The research team tested the toads and their offspring for the presence of chemical contaminants, and their offspring were examined for developmental abnormalities such as structural malformations and abnormal swimming.  “We also looked at clutch size (number of eggs), how many eggs successfully hatched, along with developmental characteristics such as pigmentation and spinal formation,” said the lead author William Hopkins of Virginia Tech.

Both the adult females and their offspring from the power plant's settling basin were compared to adults and their offspring from a reference site, which was free from contamination.  The research identified particularly high levels of selenium in the offspring from the contaminated site.  “Selenium is a fascinating trace element,” says Hopkins.  “Although it is nutritionally required as a micronutrient, there's a fine line between its essentiality and toxicity.  We found that females from areas near the power plant accumulated astonishingly high concentrations of selenium in their tissues, and then transferred nearly equivalent concentrations of selenium to their young.”

The research team uncovered one of the primary means of exposure to environmental contaminants in amphibians.  Female amphibians can transfer high levels of certain contaminants to their offspring, resulting in decreased offspring viability.  Amphibians live on land as adults and lay their eggs in aquatic systems where their larvae (tadpoles in the case of frogs) metamorphose and move onto land.  “The findings of this study show that the amphibian life cycle can also serve as a pollutant vector from the land to the water.  The pollutants can move up the aquatic food chain,” said Chris Rowe of the University of Maryland Center for Environmental Science’s Chesapeake Biological Laboratory.  He continued, “Human impacts on the surrounding landscape can ultimately affect aquatic environments through biological routes, in addition to the physical and chemical routes that have traditionally received the greatest attention."

There have been numerous studies on the detrimental effects of selenium on fish and birds. Exposure to selenium is not always obviously harmful to fully-grown vertebrates, but is particularly disruptive to their reproduction function due to its propensity to transfer from mother to egg and its subsequent effects on the developing embryo.

This research is one of the first studies to demonstrate how amphibians are exposed to contaminants through maternal transfer, which is a proven means of exposure for other vertebrates such as fish, birds, humans, and other mammals.  “Our study confirms that in amphibians, like all other vertebrate classes, this may be one of the most important means of exposure to some contaminants, such as selenium and polychlorinated biphenyls (PCBs),” says Hopkins.  “The presence of reproductive abnormalities in animals that transfer contaminants to their eggs illustrates how maternal transfer is very ecologically relevant.”

The research was funded by the US EPA and has been published in the National Institutes of Health (NIH) journal, Environmental Health Perspectives by William Hopkins and Sarah DuRant of Virginia Tech, Brandon Staub from the University of Georgia, Christopher Rowe of the University of Maryland Center for Environmental Science, and Brian Jackson of Dartmouth College.  An abstract of the article is available at http://ehp.niehs.nih.gov/docs/2005/8457/abstract.html.

CONTACT:
Dave Nemazie
410.228.9250 ext. 615
nemazie@ca.umces.edu