Scientists Identify Mechanism for Pfiesteria Outbreaks

Scientists have found that metal-mediated free radical production transforms Pfiesteria piscicida and Pfiesteria Shumway into toxic organisms that can cause estuarine fish kills, the National Oceanic & Atmospheric Administration (NOAA) announced on Jan. 16. These free radicals are activated chemicals produced as a byproduct of biological activity.

"NOAA is committed to supporting the research needed to find answers to the Pfiesteria puzzle," said 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.

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 used 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 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 the toxicity of Pfiesteria, 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 (single-celled planktonic organisms, chiefly marine, characterized by twirling motion and whip-like flagella).

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 also could 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.

For additional information, contact the NOAA Center for Coastal Environmental Health and Biomolecular Research at

This article originally appeared in the 01/01/2007 issue of Environmental Protection.

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