Sanet Post, Charles Benbrook
Response to Dale re Pesticides and Cancer
March 6, 1999
Dale Wilson's post on March 4 raises questions with the "conventional wisdom" on pesticide exposure and cancer. He did a literature search and got 153 hits; reviewed a subset of 70 abstracts. Based on his review he says "the evidence doesn't look that strong." He also did a literature search on immunosuppression and states "I could not find any epidemiological evidence of immunosuppression among ag workers."
Last, he concludes on the basis of his rather narrow -- and as shown below inadequate -- literature search that risks of injury to farmers, and respiratory problems are much more serious than pesticide-based risks.
This kind of cursory dismissal of pesticide risks is fashionable and seductive. It is repeated so often in ag circles that many people have begun to assume it must true. Indeed, it has become "conventional wisdom" and is a part of the mythology of agriculture that frustrates efforts to bring good science and reason to managing risks. The ag community has got to get beyond denial and become more familiar with the enormous science base that leads many people with no axe to grind with farmers to conclude prudent steps should be taken to reduce use/exposure to high risk pesticides.
I urge Dale to think a little more deeply about this topic, after becoming more familiar with the literature. Dale missed several thousand citations in his searches, which together constitute overwhelming evidence and agreement that pesticide exposure increases cancer risk, and that pesticide impacts on the immune system are no doubt a major mechanism leading to elevated risk factors. There is essentially no debate anymore in the toxicology community over these facts; the issues/debates involve specific cause-effect relationships and how significantly pesticide exposures (and which ones, and when) contribute to elevated cancer risks. Obviously there are huge gaps in information and no practical way to affirmatively coax out some of the linkages. And people disagree about how society should balance the benefits of pesticides with the risks they pose. These issues will never be easy to work through, but having a working understanding of the science at least helps lessen the chance of making a really bad decision.
The Blair abstract below states as directly as possible the Nat. Cancer Institute's "official" view on pesticide and cancers. It is a little dated (1995), more recent studies simply strengthen the associations. I have included a few other abstracts from Medline to give a feel for the literature.
Search on "pesticides and cancer" in the last 5 years, you get 266 citations; thousands if you go back 20 years to when cancer testing got underway.
Search on "pesticide* and immune*" you get 50 citations in last 5 years. The World Resources Institute overview of pesticides-immunotoxicity found several hundred citations worldwide. The literature is exploding in this area and the new evidence is indeed worrisome for some classes of pesticides.
Last, Dale is willing to make a leap from his, and the scientific community's current understanding of pesticide health effects to the conclusion that known, easily recorded accidental risks faced by farmers are far greater than the often hard to detect impacts of pesticide exposures. Others are not willing to make this leap. I hope Dale is right but fear he may not be.
Assessing relative risks is tricky since there are differing levels of scientific certainty in risk assessments, very different populations at risk, and the impacts on people's lives of different risks vary greatly. Some 2-3 million folks are at risk to farm accidents; the people exposed to onfarm risks have control/power over steps taken to avoid risks, and bear the responsibility, and harm, if they are not careful.
The whole population is exposed to pesticides in food, and a significant portion is also exposed through water, air and occupationally. The general public has little control over most dietary/water based exposures, and enjoys none of the "direct" economic benefits of pesticides. Sorting out what is "right" and defensible scientifically is very complex in this arena -- we do no favors by asserting this is easy or obvious.
Many in the agricultural community discount risks in the absence of definitive, simple, direct cause-effect proof. This judgement/attitude basically writes off serious inquiry of the role of pesticide exposures in the majority of adverse health effects suffered by humans, from cancer to birth defects, to immune system, reproductive and neurological problems. This is perhaps comforting to farmers and those who are convinced pesticides are always safe, but that does not make it right. I personally believe farmers, their families, farm workers, and rural neighbors are innocent victims of the need for the "system" to discount pesticide risks.
The NCI "Agricultural Health Study" is starting to produce results, which I am told are going to rather dramatically expand the range of health effects correlated to pesticide exposures and also strengthen past associations in the literature. I will update the list as I learn of the results.
chuck benbrook
Environ Health Perspect 1995 Nov;103 Suppl 8:205-8
Agricultural exposures and cancer.
Blair A, Zahm SH
Occupational Studies Section, National Cancer Institute, Bethesda, Maryland, USA.
The purpose of this report is to review the literature on cancer among persons employed in agriculture, to characterize the value of this line of research, and to recommend future directions. Farmers, despite a generally favorable mortality, appear to experience elevated rates for several cancers, including leukemia, non-Hodgkin's lymphoma, multiple myeloma, soft-tissue sarcoma, and cancers of the skin, lip, stomach, brain, and prostate. The rates for several of these tumors (i.e., non-Hodgkin's lymphoma, multiple myeloma, skin, brain, and prostate) appear to be increasing in the general population. No set of established etiologic factors explains all the cancer excesses observed among farmers, although several are associated with naturally occurring or medically induced immunodeficiencies. This suggests that there may be factors in the agricultural environment that introduce immune system deficiencies. Farmers are exposed to a variety of substances that could operate through this mechanism, including pesticides, engine exhausts, solvents, dusts, and zoonotic microbes. Studies to further characterize the cancer risk among farmers, their dependents, and farm laborers, and to identify the exposures that may be involved would not only be useful in providing a safe work environment in agriculture but may furnish considerable insight into the causes for a number of tumors that are rising in incidence in the general population.
Occup Med 1997 Apr-Jun;12(2):269-89
Pesticides and cancer.
Zahm SH, Ward MH, Blair A
Occupational Epidemiology Branch, National Cancer Institute, Rockville, Maryland 20892-7364, USA.
Last Updated on 3/7/99
By Karen Lutz
Email: karen@hillnet.com