Marine Biotoxins

Marine biotoxins are a group of naturally produced toxic chemicals that can sometimes accumulate in shellfish. Most biotoxins are produced by microscopic marine algae (phytoplankton, including diatoms and dinoflagellates), which shellfish ingest as a part of their filter-feeding nature. Accumulation of these harmful biotoxins in the shellfish creates a potential danger if the shellfish are consumed.

In the presence of suitable conditions, specific species of algae that contain these toxins may 'bloom'. Algae growth can occur very fast. This can sometimes take the appearance of a dense, sometimes visible patch near the surface of the water. The toxic algae, which forms this mass is called a 'Harmful Algae Bloom. Some species have pigments, in addition to chlorophyll, that assist in the efficient use of sunlight. This gives them a golden brown or a reddish brown colour when they bloom creating the origin of the term 'red tide'.

However, it is important to note that most species of algae or phytoplankton are not harmful and do not produce these toxins. Not all reddish plankton blooms are toxic and some toxic blooms are either invisible or green. As well, the amount of toxin produced by these organisms can vary.

In the northern hemisphere, the seasonal conditions for harmful algal blooms happen most commonly in the spring and fall. Toxic algae blooms tend to take place during the warmer periods of the year. For the Pacific Coast specifically, the months of May through October are more prone to toxic algae blooms. Yet, long term retention of the toxins by shellfish may result in the occurrence of toxic shellfish at any time of the year.

Ingesting the biotoxin contaminated shellfish can cause the following diseases, named after their most notable symptom;

• Paralytic Shellfish Poisoning (PSP)

• Amnesic Shellfish Poisoning (ASP), and

• Diarrhetic Shellfish Poisoning (DSP)

Paralytic Shellfish Poisoning

Paralytic shellfish poisoning (PSP) toxins, a family of water-souble neurtoxins, are named the 'saxitoxins'. These saxitoxins are produced by several groups of dinoflagellates (dino = armoured, flagellate = propelled by filaments). These are not simple, primitive organisms, but rather, complex and highly evolved ones. Neither plant nor animal, they possess adaptations of both. Some can feed on smaller plankton or bacteria as well as perform photosynthesis in the presence of sunlight. Many of them have the ability to form spores, encyst and drift to the bottom to wait out hard times. When conditions change, they are ready with a "starter population" to form a swift, intense bloom. Dinoflagellates can also migrate up and down in the water column in response to light and nutrients. They can also be transported long distances by winds, tides and currents.

Shellfish exposed to a bloom of PSP organisms are not usually affected by the toxins. They ingest and concentrate the cells within the digestive gland. Yet, toxins can also become concentrated in digestive and mantle tissues to varying degrees, even within the same population. For human consumers, this concentrating effect can be deadly. Fortunately, most shellfish can purge themselves of the toxins within days or weeks, once the bloom has passed.

PSP symptoms range from the tingling of the tongue and lips, followed by a numbness spreading to the extremities, to vomiting, pain, diarrhea, loss of coordination and difficulty of breathing. Without intervention, symptoms can turn into coma or death from suffocation.

Amnesic Shellfish Poisoning

Amnesic Shellfish Poisoning (ASP), is caused by domoic acid, which is a metabolic product of a marine or brackish water diatom. Domoic acid is a similar molecular size and shape to the common and beneficial amino acid, glutamic acid. Domoic acid competes with glutamic acid in the brain. It binds tightly and causes neurons, or nerve cells, to fire continuously until they become exhausted. The result is lesions, or damaged areas of brain tissue. Since brain tissue in adults does not have the ability to grow or repair itself, these effects can be permanent.

Complications such as epilepsy-like seizures may arise from the disturbed electrochemical activity associated with the lesions caused by domoic acid. ASP can cause disorientation, digestive upset, coordination loss, short term memory loss, permanent memory loss, seizures, irreversible brain damage or death.

Diarrhetic Shellfish Poisoning

Diarrhetic Shellfish Poisoning (DSP) is created by toxins (eg. Okadaic Acid), which are produced by certain dinoflagellates. DSP can create stomach pain, vomiting and diarrhea. It is often a short-lived and non life-threatening occurrence. Exceptions to this generalization are those who are young, elderly or who have existing health problems, whom are then considered more susceptible. The incidence of DSP may be underreported because its symptoms are so similar to intestinal flu, bacterial gastroenteritis or other digestive upsets. Shellfish testing programs include DSP testing in their protocols.

Marine Biotoxin Monitoring

The Canadian Food Inspection Agency (CFIA) provides a biotoxin surveillance program on the shellfish growing areas with Department of Fisheries and Oceans (DFO) assistance in enforcement and implementation of the program. Due to the risks associated with illnesses caused by toxin contaminated shellfish, sampling and investigation reports are closely examined. A Consumer Complaint Record is required for each individual that may have been affected by a related illness. In addition, CFIA conducts sentinel sampling of the harvest areas and processing plants to monitor biotoxin levels.

In the harvesting areas, each Fisheries Region has set up PSP and ASP sampling stations in order to monitor for the presence of harmful algae blooms and provide alerts whenever levels of biotoxins are detected. DSP levels are monitored in suspect harvesting areas, or based on consumer complaints. For extra safety measures, monitoring samples may also be taken from processing plants (ie. shellstock shippers, shucker-packers and other plants which handle shellstock).

The marine biotoxin monitoring program requires that a series of samples are taken from mussels in order to detect for contamination. Bags of mussels are set up at the PSP and ASP sampling stations in shellfish growing areas for the purpose of sampling. Mussels are used to detect for contamination because they pick up biotoxins faster than many other shellfish species. Due to feeding physiology different than other shellfish, mussels have increased rates of uptake and depuration of the growing water surrounding them. This causes mussels to accumulate levels of biotoxins much higher and faster than other shellfish species growing in the same waters. This increased sensitivity of mussels to biotoxin accumulation alerts the monitoring program of possible contamination before biotoxin levels rise in commercial species.

Mussel samples, as well as some commercial species samples, are sent to the CFIA laboratory for analysis on a weekly or biweekly basis. The saxitoxins action level for Paralytic Shellfish Poisoning is 80 micrograms per 100 g of meat, and the action level for Amnesic Shellfish Poisoning is 20 ppm of domoic acid.

If shellfish exceed the limits of toxin sampling, a closure order is issued under the Management of Contaminated Fisheries Regulations and is signed by the Regional Director General of the Department of Fisheries and Oceans. Throughout closure, the contaminated area is patrolled and closure signs are posted as a warning.

A closure for the contaminated area remains until the biotoxin levels of the mussels decrease below cautioned levels, and a time interval sufficient in length to permit the natural biological cleansing of the shellfish has elapsed. When this criteria has been met, with a confirmed verification that the water has sustained biologically acceptable levels over the cleansing semester, the harvesting closure may be lifted.

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