IS SILVER LAKE TOXIC?

  Matt Hoffert, Kerry Bohl, Edward J. Brown and Maureen E. Clayton

   Cyanobacterial blooms in phosphorus-contaminated lakes can produce toxins that are potentially dangerous to humans and wildlife.  We examined the concentration of the toxin microcystin-LR in Silver Lake throughout the summer.  Samples were prepared by filtration or centrifugation, and microcystin-LR concentrations were measured by ELISA (Enzyme-Linked Immunosorbent Assay).  Extraction efficiencies of the different methods were compared.  Microcystin-LR concentrations in the lake water itself were at or near the 48 h LC50 for Daphnia.  These concentrations are not toxic to humans and other large wildlife, but they most likely affect zooplankton populations, which can have a drastic effect on larger fish and the overall ecosystem of the lake.  It seems the microcystin-LR concentrations indirectly decrease the number of fish and other wildlife in and around Silver Lake.

This project was supported, in part, by the Roy J. Carver Charitable Trust, the Iowa Space Grant Consortium, Merck Pharmaceuticals and the American Association for the Advancement of Science.