by Dr. Leah Bendell and Dr. George Kruzynski In the interest of public health, we believe the statements made by Matthew Wright, BC Shellfish Growers Association, in his letter to the editor [“Cadmium effects unfounded,” January 12, 2011] need to be corrected.
1. “Cadmium is in everything from vegetables to the air we breathe.” One serving of oysters (six 40-gram oysters) provides 260 times more cadmium than a one-cup serving of spinach. You would have to eat 390 mid-size tomatoes to obtain the cadmium from one serving of BC oysters. Air concentrations of cadmium are negligible unless you are close to an industrial source such as mining.
2. “To attribute any adverse health effects from cadmium absorption to shellfish consumption is unfounded.” It is the total intake of cadmium from all sources that is important. In 2009 the European Food Safety Authority set the safe intake from combined sources at 2.5 micrograms cadmium per kilogram body weight per week. An adult eating more than six oysters per month will exceed the safe total intake from oysters alone, without considering other less-avoidable sources.
3. “A study by the Center for Disease Control (CDC) and Prevention-Atlanta...states that there is no direct link between BC oyster consumption and increased levels of cadmium in the body.” Neither we nor the CDC and Prevention-Atlanta were able to find such a study. Wright is likely confusing one done by R. Copes et al (2008) of the BC Center for Disease Control and UBC which concluded the opposite: “a rise in blood Cd was observed after 12 years of farming oysters, likely caused by consumption of oysters during this period. Oyster derived Cd is bioavailable and affects body stores of the metal.”
4. “The Canadian Food Inspection Agency (CFIA), through vigorous testing regimes, has confirmed...no scientific evidence linking adverse health effects to naturally occurring cadmium found in shellfish...It recently revisited this issue...and recommended that no changes be made to Health Canada’s consumption guidelines.”
CFIA has no such mandate. Director Paul Littlewood, for BC-Coastal Region, notes “To clarify our respective roles, Health Canada is responsible for establishing food safety standards. The CFIA enforces these standards through inspection, testing and communicating with regulated parties and the public. Health Canada conducts Health Risk Assessments and advises on consumption guidelines, which may in part be informed by the data collected by the CFIA.”
5. “People have been eating farmed shellfish from BC for over a hundred years and there has never been one direct link to adverse health effects documented.” The objective is to ensure that the public are aware of shellfish consumption limitations in light of the cadmium contents of their daily diet. This will ensure that their overall exposure to cadmium does not exceed current safe intake limits (European Food Safety Authority, 2009) and long-term health impacts from this source of (natural) contamination are avoided.
Dr. Leah Bendell is professor in biological sciences, Faculty of Science, and director of environmental science, Faculty of Environment, Simon Fraser University. Dr. George Kruzynski is a retired Fisheries and Oceans Canada research biologist who specialized in aquatic toxicology and conducted an investigation into the source of cadmium contaminating BC cultured oysters.
