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Research News about Deformed Frogs in Minnesota

As of July 1, 2001, the MPCA is no longer researching the deformed frogs in Minnesota. Funding for the research was eliminated by the Minnesota Legislature.

From 1995 through 2000, the MPCA collected nearly 25,000 frogs from 195 sites in Minnesota. The frogs were collected at critical stages of their lifecycle development process and sent them to the U.S. Geological Survey (USGS), which examined the tissue to determine at what stage malformations began to occur and what possible mechanisms might have triggered the malformations. The MPCA also collected water and sediment samples at various study sites around Minnesota and sent them to the National Institute of Environmental Health Science (NIEHS) for testing and analysis.

In 1999, a California researcher made news with a study that established the role of parasitic flatworms (Ribeiroia) in malformations of tree frogs in California. The MPCA had looking at parasites as a potential cause for several years. Dr. Dan Sutherland, a parasitologist from the University of Wisconsin who worked with the MPCA, found significant numbers of ribieroia at only one Minnesota site, low numbers at another, and none at other study sites. So far the parasite theory, while interesting, has not explained Minnesota's malformed frogs beyond possibly one site.

Conclusions from Minnesota Research

Based on the Minnesota team's effort through 2000, "natural" causes such as larval predation and infectious agents have been all but eliminated as possible causes of the widespread frog malformations observed in Minnesota. Parasites may be a factor at one study site, but apparently do not cause the malformations seen at other sites.

The list of potential causes developed by the Minnesota team to this point includes:

• Something in the Water. The NIEHS found that water from study sites in Minnesota and Vermont causes malformed frogs in the laboratory, and that water from "normal" sites (no malformed frogs) does not. Some of the chemicals in the water have been identified and tested for their ability to cause frog malformations. The fungicide Maneb and propylthiourea, a pesticide, were shown to cause limb malformations. Several papers have been published on the results of this ongoing work.
• Endocrine Disruptors. The thyroid gland plays a significant part in controlling frog metamorphosis. NIEHS recently reported that adding thyroid hormone to water and sediment extracts from study sites reduces the number of limb malformations observed in the lab, and adding anti-thyroid chemicals increases malformations. This suggestions that one or more chemicals present at our study sites may be acting as endocrine disruptors and interfering with the normal development process. The MPCA has begun a special LCMR-funded project to measure vitellogenin in frogs at affected and normal sites, which will provide more clues on the potential role of endocrine disruption.
• Ultraviolet Light. The U.S. EPA and others have established that ultraviolet light, under laboratory conditions, can cause malformations in frogs. We are working with the USGS to measure ultraviolet light penetration at our study sites. And we are looking at how UV may be breaking down chemials in the environment into other compounds that could be contributing to the malformations.

Some researchers are continuing to examine frog tissue for certain types of damage that can provide clues to what is causing the malformations. For example, certain chemicals can interfere with limb formation or bone development in characteristic ways. Certain malformations, if present, may indicate that these chemicals are playing a role.

More Information and Related Links

Information on deformed frog research that may be continuing may be found at the following Web sites.

• National Institute of Environmental Health Sciences
• US Geological Survey - Fact Sheet on Malformed Frogs in Minnesota
• USGS National Wildlife Health Center
• North American Reporting Center for Amphibian Malformations

Malformed frogs have captured the attention of many people around the world. The MPCA continues to get many calls about what's happening with the frogs. People are very much concerned about the problem. Questions regarding malformed frogs may be referred to Ralph Pribble, MPCA, 651-757-2657.