PARENT SESSION
WA3 - Toxicology of the Thyroid System
Chair: Brown, Scott1, 1 Environment Canada, Burlington, OH
Co-chair: Digetz, Sig2, 2 US EPA, Duluth, MN
8:00 AM to 12:00 PM - Wednesday, 20 November 2002
Room Ballroom H
(510) Assessing Thyroid Disruption in Amphibians Exposed to Ammonium Perchlorate Under Laboratory and Field Conditions.
Carr, James*,1, Goleman, Wanda1, Hu, Fang1, Wages, Michael1, 1 Texas Tech University, Lubbock, TX, USA
ABSTRACT- Perchlorate occurs in ground and surface waters in 44 states as a result of ammonium perchlorate (AP) discharge from rocket fuel manufacturing facilities or the demilitarization of missiles. Perchlorate also has been used for years to experimentally manipulate amphibian metamorphosis, although usually at concentrations much greater than reported in contaminated waters. Laboratory studies indicate that environmentally relevant concentrations of AP alter sex differentiation and inhibit thyroid function and metamorphosis in Xenopus laevis, the South African Clawed frog. Whether similar responses occur in natural amphibian populations exposed to AP has not been well studied. Beginning in the Fall of 1999, water samples were collected from perchlorate-exposed and reference sites at Longhorn Army Ammunition Plant (LHAAP) in East Texas and McGregor Naval Weapons Industrial Reserve Plant (NWIRP) near Waco, Texas. Water samples were examined for their ability to disrupt thyroid function in the US EPA EDSTAC frog metamorphosis (tail resorption) assay. Our results indicate that this assay fails to detect ppb concentrations of perchlorate, possibly because the assay calls for using late-stage (Nieuwkoop-Faber stage 60) tadpoles. Our data suggest that late-stage X. laevis tadpoles are not as sensitive to AP as tadpoles exposed prior to thyroid differentiation, around NF stage 51. In addition, we have collected developing and adult frogs inhabiting perchlorate-exposed and reference sites at LHAAP and NWIRP. Of hundreds of animals examined, evidence of thyroid disruption had been found only in developing frogs inhabiting perchlorate-contaminated sites at LHAAP. Developing frogs exposed to perchlorate exhibit hypertrophied follicle epithelium and extensive colloid depletion. We conclude that thyroid histopathology is a useful and sensitive tool for assessing thyroid disruption in developing frogs exposed to perchlorate under field conditions. The US EPA EDSTAC frog metamorphosis assay needs to be modified to accommodate full larval period exposure in order to increase the sensitivity of this method for detecting perchlorate in field collected water samples.
Key words: amphibian, anuran, ammonium perchlorate, metamorphosis