The identification, analysis and control of hazards that present a risk of contamination of live shellfish

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Introduction

The purpose of this document is to provide information on the hazards that can be present in live shellfish and some example control measures that could help prevent or reduce the risk of contamination of the shellfish. This is not intended as an exhaustive list of measures. Always ensure that the control(s) chosen are tailored to the uniqueness of your business and shown to be effective for your situation.

Hazards

Biological hazards

Pathogens can be found in the waters of the shellfish harvest, wet storage or relay areas and can present a risk of contamination of the shellfish. The shellfish can accumulate and become contaminated with the pathogens when filtering the surrounding water to feed. The presence of these pathogens in shellfish consumed in a raw or partially cooked state can present a risk of injury to human health.

The pathogens can be naturally occurring or the result of contamination by human or animal fecal matter. Naturally occurring pathogens include bacteria such as:

  • Vibrio vulnificus
  • Vibrio parahaemolyticus
  • Vibrio cholerae

Pathogens from human and animal fecal sources include bacteria and viruses such as:

  • Salmonella spp.
  • Shigella spp.
  • Campylobacter jejuni
  • Yersinia enterocolitica
  • Vibrio cholerae
  • Hepatitis A
  • Norovirus

Example sources of pathogens include:

  • discharge from waste water treatment plants
  • sewage contamination
  • processing establishments
  • direct discharge of sewage from boats, harvest vessels and maintenance vessels in shellfish areas
  • dredging
  • private homes and malfunctioning septic systems
  • agricultural animals
  • wildlife, marine mammals or birds
  • natural events such as herring spawning which can attract birds or mammals
  • birds roosting on aquaculture equipment such as floating bags or buoys

Natural toxins

Natural toxins can be found in the waters of the shellfish harvest areas and can present a risk of contamination of the shellfish. Most of these toxins are produced by naturally occurring marine algae (phytoplankton). The toxins can accumulate in shellfish when they filter the water to feed on the algae. Natural toxins cannot be reliably eliminated by heat treatment (cooking) so their presence in shellfish consumed in a raw or cooked state can present a risk of injury to human health.

The natural toxins that can be found are:

  • Azaspiracid
  • Amnesic shellfish poison (Domoic Acid)
  • Brevetoxins
  • Diarrhetic shellfish poison (Okadaic Acid)
  • Paralytic shellfish poison (Saxitoxins)
  • Pectenotoxins

Environmental chemical contaminants and pesticides

Environmental chemical contaminants and pesticides can be found in waters of the shellfish harvest areas and can present a risk of contamination of the shellfish. Chemical contaminants cannot be eliminated by heat treatment (cooking) so their presence in shellfish consumed in a raw or cooked state can present a risk of injury to human health.

Chemical contaminants include:

  • Heavy metals such as Mercury
  • Pesticides such as Dichlorodiphenyltrichloroethane (DDT), Hexachlorobenzene (HCB) (BHC), heptachlor, chlordane, dieldrin, endrin, aldrin, mirex
  • Hydrocarbons such as petroleum

Example sources of chemical contaminants include:

  • Mining
  • Pulp mills
  • Urban or agricultural runoffs

Control measures

The hazards that may lead to the contamination of shellfish need to be controlled with measures that are shown to be effective.

Controls at the harvest site

In Canada, regulatory controls are in place to prevent the harvesting of shellfish contaminated by pathogens, marine biotoxins and environmental contaminants. These controls are administered and enforced jointly by the Canadian Food Inspection Agency (CFIA), Environment and Climate Change Canada (ECCC) and Fisheries and Oceans Canada (DFO) under the Canadian Shellfish Sanitation Program (CSSP).

Under the CSSP, the water quality in shellfish growing and harvest areas is surveyed to identify actual and potential sources of pollution. The areas and their classification for the harvesting of shellfish are established based on their compliance with Canadian water quality standards and sanitary conditions. The levels of naturally occurring marine biotoxins are monitored to prevent the harvesting of shellfish that could be harmful to human health. The status of the shellfish harvest areas, as open or closed for shellfish harvesting, is identified through the real-time shellfish harvesting map.

Shellfish in contaminated areas can only be harvested if a licence to harvest has been issued under the Management of Contaminated Fisheries Regulations and the shellfish are decontaminated using an approved decontamination plan. Refer to the document Depuration of bivalve shellfish and section 9.4.2 of the CSSP manual for more information about decontaminating shellfish.

For areas subject to a conditional management plan, due to the operation of a waste water treatment plant, the owner or operator of the wastewater treatment plant is required to notify federal authorities of any sewage discharge. The process requires them to provide detailed information on the event in the Wastewater Treatment Plant Reporting Tool. DFO and all subscribers to the Wastewater Treatment Plant (WWTP) Discharge notification service are then notified of the event. Upon receiving notification, harvesters have to immediately stop harvesting activities in the area and take the necessary measures to prevent potentially contaminated bivalve shellfish from entering the marketplace. Harvesters stay informed of the status of shellfish harvest areas with the real-time shellfish area map.

Control measures to reduce the risks associated with Vibrio parahaemolyticus in live oysters are outlined in the document Measures to control the risk of Vibrio parahaemolyticus in live oysters.

Control measures applied by an operator

An operator should apply control measures that ensure their shellfish are sourced from:

  • harvest areas classified as "approved" or "conditionally approved" and in the "open" status by:
    • checking the real-time shellfish harvesting map regularly to stay informed of the status of shellfish harvest areas, sanitary closures, biotoxin closures and emergency closures
    • subscribing to DFO's Wastewater Treatment Plant (WWTP) Discharge notification service to stay informed of harvesting areas that will be placed in "closed" status due to a discharge event
    • immediately applying the necessary measures, upon receiving notification of a sewage discharge event, to prevent potentially contaminated bivalve shellfish from entering the marketplace
    • maintaining a list of commercial shellfish harvesters who hold a licence issued by DFO
    • establishing harvest plans that identify, in advance, the harvesters and location of harvest
    • verifying that the shellfish received were appropriately tagged with complete and accurate harvest information and questioning harvesters on the harvest location and its status at the time the shellfish were harvested
    • verifying the marine biotoxin levels on a regular basis when shellfish are harvested from offshore harvest areas
  • a depuration facility or relay operation only when the shellfish were decontaminated using an approved method.
  • harvest vessels that have adequate control measures to prevent contamination of shellfish by human waste and that have sanitary practices on the use of human waste receptacles or washroom facilities
  • harvesters and suppliers that have time and temperature controls to prevent the growth of pathogens at harvest, and after harvest during the holding and transportation of the shellfish
    • have a SFSA to ensure controls are in place to prevent the growth of pathogens
    • observe harvesting practices
  • an integrated multi-trophic aquaculture site only when an Integrated Multi-trophic Aquaculture Management Plan (IMTAMP) approved by the Regional Interdepartmental Shellfish Committee (RISC) is in place as described in the CSSP manual
    • have a SFSA to ensure that controls are in place to prevent contamination of the shellfish
  • a near shore wet storage area only when the area is in the open status at the time the shellfish are removed
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