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 . The increase in estrogen by atrazine results in feminization of males in fish, amphibians, and reptiles. “Feminized” male fish  and amphibians produce eggs and egg yolk [16, 18] and some males even grow ovaries (become hermaphrodites) [3, 4, 17].
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].