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Tyrone Hayes

The mechanisms underlying the detrimental effects of atrazine in amphibians and rodents are common to all animals, including humans. In particular, laboratory rodents are considered surrogates for humans and thought to predict effects in humans. Thyroid hormones, testosterone, estrogens, and the stress hormones are identical in all animals and serve similar functions regardless of the species. The brain neurohormones are identical in all animals and the sequence of prolactin very similar in all animals.

As a result of the similar hormones and similarities in functions, atrazine predictably has similar effects across wildlife species and laboratory animals. The results in animal studies predict effects in humans, which cannot be studied experimentally. Atrazine has been linked to spontaneous abortions in humans [1]. Atrazine not only reduces sperm production in fish, amphibians, and laboratory rodents, but is associated with impaired fertility and low sperm counts in humans [2]. The induction of the mechanism for depleting testosterone and converting it into estrogen (increased expression of the enzyme aromatase) was, in fact, discovered originally in human cancer cells [3-6] and tissues, and has been characterized in great detail [7, 8]. Further, similar to atrazine’s induction of prostate cancer and mammary cancer in laboratory rodents, men exposed to atrazine in a Syngenta production facility in Louisiana developed prostate cancer at 8.4 times the rate of unexposed factory workers [9, 10] and women whose well water was contaminated with atrazine were more likely to develop breast cancer when compared to women who lived in the same area, but who do not drink well water [11]. Most significantly, the importance of atrazine’s induction of aromatase and its relationship with breast cancer and prostate cancer, is best appreciated when one considers that Novartis, the same company that made atrazine (an aromatase inducer) now markets the chemical, letrozole (an aromatase inhibitor) for the treatment of breast cancer and prostate cancer [12].

Further, as studies in laboratory rodents are conducted to allow us to better predict effects in humans, concern is raised regarding several aspects of public health. Based on studies in laboratory rodents and the association between atrazine and the conditions described above, atrazine is likely involved (but not necessarily the only factor) in decreased fertility in both men and women, increased spontaneous abortion rates, decreased birth weight, and prenatal and adult exposure is likely linked to increased breast cancer and prostate cancer rates (the two most common cancers in women and men, respectively). Furthermore, also keep in mind that many of the studies showing the inhibition of immune cells (including the cells that kill cancer) by atrazine were conducting using human cells. Given that approximately one million people per day and 60% of all Americans are exposed to atrazine, this is a concern.

Atrazine likely promotes reproductive cancers in humans

1. What is Atrazine

2. Environmental Contamination

3. Ecological Impacts

4. Endocrine Disruption

5. Neural Damage

6. Pregnancy loss

7. Reproductive Cancers

8. Endangered Species

9. Risks and Benefits

Perhaps most important, based on laboratory rodent studies, exposures to atrazine (and other pesticides) may have their greatest effects, before individuals are even born. Several studies in laboratory rats and even in humans are now showing that exposure to pollutants in the womb can contribute to diseases such as cancer, immune suppression and learning disabilities later in life.
Given the increase in breast and prostate cancer rates in the US, this is a major concern. The immunosuppressive effects are also a concern. These concerns are amplified for ethnic minorities who can experience death rates from some cancers up to two times higher than Whites. Further, minorities are more likely to work in occupations (factories, agriculture) where they will be exposed, more likely to live in areas where they will be exposed, and less likely to have access to adequate healthcare. Similarly, the detrimental effects of atrazine on immune function in fish, amphibians, and lab rats is reflected in studies showing that atrazine destroys function in human immune cells [13-16] including immune cells necessary to fight cancer in humans [12].