title: Hermaphroditic, demasculinized frogs after exposure to the herbicide atrazine at low ecologically relevant doses.
abstract: Atrazine is the most commonly used herbicide in the U.S. and probably the world. It can be present at several parts per million in agricultural runoff and can reach 40 parts per billion (ppb) in precipitation. We examined the effects of atrazine on sexual development in African clawed frogs (Xenopus laevis). Larvae were exposed to atrazine (0.01-200 ppb) by immersion throughout larval development, and we examined gonadal histology and laryngeal size at metamorphosis. Atrazine (> or =0.1 ppb) induced hermaphroditism and demasculinized the larynges of exposed males (> or =1.0 ppb). In addition, we examined plasma testosterone levels in sexually mature males. Male X. laevis suffered a 10-fold decrease in testosterone levels when exposed to 25 ppb atrazine. We hypothesize that atrazine induces aromatase and promotes the conversion of testosterone to estrogen. This disruption in steroidogenesis likely explains the demasculinization of the male larynx and the production of hermaphrodites. The effective levels reported in the current study are realistic exposures that suggest that other amphibian species exposed to atrazine in the wild could be at risk of impaired sexual development. This widespread compound and other environmental endocrine disruptors may be a factor in global amphibian declines.
authors.affiliation: Laboratory for Integrative Studies in Amphibian Biology, Group in Endocrinology, Museum of Vertebrate Zoology, Department of Integrative Biology, University of California, Berkeley, CA 94720-3140, USA. tyrone@socrates.berkeley.edu
authors.forename: Tyrone B
authors.initials: TB
authors.lastname: Hayes
authors.forename: Atif
authors.initials: A
authors.lastname: Collins
authors.forename: Melissa
authors.initials: M
authors.lastname: Lee
authors.forename: Magdelena
authors.initials: M
authors.lastname: Mendoza
authors.forename: Nigel
authors.initials: N
authors.lastname: Noriega
authors.forename: A Ali
authors.initials: AA
authors.lastname: Stuart
authors.forename: Aaron
authors.initials: A
authors.lastname: Vonk
mesh_terms: D000818:Animals; D001280:Atrazine / Q000009:adverse effects*; D012734:Disorders of Sex Development; D004305:Dose-Response Relationship, Drug; D004967:Estrogens / Q000378:metabolism; D005260:Female; D006540:Herbicides / Q000009:adverse effects*; D006863:Hydrogen-Ion Concentration; D008297:Male; D008675:Metamorphosis, Biological / Q000187:drug effects; D009132:Muscles / Q000187:drug effects; D012727:Sex Characteristics; D012733:Sex Differentiation / Q000187:drug effects; D012737:Sex Factors; D013739:Testosterone / Q000096:biosynthesis; D013997:Time Factors; D014982:Xenopus laevis
chemical_list: D004967:Estrogens; D006540:Herbicides; D013739:Testosterone; D001280:Atrazine