Study highlights danger of shellfish toxins
toxin found in contaminated shellfish, according to a new US study.
While the Duke University Medical Center researchers note that eating seafood offers significant health benefits, they said their findings suggest that the current threshold of toxin at which affected fisheries are closed should perhaps be lowered.
The study found that naturally occurring marine toxin domoic acid can cause subtle but lasting cognitive damage in rats exposed to the chemical before birth.
The researchers saw behavioral effects of the toxin in animals afterprenatal exposure to domoic acid levels below those generally deemed safe for adults.
The findings in rats, claim the scientists, imply that the toxin might negatively affect unborn children at levels that do not cause symptoms in expectant mothers.
"The findings suggest we may need to re-evaluate monitoring of waters, shellfish and fish to make sure that the most sensitive parts of the human population are protected from toxic exposure to domoic acid," said project scientist Edward Levit.
In 1987, more than 100 people in Canada became ill after eating cultured mussels contaminated with domoic acid. The incident led to three deaths and memory loss in several others.
First detected in the U.S. on the Washington coast in 1991, domoic acid is produced by microscopic algae, specifically the diatom species called Pseudo-nitzschia. When shellfish and crabs ingest the algae, the toxin can become concentrated in their bodies.
Humans eating contaminated seafood develop symptoms including vomitingnausea, diarrhea and abdominal cramps. In severe cases, the toxin leads to neurological damage, characterized by headaches, confusion, coma and even death.
Since the discovery of domoic acid on the West Coast, officials therecollect regular samples of affected marine animals, including razor clams and Dungeness crabs. Fisheries are closed when domoic acid levels reach 20 parts per million (ppm) in the animals' tissues, the level at which the FDA deems the toxin unsafe for human consumption.
To explore the toxin's effects during development, the Duke teamadministered domoic acid to pregnant rats at three levels - each belowthose found to cause convulsions or fetal loss. Others animals did notreceive the toxin. The researchers then conducted a battery of behavioral tests on the exposed and normal animals to determine the effects of early domoic acid on movement and working memory.
Rats with a history of domoic acid exposure showed greater initial activity in a maze test than control rats, followed by a rapid decline. Moreover, domoic acid exposure affected cognitive function in complex ways, the researchers reported.
The researchers reported their findings in a forthcoming special issuededicated to research on marine toxins of Neurotoxicology and Teratology.
