Rachel Was Wrong

Rachel Carson’s Silent Spring ushered in an era of national concern over the potential effects of synthetic chemicals. Published in 1962, Carson’s book suggested that the human use of synthetic chemicals amounted to a "relentless war on life" and that modern society was "losing the right to be called civilized." Americans experienced widespread angst over the potential carcinogenic effects of chemicals over the subsequent decades. As it turns out, Rachel Carson was wrong.

Last month, the National Research Council, the research arm of the National Academy of Sciences, released a report on carcinogens in the human diet. Over thirty years after Silent Spring’s publication, a wealth of scientific evidence suggests that many of the concerns Carson raised were unfounded.

Plants have evolved numerous chemicals that serve as defensive agents against predators. Some kill predators outright, others act as deterrents in some fashion. Many of these substances can be considered natural pesticides, and are quite common. These chemicals are likely present in our diet in amounts exceeding the residues of synthetic pesticides.

Nearly a decade ago Bruce Ames, of the University of California at Berkeley, began to point out that many naturally occurring chemicals tested positive for carcinogenicity in lab tests on rodents. In fact, the percentage of naturally-occurring chemicals identified as "carcinogenic" in rodent bioassays does not differ significantly from that of synthetic chemicals. This led Ames to the conclusion that insofar as there was a cancer risk in the human diet, it was more likely the result of naturally-occurring chemicals than synthetics. There are after all, many more naturally occurring chemicals than synthetic. More importantly, Ames posited that the cancer threat posed by food was likely small to nonexistent. The NAS report confirmed the Ames thesis.

The NAS study concluded that based upon existing exposure data, the great majority of naturally occurring and synthetic chemicals in the diet appear to be present at levels below which any significant adverse biological effect is likely. So low, in fact, that they are unlikely to pose any appreciable cancer risk whatsoever.

The study also concluded that natural components of the diet may prove to be of greater concern than synthetic components with respect to cancer risk. Synthetic chemicals account for a tiny fraction of the daily dietary intake of substances that have been labeled carcinogens in lab tests. Because of the greater abundance of naturally-occurring substances in the diet, the total exposure to naturally-occurring carcinogens far exceeds the exposure to synthetic carcinogens.

Another finding of the NAS study was that the basic mechanisms involved in the entire process of cancer — from exposure of the organism to expression of tumors — are similar, if not identical for synthetic and naturally occurring carcinogens. The NAS study concluded that there was no notable difference between synthetic and naturally occurring carcinogens. The argument made by many environmentalists that the human body has evolutionary defenses against natural carcinogens, but not against synthetic ones, does not hold water.

Despite the strong scientific consensus that underlies the NAS report, many environmentalists (who have made their careers opposing the trace levels of pesticides on foods) still can’t seem to believe it. Al Meyerhoff, senior attorney for the Natural Resources Defense Council told the New York Times that despite the report, synthetic chemicals "can still cause thousands of cancers in consumers, and they should be avoided whenever possible." Psychologists usually refer to this as denial.

The NAS study reviewed the issue of how many cancers might be caused by carcinogens in the diet. In citing one study the authors acknowledged that "except for alcohol, the known dietary carcinogens could not account for more than a few hundred cancer cases." This amounts to less than 0.01 percent — one ten-thousandth — of all cancers. What actually does cause cancer, if not pesticide residues and other chemicals, is not earth shattering news. Smoking, excessive alcohol consumption, and over eating were listed as the biggest contributors to an increased cancer risk.

But just when you thought it was safe to go back into the supermarket, environmentalists have created another environmental affliction. Using cancer as a scare tactic appears to be waning, so environmentalists have latched onto a new cause celebré — endocrine disrupters.

The new theory is that certain synthetic chemicals, such as DDT, PCBs, various organochlorines and other synthetic chemicals, mimic estrogen or other hormones and can interfere in human development and reproduction. Among the charges made is that these chemicals are responsible for a global decline in human sperm counts — even though there is no conclusive evidence that sperm counts are declining.

This collective hypochondria is laid out in the new book by World Wildlife Fund Senior Scientist Theo Colburn, environmental writer Diane Dumanowski, and W. Alton Jones Foundation Director John Peterson Myers. Their collective angst is ominously entitled, Our Stolen Future.

Unfortunately for the proponents of synthetic endocrine disruption, mother nature has already beaten them too it. Just as they produce carcinogens, a large number of plants routinely produce significant quantities of hormone mimicking chemicals. The human diet is simply filled with foods that contain naturally-occurring endocrine disrupters from genestein in soybeans to cafesterol in coffee.

Given the wealth of human exposure to these substances, if there were widespread human effects, the world would have seen them by now. The lack of compelling data suggests that the kids are all right, and there is no cause for alarm. The issue of endocrine disruption clearly warrants further study, but not the sort of hysteria routinely ginned up by environmental activists.

Let’s just hope that it doesn’t take science 30 years to do for concerns about endocrine disrupters what it did for concerns about cancer.

Jonathan Tolman’s CEI study "Nature’s Hormone Factory: Endocrine Disrupters in the Natural Environment" is available from CEI for $6.00.