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Shellfish monitors keep tabs on deadly toxins
Kitsap Sun - 8/26/2017
Aug. 26--SILVERDALE -- Using a stubby rake, Dayna Katula popped loose a clump of mussels from beneath a public dock in Silverdale last Wednesday and tossed them onto the wooden planking.
The blue-black bivalves looked healthy, vibrant and delicious. They were also, quite possibly, poisonous.
There is no way to tell by look, smell or taste, whether a shellfish contains the toxins that cause potentially fatal illnesses in humans, including paralytic shellfish poisoning. That is why Katula and other Kitsap Public Health District specialists, assisted by volunteers, continually sample mussels at set stations along the county's shoreline, sending specimens away to a lab for analysis.
A "hot" mussel -- one with high toxin levels -- prompts health officials to close shellfish harvests on surrounding beaches. Up go the familiar red warning signs.
Shellfish monitoring is some of the most important work carried out by the county's health district because it has the potential to directly save lives. A person who eats toxic shellfish can feel tingling within minutes and slip into a coma in less than an hour.
"If you don't do your job today, someone could die," said Jim Zimny, who manages the district's shellfish program. "It's that important."
As of Friday, recreational shellfish harvests were closed on every inch of coastline along the east side of Kitsap County, largely because of the risk of paralytic shellfish poisoning, which is caused by invisible phytoplankton blooms.
Widespread closures are a regular occurrence in the summer but, due in part to the vigilance of health officials, only a handful of paralytic shellfish poisoning cases have been reported in the county in the past five years.
Virtually every case involved someone who harvested in a closed area, Zimny said.
"The reason this happens -- and it's always the same story -- is because they don't acknowledge the signs."
Testing for toxins
At the Silverdale dock, Katula dropped her mussel samples into a clear plastic bag and weighed them with a portable scale.
Silverdale is one of about a dozen monitoring stations around Kitsap where health district staff and volunteers collect mussel samples as least once every two weeks, year-round. Samples from the peninsula, and from stations around Washington, are packed on ice and shipped to a public health laboratory in laboratory in Shoreline -- the largest shellfish testing facility of its kind.
On a visit Friday, the lab smelled faintly like a seafood market. Staff unpacked mussel samples, washed the specimens and shucked away the shells before blending the mussel meat into a smoothie-like liquid.
While marine biotoxins affect many varieties of shellfish, including clams and oysters, experts use mussels as a "sentinel" species. Mussels absorb and release toxins more rapidly than other shellfish, so a sample of their tissue gives scientists an accurate snapshot of toxin levels in their environment.
To check for paralytic shellfish poisoning, lab workers use a process to isolate the toxins in a clear liquid. Toxin levels are then tested using what's called a bioassay. The concentrated liquid is injected into live mice and workers track the time it takes the mice to die.
Jerry Borchert, who leads the state's marine biotoxin program, said the bioassay system has been used for decades and is considered the "gold standard" for testing paralytic shellfish poisoning. It's the only method proven to measure the toxin with the accuracy and speed needed to protect public health. Tests not involving live animals are being developed but aren't yet ready to implement.
"We have been working for years on an alternative," Borchert said.
When a mussel sample is found to have paralytic shellfish poisoning levels above the allowable threshold -- 80 micrograms of toxin per 100 grams of tissue -- the lab calls Borchert, who issues an advisory closing shellfish harvests in the area where the sample was gathered. Local health officials spring into action, posting warning signs at public beaches along affected shoreline.
Closed areas are sampled weekly. Harvests can be reopened after consecutive samples show toxin levels below the allowable threshold.
Paralytic shellfish poisoning is the predominate biotoxin affecting harvests in Puget Sound. The Shoreline lab tests for two other types of shellfish poisoning -- amnesic and diarrhetic -- that have cropped up in Washington in recent years. As their names suggest, amnesic poisoning can cause permanent, short-term memory loss, while diarrhetic poisoning causes nausea and diarrhea.
Areas affected by the biotoxin shift from season to season as phytoplankton growth fluctuates. A mussel sample went hot for diarrhetic shellfish poisoning Wednesday in Port Orchard marina, which was already closed to harvests.
"That's why you always monitor, because you just never know," said Blaine Rhodes, director of the state's office of environmental laboratory sciences.
An early warning
Marine biotoxin events are difficult to predict but nature does offer scientists something close to an alarm system.
While collecting mussels in Silverdale on Wednesday, Dayna Katula also scooped up a sample of seawater from Dyes Inlet using a tube attached to a cone-shaped net. Water in the tube looked hazy, a sign that it was teeming with phytoplankton.
"We monitor phytoplankton as an early warning for shellfish poisoning," Katula explained.
Katula analyzes phytoplankton samples under a microscope in her Bremerton office, sorting through a jungle of wriggling organisms in search of the few species that produce toxins in shellfish. She knows each by sight.
Alexandrium catenella, the culprit behind paralytic shellfish poisoning, develops as translucent balls that join together into chains. The Dinophysis that cause diarrhetic shellfish poisoning look a bit like microscopic water pitchers.
Katula is part of a network of government workers, shellfish growers and volunteers who relay data on phytoplankton to the Sound Toxins program. Health officials use information on where phytoplankton are appearing to prioritize shellfish sampling and stay on top of toxic blooms.
"It's amazing how well it works," Teri King with Washington Sea Grant said.
Phytoplankton monitored by scientists are enjoying longer growing seasons than they did in the past.
Borchert with the state Department of Health said 15 years ago shellfish closures would typically start in June or July. Now closures begin as early as April and can stretch into fall. The trend is likely due to changes in climate, he said.
"We're seeing closures happening earlier in the year and lasting later in the year," he said, noting the trend has been especially pronounced in a few Washington counties.
Zimny at Kitsap Pubic Health said longer growing seasons haven't been as noticeable in Kitsap, and the timing of toxic blooms remains largely unpredictable -- the county's first closure this year occurred in August.
A hard rain after a long dry period will frequently kick off phytoplankton growth and lead to shellfish closures, Zimny said. Stormwater washes built-up nutrients into the ocean, which act as fertilizer for the tiny plant organisms.
However, Borchert said there's no direct link between sewage overflows and increased toxins in shellfish. Counterintuitively, the nutrients pumped into the water during a sewage spill may cause such a proliferation of plankton growth that toxin-producing species are crowded out, Borchert said.
Scientists do know toxic phytoplankton blooms occur even in pristine water, making constant sampling all the more critical.
"It's a public health protection effort and it's very important," Zimny said.
For more information on shellfish safety, go to kitsappublichealth.org or doh.wa.gov.
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