of the ban, malaria was close to being eradicated. Malaria experienced a resurgence after DDT was banned and currently causes millions of deaths each year throughout the world. This mortal enormity is at least partially attributable to the decision to prohibit the use of DDT.⁶⁶

The Tragedy of Eradicating DDT Instead of Mosquitoes

“There was once a town in the heart of America where all life seemed to live in harmony with its surroundings,” Silent Spring’s first chapter famously begins. But by the next page, the idyllic had become the apocalyptic:

Then a strange blight crept over the area and everything began to change. Some evil spell had settled on the community: mysterious maladies swept the flocks of chickens; the cattle and sheep sickened and died. Everywhere was a shadow of death. The farmers spoke of much illness among their families. In the town the doctors had become more and more puzzled by new kinds of sickness appearing among their patients. There had been several sudden and unexplained deaths, not only among adults but even among children, who would be stricken suddenly while at play and die within a few hours. . . . No witchcraft, no enemy action had silenced the rebirth of new life in this stricken world. The people had done it to themselves.⁶⁷

Although, in succeeding chapters, Carson describes numerous chemicals that could be implicated in the health and environmental degradation that enveloped this fictional town—most notably a plethora of pesticides including dieldrin, endrin, heptachlor, lindane, and parathion—by the book’s end there is little doubt that DDT is the prime suspect. DDT is discussed on 51 of Silent Spring’s 297 pages—far more than any other chemical in the book. Almost overnight, DDT went from being considered a public health savior— its mosquito-killing ability credited with preventing millions of malaria deaths worldwide since the end of World War II—to being public enemy number one.

Some 10 years after Silent Spring’s publication, what may have been the first use of the precautionary principle in a legal setting in the United States came during the DDT cancellation hearings that preceded the pesticide’s ban. After a federal court canceled all uses of DDT in the United States, a group of chemical manufacturers asked for a hearing to plead its case. Between August 1971 and March 1972, expert witnesses and lawyers representing chemical companies and their environmentalist opponents appeared before a hearing examiner, where they produced about 9,000 pages of testimony. Twenty-seven manufacturers, USDA, and several agricultural users defended DDT, while EPA, the Environmental Defense Fund, the Sierra Club, the National Audubon Society, and the Western Michigan Environmental Action Council argued against the insecticide. Using money from a fund Carson had provided in her will, the Audubon Society helped finance the “prosecution’s” case.

This “trial of DDT” is vividly described in The Gentle Subversive: Rachel Carson, Silent Spring, and the Rise of the Environmental Movement, a sympathetic book by Mark Hamilton Lytle about Rachel Carson’s life and influence:

Each side presented its evidence and then faced hostile cross-examination from opposing attorneys. The burden of proof lay with the industry and its allies, who had to establish that DDT was not harmful to animals, to consumers, or to those who applied it. Most contentious was the question of whether DDT caused cancer or other human health problems. A lesser issue arose about whether DDT was needed to control disease-bearing insects.⁶⁸ [Emphasis added.]

DDT’s supporters managed to meet the high standard of proof required of them. As Ronald Bailey noted in “Silent Spring at 40”:

After listening to that testimony, the EPA’s own administrative law judge declared, “DDT is not a carcinogenic hazard to man. . . . DDT is not a mutagenic or teratogenic hazard to man. . . . The use of DDT under the regulations involved here [does] not have a deleterious effect on freshwater fish, estuarine organisms, wild birds or other wildlife.⁶⁹

In his decision to permit DDT’s continued use in the United States, the judge noted that evidence suggesting possible risks from the use of DDT must be weighed against “the well documented proof of the benefits that DDT has bestowed on mankind.”⁷⁰

In June 1972, Ruckelshaus overruled EPA’s administrative law judge and banned the use of DDT in the United States. His final order had “precautionary principle” written all over it: “The evidence of record showing storage [of DDT] in man and magnification in the food chain is a warning to the prudent that man may be exposing himself to a substance that may ultimately have a serious effect on his health.”⁷¹

Ultimately, it was the judge—and not Ruckelshaus—who was correct about DDT and its alleged risks. Virtually everyone now agrees that DDT can harm certain bird species: its magnification up the food chain does cause thinning to occur in the eggs of raptors (including the bald eagle, the peregrine falcon, and the osprey), resulting in a decline in the numbers of those birds. But despite intensive research, little evidence has turned up to support Carson’s contention that DDT poses dangers to people, as even her supporters have acknowledged: “Carson strongly believed that DDT would be proven harmful to human beings, but this has not yet been borne out by research.”⁷²

The ban on DDT’s use in the United States fulfilled one of Rachel Carson’s main goals in writing Silent Spring. It was “celebrated by many environmentalists as one of the twentieth century’s greatest environmental victories.”⁷³ But in retrospect, the DDT ban constitutes one of Silent Spring’s most unfortunate legacies, as Donald Roberts and Richard Tren vividly describe in this volume.

Not content with a ban on DDT’s use in the United States, environmentalists mounted a campaign for a worldwide ban. And even though malaria had staged a comeback in many parts of the developing world, an international agreement aimed at phasing out DDT’s use worldwide was reached in December 2000 under the auspices of the United Nations Environmental Programme. As Goklany notes, the rationale offered for a global DDT ban was that “the Precautionary Principle requires it.”⁷⁴

Thanks to a compromise with developing countries still using DDT to control malaria, the global DDT ban has not been implemented. But even in the absence of an “official” ban, Silent Spring’s success in demonizing DDT has sharply curtailed the pesticide’s global use, allowing malaria cases to surge:

We know that whatever harm DDT may have caused, ceasing its use in many countries was absolutely catastrophic. Well-documented is the case of Sri Lanka, in which 2.8 million malaria cases per year in 1948 dwindled to but 17 cases after fifteen years of DDT spraying. But after spraying was stopped in 1964, as a direct result of Carson’s book, malaria cases quickly shot back up to almost their original level.⁷⁵

About 250 million people now contract malaria each year and nearly one million people die from the disease. The vast majority of malaria cases and deaths occur in developing countries—mainly because use of DDT has helped in almost completely eliminating malaria from the developed world. As Goklany stresses in his book, a rational use of “precaution” in guiding a decision on a global DDT ban would involve balancing costs and benefits:

[P]rohibiting DDT use worldwide would most likely lead to substantial net increases in death and disease because the net harm caused by such a ban in the developing countries far outweighs its net benefits in the developed world. The harms are greater in magnitude and more certain and are likely to occur more rapidly than the benefits. Thus, under the Precautionary Principle, there ought not to be a global ban on DDT use.⁷⁶

Goklany goes on to note that an even better case can be made for banning DDT in developed countries while permitting its continued use as an indoor spray in countries where malaria remains a threat. “Specifically,” he says, “the Precautionary Principle supports a two-tiered approach toward DDT; that is, the policy for countries where malaria has been eradicated is different from that for countries where malaria is still prevalent or threatens to make a comeback.”⁷⁷

Unfortunately, Goklany’s vision of a wisely used precautionary principle is far removed from the principle defined in the Wingspread Consensus Statement. As was true of Silent Spring, the precautionary principle ignores the benefits inherent in the chemicals and technologies that it targets. DDT may be the most extreme example of damage from the precautionary principle. But unless its influence is curtailed, this principle that was created “to protect human health and the environment” can be expected to cost many more lives in the future.

Just as a parent and child share certain traits, Silent Spring and its offspring, the precautionary principle, are examples of the seductive— and ultimately destructive—power of seemingly reasonable proposals for minimizing harm and improving health. In the case of Silent Spring, an acclaimed author was making an argument that, on its surface, was logical in the extreme: Since herbicides and insecticides kill weeds and insects, those chemicals must also pose a threat to humans and other nontarget organisms inevitably exposed to them; therefore, banning those chemicals will serve the interests of people and their environment. But as we know, Silent Spring’s most notable “accomplishment”—the ban on DDT’s use in the United States and its pariah status in the rest of the world—may well have led to millions of deaths from malaria and other insect-borne diseases. The precautionary principle, with its patina of “better safe than sorry,” is similarly appealing. After all, what could be the harm in preventing the use of a technology that could pose serious risks to public health and the environment? But, as this chapter has shown, regulations guided by the precautionary principle can actually backfire badly.

Silent Spring and the precautionary principle teach us that translating popular and appealing ideas into policy can lead to serious unintended consequences. This was illustrated most recently by the public-health debacle in which life-saving childhood vaccines were falsely linked to autism, causing vaccination rates to drop⁷⁸ and measles outbreaks to occur.⁷⁹ Clearly, this is a lesson that we ignore at our peril.

“Look before you leap,” the precautionary principle urges. By the same token, society must constantly guard against the principle’s siren song. Whenever the principle is invoked to justify regulatory action, we must examine such proposals scientifically and objectively so that unintended consequences can be avoided.