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Synthesis/Regeneration 31   (Spring 2003)

Adverse Medical Effects of Pesticides

by Daniel McKeel, MD,
Washington University School of Medicine

The unfortunate practice about which I am writing is the excess aerial spraying from trucks of pesticides such as permethrin, sumithrin, DEET and the synergist, PBO or piperonyl butoxide. The latter agent, PBO, inhibits liver detoxifying enzymes and thus markedly prolongs the primary pesticide effects on the body. PBO is suspected of causing anorexia (loss of appetite), coma, convulsions, possibly cancer, skin irritation, liver and kidney damage, prostration due to circulatory collapse, tearing of the eyes, unsteadiness, vomiting and weight loss. Liver and kidney damage are the chronic effects of PBO.

Children who are chronically exposed to pesticides suffer brain damage that impairs their ability to learn.

Using these “safe” pesticides is far from innocuous, despite some claims by the manufacturer’s and agencies that conduct the massive mosquito spraying campaigns. [1] In addition, the toxic compounds are not the most effective way to control culex vector populations. The pesticides of concern also are extremely toxic to fish and some bird species.

In the case of massive aerial pesticide spraying and West Nile virus diseases, truly, the “cure” is worse than the disease. The benefit-to-risk ratio of massive spraying to control culex is low compared to other more effective methods such as the elimination of mosquito breeding areas such as standing water. Remember also that less than 1% of people who are exposed to West Nile Virus ever develop any symptoms at all. Many persons with WNV have a very mild, self-limited illness that requires no specific medical treatment at all. The cases of serious WNV illness that require hospitalization are therefore a very small percentage of total infected cases. To put the WNV epidemic in perspective, as of September 4, 2002, the CDC in Atlanta reported 2,121 human cases of WNV and 95 deaths during all of 2002; a mortality rate of 4.5%.

...truly, the “cure” is worse than the disease.

The estimated number of pesticide deaths in the US is considerably higher on an annual basis. Much of the acute toxicity data on pesticides comes from worker illnesses and deaths during the manufacturing process.

Pesticides cause serious skin irritation to at least 30% of people who use them. Other known acute health effects of pesticides include exacerbation of asthma, induction of seizures with large overdoses (with resulting death in 30% of cases in children), headaches, nausea and vomiting.

The class of pesticides used to mosquitoes are also suspected of being possible carcinogens by impairing the function of bodily immune defenses. Estrogenic effects may contribute to breast cancer and infertility in adult women.

What about more chronic effects of pesticide exposure? Children and elderly adults are especially vulnerable to the long-term detrimental effects of pesticides. [2] The longer-term general problem with the toxic pesticides and synergists is that they gain access to lipid deposits in the subcutaneous fat and in the myelin component of the central nervous system.

Once the lipophilic fat-seeking toxins infiltrate lipid-rich organs and tissues, the health effects are long lasting. This is in sharp contradiction to popular ads from pesticide vendors which imply the pesticides are completely safe for common local use on skin. Children who are chronically exposed to pesticides suffer brain damage that impairs their ability to learn during their formative school years.

These chronic effects are similar to those caused by chronic lead exposure in the children in Herculaneum, Missouri, living near the Doe Run lead smelter. They begin insidiously and the child may be considered dull, or inattentive, or just a “slow learner” by their teachers, friends and parents. The only way to tell what is wrong is by giving them detailed neurologic examinations and using behavioral testing methods that are often costly and not widely available or known about. Once the cognitive deficit is obvious, it is probably too late to reverse the damage.

Why do I say this? Because there is an even more sinister side to chronic pesticide over-exposures. Dr. Philip Landrigan, a prominent researcher at the Center for Children’s Health and the Environment, points out that each year 2,000 to 3,000 new chemicals are brought to EPA for review prior to manufacture. [3] Also, 15,000 chemicals are produced in quantities greater than 10,000 pounds per year. An amazing 2,800 chemicals are produced in quantities greater than one million pounds per year.

Only 43% of high volume chemicals have been tested for human toxicity, and only 7% are ever screened for possible adverse behavioral effects such as learning disabilities due to brain dysfunction. In addition, the combined effects of simultaneous overexposure to even 2 or 3 chemical toxins such as pesticides is particularly difficult to study. The difficulty of identifying individual bad effects of each separate toxin seriously impairs our ability to learn about them.

Based, therefore, on the large body of medical evidence that pesticides of the type being used in massive amounts to attempt to control Culex and West Nile Virus related diseases cause acute and chronic harm to humans, I would argue that the “cautionary principle” should prevail. When one further considers that the Centers for Disease Control in Atlanta does not recommend massive aerial “adulticide” pesticide spraying, the case is strong against the widespread “pump and dump” spraying practices that are rampant in many towns.

Daniel McKeel, M.D., is a practicing physician and an anatomic pathologist and a member of the Barnes-Jewish Hospital Infection Surveillance committee. Dr. McKeel is also an Associate Professor of Pathology and Immunology at the Washington University School of Medicine where he has been on the faculty since 1974.


1. See http://www.safe2use.com/poisons-pesticides/inerts/piperonyl-butoxide.htm.

2. Bruckner, James V., Differences in sensitivity of children and adults to chemical toxicity: The NAS panel report. Regulatory Toxicology and Pharmacology, 31: 280–285, 2000.

3. Landrigan, Philip J., Minireview: Pesticides and polychlorinated biphenyls (pcbs): an analysis of the evidence that they impair children’s neurobehavioral development, Molecular Genetics and Metabolism, 73: 11–17, 2001.

[21 apr 03]

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