Submitted to: Environmental Monitoring and Assessment
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/20/2002
Publication Date: 1/20/2004
Citation: Garber, Eric A.E., Erb, Judith L., Magner, Joseph, and Larsen, Gerald. 2004. Low levels of sodium and potassium in the water from wetlands in Minnesota that contained malformed frogs affect the rate of Xenopus development.Environmental Monitoring and Assessment. 90:45-64. Interpretive Summary: Water samples were collected between 1999 and 2000 from wetlands in Minnesota that contained malformed frogs. The water samples were analyzed for 14 minerals and screened for the presence of toxins by studying the development of African Clawed frog fertilized eggs into tadpoles. Results indicated that water from two lakes, CWB and ROI2, caused tadpole lengths to be reduced 20% after 96 hr of development of the tadpole. This reduction in length of tadpoles reared in water from ROI2 was prevented by addition of sodium, while addition of both sodium and potassium were required to prevent the reduction in length of tadpoles reared in water with the same mineral content as water from lake CWB. Seasonal fluctuations in the sodium and potassium content at the ROI2 lake and another Minnesota lake which contained malformed frogs (NEY) also correlated reduction in length of Xenopus tadpoles. It was also found that Xenopus tadpoles reared on water from lake ROI2 for an additional 24 hrs had gut abnormalities which were not present in embryos reared in purified water with the mineral composition of lake ROI2 water. Embryos reared on water from lake ROI2 to which additional minerals were added at levels used to rear the African Clawed frog were neither retarded nor abnormal. It is proposed that climatic cycles, such as a series of wet years, may have an influence on the mineral composition at selected wetlands which caused a delay in frog development. It is thought that this could alter windows of susceptibility of the frogs to the agents that cause malformations.
Technical Abstract: Water samples were collected between 1999 and 2000 from wetlands in Minnesota that contained malformed frogs. The water samples were analyzed for 14 minerals/ions and screened for the presence of biologically active compounds using Xenopus laevis. Results indicated that water from two sites, CWB and ROI2, induced severe retardation with embryo lengths reduced 20% after 96 hr of development. The developmental delay observed with water from ROI2 was alleviated by supplementation with sodium, while both sodium and potassium alleviated the developmental delay observed with water whose mineral content mimicked that of CWB. Seasonal fluctuations in the sodium and potassium content at ROI2 and NEY correlated with changes in the rates of Xenopus development. Xenopus embryos reared on water from ROI2 for 120 hr displayed gut malformations not present in embryos reared on a synthetic media designed to mimic the mineral content of the water from ROI2. Embryos reared on water from ROI2 supplemented with minerals at levels comparable to that routinely employed in the rearing of Xenopus were neither retarded nor malformed. It is proposed that climate-driven hydrology may influence the mineral composition at selected wetlands and delay development, which may alter window(s) of susceptibility towards biologically active agents and the occurrence of malformed frogs.