The End of Doom (17 page)

Similarly, the British organization Cancer Research UK observes that for most people “harmful chemicals and pollution pose a very minor risk.” How minor? Cancer Research UK notes, “Large organizations like the World Health Organization and the International Agency for Research into Cancer have estimated that pollution and chemicals in our environment only account for about 3 percent of all cancers. Most of these cases are in people who work in certain industries and are exposed to high levels of chemicals in their jobs.” Like the American Cancer Society, Cancer Research UK advises, “Lifestyle factors such as smoking, alcohol, obesity, unhealthy diets, inactivity, and heavy sun exposure account for a much larger proportion of cancers.”

These statements by the American Cancer Society and Cancer Research UK mirror the findings of
Carcinogens and Anticarcinogens in the Human Diet,
the definitive 1996 report from the National Academy of Sciences. The NAS concluded that levels of both synthetic and natural carcinogens are “so low that they are unlikely to pose an appreciable cancer risk.” Worse yet from the point of view of anti-chemical crusaders, the NAS added that Mother Nature's own chemicals probably cause more cancer than anything mankind has dreamed up: “Natural components of the diet may prove to be of greater concern than synthetic components with respect to cancer risk.”

In
Silent Spring
Carson cites data showing that American farmers were then applying about 637 million pounds of pesticides to their crops. The most recent Environmental Protection Agency estimate is that farmers used 1.1 billion pounds in 2007. (The amount of insecticide applied to crops has been falling recently, as farmers adopt genetically enhanced insect-resistant crop varieties.)

What factors really do increase cancer risk? Smoking, drinking too much alcohol, sunburns, and eating too much food. In fact, while overall cancer incidence has been falling, cancers related to obesity—that is to say, pancreatic, liver, and kidney cancers—have risen slightly.

The DDT Ban: Environmentalism's First Triumph

The first notable triumph of modern environmentalism occurred in 1972—the banning of the pesticide that Carson so abhorred, DDT.

In 1967, the activist group the Environmental Defense Fund began bringing lawsuits against the manufacturers of DDT and agitating for bans on the pesticide in various state legislatures. By 1971, the first administrator of the newly created Environmental Protection Agency, William Ruckelshaus, ordered a hearing to look into the claims against DDT. After seven months of hearings, which produced 9,362 pages of testimony by 125 witnesses, EPA judge Edmund Sweeney ruled, “DDT is not a carcinogenic hazard to man … is not a mutagenic or teratogenic hazard to man … [and 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.”

But EPA administrator Ruckelshaus overruled Sweeney and banned DDT on January 1, 1972. Later Ruckelshaus would justify his actions by declaring, “The ultimate judgment [on DDT] remains political. Decisions by the government involving the use of toxic substances are political with a small ‘p.' In the case of pesticides in our country, the power to make this judgment has been delegated to the Administrator of the Environmental Protection Agency.” Ruckelshaus also noted in his decision that “Public concern over the widespread use of pesticides was stirred by Rachel Carson's book,
Silent Spring
.” Unfortunately, Ruckelshaus's decision set a deleterious precedent: politics and panic have figured hugely in environmentalist campaigns and regulation ever since.

Carson described the choice humanity faced as a fork in the road to the future. “The road we have long been traveling is deceptively easy, a smooth superhighway on which we progress at great speed, but at its end lies disaster,” she declared. “The other fork of the road—the one ‘less traveled by'—offers our last, our only chance to reach a destination that assures the preservation of our earth.” This kind of apocalyptic rhetoric is now standard in today's policy debates. In any case, the opposition to
Silent Spring
arose not just because Carson was attacking the self-interests of certain corporations (which she certainly was), but also because it was clear that her larger concern was to rein in technological progress and the economic growth it fuels.

Through
Silent Spring,
Carson provided those who are alienated by modern technological progress with a model of how to wield ostensibly scientific arguments on behalf of policies and results that they prefer for other reasons. “The hostile reaction to
Silent Spring
contained the seeds of a partisan divide over environmental matters that has since hardened into a permanent wall of bitterness and mistrust,” writes Souder. He adds, “There is no objective reason why environmentalism should be the exclusive province of any one political party or ideology.” That conclusion is flatly wrong.

It is this legacy of public policy confirmation bias that Yale law professor Dan Kahan and his research colleagues are probing at the Yale Cultural Cognition Project. In a recent study concerning how Americans perceive climate change risk published in
Nature Climate Change
, Kahan and his colleagues find that people listen to information that reinforces their values and ignore that which does not. They observe that people who are broadly identified as being on the political left “tend to be morally suspicious of commerce and industry, to which they attribute social inequity. They therefore find it congenial to believe those forms of behavior are dangerous and worthy of restriction.” On the other hand, those broadly considered as being on the political right are proponents of technological progress who worry about “collective interference with the decisions of individuals” and “tend to be skeptical of environmental risks. Such people intuitively perceive that widespread acceptance of such risks would license restrictions on commerce and industry.”

As trust in other sources of authority—politicians, preachers, business leaders—has withered over the past fifty years, policy partisans are increasingly seeking to cloak their arguments in the mantle of objective science. However, the Yale researchers find that greater scientific literacy actually produces greater political polarization. As Kahan and his fellow researchers report, “For ordinary citizens, the reward for acquiring greater scientific knowledge and more reliable technical-reasoning capacities is a greater facility to discover and use—or explain away—evidence relating to their groups' positions.” In other words, in policy debates, scientific claims are used to vindicate partisan values, not to reach an agreement about what is actually the case. This sort of motivated reasoning applies to partisans of both the political left and right, and both learned it from Rachel Carson.

DDT and Birds

Rachel Carson heard and cited anecdotal reports of various birds either dying of acute DDT poisoning or experiencing reproductive problems, thus giving birth to her title conceit. Her book was a popular phenomenon, and not surprisingly her claims drew the attention of a lot of researchers.

The situation regarding the harm that DDT caused some bird species is not as straightforward as one might like. Science always deals with provisional conclusions. The main hypothesis is that exposure to DDT thinned the eggshells of birds, causing them to break before hatching. Not much scientific work has been done on eggshell thinning for the past three decades, so most of the relevant scientific literature is quite dated. The significant articles were published before 1980. “[The issue] kind of died out. There's a general lack of interest,” agreed Daniel W. Anderson. Anderson, at the Department of Wildlife, Fish, and Conservation Biology at the University of California at Davis, was one of the original researchers on eggshell thinning. He blames the lack of new research on a lack of funding. Besides, Anderson observes, “The questions about eggshell thinning were pretty well answered, so people moved onto other things.”

The DDT/eggshell thinning bandwagon got really rolling with two scientific articles. The first study, “Decrease in Eggshell Weight in Certain Birds of Prey,” by British Nature Conservancy researcher D. A. Ratcliffe, was published in
Nature
on July 8, 1967. Ratcliffe claimed that the incidence of broken eggs in the nests of peregrine falcons, sparrowhawks, and golden eagles had increased considerably since 1950. He compared eggshells collected before 1946 with eggshells collected afterward and found that the eggshells of post-1946 peregrine falcon weighed 19 percent less; those of sparrowhawks weighed 24 percent less; and those of golden eagles 8 percent less. Ratcliffe dismissed lack of food and radioactive contamination as explanations for the thinning, but noted “some physiological change evidently followed a widespread and pervasive environmental change around 1945–1947.… For the species examined, frequency of egg-breakage, scale of decrease in eggshell weight, subsequent status of breeding population, and exposure to persistent organic pesticides are correlated. The possibility that these phenomena are links in a causal chain is being investigated,” he concluded.

Those British results were soon bolstered by the study “Chlorinated Hydrocarbons and Eggshell Changes in Raptorial and Fish-Eating Birds,” published in an October 1968 issue of
Science,
and authored by Daniel Anderson and Joseph Hickey, both at the University of Wisconsin. “Catastrophic declines of three raptorial species in the United States have been accompanied by decreases in eggshell thickness that began in 1947, and have amounted to 19 percent or more, and were identical to phenomena found in Britain,” they declared. The three species were peregrine falcons, bald eagles, and ospreys. They claimed that the eggshell thinning coincided with the introduction of chlorinated hydrocarbon pesticides such as DDT, and concluded that these compounds were harming certain species of birds at the tops of contaminated food chains.

Still, the researchers just had a correlation between DDT and eggshell thinning. So some did what good scientists should do—they experimented. Joel Bitman at the US Department of Agriculture fed Japanese quail a diet laced with DDT. His study, “DDT Induces a Decrease in Eggshell Calcium,” published in
Nature
on October 4, 1969, found that the quail dosed with DDT had eggshells that were about 10 percent thinner than those of undosed quail. However, Bitman's findings were eventually overturned because he had also fed his quail a low-calcium diet. When the quail were fed normal amounts of calcium, the thinning effect disappeared. Studies published in
Poultry Science
found chicken eggs almost completely unaffected by high dosages of DDT.

It's not DDT per se that is thought to do the damage to eggshells, but a DDT metabolite known as DDE. Thus the most persuasive feeding study refers to it: “DDE-Induced Eggshell Thinning in the American Kestrel: A Comparison of the Field Situation and Laboratory Results.” This groundbreaking study was published in the
Journal of Applied Ecology
by Jeffrey Lincer in 1975.

Kestrels, commonly called sparrowhawks, are small falcons. Lincer noted that the “inverse correlation between DDE in North American raptor eggs and eggshell thickness is clear but does not prove a causal relationship since other chemicals or factors could be involved.” So to find out what effect DDE might have, Lincer fed captive kestrels a DDE-laced diet and then compared their eggs with those taken from the nests of wild kestrels. Lincer found that dietary levels of 3, 6, and 10 parts per million (ppm) of DDE resulted in eggshells that were 14 percent, 17.4 percent, and 21.7 percent thinner respectively. “Despite the recent controversy, there can be little doubt now as to the causal relationship between the global contaminant DDE and the observed eggshell thinning and the consequent population declines in several birds of prey,” concluded Lincer.

Still, there is a piece missing in the full scientific picture. Despite considerable research, no one has ever identified the physiological mechanism(s) by which DDE causes eggshell thinning, according to Anderson.

There is another possibly confounding issue as well. In 1998, Royal Society for the Protection of Birds researcher Rhys Green published a study in the
Proceedings of the Royal Society B
that found that eggshell thinning of some bird species had begun fifty years before the introduction of DDT.

On the contrary side are studies that showed that DDT did not cause eggshell thinning in chickens and Japanese quail. Anderson agrees that the evidence shows that gallinaceous birds (poultry and fowls), herring gulls, and most passerine birds “aren't as sensitive to DDE as raptors.” More than half of all bird species are passerine or perching birds, including crows, robins, and sparrows. But even though chickens and quail fed very high concentrations of DDE and an adequate amount of food experienced essentially no eggshell thinning or other reproductive problems, science shows pretty conclusively that it's another story for raptors.

Anderson notes that DDT and DDE levels in nature have been falling for decades. Populations of bald eagles, peregrine falcons, ospreys, and brown pelicans have all bounced back. In 1969, researchers reported finding total DDT accumulations ranging from 5,000 ppm to 2,600 ppm in the fat of North American peregrine falcons. Today, one would typically find 50 ppm in raptors, according to Anderson. Such body burdens would yield only about 2.5 ppm in eggs. Anderson notes that there appears to be a threshold of 1 to 3 ppm for DDE in eggs below which there is no eggshell thinning in even sensitive bird species. Dusting DDT on the walls of houses in developing countries to control for mosquitoes seems unlikely to cross that threshold for birds.

The Pesticide Fight Today

The environmentalists won the fight about DDT in America, so why is it still a sensitive political issue today? The main reason is the continuing fight to save millions of people from malaria. Whatever it does to different types of eggshells, DDT remains unquestionably one of the most effective ways to control the mosquitoes that carry the malaria parasite. Still, international environmentalists have instituted through the UN strict controls on DDT, with an eye on an eventual permanent ban.