SHOWS PFIESTERIA TRIGGERED BY MULTIPLE COMPONENTS
Jan. 16, 2007 — NOAA National Centers for Coastal Ocean Science scientists, along with colleagues from the National Institute of Standards and Technology, Medical University of South Carolina and College of Charleston have identified that it is metal-mediated free radical production that transform Pfiesteria piscicida and Pfiesteria Shumway from harmless dinoflagellates into toxic organisms that can cause estuarine fish kills. These free radicals are activated chemicals produced as a by-product of biological activity. (Click NOAA image for larger view of harmful algal bloom in Lake Erie taken on Sept. 15, 2006. Click here for high resolution version. Please credit “NOAA.”)
The findings were published on the journal Environmental Science and Technology's Web site and are slated for print publication in the February 2007 issue of the peer reviewed journal of the American Chemical Society.
"NOAA is committed to supporting the research needed to find answers to the Pfiesteria puzzle," said retired Navy Vice Admiral Conrad C. Lautenbacher, Jr., Ph.D., undersecretary of commerce for oceans and atmosphere and NOAA administrator. "The economic impact of harmful algal blooms in the United States averages $49 million yearly, but individual outbreaks can be extremely costly. The 1997 Pfiesteria bloom in Chesapeake Bay cost the Maryland seafood and recreational fishing industries almost $50 million in just a few months."
The team, led by Peter Moeller, Ph.D., of the NOAA Center for Coastal Environmental Health and Biomolecular Research in Charleston, S.C., identified new components, with emphasis on heavy metals, contributing to Pfiesteria toxin mortalities in certain estuarine fish species. The experiments were designed to isolate key components that lead to mortality in these fish.
Laboratory experiments were performed using sheepshead minnows—a species found in brackish conditions and tolerant of low-oxygenated water that may otherwise be inhospitable to other fish species. The experiments utilized variations in temperature, Pfiesteria bacteria, heavy metals commonly found in estuaries, brackish water and natural light.
"Definitive mortality rates in fish occurred within six hours under precise conditions of metals, temperature, light and Pfiesteria toxin," said Moeller, a NOAA research organic chemist. "After activation, the Pfiesteria toxins quickly decomposed rendering the toxin undetectable."
Moeller's collaborators at the National Institute of Standards and Technology and the Medical University of South Carolina were able to characterize the metal-containing toxin using five distinct instrumental methods: nuclear resonance spectroscopy; inductively coupled plasma mass spectrometry; liquid chromatography particle beam glow discharge mass spectrometry; electron paramagnetic resonance spectroscopy, and x-ray absorption spectroscopy. The results showed that the high toxicity of the metal-containing toxins is due to metal-mediated free radical production.
This activity can explain Pfiesteria's toxicity, as well as the previously reported difficulty in observing the molecular target due to the ephemeral nature of radical species. These findings represent the first formal isolation and characterization of a radical forming toxic organic-ligated metal complex from an estuarine/marine dinoflagellate.
The findings add an increased understanding of how metals, commonly found in the estuarine and marine environment, interact with the biological systems in the environment and how those interactions potentially impact both marine animals and human health.
The discovery may not only help solve one of the more intriguing scientific puzzles of the 1990s but may also lead to a new way at looking at the toxicity of harmful algal blooms. These blooms are increasing globally and threatening human and marine health, as well as having significant economic impacts.
Moeller's team made the discovery after noting previous scientific research into the presence of free metallic radicals in the formation of toxins in other harmful algal blooms, including research that dates back to the 1920s.
"We found in looking at the literature as far back as the 1920s, that in previous research that it was the presence of a series of compounds and factors in most cases where there was a triggered toxicity of the organism," said Moeller. "We developed a hypothesis that heavy metals were the key compounds and that when combined with exposure to light and other environmental cues, they cause the formation of a toxin. Once those precise variables change the toxin disappears."
Pfiesteria, originally identified in 1988 by North Carolina researchers JoAnn Burkholder and Ed Noga and characterized with assistance from Florida researcher Karen Steidinger, is believed to be the source of significant fish kills in the mid-Atlantic region, particularly in the Neuse River in North Carolina and the Chesapeake Bay's estuary systems during the mid-1990s.
Although it killed significant numbers of fish, it was determined that consuming fish affected by the toxin was not harmful to humans. It was, however, identified as a source of respiratory and skin rashes among fishers in the areas at the time of the fish mortality events.
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