BIOACCUMULATION AND BIOMAGNIFICATION - Marine Pollution: What Everyone Needs to Know - page 157

last only a few days in nonlethal cases. The most severe cases
can result in respiratory arrest within 24 hours of consump-
tion, because the toxin paralyzes the diaphragm, making it
impossible to breathe. PSP is prevented by large-scale moni-
toring programs (measuring toxin levels in shellfish) and rapid
closures of toxic areas to harvesting of shellfish. In addition to
measuring toxin levels in shellfish, predictions of blooms are
based on the amount of Alexandrium in its cyst (dormant) stage
detected in sediments the previous fall. In order to protect pub-
lic health, shellfish beds are closed when toxicities rise above a
certain level, often during the peak harvesting season. Due to
effective monitoring by state agencies, there have been no ill-
nesses from legally harvested shellfish recently, despite some
major blooms. However, there have been some severe poison-
ings of individuals who ignored closure signs. The toxin is not
destroyed by cooking the shellfish. Some shellfish can store
the toxin for several weeks, but butter clams can store it for up
to two years. PSP has been implicated as a cause of deaths of
marine mammals such as sea otters after eating butter clams
that accumulated saxitoxin. Ingestion of saxitoxin-containing
mackerel was implicated in the deaths of some humpback
whales. Deaths of fish including endangered sturgeon have
also been associated with Alexandrium blooms.
What is diarrhetic shellfish poisoning (DSP)?
Diarrhetic shellfish poisoning (DSP), as its name suggests,
causes diarrhea, although nausea, vomiting, and cramps are
also common. Symptoms usually set in shortly after ingest-
ing infected shellfish, and last for about one day. The toxin is
okadaic acid, which causes intestinal cells to become very per-
meable to water, resulting in diarrhea with a risk of dehydra-
tion. The causative organism is the dinoflagellate Dinophysis ,
which is widely distributed. DSP is a significant problem in
northern Spain, Ireland, and the Mediterranean/Adriatic Sea.
The toxin has been detected in shellfish in Eastern Canada.