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February 11, 2009
California sea lion at the surface in Channel Islands National Marine Sanctuary.
High resolution (Credit: NOAA)
Exposure to two environmental poisons—DDT and domoic acid--during brain development can increase the number of epileptic seizures and their intensity in a laboratory model for human epilepsy, according to a report by NOAA scientists.
The finding sheds new insight into epileptic seizure patterns noted in California sea lions in Channel Islands National Marine Sanctuary and National Park.
The report in the January issue of the journal Environmental Health Perspectives identifies for first time the interaction of these toxins and how the timing of their exposure in pregnant animals can affect the health of offspring. The researchers had previously noted that exposure to domoic acid during fetal development in sea lions can lead to brain seizures when they attain juvenile age, two to four years. The new findings point to exposure to residual environmental DDT as contributing to the increased seizure behavior that has been noted in the Channel Island sea lions.
“These findings will help us better understand the origins of this behavior and are the first to reveal the interaction between two noted stressors of this animal population,” said John Ramsdell, Ph.D., an environmental scientist at NOAA’s National Center for Coastal Environmental Health and Biomolecular Research laboratory in Charleston, S.C.
DDT, a pesticide banned in the 1970s, still persists at high but declining levels off the southern California coast. Domoic acid is a neurotoxin produced by harmful algal blooms, which have been fueled by climate oscillations and coastal pollution over the last decade in this region. Algal blooms have been increasing in the sea lions' habitat, resulting in more cases of acute poisoning and increased concern over the long-term effects of algal toxins and how they interact with other changes in the marine environment.
Scientists working under Ramsdell conducted the first-of-its-kind analysis of potential interaction of DDTs and domoic acid during brain development in zebrafish, which are used as a laboratory model for epilepsy. The zebrafish were analyzed for seizure behavior under conditions that mimic both maternal transfer of DDT during the course of brain development and exposure to a harmful algal bloom shortly after brain maturation.
Young zebrafish that accumulated DDT concentrations that initially caused no observable effects showed increased sensitivity to domoic acid and more intense seizures. Levels of DDT and domoic acid in the zebrafish were within the range found in fetal California sea lions.
DDT, originally linked to eggshell thinning in birds, was recognized as an environmental hazard in the early 1960s by author and scientist Rachel Carson, who described how it can be passed from mother to embryo in the womb. The presence of DDT and domoic acid have each been associated with poisoning during birthing season at the Channel Island sea lion rookeries. The potential threat caused by their interaction has only just now been investigated.
Scientists in NOAA's Oceans and Human Health Initiative are studying how harmful algal blooms and marine ecosystem contaminants affect marine mammals to determine if similar impacts could affect humans exposed to the similar harmful toxins.
NOAA scientists are learning about the effects of each individual stressor and addressing the more difficult task of understanding how multiple stressors can interact to cause greater harm. This “place-based” research is part of a partnership between NOAA’s Centers for Coastal Ocean Science and NOAA’s National Marine Sanctuaries to conduct research to investigate how natural- and human-caused environmental changes affect the marine environment.NOAA understands and predicts changes in the Earth's environment, from the depths of the ocean to the surface of the sun, and conserves and manages our coastal and marine resources.