On 11 Feb 2015, the Centre for Food Safety (CFS) announced that two dried mushroom samples exported from China were detected with toxic metal “cadmium”, at levels (0.13 – 0.15 ppm) exceeding the legal limit (0.1 ppm).
Benefits and Risks of Edible Mushroom
Edible mushrooms have long been considered as delicious and health foods. For example, shiitake mushroom (Lentinula edodes) is a very common festive food in the Chinese New Year.
Mushrooms are widely consumed because of their high nutrition values, such as high protein, vitamin (e.g. B1, B2, C & D), fiber (e.g. beta-glucan) and mineral (e.g. iron, zinc & selenium) contents, as well as low calories.
However, several species of mushrooms are known to be capable of accumulating high levels of toxic contaminants including cadmium from their growing environment.
Toxicity of Cadmium
Cadmium is a heavy metal of particular concern. It is particularly toxic to kidneys and bones, and can impair human health. Therefore, maximum permitted levels for cadmium in foodstuffs have been set by different countries. In Hong Kong, the legal limit of cadmium in “cereal and vegetables” is 0.1 ppm.
Sources of Cadmium
Cadmium is a naturally occurring element. It can enter the environment (air, water and soil) in many ways. Human activities like metal mining and burning of coal can release cadmium into the air. Cadmium can also enter water via industrial wastewater discharge. Morever, cadmium can pollute soil due to release of car exhaust, fertilizer usage, and the deposition from the air.
Cadmium in the environment may be finally taken up and accumulated in plants growing there. The concentrations of cadmium in mushrooms can vary widely by countries and geographic regions, depending on their contamination levels.
Dietary Intake of Cadmium
Generally speaking, food is the major source of cadmium for the general population.
The reported levels of cadmium in most food categories are low (0.0001 to 0.04 ppm). However, certain foods including wild mushrooms can contain high levels of cadmium. The cadmium level in dried mushroom samples announced by the CFS was up to 0.15 ppm.
In order to assess the adverse health impact caused by consumption of a mushroom product, we should not only look at the level of cadmium in mushroom, but also the quantity of the food consumed.
The reported mean cadmium exposure in adults at different countries/regions ranged from 2.2 to 12.0 µg kg-1 body weight per month. This is below the safety reference value (Tolerable Monthly Intake TMI) of 25 µg kg-1 body weight established by JECFA.
However, the possibility of exceeding TMI depends on personal dietary habits and cadmium level in foods. For example, individuals who frequently eat food (e.g. mushroom) grown in heavily contaminated soil may be at increased risk of adverse renal effects caused by cadmium.
Safeguard Food Safety of Edible Mushroom
i. Food Safety Assurance at Source
The problematic mushroom products announced by the CFS came from China. As such, the Mainland authorities should investigate the areas where mushroom is cultivated and harvested, and ensure they are fit for production and free from heavy metal (and other pollutant) contamination.
In addition, all exporting farms should adopt Good Agricultural Practice (GAP) as a food safety assurance tool for safe mushroom production.
ii. Supplier Audit
Local food trade especially importers should also take appropriate affirmative steps for food product sourcing. Importer must understand the potential hazards and regulatory standards associated with mushroom products, and ensure their suppliers (e.g. Mainland farmers) are able to supply product meeting the legal requirements.
As such, suppliers should be on-site audited from time to time and then ranked. Those suppliers providing occasional substandard products should be audited more frequently, or no longer used.
(Food Safety News, 2012)
Indeed, more and more big companies choose to employ independent assessor to perform food audits on their food suppliers. By doing so, an independent and impartial assessment can be done without deploying tremendous internal resources of the companies.
iii. Imported Food Testing
Testing of imported mushroom is not the sole responsibility of the government. Importers are recommended to obtain assurances that the mushroom products they import are safe, wholesome and of acceptable quality, and meeting the legal requirements.
Food testing at the import level is therefore essential for verifying food products are “good”. Please note that testing of mushroom should not be limited to cadmium. This is because other food safety hazards can also be found in mushrooms at various points along the production, handling and marketing chain: 1) microorganisms (e.g. pathogenic bacteria); 2) chemicals (e.g. heavy metal lead, pesticide residues and toxins) and 3) physical hazards (e.g. foreign objects like glass).
As such, the trade should prepare an annual risk-based testing plan for their imported foods, clearly indicating the types and frequencies of tests to be conducted, and review suitability of the plan periodically.
Wish you a Healthy, Happy and Fruitful Year of the Ram!