ATHENS, Ga., Mar. 11 (AScribe Newswire) -- Science sometimes requires sacrifice: animal and plant subjects are routinely analyzed by scientists studying the ways in which they react with their environments. At times, this analysis requires killing the subject; for instance, to effectively measure contaminant load or transfer of nutrients. Such destructive methods may not always be necessary according to a paper just out in Environmental Toxicology and Chemistry by a University of Georgia researcher at the Savannah River Ecology Laboratory.
William Hopkins has been studying the effect of selenium (Se) on various reptiles and amphibians for years on the Savannah River Site, a U.S. Department of Energy site in Aiken, S.C., where coal-powered energy has produced areas contaminated with selenium and arsenic. Determining how these contaminants proceed through the food web is of concern to many scientists. Doing this without killing the study subjects is of interest to Hopkins. This study provides the first description of functional relationships among contaminant concentrations in diet, target tissues and nondestructive tissue samples in reptiles, and is among the few ever developed for any vertebrate.
"Nondestructive sampling methods, such as removal of feathers, are desirable in ecological monitoring programs that seek to minimize the impacts of harvesting organisms for study," said Hopkins.
As reptiles and amphibians do not have feathers or hair that can easily be sampled, using them as study animals has meant sacrificing the animals. Many reptiles and amphibians are declining worldwide and Hopkins wanted to develop a model using less destructive methods. Using two species of snakes (banded water snakes and brown house snakes) and blood and tail tissue biopsies, Hopkins found strong positive correlation among selenium concentrations in blood, biopsies and tissues of toxicological concern (e.g., liver and eggs).
"Although the current paucity of toxicity data on reptiles precludes tests of our models, we demonstrate how the equations describing these relationships might be used to make predictions about selenium accumulation in target organs for risk assessment," he explained.
In one study, captive snakes were fed selenium-contaminated fish from a wetland downstream from a coal-burning plant, a reference site, or from both sites, for two years. In another, mice injected with selenium were used as the contaminated prey items for ten months. In the first study, the snakes showed significantly elevated tissue concentrations of selenium, exceeding those known to be toxic to other vertebrates. In the second, selenium in target organs and maternally transferred to eggs exceeded established toxicity thresholds for birds and fish.
At the end of each of these experiments, a blood sample was collected from each snake and a tiny portion of the tail of each subject was removed. The snakes were then dissected and organs removed. Focusing on the two nondestructive tissues, the scientists could make predictions about both current exposure to the contaminant and the composite archive incorporated into multiple tissue matrices.
Hopkins and colleagues tested their mathematical models in another recent paper published in Environmental Pollution. Lizards were raised on Se-enriched invertebrates and tail biopsies were then retrieved from these animals. Concentrations of Se in the tails were used to test the models.
"We were actually surprised at how effective our nonlinear models were at predicting target organ concentrations from tissue biopsies," said Hopkins. "Despite the fact that we were comparing different taxa [lizards and snakes] under different exposure scenarios, the actual selenium values were within half a microgram of our predicted Se concentrations."
Real-world application of the models developed by Hopkins will require more study under field conditions but offer a potential alternative to sacrificing animals for assessments.
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From Functional Relationships Among Selenium Concentrations in the Diet, Target Tissues, and Nondestructive Tissue Samples of Two Species of Snakes, by William Hopkins, Joel Snodgrass, Jennifer Baionno, John Roe, Brandon Staub and Brian Jackson.
Also see: Hopkins, W.A., B.P. Staub, J.A. Baionno, B.P. Jackson, L. Talent. 2005. Transfer of Se from prey to predators in a simulated terrestrial chain. Environmental Pollution 134:447-456.
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Kim Cretors, News Bureau Manager
UGA News Service
A201 Stegeman Coliseum
Athens, GA 30602-4371
706/542-6927 (o) -) 706/583-0372 (f)
kcretors@uga.edu -) www.uga.edu/news
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Contact Information:
Contact: Rosemary Forrest, 803/725-2473, forrest@srel.edu William Hopkins, 803-725-7827, hopkins@srel.edu
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