Hermaphroditic, demasculinized frogs after exposure to the herbic ide

Mike Quinn Mike.Quinn at tpwd.state.tx.us
Tue Apr 16 18:02:52 EDT 2002


Proc. Natl. Acad. Sci. USA, Vol. 99, Issue 8, 5476-5480, April 16, 2002

Ecology

Hermaphroditic, demasculinized frogs after exposure to the herbicide
atrazine at low ecologically relevant doses 

Tyrone B. Hayes*, Atif Collins, Melissa Lee, Magdelena Mendoza, Nigel
Noriega, A. Ali Stuart, and Aaron Vonk 

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 

Communicated by David B. Wake, University of California, Berkeley, CA, March
1, 2002 (received for review December 20, 2001) 

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 (0.1 ppb) induced hermaphroditism
and demasculinized the larynges of exposed males (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. 

-------------------------------------------------------------------------
* To whom reprint requests should be addressed. E-mail:
tyrone at socrates.berkeley.edu. 

www.pnas.org/cgi/doi/10.1073/pnas.082121499
 



 
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