The Hazards of Harvesting - Marine Biotoxins

December 1999 - January 2000

This is an article from WaveLength Magazine, available in print in North America and globally on the web.

by Rupert Wong

Marine biotoxins are a naturally occurring phenomenon. The causative organisms will proliferate when growing conditions are optimal. Effects on humans following consumption of contaminated bivalves are potentially fatal, but more often only debilitating while the toxins run their course.

CONDITIONS Spring and summer months bring favorable weather for kayaking and camping. Conditions such as warmer water and longer daylight hours are also some of the key elements that provide improved growth for microscopic, single celled plants called algae. When the right combination of conditions are optimal for algal growth, a 'bloom' can occur. This rapid reproduction of cells in the sea often results in perceptible color changes and spectacular displays of bioluminescence.

CAUSATIVE ORGANISMS Blooms of dinoflagellates belonging to the genus Alexandrium are responsible for paralytic shellfish poisoning (PSP). Alexandrium occurs naturally in BC coastal waters and present a potential health hazard to people who consume bivalve such as clams, oysters, scallops and mussels. Diatom blooms belonging to the genus Pseudo-nipzchia are the causative agent for amnesic shellfish poisoning (ASP). ASP was the cause found in the deaths of people who had consumed Atlantic bivalves in PEI (mid 80s). Pseudonipzchia also occurs naturally in BC coastal waters.

SYMPTOMS AND CHARACTERISTICS The PSP toxin acts as a neurotoxin blocking the sodium channel between nerves. The onset of symptoms after ingestion of contaminated bivalves are tingling and numbness of the tongue, lips, facial muscles and extremities. As the toxin spreads further, neurotransmission is interrupted and coordination becomes impaired. In extreme cases breathing may be arrested. The active agent in ASP is domoic acid. Onset of symptoms include severe nausea, vomiting and diarrhea. ASP also acts on the nervous system. Higher concentrations of domoic acid in the system can cause short term memory loss (amnesia), and in extreme cases death.

TREATMENT AND PREVENTION Since 1996 less than 20 reported cases of marine biotoxin poisoning have occurred in BC coastal communities. Many more cases go unreported as symptoms can be mild and often non-lethal. In 1997, victims of PSP who chose to ignore warnings and closures were air-evacuated from Pender Island. Some believe that bivalve consumption is safe during months with an R. Not true for the Pacific coast where conditions optimal for algal growth can occur throughout winter. Another misconception is that heat from cooking denatures the toxin. Anyone suspecting that they have consumed contaminated bivalves should seek medical attention immediately. Continued assimilation of toxins can be reduced by minimizing physical activity and inducing vomiting (providing the risk of aspiration is minimal). Information is readily available on the status of marine biotoxin closures. Annually published saltwater sport fishing guides contain important information designating permanently closed areas. Current area and sub-area notices reporting warnings and closures are readily available over the telephone or Internet. Toxicity is established by injecting lab mice with an extract of mussel tissue. Not a procedure you'll find in your sea kayaking manual. The best avenue of prevention is to be an informed traveler and to obey all warnings and closures.

MONITORING AND CLOSURES The risk of marine biotoxin and pollution to public health has necessitated the establishment of monitoring programs for shellfish as well as shellfish growing waters. Shellfish monitoring is carried out by the Canadian Food Inspection Agency (CFIA) while closures and warnings are administered by DFO. Shellfish testing is carried out regularly from shell stock collected at key locations and supplemented by verification samples from commercial facilities. When PSP toxicity levels are detected in excess of 80 micrograms of toxin per 100 grams of edible tissue, the area of harvest qualifies for closure. The upper limit for ASP closure is 20 parts per million. Klaus Schalli is an agriculture and shellfish specialist at CFIA. He says that due to the spontaneous nature of toxic phytoplankton blooms it is impossible to delineate closure boundaries exactly. The decision to close an area not only involves the upper limit criteria from site samples, but also the dynamics of the algae bloom.

HAZARDS OF PERCEPTION By the time we perceive a noticeable color change in the water, commonly known as red tide, bivalves may have accumulated algae to toxic levels. And not all red algae produce harmful toxins. Fact is that we can't perceive the dangers of PSP or ASP while paddling in our kayaks or walking on the beach. Science is years away from developing a field litmus test for measuring marine biotoxin. Until then a healthy measure of caution is needed to ensure a safe trip.

BEFORE YOU GO Check the Saltwater Sport fishing Guide for areas of permanent closure and overview map with area & sub-area designations. Check area and sub-area postings and notices for current warnings and closures found at regional DFO offices. Or browse the comprehensive DFO web site Fisheries Management link at http:// www.pac.dfo-mpo.gc.ca
Contact the DFO 24 hr shellfish information voice bulletin (604-666-2828).

FOR MORE INFORMATION If you want more information about marine biotoxins, contact agriculture and shellfish specialist, Klaus Schalliek at CFIA, 604-666-4427 ext. 277 or email: schalliek@em.agr.ca.

Rupert Wong is a professional biologist working in the area of fish habitat restoration. He is the owner of West Coast Expeditions, a well established eco-tour company specializing in family oriented educational paddling programs. He can be reached at 800-665-3040. Check out the West Coast Expeditions website at: www.island.net/~nature