Science and Law
22nd March 2013

Science Fails to Demonstrate Adverse Health Effects of Pesticides

The impending arrival of spring conjures up images of verdant lawns, robust gardens, and fresh summer fruits. But recent articles impugning the safety of pesticides make these harbingers of spring somewhat less appealing.

Science Fails to Demonstrate Adverse Health Effects of Pesticides

The impending arrival of spring conjures up images of verdant lawns, robust gardens, and fresh summer fruits. But recent articles impugning the safety of pesticides make these harbingers of spring somewhat less appealing. Before you buy into the notion that pesticides are hazardous, it’s important to conduct a thoughtful analysis of the scientific literature on the issue.

In one recent article, Mostafalou reviews the general evidence that pesticides potentially cause a cornucopia of health issues, including cancer, birth defects, reproductive disorders, Parkinson’s disease, Alzheimer’s, ALS, diabetes, cardiovascular disease, chronic nephropathies, and respiratory disease, among others. Based on this extensive list of adverse health claims, it appears that there is a great deal to worry about from pesticide exposure. Indeed, the article concludes: “The relationship between these diseases and environmental exposures, particularly pesticides, increasingly continues to strengthen.”

In another article, Ioannis focuses on the alleged connection between pesticides and dementia.The article concludes, “To this date several studies have provided evidence for an increasingly important epidemiological link between cognitive decline and pesticide exposure…”

Both articles conclude that pesticides pose a serious health risk to humans. However, neither piece offers an objective review of the available scientific literature. They selectively focus on research studies that support the relationship between pesticides and adverse health effects. They neglect to consider the substantial research that fail to report a connection.

In addition to focusing only on research that demonstrates a link between pesticides and adverse health effects, the articles review the theoretical (unproven) mechanism through which pesticides could cause adverse health effects. But they concede little is known about the mechanism.

Finally, both articles evaluate the various chemical ingredients in pesticides in animal studies. In general, animal studies evaluate much higher doses than people would be exposed to in the real world. Thus, studies of the type cited in the Mostafalou and the Ioannis papers make use of two different extrapolations: (1) assuming that data in animals can be extrapolated to humans; and (2) assuming that data from high dose exposures can be extrapolated to lower dose exposures. Indeed, EPA has stated:

“Pesticides are designed to (in most cases) kill pests. Many pesticides can also pose risks to people. However, in many cases the amount of pesticide people are likely to be exposed to is too small to pose a risk.”

 The authors of both articles failed to perform a systematic analysis of the evidence, known as a “systematic review” or “weight of the evidence” analysis. A critical feature of this approach is that all of the evidence is identified and collected systematically, according to specific rules.

When the evidence is evaluated systematically according to an objective set of criteria, quite a different picture emerges. For example, investigators at Mt. Sinai School of Medicine recently performed a weight of the evidence analysis on the carcinogenicity of one commonly used herbicide, atrazine. In their abstract, they state:  “A weight-of-evidence approach leads to the conclusion that there is no causal association between atrazine and cancer and that occasional positive results can be attributed to bias or chance.”

Another evaluation used a similar weight of the evidence approach to determine if there was any reliable evidence to support a causal link between pesticides and colon cancer and rectal cancer in agricultural pesticide applicator populations (individuals who apply pesticides in the field). Similar to the Mt. Sinai study, these investigators conclude that when evaluated rigorously and systematically, there was no evidence to support a causal association.

Above image courtesy of Toa55 / FreeDigitalPhotos.net

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