🦪 Domoic Acid & Shellfish – A Major Health Concern

In 1991, a relatively new marine toxin, domoic acid, was first detected on the West Coast of the U.S. When this marine toxin was discovered in certain West Coast fish and shellfish, recreational and commercial fisheries were closed. These closures had serious economic impacts on those communities dependent on these fisheries. One of the most heavily impacted was Washington’s razor clam fishery, which remained closed for a full year.

In North America, domoic acid has been responsible for several deaths and both permanent and transitory illness in more than 100 people. The toxin is produced by marine diatoms, which are members of the genus Pseudo-nitzschia. Both shellfish and fish can accumulate this toxin without apparent ill effects. However, in humans the toxin crosses into the brain and interferes with nerve signal transmission.

Eating of fish or shellfish containing the toxin causes the human illness known as amnesic shellfish poisoning (ASP). Symptoms include vomiting, nausea, diarrhea and abdominal cramps within 24 hours of ingestion. In more severe cases, neurological symptoms develop within 48 hours and include headache, dizziness, confusion, disorientation, loss of short-term memory, motor weakness, seizures, profuse respiratory secretions, cardiac arrhythmia and coma. People poisoned with very high doses of the toxin can die. There is no antidote for domoic acid. Research has shown that razor clams accumulate domoic acid in edible tissue (foot, siphon and mantle) and are slow to depurate (purify) the toxin. Research has also proven that cooking or freezing affected fish or shellfish tissue does not lessen the toxicity.

In 1987, more than 100 individuals became ill after consuming cultured mussels (Mytilus edulis) harvested off the Canadian province of Prince Edward Island. The mussels were found to be contaminated with domoic acid, which had previously not been observed in shellfish. This 1987 incident led to the subsequent death of three elderly individuals and caused permanent short-term memory loss in several survivors.

The deaths of more than 400 California sea lions in 1998 have been traced to a domoic acid-producing algae. An examination of the animals showed their brain tissue had been almost totally destroyed by domoic acid. It was found that the sea lions had eaten large quantities of anchovies, small fish that had fed on the domoic acid-producing algae.

Since the 1991 discovery of domoic acid along the Washington coast, regular samples of both razor clams and Dungeness crab are collected by Washington Department of Fish and Wildlife (WDFW) staff in cooperation with the Quinault Indian Nation. Samples are turned over to the Washington Department of Health (DOH). Domoic acid levels in these samples are then measured using a chemical technique known as high performance liquid chromatography (HPLC) at the DOH Public Health lab in Shoreline, Washington. The level of domoic acid determined to be unsafe for human consumption by the Federal Food and Drug Administration (FDA) is 20 ppm in shellfish meat tissue. In 1992 DOH choose to adopt the lower action level of 15 ppm because of the rapid rate domoic acid levels can rise thus providing an additional safety buffer. In September of 2000, DOH decided to return to the 20 ppm federally accepted action level. This decision was a direct result of the close cooperation between WDFW and DOH speeding the collection, delivery and analysis of razor clam samples for domoic acid.