Biotoxin Monitoring ProgramEntry ID: gomc_9
Abstract: Bivalve shellfish are highly sensitive to the quality of their marine
environment. They feed on microscopic plants that can sometimes produce marine
biotoxins, which can build up in their tissues. Eating shellfish with high
levels of these biotoxins can lead to serious and potentially fatal illness.
Paralytic Shellfish Poisoning (PSP), as well as ... Amnesic Shellfish Poisoning
(ASP) and Diarrhetic Shellfish Poisoning (DSP) are the most common human
illnesses associated with marine biotoxins in Canada. Bacteria, viruses, metals
and contaminants may also build up in the tissues of bivalve shellfish and
cause food safety concerns for consumers.
The Canadian Food Inspection Agency (CFIA) monitors shellfish harvesting areas
to provide early warning of PSP toxins (and other toxins) in shellfish.
Hundreds of sites in Atlantic Canada, Quebec and British Columbia are regularly
tested for PSP toxins. The Agency analyzes shellfish samples and, when levels
are unacceptable, it notifies the Fisheries and Oceans Canada (DFO) which takes
immediate action to close the affected area to shellfish harvesting. When areas
are closed, signs are posted, media are notified, and DFO fishery officers
patrol the areas to prevent the harvesting of shellfish.
With an area of 250,000 square kilometres, over 35 commercially harvested
marine species and a great variety of fish in its rivers and estuaries, the
Gulf of St. Lawrence constitutes one of the world's largest enclosed seas, a
highly productive ecosystem, and a major arena of commercial fishing in
Waterbody or Watershed Names: Gulf of Saint Lawrence
Sponsor: Canadian Food Inspection Agency
Additional Information OR Comments: Fact sheets are available from the website.
Other information on closures and fishing maps are available at
A file containing all pertinent sanitary survey information, including the
dates and results of preceding surveys and reports is maintained by the
shellfish control agency for each classified shellfish area.
Quality In order to maintain reliability of bioassay results, the period of time
between the digging of shellfish and extraction should be uniform and limited.
Each sample must be properly identified with the area of digging, the species,
the date of digging and the sampling officer's name. Samples should be stored
at refrigerated ... temperatures 2 to 7 degrees C (35 to 45 degrees F) until
In the case of aquaculture operations, samples may be collected at the
establishment if the same standards of continuity and sample handling are
Regions should have in place a monitoring program to adequately monitor marine
biotoxins. As levels begin to rise, sampling frequency is to be increased in
accordance with the speed of the rise to ensure timely closure. Areas that have
been closed are to be monitored on a regular basis but with increased frequency
as PSP scores decline toward acceptable levels. The objective is to ensure that
shellfish areas are closed when:
1. PSP toxin levels reach 80 µg/100 g and are opened only when toxin levels
are consistently below 80 µg/100 g;
2. ASP toxin levels reach 20 µg/g and are opened only when toxin levels are
consistently below 20 µg/g; and
3. DSP chemical analysis gives okadaic acid and/or DTX-1, singly or in
combination, of less than 1 microgram per gram (µg/g) of digestive tissue
(equivalent to approximately 20 µg/100g soft tissue) and are opened only when
consistently below this level.
Should departures from the scheduled sampling and/or analyses occur, due to
weather conditions, absence of staff, diversion of sampling/analytical
resources to areas of higher concern, then factors such as previous toxic
history, harvesting activity and other supporting results should be considered
and documented in a derogation report for the justification in not closing an
In addition to normal sampling, when certain species are used for canning
(e.g., butter clams in British Columbia) a special Harvesting License (Annex
11B) is required, and the shellfish must be tested for PSP prior to release for
Bacteriostatic or bactericidal agents, such as chlorine, silver, lead, and
various organic complexes, can significantly reduce bacterial densities in a
sample. Contaminating nutrients can cause unwanted growth of organisms in the
sample which would result in an overestimation of bacterial densities.
Both of these problems can be greatly reduced by insuring that:
a) all glassware used in the analyses is free from such substances;
b) distilled/deionized water used in media preparation is not contaminated with
bacterial, fungal or algal growth; and
c) samples are processed as quickly as possible after collection.
Growth of certain organisms in the test media which are not of importance to
the specific analysis performed can give false positive results, thereby
overestimating the true bacterial density. However, the specificity of the test
media normally eliminates most of these organisms. Incubation temperatures are
critical, and slight changes can alter the kinds and numbers of bacteria
growing in the test media.
Precision and Accuracy
The bacterial density calculated by the MPN method is a statistical estimation
and should be treated as such. The 95 percent confidence limits for the 5-tube
MPN test, range between 24% and 324% of the MPN; thus, the results of a single
sample are by no means conclusive. Accuracy increases with increased sampling,
and normally a minimum of five samples are required at each sample location to
better approximate the true bacterial density.
Access Constraints There is no open public access to data. All requests must be individually
directed to a specific Shellfish Control Agency for each of the classified
shellfish areas in the region, i.e., Eastern Nova Scotia, SW Nova Scotia, New
Brunswick. Requests may be made by calling the Biotoxin Monitoring Program
Office in Yarmouth, NS at 902-742-6874.
Use Constraints The agency is not obligated to release data to the public. Constraints may
exist and should be discussed when making requests.
Data Set Progress
Distribution Media: Various Online Data Transfer method
Role: DIF AUTHOR
Phone: (902) 742-6846
Email: whiteka at inspection.cg.ca
215 Main Street
Province or State: Nova Scotia
Postal Code: B5A 1C6
Creation and Review Dates
DIF Creation Date: 2006-08-28
Last DIF Revision Date: 2009-03-26