ec3545handout10

Pollution, Pesticides, and Cancer Prevention: Misconceptions

There is, increasingly, in the U.S. (and perhaps elsewhere) a growing fear, a fear that I call "microchemophobia;" moreover, we may be entering an era when scientists are having less impact on important policy decisions (e.g. nuclear power) than are those without particular expertise in the area who happen to be more savvy with politics and media manipulation. In the present context, over the years I have repeatedly found that environmental economics students at C.U. enter my class with strongly-held beliefs that 1) cancer is a growing threat to mankind and 2) pollution, pesticides, food additives and other "synthetic chemicals" are the principle cause of the cancer epidemic. I am not sure why these beliefs are so strongly held (brainwashing?) but it turns out that both beliefs are demonstrably wrong.
Most of the material of this handout is paraphrased (or quoted) from Bruce N. Ames and Lois Swirsky Gold, "Environmental Pollution, Pesticides, and the Prevention of Cancer: Misconceptions," (FASEB Journal, July 21, 1997--modified from testimony on 3/6/97 for the U.S. Senate Hearing on Environmental Risk Factors for Cancer). Ames is Professor of Biochemistry and Molecular Biology and Director of the National Institute of Environmental Health Sciences Center, University of California, Berkeley (see his web site under "Bruce Ames"). His 380 publications have led to his being the 23rd most-cited scientist in all fields. Gold is Director of the Carcinogenic Potency Project at the National Institute of Environmental Health Sciences Center, U.C., Berkeley. Ames in particular is the "real deal" in terms of his qualifications and expertise--if you disagree with much of the following, be prepared to defend your position with research published in top, peer-reviewed journal articles! I would, of course (I want to know the "truth" insofar as it is knowable), welcome course papers taking issue with any of the following contentions.

The major causes of cancer are smoking (1/3 of U.S. cancer--90% of lung cancer--and 1/4 of heart disease; 400,000 premature deaths each year from this source), dietary imbalances (1/3 of U.S. cancer--especially lack of fruits and vegetables, with quarter of population having least fruits and vegetables having twice the cancer risk of the top quarter; only 22% of Americans get the recommended 5 servings of fruits and vegies daily), chronic infections (9% in developed world, but 20% in undeveloped countries), hormonal factors (primarily life-style--lack of exercise, obesity, alcohol affect hormone levels, hence risk; synthetic chemicals trivial contributors), and other (excess alcohol, sun, viruses, genetic factors that interact with the preceding).
There is no epidemic of cancer, except for lung cancer due to smoking (and cancers related to deliberate sun exposure). Cancer mortality rates (age-adjusted) have declined 16% since 1950. Some of the most dramatic declines have occurred in the 1990s.
Regulatory policy focusing on traces of synthetic chemicals is based on misconceptions about animal cancer tests. In particular: a) rodent carcinogens are not rare, with half of all chemicals tested in standard high dose animal cancer tests, whether occurring naturally or produced synthetically, testing as "carcinogens." b) there are high-dose effects in rodent cancer tests that are not relevant to low-dose human exposures and which contribute to the high proportion of chemicals that test positive. c) the focus of regulatory policy is on synthetic chemicals (77% of tests), although 99.9% of the chemicals humans ingest are natural--e.g. coffee has over 1,000 chemicals in it; of the 28 that have been tested, 19 are rodent carcinogens (and, of course, plants in the human diet contain thousands of natural pesticides which protect them from insects and other predators: 63 have been tested and 35 are rodent carcinogens).
There is no convincing evidence that synthetic chemical pollutants are important for human cancer (e.g. we are exposed to 0.09mg/day of the 200 "worst" synthetic chemicals (a single cup of coffee gives a year's worth of equivalent known rodent carcinogens--and only 3% of the chemicals in coffee have been tested!). We receive 10,000 times the exposure to natural pesticides (1.5gm/day) and cooking food adds another 2gm/day in carcinogens and mutagens! Of particular note to environmental economics: median toxic control program costs 146 times more per life year saved than the median medical intervention and, importantly, if we are successful at reducing synthetic pesticides but that raises the prices of fruits and vegetables, consumption of fruits and vegetables will fall increasing cancer, particularly among the poor.
"Prevention of cancer will come from knowledge obtained from biomedical research, education of the public, and from lifestyle changes by individuals. A re-examination of priorities in cancer prevention, both public and private, seems called for."