Variation in somatic and ovarian development: predicting susceptibility of amphibians to estrogenic contaminants.

Division of Biological Sciences, University of Missouri, 212 Tucker Hall, Columbia, MO 65211, USA. <>
General and Comparative Endocrinology (Impact Factor: 2.67). 06/2008; 156(3):524-30. DOI: 10.1016/j.ygcen.2008.03.001
Source: PubMed

ABSTRACT Although amphibian sex determination is genetic, it can be manipulated by exogenous hormone exposure during sexual differentiation. The timing of sexual differentiation varies among anuran amphibians such that species may or may not be a tadpole during this period, and therefore, may or may not be exposed to aquatic contaminants. Estrogenic contamination is present in amphibian habitats worldwide. We examined three species with varying somatic and ovarian developmental rates to assess their susceptibility to estrogenic contaminants. American toads (Bufo americanus), gray treefrogs (Hyla versicolor), and Southern leopard frogs (Ranasphenocephala) were exposed as larvae to 17-beta-estradiol (10(-7)M), three concentrations of a widespread herbicide (1, 3, 30 ppb atrazine), or a solvent control (ethanol). Somatic and ovarian developmental stages as well as time to metamorphosis were recorded. Toads and treefrogs were examined at three weeks and metamorphosis, while leopard frogs were examined at three, six, and nine weeks as well as at metamorphosis. Our results demonstrate that each species displays heterochronic somatic and ovarian development. Further, the more rapid of the two rates determines the susceptibility to estrogenic contaminants. These results suggests that amphibians with shorter larval periods, and therefore quicker somatic developmental rates (i.e. American toads, gray treefrogs), are more susceptible to somatic treatment effects (i.e. prolonged time to metamorphosis) due to estrogenic contaminants. Moreover, the results suggest that amphibians with relatively rapid ovarian development (i.e. Southern leopard frogs) are more susceptible to gonadal treatment effects caused by estrogenic contaminants.

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    ABSTRACT: Evidence suggests that chemicals acting as endocrine disruptors can modulate amphibian sex differentiation and induce sex reversal and gonadal abnormalities. However, consequences of gonadal abnormalities such as testicular oocytes on amphibian reproductive potential remain unclear. Assessing this linkage requires suitable experimental models, such as partial life-cycle exposure, in order to correlate accessible endpoints with apical endpoints indicative of reproductive fitness. Larvae of the emerging amphibian model Silurana tropicalis were exposed to EE2 in the ng/L range from NF stage 51-52 until completion of metamorphosis, and endpoints related to the reproductive function were assessed on completion of metamorphosis and at sexual maturity. Exposure to EE2 skewed the sex ratio toward phenotypic females in the treated groups, but also affected growth and development of the tadpoles. At sexual maturity, absence of one or both oviducts was observed in some female frogs that had been exposed to EE2. Regressed testicular oocytes were observed in most males, including males from the control group. The occurrence of regressed testicular oocytes seems to be dependent on genetic background, rather than xenoestrogens exposure. Mature testicular oocytes and presence of oviduct-like ducts in frogs displaying testis were only seen in treatment groups exposed to EE2. The incidence and the severity of gonadal abnormalities observed in Silurana tropicalis males and females exposed to EE2 were dependent on the nominal dose but also dependent on parentage. No link could be made between gonadal abnormalities
    01/2010, Degree: MPhil, Supervisor: Daniel B Pickford
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    ABSTRACT: This document is a preliminary problem formulation for atrazine to fulfill Registration Review requirements under FIFRA. In a problem formulation, available information, including stressor sources and characteristics, exposure, ecological effects on plants and animals (e.g., amphibians, fish, invertebrates, birds, and mammals), and characteristics of the ecosystem(s), is used to identify missing information and assessment endpoints and to develop a preliminary assessment of the problem. The document consists of two main sections. In the first section is background material on the regulatory history, use and usage, ecotoxicity data, environmental fate data, and environmental monitoring data for atrazine (Chapter I). These data serve as the foundational data for the risk assessment. This section also contains a critical review of published atrazine testing with amphibians (Chapter II). The second section includes the analysis plan (Chapter III) for the risk assessment. This section also provides a detailed plan on the methods used to assess risk in light of information on use/usage, ecotoxicity data, and environmental fate data. A key aspect of this section is identifying and addressing uncertainties in the risk assessment. The topics are:  Chapter IV – The methodology for determining the level of concern for atrazine  Chapter V - A strategy for using the PATI-derived CE-LOC for identification of vulnerable watersheds Charge questions to the FIFRA SAP can be found in the relevant sections of Chapters I, II, IV, and V. All materials presented at this meeting can be found in the federal register at!docketDetail;dct=FR%252BPR%252BN%252BO%252BSR;rpp=25;po=0;D=EPA-HQ-OPP-2012-0230
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    ABSTRACT: This addendum and the attached problem formulation for atrazine, titled "Problem Formulation for the Reassessment of Ecological Risks from the Use of Atrazine," prepared for the June 12-15 2012 FIFRA Scientific Advisory Panel (SAP or the Panel) meeting, together serve as the problem formulation for the ecological risk assessment to be conducted for the registration review of atrazine. The appendices to the June 2012 problem formulation document are not attached here but can be found in the SAP public docket at (EPA-HQ-OPP-2012-0230). Functioning as the first stage of the risk assessment process for registration review, this problem formulation provides an overview of what is currently known about the environmental fate and ecological effects associated with atrazine and its degradates. It also describes the preliminary ecological risk hypothesis and analysis plan for evaluating and characterizing exposure and risk to non-target listed and non-listed species in support of the registration review of atrazine. Additionally, it describes the plan for evaluating and characterizing exposure from drinking water for the human health assessment. The database for environmental fate and transport, and ecological effects data for atrazine is sufficient for risk assessment such that no additional data are needed at this time. The purpose of this addendum is to address comments received from the SAP during the June 12-15, 2012 meeting, and to provide an update on the ecological monitoring program being conducted by the registrant as a result of the 2003 atrazine Interim Reregistration Eligibility Decision. The 2012 SAP meeting on atrazine focused on three major topic areas: 1. the evaluation of the atrazine amphibian toxicity data, 2. the method for determining the level of concern for aquatic plant communities, and 3. the development and implementation of methods for a quantitative interpretation of atrazine occurrence data in surface water. At this meeting, EPA scientists presented the state of knowledge concerning the ecological effects and exposure information for atrazine, and the proposed plan for analyzing the data and characterizing risks to non-target organisms, including plant community effects. The materials presented by the EPA and stakeholders, as well as meeting minutes and the SAP response to the charge questions, can be found in the public docket (!docketDetail;rpp=25;po=0;D=EPA-HQ-OPP-2012-0230) and the FIFRA SAP webpage ( While most of the SAP’s comments are addressed in the following pages, some of the recommendations will require additional time and investigation, and will be addressed prior to the completion of the registration review ecological risk assessment.
    Federal register 06/2013;