OCCURRENCE OF INTERSEX AMPHIBIANS IN BIG BEND NATIONAL PARK: ARE ENVIRONMENTAL FACTORS TO BLAME?

There is increasing concern about global declines in amphibian populations. Aquatic habitat degradation due to chemical contamination has been partly implicated in these declines. The primary aim of this study was to conduct a biomarker survey of amphibians in the Big Bend region of the Rio Grande Basin in the context of general water quality and potential contaminant exposures. The study focused on the Rio Grande leopard frog (Rana berlandieri). Indices of aquatic habitat quality included standard water quality measures and the presence and level of contaminants such as trace metals and organochlorine pesticides. Perhaps the most notable finding from the biomarker analysis was the presence of testicular oocytes in 17 percent of the male frogs examined. All intersex frogs were collected from river/creek sites where cadmium (Cd) levels where measurable (sometimes exceeding federal criteria for freshwater aquatic life), whereas no intersex frogs were observed in sites where Cd was found only at trace levels. Cd has been reported by some studies as having estrogenic activity at low levels. The source of Cd in water bodies within the park is uncertain. Overall, the results of this study raise concerns about the presence of contaminants and their potential long-term effects on the aquatic biota of the Big Bend region. However, the sample sizes for this study were small and definite cause-effect associations cannot be made. Additional studies are needed to assess such relationships.