BC Oysters Face Cadmium Challenge

Canada's toxic policies fail again. Health Canada's risk assessment says BC oysters should be consumed "in moderation" but no one told the local shellfish farmers or communities about the advice.

by Delores Broten

In 1999, shipments of oysters from British Columbia were turned back from the Hong Kong market because they exceeded limits on cadmium for imported shellfish. In 2000, testing of farmed oysters around Georgia Strait by the Canadian Food Inspection Agency (CFIA) confirmed that some BC oysters were extremely high in cadmium and the mean cadmium content was one third higher than Hong Kong standards.

Fisheries and Oceans Canada began to study the issue, published a report by George Kruzynski on the web (http://www.dfo-mpo.gc.ca/csas/), and held an international experts workshop on the problem in March 2001. Clams do not bind cadmium to their tissue like oysters and scallops do.

British Columbia's oyster aquaculture industry has built itself from the ground up, overcoming many problems as it has developed from low income back-breaking beach operations based on wild seed, to a mechanised deep water culture. Today the BC industry is worth about $15 million and employs over 1,000 people, exporting two thirds of the product to the United States.

The BC government is in the midst of an aggressive plan to expand the shellfish aquaculture industry by 10% a year for a decade, to provide government revenues and rural employment. In a classic but small- scale BC land use conflict, those plans are being challenged by local neighbourhood organizations and the Alliance for Responsible Shellfish Farming. Many neighbours find the visual, noise, and garbage impacts of a newly-mechanised oyster industry unacceptable in rural residential bays. Growers respond that they are hard-working people trying to make an honest living.

Further, biologists are starting to examine the ecological impacts of the industry on foreshore and bird habitat, a shock to an industry which has always prided itself on its environmental sustainability. In areas like Cortes Island's Gorge Harbour, the tension has been aggravated by an industry-sponsored study purporting to show the feasibility of massive expansion. In rural communities, it is never difficult to arouse social animosities, fought out with outrageous accusations and tedious zoning battles. The government's appointment of Brian Kingzett, a grower and advisor to the BC Shellfish Growers' Association (BCSGA) as the gatekeeper for public comment on a new Code of Practice for the industry has not inspired confidence. The Alliance for Responsible Shellfish Farming calls it a "clear conflict of interest."

In the midst of these issues, in early February 2002, Health Canada issued a risk assessment advising that "regular consumers, including fisher persons or subsistence eaters" limit their consumption of British Columbia oysters to twelve a month for adults and one and a half for children, due to high cadmium content. Because cadmium is slowly accumulated and stored in the liver and kidney, Health Canada focused on the long-term local consumer.

For retail customers, "consumption in moderation, as part of a well-balanced diet, of a mix of commercially-sold oysters" containing the coastal mean of 2.6 parts per million cadmium "would not pose an imminent health risk to adults." Consumption at the retail level by children might be assessed as "problematic" except that most children don't eat a lot of oysters, and their cadmium intake (and storage) will be averaged over a lifetime.

Cadmium is a toxic metal, which threatens world food supply in rice or other staples. The World Health Organization has established an estimate of safe consumption levels for cadmium, a Provisional Tolerable Weekly Intake, of 490 micrograms per week for a 70 kg. man, and less for smaller people, eg.) 350 micrograms for a 50 kg. person. Twelve Pacific oysters a month, every month, containing the mean amount of cadmium, plus the cadmium in other food, would put a 70 kilogram adult very close to the advisable consumption for cadmium. Health Canada calls 12 oysters four and a half servings (!)

Accumulation of low levels of cadmium, some of which is retained in the liver and kidneys, can be tolerated, but high levels of consumption can sometimes lead to kidney and lung impairment, bone frailty, possible nerve and brain impairment, and reproductive problems for male development. Many of these effects for human health are disputed, probably because there is variability between species and groups of people. There is no disagreement that inhaled cadmium is almost certainly a human carcinogen.

Health Canada noted a high variability in test results from different locations along the BC coast, which means that many oysters are low in cadmium and perfectly fine, while others have so much cadmium in them that two or three would contain the weekly suggested limit for cadmium ingestion.

Cadmium is absorbed in minute amounts from most of our food, such as rice and potatoes, at levels of between one fifth to three quarters of the World Health Organization estimated tolerable weekly intake on a long term basis. In 1994, the Canadian Environmental Protection Act Priority Substances report on Cadmium and its Compounds, after examining food and air issues, reported that "several lines of evidence indicate that members of the general population in Canada are exposed to cadmium compounds in amounts that are at or near those that have been associated with mild effects on the kidney." A more recent UN assessment agrees, "There is only a relatively small safety margin between exposure in the normal diet and exposure that produces deleterious effects."

The crux of the toxics policy failure in Canada is this: Three months after the Health Canada risk assessment was sent to the Canadian Food Inspection Agency (CFIA), no one has informed the local populations, small growers, or doctors along BC's coast, of Health Canada's advice to "take it easy" on the oysters.

Klaus Schallie of CFIA which asked Health Canada for the risk assessment, has drawn up a "multi-stakeholder committee" of federal and provincial government representatives and the BC Shellfish Growers Association to discuss the "communication strategy" for telling the public. In toxics policy lingo, this is called the risk management stage. As of the end of May, Schallie planned for that committee to meet to start discussing how to communicate the problem, "in a month or so." In fact, a wide circle of bureaucrats and scientists already know about the risk assessment.

The only folks not "in the loop" are those whose health is most likely to be affected — local people eating oysters, some of them off particular beaches and rafts which may be hot spots for cadmium contamination — and new investors, including First Nations, who are being encouraged to enter the industry as part of government-driven economic growth.

The concern expressed by most government bureaucrats, in particular those at CFIA, and the provincial Ministry of Agriculture Food and Fish, is to preserve the market for Pacific oysters. Most of the bureaucrats have evolved defensive but not particularly scientific arguments why the BC coastal public should not yet be informed of the risk assessment. The various arguments range from lifestyle, "I personally eat a lot of oysters and I'm healthy," to historical, "The First Nations ate lots of native rock oysters and they were ok."

Of course, the old stand-by is always, 'It's not our responsibility,' with the finger being pointed back to CFIA. Only Fisheries and Oceans agrees that shellfish advisories for recreational harvesting are part of their mandate (for example they run the Paralytic Shellfish Poisoning warning hotline) but the cadmium issue presents new challenges because the bureaucratic ball is in CFIA's court.

BC Ministry of Health Doctor Ray Copes, only recently informed of the problem, suggested that some local research would be a good start, since cadmium absorption depends on individual nutrition, zinc and calcium levels, age, and sex. "If very little gets in, you don't have a problem, and we don't have that information." Copes emphasized that public health was his mandate, but pointed out that, although cadmium does certainly have chronic toxicity effects on long term exposure, it is "a problem, not an emergency."

The BC government considers the issue of cadmium-contaminated product to be irrelevant to its lease expansion plans and so far is not even considering cadmium measurements as a site feasibility criteria. The US provides a prime market for BC shellfish, and their allowable levels, at 3.7 parts per million, are almost twice as high as those at the Hong Kong border (2 ppm). Inside Canada, there are no restrictions on cadmium levels. Therefore, the provincial government foresees no problem.

The BCSGA, whose consultant is shellfish grower Brian Kingzett, appears to have been trying to keep the lid on news about the cadmium levels. Kingzett complained to their superiors that scientists who spoke by invitation of Friends of Cortes Island to a community meeting in January were guilty of unprofessional conduct and fear-mongering. The BCSGA first agreed to participate and then withdrew from research that the scientists at Fisheries and Oceans and several BC universities had been planning for over a year.

The scientists think a "grow out" experiment, at many different sites by various methods, with regular sampling every month, will tell them when and where in the oysters' life, the cadmium enters. This information could allow growers to site or time their operations to avoid high cadmium inputs. For example, some (clearcut) watersheds may be leaching high cadmium from exposed rock, or beach versus in-water life cycles might change the cadmium uptake, or it may occur only at certain times of the year, with certain plankton blooms or at particular oyster ages.

When BCSGA withdrew from the research, funding from an aquaculture development fund was lost. The research is now stalled, partially done. [BCSGA did not respond to a request for a statement about their position on cadmium for this article.]

That the research was able to proceed at all was due to the co-operation of individual growers along the coast, who want to get to the bottom of this problem. Many members of the shellfish industry have been proactive in working for clean water and they are proud of their environmental record. The Cortes Island Shellfish Growers' Co-op, whose 55 independent members are clear that ignoring the problem will not make it go away, are serious about wanting more information. "We are joining the search for answers," says spokesman Cec Robinson, "because we want to do the right thing. I want to know what is the best way to grow oysters to avoid cadmium uptake."

In Other Countries

Northern European countries have moved to control cadmium releases. Levels in the population and the North Sea are falling. Air pollution controls are capturing airborne cadmium. Sweden, Finland, Denmark and others control the amount of cadmium allowed in fertilizer, and Sweden taxes fertilizer based on its cadmium content. Sweden, Denmark, Germany, Austria, and the Netherlands strictly regulate the amount of cadmium in plastics and Sweden bans its use as a stabilizer in plastic.

Missing medical data:

Cadmium absorption is a complicated process, affected by many factors, from the type of cadmium compound to the amount of zinc, iron and calcium in the diet, which allow the body to eliminate the metal.

The real impact on frequent oyster consumers is unknown. It is unknown whether oysters, not only delicious but also nutritious, with high levels of calcium, zinc and iron cause the body to process cadmium differently than other foods. Their frequency of consumption is also different than other foods. However, the Health Canada recommendation is solidly based on what is known at this time.

What causes it?

Cadmium, a metal, occurs naturally in the environment often in association with zinc and other minerals. Industrial sources and uses include:

  • zinc smelters like Trail, where airborne cadmium releases have been high;
  • nickel-cadmium rechargeable batteries;
  • coatings, paints and plastics, including some of the PVC used in aquaculture;
  • sewage outfalls and treatment plants, industrial effluents including pulp mill discharges, and storm water run off;
  • phosphate fertilizers, which often contain cadmium by natural association, subject to run off and leaching;

It seems likely, although not yet proven, that cadmium is being released into Georgia Strait from old mines and erosion due to development and clearcut logging. Significant amounts of cadmium are also already in sediments in some places, notably Cortes Island, and may be resuspended by aquatic life or upwellings.

Preliminary studies, including US tests, suggest there may be an increasing concentration from south to north. The Pacific Ocean may cycle cadmium. Scientists also say cadmium in storm water run off from the Fraser Delta and from Puget Sound would travel to northern Georgia Strait. Some aquaculture equipment leaches significant cadmium from the PVC. Scientists down play apparently increasing cadmium levels based on historical samples, due to the lack of information about earlier sampling methodology.

In the wild: Colorado Ptarmigan

In December 2000, scientists reported that more than half the white-tailed ptarmigans in a 10,000 square kilometre area of south-central Colorado, called the "ore belt," were suffering from cadmium poisoning. The birds had damaged kidneys and their bones were low in calcium. Many of the birds had fractures. The birds eat willow, which accumulates cadmium, as do some other plants. Cadmium is natural in the area, but abandoned mines may have mobilised more of the metal.

* Oregon State University News, December 2000

Health impacts
  • Known human carcinogen (International Agency for Research on Cancer).
  • Reproductive toxin affecting male development (California Proposition 65 List).
  • Cadmium stays in the body a very long time, and long-term exposure in food or water leads to a build up in the kidneys and possible kidney disease, lung damage and fragile bones.
  • Test animals showed high blood pressure, low blood iron, liver disease and nerve or brain damage. These effects have not been shown in humans.
  • Babies of animals exposed to high levels in food had changes in behaviour and learning ability and possible changes in birth weight and skeleton. Effects on human children are unknown. Some cadmium crosses the placenta, and can be found in breast milk.
  • Some communities in New Zealand eat high cadmium shellfish with no apparent effect.
  • Diets adequate in iron, calcium and zinc appear to lower cadmium absorption. (Oysters are also extremely high in those elements.) Women seem more vulnerable than men, perhaps because of low iron levels. Older people are less vulnerable.
  • Japanese women on a poor post-war diet, eating rice grown on cadmium-contaminated ground, developed Itai-Itai ("ouch ouch") disease, characterised by kidney failure, muscle cramps and fragile, painful bones, especially in the spine and femur.


[From WS June/July 2002]

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