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DOMOIC ACID, RAZOR CLAMS - USA (WASHINGTON)
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A ProMED-mail post
<http://www.promedmail.org>
ProMED-mail, a program of the
International Society for Infectious Diseases
<http://www.isid.org>
Date: 1 Apr 2002
From: Candida St.John <candida@whitmanco.com>
Source: Washington Department of Fish and Wildlife
<http://www.wa.gov/wdfw/fish/shelfish/razorclm/domacid.htm>
Domoic Acid
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The fishing of Pacific razor clam, one of the most sought after
shellfish in Washington State, is being adversely affected by the
sudden increase of domoic acid, a naturally occurring marine toxin.
The toxin is caused by a number of different species of microscopic
marine diatoms of the genus Pseudonitzschia.
The human illness known as amnesic shellfish poisoning (ASP) is
caused by eating fish, shellfish or crab containing the toxin.
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, coma,
and possibly death. There is no antidote for domoic acid.
Toxin levels are measured in samples collected by Washington
Department of Fish and Wildlife (WDFW) staff, the Quinault Indian
Nation, and the Quileute Tribe. Samples are turned over to the
Washington Department of Health (DOH) lab in Seattle. The samples are
then measured using a chemical technique known as high-performance
liquid chromatography (HPLC). The level of domoic acid determined to
be unsafe for human consumption by the federal government is 20 ppm
in molluscan shellfish.
In 1992 DOH established an 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 made a decision 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 clams samples 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. It should be noted that cooking or freezing the clams does
not lessen the toxicity.
The 1998 outbreak of domoic acid began in southern California, where
high concentrations of various species of Pseudonitzschia where
found. In May of 1998, large numbers of California sea lions were
found stressed and showing obvious signs of neurological disorders.
(To learn more details about domoic acid and the California episode,
visit the National Marine Fishery Service Westcoast Marine Biotoxin &
Harmful Algal Bloom Newsletter). Some 80 sick sea lions washed onto
shore and many were taken to the Marine Mammal Center in Sausalito.
Over 50 of these sea lions eventually died from domoic acid
poisoning. Stomach analysis showed they had eaten significant amounts
of anchovies and sardines which had very high levels of domoic acid
in them. Urine analysis from the sea lions also confirmed domoic acid
in their system.
The concentration of Pseudonitzschia cells appeared to move up the
Pacific coast. In May 2001, razor clams in Oregon showed domoic acid
levels of 35 ppm. By June those levels had risen to 54 ppm and by
July almost 60 ppm. Washington State razor clams began showing
increases in domoic acid levels in late July. By August domoic acid
was at 14 ppm in razor clams, just below the action level of 15 ppm.
In September levels rose to 23 ppm which was above the action level
and then from 40 to 94 ppm. The most recent levels recorded in the
October testing showed levels of 61 to 287 ppm in Washington. It
should be noted that Oregon's October sampling ranged from 220 ppm to
308 ppm in razor clams.
----
Candida St. John
Environmental Scientist