Course:FNH200/Projects/2026/Poisoning in Oysters

Team Introduction

This page is for GROUP 25 from FNH 200 942 (Summer T2 2026). Our team members are as follows:

• Joshua Hart
• Ahaana Mitra
• Julian Renzetti
• Leah Song
• Tyler Tran

Background Information

This article details safe oyster production and consumption in British Columbia. As noted by Statistics Canada, BC is Canada's largest producer of oysters, topping out at roughly 7,200 oysters in 2024. The BC Shellfish Grower's Association also wrote that BC is the 12th largest producer of Pacific oysters in the world, operating under strict regulations and sustainable farming practices. The following sections will outline how oysters are consumed in Canada, some of the unique processing procedures for farming and selling oysters, and noteworthy safety hazards when it comes to consuming oysters in BC.

Oyster Consumption Habits in Canada

Common raw oyster recipe

In BC, there are specified limits to how many oysters you can consume. Oysters are a known source of cadmium, given that oysters are filter feeders by nature. In particular, the BC coastline has some of the highest reported levels of cadmium in Pacific Northwest oysters, ranging from 1-4 ppm. Prolonged cadmium intake puts consumers at risk of kidney malfunction and bone density loss, as stated by the BC Centre for Disease Control. As a result, Health Canada does not prescribe high-risk groups (pregnant women, young children) to consume oysters and for adults to cap their monthly limit at a maximum of 12 oysters.

Oyster Farming in BC

Oyster tray culture

Most of BC's oyster industry focuses on sustainable farming, as opposed to wild oyster harvesting, with everything taking place on BC's coastlines. Farming first begins by breeding oyster larvae into seeds by using specialized tanks. Afterwards, these seeds are then placed in a "flupsy", or a floating containment area (as shown on the right) within ocean waters to allow oyster culture to filter for nutrients derived from algae and other marine plants. These nutrients may include calcium carbonate, which builds up the characteristically thick protective shell of the oyster. Upon reaching the juvenile stage after approximately one year, oysters are then transferred into larger "growout systems", where they will reach adult stage after another two years. These systems include separate trays and cages which can be individually handled to harvest each rack once the oysters are matured.

Current Events in BC Oyster Industry

Campylobacter jejuni bacteria

While BC is well-known for their high-quality oyster processing standards, many advocates for food safety have called out the provincial government on multiple outbreaks stemming from active oyster harvesting areas in BC such as Baynes Sound. These outbreaks range from norovirus (AKA stomach flu) to bacterial infections such as campylobacter, which is generally correlated to raw meats and unpasteurized dairy products. Further investigations have found evidence of improper sewage treatment and disposal which have contaminated oyster farming areas, thereby causing many recalls and public health concerns throughout British Columbia.

Alongside from the rising risk of consuming contaminated shellfish, there's several cases of massive oyster die-off events in BC from Pacific oyster-specific diseases. This prompted unease amongst researchers and oyster farmers alike, along with calls to make the BC oyster industry more resilient to the impacts of rising ocean temperatures, contamination events, and foreign spat (seed) transplants.

Paralytic Shellfish Poisoning (PSP)

Context and Origin

A sign on a beach warning the public of a PSP infection

PSP is a type of poisoning that can occur from the consumption of various bivalve shellfish. It can also occur in lobsters and crabs that feed on infected shellfish. Because shellfish feed by filtering microscopic organisms from the water, they ingest all kinds of organisms from their environment indiscriminately. The toxins within these organisms can build up in the system of the shellfish, reaching levels that are toxic to humans. Interestingly enough, these toxins do not appear to have any impact on the shellfish themselves. PSP specifically is caused by the buildup of neurotoxins in the water, which are produced by algae from the genus Alexandrium, Gymnodinium, and Pyrodinium. These algae types thrive in warmer waters, and if the conditions are favourable they will reproduce enough to create algae blooms, and these large pools of algae will contaminate the surrounding environment . These neurotoxins are not destroyed by cooking or freezing, so the only way to ensure safety of oysters is to avoid contract with these toxins all together. Once the oysters are infected, they are no longer safe for consumption in any form.

Symptoms and Treatment

The symptoms of PSP can present themselves as minor and then progress quickly. Symptoms can start off as tingling in the extremities, combined with possible nausea and light-headedness. These symptoms can start anywhere from a few minutes to 2 hours after exposure. After some time, symptoms can progress to paralyzation of the arms and legs. In some cases, poisoning can be fatal. This is because paralyzation can progress so far that the muscles in the chest that control breathing become paralyzed, leading to the loss of the ability to breathe and suffocation.

Treatment options for PSP are limited. There is no known antidote for the toxin, and there are no medications to treat the poisoning. Once infected, the only thing that can be done is to wait for the toxin to pass through the body naturally. If symptoms are severe and breathing is impacted, the recommendation is to call 911. The only treatment in this case is to put the victim on a respirator, to allow for mechanical breathing while they wait to regain control of their chest muscles.

Climate Change Impact

Harmful Algae Blooms

Example of algae bloom

Rising ocean temperatures are creating more favourable conditions for the toxin-producing algae behind PSP. A 2017 study in PNAS found that ocean warming since 1982 increased both the growth rates and bloom-season length of harmful algae, identifying the Salish Sea and Alaskan coastline as regions where new blooms have emerged. Public health researchers similarly note that as climate change continues to raise sea temperatures and shift nutrient cycling, harmful algal blooms are expected to become more frequent and widespread along BC's coast, increasing the public health risk from shellfish poisoning.

Future Outlook

A 2021 BC Centre for Disease Control review of 62 documented PSP cases in BC between 1941 and 2020 found that poisonings are increasing in frequency. This is a trend linked to rising sea surface temperatures. Most cases involved self-harvested shellfish rather than commercial product, suggesting recreational and Indigenous harvesters face growing exposure as warming waters expand algal habitat. This points to a need for increased water monitoring, educating harvesters, and climate-adaptive closure protocols to keep pace with a changing coastline.

Regulations and Future Improvements

Quality Assurance of BC Oysters

British Columbia enforces a strict chain-of-custody system to keep live oysters safe from harvest all the way to the retail shelf. Provincially licensed seafood processors are required to keep detailed distribution records; who bought the product, when it shipped, who transported it, and the original harvest tag information, including the harvest date, location, and the harvester's identity . These records have to be kept for at least three years, so if a foodborne illness outbreak or recall happens, public health inspectors can trace the affected oysters back to the exact marine plot they came from .

Once oysters are sold in retail or food service, they must meet additional quality standards set by the BC Centre for Disease Control. Vendors and restaurants must keep oysters refrigerated at 0°C to 4°C to inhibit bacteria like Vibrio parahaemolyticus . Additionally, all official bivalve harvest tags must be retained for at least 90 days after sale or shucking, ensuring accountability and quick traceability within the BC seafood supply chain .

Canadian Shellfish Sanitation Program (CSSP)

At the national level, the safety of live bivalve molluscs in Canada falls under the Canadian Shellfish Sanitation Program (CSSP), a federal food safety program run jointly by three regulatory bodies :

• Environment and Climate Change Canada (ECCC) monitors marine water quality along the coast, running sanitary and bacteriological surveys and checking for pollution sources like agricultural runoff or municipal sewage. Based on these findings, ECCC classifies shellfish harvesting waters as approved, conditionally approved, or restricted.
• The Canadian Food Inspection Agency (CFIA) oversees biotoxin, chemical, and microbiological surveillance in harvesting areas. It also licenses and inspects federally registered shellfish processing plants, checks that they meet national sanitation standards, and can recommend area closures or product recalls when pathogen or toxin levels get too high .
• Fisheries and Oceans Canada (DFO) enforces the harvest area openings and closures that ECCC and CFIA recommend, keeps an eye on harvesting activity on the water, and patrols the coastline to prevent illegal harvesting from contaminated or off-limits sites .

Together, these three agencies make sure only oysters from clean, monitored waters reach the public. This is what protects British Columbia's reputation for premium Pacific oysters. By coordinating water quality, processing standards, and harvest enforcement, the CSSP lowers the risk of heavy metals like cadmium, biotoxins like PSP, and pathogens like Campylobacter and norovirus. As climate change brings warmer waters and more algal blooms to BC's coast, the program's real-time monitoring and closure protocols matter more than ever for public health and the industry's future.

Improving Oyster Processing Regulations

A biologist and geneticist remove oyster sperm and eggs at an oyster breeding center focused on sustainable oyster farming.

The Canadian Shellfish Sanitation Program provides a strong system for monitoring harvesting waters, processing facilities, and distribution, however emerging risks such as warmer ocean temperatures, harmful algal blooms, and the increasing prevalence of Vibrio bacteria may require more frequent monitoring and faster regulatory responses.

The Canadian government is now helping the oyster industry by providing funding to help growers and processors deal with disease-related losses. For example, in Prince Edward Island the federal support helps the industry manage the effects of diseases, which has affected oyster production and created challenges for growers and processing facilities.

Oyster growers in British Columbia have called for stronger government action to address the environmental causes of oyster recalls. The British Columbia Shellfish Growers Association pointed to problems such as aging wastewater infrastructure, septic systems, and vessel discharge as sources of contamination that can contribute to norovirus risks. Farmers already follow strict harvesting regulations and can voluntarily close areas when contamination is suspected, but growers argue that protecting shellfish waters also requires action beyond the farm.

Addressing Climate Change Policy

As discussed in the section on climate change, it is having a significant effect on oyster growth and productivity. In response, government agencies have considered implementing programs to support the oyster industry, while industry associations have advocated for increased support, resources, and adaptation measures. In British Columbia, for example, the provincial government partnered with the BC Shellfish Growers Association, Vancouver Island University, and the Hakai Institute on initiatives to increase the supply of disease-resistant oyster seed, expand climate-change monitoring, and identify priorities for future investment and action.

Exam Question

Question: Cooking oysters in an oven/grill at a temperature of 500°F degrees or more will guarantee safe consumption. (T/F)

• True
• False

Answer: False.

Explanation: This question proves a key element of food safety - the internal temperature of the food is more relevant in determining the viral/bacterial properties as opposed to the cooking appliance temperature. According to Health Canada, shellfish must be cooked to an internal temperature of 74°C (165°F) or higher to kill any traces of Vibrio bacteria and norovirus. Since the question does not specify how long the oysters should be cooked at 500°F, it will not guarantee safe consumption.