Ecological Impacts of Atrazine

1. Biography

About

Tyrone Hayes

Endocrinology is the study of hormones. Hormones (endocrine substances) control growth, reproduction, metabolism, development, behavior, immune function, and stress, among other functions critical for life. Hormones are also important in many disease states including diabetes and cancer. Endocrine disruptors, such as atrazine, which interfere with hormone production and/or activity, can affect any of these processes.

In particular, atrazine inhibits production of testosterone (the male sex hormone) and induces estrogen production (the female sex hormone), upsetting the balance between these two hormones. This effect of atrazine has been observed and published in fish [1, 2], amphibians [3, 4], reptiles [5, 6], and mammals [7-14]. The result is chemical castration (demasculinization) and feminization. In fish [1, 2], amphibians [3, 4, 15-20], and laboratory rodents [7, 8, 10], the decrease in testosterone results in decreased sperm counts, impaired fertility, and a reduction in masculine features. Similarly, atrazine exposure is associated with decreased sperm and reduced fertility in humans [21]. The increase in estrogen by atrazine results in feminization of males in fish, amphibians, and reptiles. “Feminized” male fish [2] and amphibians produce eggs and egg yolk [16, 18] and some males even grow ovaries (become hermaphrodites) [3, 4, 17].

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Figure 1. Atrazine induces gonadal malformations in males. The testes in this Northern leopard frog have been feminized. Not only have eggs developed,but they have accumulated yolk and are bursting through the surface of the testes.

In laboratory rodents, atrazine-induced estrogen production and causes reproductive cancers (prostate cancer in males [22, 23] and breast cancer in females [22, 24]) to develop. In fact, female rats exposed to atrazine, will produce male offspring with prostate disease, if dams (mothers) are exposed while pregnant or suckling [23].

Atrazine also causes immune system failure in animals. This effect has been shown in amphibians and laboratory rodents. In amphibians, atrazine exposure impairs immune function and increases susceptibility to disease [25-29].

Immune cells are unable to eliminate disease pathogens [28] and exposed amphibians are more likely to succumb to viral diseases [25, 26], bacterial infections [27] and macroparasites [30, 31], including the parasites that cause limb deformities in amphibians [29]. Similarly, atrazine exposure in rodents impairs immune function [32-40] and decreases an exposed animal’s ability to fight cancer [33] and other diseases. Further, atrazine exposure in rodents can lead to hypersensitivity [36], making exposed animals more susceptible to allergies. Most likely, the negative effects on immune function are due to an atrazine-induced increase in the stress hormones (corticoids). In salmon, the atrazine-induced increase in stress hormones in fresh water smolt, impairs the ability of exposed fish to return to the ocean leading to high mortality in these commercially important fish [41].

Figure 2. Leopard frog exposed to pesticide mixture, containing atrazine. Animal has contracted meningitis induced by bacterial infections.