One of the great attractions of Canada's coastal provinces is the selection of seafood delicacies. Among the favorites are oysters clams, cockles, mussels and quahogs harvested from Canada's miles of beaches and rocky coastline. These shellfish are the common types of bivalve molluscs, that is, those shellfish with a soft body enclosed by two shells or valves joined by a hinge. These bivalve molluscs are the shellfish referred to in this Fact Sheet.

Only the shellfish classed as bivalve molluscs feed by filtering the water that washes over the shellfish bed. Because of their feeding mechanism, these shellfish can accumulate chemical and/or bacteriological pollutants and naturally occurring toxins from the surrounding waters even at a considerable distance from pollution sources. A single mussel, for example, may filter up to 300 times its weight in one hour This represents a substantial amount of water.

With the objective of protecting public health, Canada signed a Bilateral Agreement with the United States in 1948 to guarantee the quality of shellfish products prior to export. The standards and protocols developed from this agreement form the basis of the Canadian Shellfish Sanitation Program (CSSP). This program, jointly run by Environment Canada, the Department of Fisheries and Oceans and the Canadian Food Inspection Agency, ensures that:

• bivalve molluscan shellfish are harvested from growing areas meeting approved federal water quality criteria;
• potential pollution sources in these areas are identified
• all shellfish sold commercially are harvested, transported and processed in an approved manner

The Canadian program also protects the recreational harvester by classifying sports harvest areas in addition to commercial beds.

Environment Canada has two main CSSP program responsibilities which are implemented by its Shellfish Water Quality Protection Program. These responsibilities include undertaking sanitary and water quality surveys in order to make recommendations as to the classification of shellfish growing areas. Bacteria called faecal coliforms are used as indicators of contamination from sewage and other faecal pollution sources. High standards for water quality are demanded in areas where shellfish are harvested. This activity helps to minimize the potential health risks associated with consuming molluscan shellfish and protects public health. EC’s other responsibilities under the CSSP include the promotion of pollution prevention and remediation of shellfish growing areas.

The Department of Fisheries and Oceans (DFO) is the lead agency with regards to the controlled relaying and depuration and harvesting of shellfish from classified areas. DFO is responsible for the enforcement of closure regulations and enacting the opening and closing of shellfish growing areas under the authority of the Fisheries Act and Regulations. The Canadian Food Inspection Agency (CFIA) is the lead agency with regards to the handling, processing, marketing, import and export of shellfish. CFIA is also responsible for the management of the marine biotoxin monitoring program.

Bacteriological Pollution

There waters are polluted by human and animal faeces through sewage and landwash, bacteria and viruses can be concentrated in the shellfish to much higher levels than those found in the surrounding waters. This becomes a public health concern because many potentially harmful bacteria and viruses can be ingested when people eat contaminated shellfish and become ill. Consequently, federal water quality standards to measure the sanitary quality of shellfish waters are rigidly enforced In Canada, shellfish growing areas must be approved prior to the harvesting of shellfish for human consumption. These areas are classified as approved, conditionally approved, or closed according to the sanitary on toxic conditions of the area. Chemical Pollution

A further cause of shellfish contamination is chemical substances such as metals, pesticides and chlorinated organic chemicals Such chemicals may constitute a threat (a) to human health through consumption of contaminated shellfish, (b) to the shellfish that may be affected by exposure to very low levels of the chemical and (c) to the ecosystem in general where they accumulate and magnify up through the food chain. These chemicals are largely associated with discharges from industrial and municipal treatment processes and can include substances such as mercury, copper, zinc, dioxins and furans.

Natural Biotoxins

The shellfish growing regions of Canada, i.e. British Columbia, Quebec arid the Atlantic provinces, including Newfoundland, are also subjected to natural contamination by toxins produced by microscopic marine organisms. The most significant toxin is called paralytic shellfish poison (PSP) and is produced by one-celled organisms called dinoflagellates. In warm weather this organism proliferates or "blooms" causing a discoloration of the water called a red tide. However, not all visible red tides are toxic and the discoloration may not be necessarily red. When a red tide washes over mollusc beds, the shellfish strain the organisms from the water in great numbers, accumulating the poison.

Another natural biotoxin recently identified in Canadian waters is domoic acid (also known as amnesic shellfish poison, ASP). Consumers are protected from these biotoxins by a comprehensive testing program for shellfish in all harvesting areas The frequency of testing for PSP and ASP toxins is higher where they are known to occur more regularly. This testing includes samples collected from harvest areas and federally registered shellfish processing plants.

There are a few shellfish closures specifically due to chemical contamination (one closure for cadmium and lead contamination on the east coast, and two closures for dioxins on the west coast). There are many more closures due to natural biotoxins, however, most shellfish closures in Canada result from bacteriological pollution. Sources include:

• treated and untreated municipal sewage discharges;
• landwash from agricultural and urban areas;
• see page from poorly operating septic tank and tile field disposal systems;
• direct discharges of raw sewage from moored or anchored boats and from shore-side residences;
• treated and untreated industrial wastes:
• wildlife and domestic animals;
• marine mammals.

At any one time, areas closed to shellfish harvesting can be numerous and extensive. In 1992, approximately 3,018 square kilometres were closed to harvesting in all three shellfish regions of Canada due to bacteriological pollution. The risk of harvesting shellfish from polluted waters increases with proximity to highly urbanized or agricultural areas. The pollution conditions are often aggravated by rainfall, which can result in sewage-contaminated run-oft or effluent from overloaded sewage treatment systems reaching the shellfish beds. The areas that are near towns, villages and other human habitation are often closed year-round. Other areas are closed for set periods of time.

As more of our coastlines are developed for farming, industrial and residential uses, potential problems must be addressed through:

• the proper collection, treatment and discharge of sewage;
• the proper location of industrial waste treatment plants and their outfalls;
• the strategic location of shellfish farms;
• the development of seasonal harvesting strategies;
• the proper operation and maintenance of domestic septic systems;
• prohibition of direct discharges from boats; and
• the control of run-off from land.

When harvesting, handling and storing shellfish, consumers can protect themselves from potential problems by following a few simple rules:

Harvesting: Before an outing, check with a local federal Fisheries Officer for an update on the safety of specific shellfish growing areas. It is dangerous and illegal to harvest shellfish in "closed" contaminated areas.

Do not harvest shellfish from:

• areas that are marked "closed" due to any type of contamination
• any area within 125 meters of a wharf or dock

Handling and Storage: Oysters, clams and mussels purchased in the shell should be refrigerated but not frozen If they open and do not close when tapped, they are dead and should not be eaten. Fresh bivalve shellfish should also be kept in containers that allow free circulation of air. Shucked shellfish should be refrigerated at all times and eaten within 2-3 days. Bacteria are destroyed when the shellfish are well-cooked.

Sickness: If you experience any sickness linked to eating shellfish, report the problem immediately to your doctor and your provincial Department of Health.

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