SEQUIM — A mystery toxin that sickened recreational shellfish harvesters last summer after they ate mussels from Sequim Bay appears to be subsiding.
In fact, a state ban on shellfish harvesting in the bay could be lifted before the month’s end, a state health official said Thursday.
Sequim Bay is the only body of salt water where diarrheal shellfish poisoning, or DSP, has been found in the United States.
The DSP discovery has baffled health officials, who cannot explain why it suddenly showed up in Sequim Bay and not, for example, in Discovery Bay just to the east.
DSP comes from a toxin produced by a type of plankton long known to live in high concentrations in Sequim Bay and around Puget Sound but never in concentrations that can cause gastrointestinal illness.
In high concentrations, DSP contaminates food, though it may not look or smell spoiled.
DSP can cause diarrhea, nausea, vomiting, abdominal cramps and chills.
The report prompted the agency to run tests for the toxin, which found levels exceeding the international standard set by the European Union.
The toxin has only been found in Europe and parts of British Columbia before it was confirmed in Sequim Bay.
Jerry Borchert, a health adviser with the state Department of Health who took samples of mussel tissue from Sequim Bay on Wednesday, said he expects the bay will be cleared and the closure lifted within the next two weeks after test results come back from the lab.
“I suspect it will. The big blooms are over,” Borchert said.
“The numbers have dropped off. We’re not seeing the phytoplankton anymore that causes the toxin.”
Cooler water temperatures might be one reason, Borchert said.
Signs warning of the closure have been posted at Sequim Bay State Park, a popular public shellfish beach about five miles east of Sequim off U.S. Highway 101.
A commercial closure in Sequim Bay has already been lifted, Borchert said, after tissue samples taken from oysters and clams showed toxin levels below what is considered a threat.
A man and two children from King County were sickened in June after they ate mussels they harvested in Sequim Bay.
As a result, the ban on both recreational and commercial harvesting of all types of shellfish in Sequim Bay began Aug. 8, and a recall for all commercially sold shellfish also went into effect.
Mussel tissue samples taken Sept. 8 in Sequim Bay showed results definitely below the toxicity threshold of 16 micrograms per 100 grams of shellfish tissue, a measure used by the Environmental Protection Agency, Borchert said.
In contrast, one mid-summer sample found levels 10 times above the safety threshold.
Borchert said the state Health Department is closely watching shellfish-rich Discovery Bay on the Clallam-Jefferson County line because levels were notably creeping up as well.
But they never reached levels requiring a closure.
“Mussels were really close to it,” just below 16 micrograms per 100 grams of shellfish tissue, Borchert said of a September sample taken in Discovery Bay.
Tests have been done by a federal Food and Drug Administration lab in Alabama because the state Department of Health has no lab-testing facilities.
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Sequim-Dungeness Valley Editor Jeff Chew can be reached at 360-681-2391 or at jeff.chew@peninsuladailynews.com.
