Whatcom County beaches remain closed to recreational shellfish harvesting as public health officials continue to study a new marine toxin found in higher concentrations here than anywhere else in the state.

Responsible for diarrhetic shellfish poisoning, or DSP, the toxin can cause flu-like symptoms and sicken people who eat tainted shellfish, and is an emerging health threat.

All Whatcom County beaches have been closed since early July to recreational shellfish harvesting, initially because of high levels of another toxin that is responsible for paralytic shellfish poisoning.

But as those toxins began to level off, DSP appeared and then increased - causing the ongoing closure.

"This is a toxin that is pretty new to Washington state," said Tom Kunesh, environmental health supervisor for Whatcom County Health Department. "It's a toxin that's common, I guess, in Europe."

Shellfish in stores and restaurants are tested for marine toxins before going to market.

DSP was detected offshore of Whatcom County for the first time this summer, and for the first time in the state in June 2011, in Sequim Bay when three people were sickened.

Those DSP-caused illnesses were the first in the United States. (No such illnesses have been reported in Washington state this year.)

DSP illnesses linked to eating mussels also were identified in southern British Columbia last year.

Symptoms of DSP include diarrhea and vomiting, and last up to three days.

The toxin is produced by microscopic algae that are found naturally in the environment - specifically the dinoflagellate Dinophysis, according to the state Department of Health.

Shellfish eat these algae, which aren't a problem until - for reasons that scientists are still trying to figure out - they start producing toxins that, in turn, accumulate in shellfish until they are unsafe for human consumption.

The DSP level that triggers a closure is 16 micrograms of toxin per 100 grams of shellfish meat.

Samples taken from blue mussels in August from three sites in Whatcom County were all above that threshold for recreational shellfish harvesting, according to Kunesh.

Those locations were:

? Birch Bay Village Marina, where the level was lowest, at a little more than 22 micrograms of toxin per 100 grams of shellfish meat;

? Semiahmoo Marina, where the level was about 45 micrograms of toxin;

? Squalicum Harbor, where the level was a whopping 184 micrograms of toxin per 100 grams of shellfish meat.

Symptoms are expected in the 30 to 50 micrograms range.

"You'll likely get sick," Kunesh said.

The previous high for the state was 160 micrograms per 100 grams of shellfish measured in Sequim Bay last year, according to Jerry Borchert, public health adviser in the state's marine biotoxin program.

CHECK BEFORE YOU DIG

Check this Department of Health webpage or call the Shellfish Safety Hotline at (800) 562-5632 before harvesting shellfish recreationally.

Additional information on diarrhetic shellfish poisoning is available at this webpage.

Reach KIE RELYEA at kie.relyea@bellinghamherald.com or call 715-2234.