Whether dining out or staying in for a cosy home-cooked meal, ceramic tableware is often used on a daily basis. The raw materials for ceramic tableware are different types of pottery or porcelain clay, which undergo the processes of shaping, glazing,and high temperature firing to become finished products with kaleidoscopic colours. However, if poor quality glazes are used or the production process is not properly controlled, ceramic tableware may release harmful heavy metals such as lead and cadmium, which may then migrate into food. The Consumer Council tested 30 models of ceramic tableware commonly available on the market, including 15 ceramic cups and 15 ceramic bowls, under simulated use at room temperature and microwave heating. It was found that about 35% (11 models) released varying concentrations of lead and over 10% (4 models) released cadmium from internal surfaces or drinking rim area in the test at room temperature, but the levels of lead and cadmium released from concerned models were below the upper limits stipulated by relevant international and Mainland standards. As for 13 models labelled as microwavable, no detectable lead and cadmium were released from internal surfaces under the simulated high-temperature use, thus the finding is satisfactory. Nevertheless, the Council recommends relevant manufacturers to review manufacturing processes and monitor the quality of their products to further minimise the possibility of the release of heavy metals, hence reducing health risks posed to consumers due to exposure to hazardous heavy metals for prolonged use.
The Council purchased 15 ceramic cups and 15 ceramic bowls from department stores and household product shops for testing. Prices of the models varied considerably, with the ceramic cups ranging from $10 to $310, of which 4 were labelled as microwavable; while prices of the ceramic bowls ranged from $11 to $140, with 9 labelled as microwavable. The models were tested for lead and cadmium release according to their labelling information and intended use with reference to the international standard ISO 6486-1, the French regulation DGCCRF, and the Mainland standards GB 31604.34 and GB 31604.24. With reference to the requirements of ISO 6486-1, 4 identical pieces of the same model were tested, and the amount of lead and cadmium released from any one piece shall not exceed the upper limit of the relevant requirements.
About 35%of Models Detected with Lead and Over 10% with Cadmium
As the internal surface of cups and bowls is the major part that comes into direct contact with food, and consumers’ lips would come into contact with the rim of cups and bowls, the tests respectively examined lead and cadmium released from the internal surfaces as well as the rim. The International Agency for Research on Cancer (IARC) classifies inorganic lead compounds as Group 2A substances (probably carcinogenic to humans), in which an excessive intake over prolonged periods could impair the development of the brain and central nervous system in foetuses, infants and children, resulting in reduced intelligence quotient, stunted growth, and hyperactivity. As for cadmium, it can be accumulated in kidneys and prolonged intake may impair kidney function. Some studies found that cadmium may impede calcium absorption and may cause softening of the bones, and the IARC has classified cadmium and cadmium compounds as Group 1 substances (carcinogenic to humans). The test simulated use under ambient temperature in accordance with the international standard ISO 6486-1. For the internal surface test, 4% acetic acid was poured into the samples, while for the drinking rim test, a 2cm wide section measured downwards from the upper edge was immersed in 4% acetic acid. Both were left to soak for 24 hours at 22°C, with lead and cadmium levels in the acetic acid solution being measured afterwards. This test simulated the release of harmful substances from tableware when acidic foods are served at room temperature for a long period of time, which represents a very stringent condition for comparative test of ceramic products.
It was found that around 35% of the models (11 models), including 6 ceramic cups and 5 ceramic bowls, released lead either from the internal surface or the rim, with detected levels ranging from 0.10mg/l to 1.00mg/l in the internal surface test and 0.10mg to 0.31mg per article in the drinking rim test. Among these models, 6 released lead from both the internal surface and the rim, but all levels were in compliance with the requirements of the relevant standards[1].
Cadmium was found to be released from over 10% (4 models) of the models, all of which were ceramic cups. Among them, 3 released cadmium at levels ranging from 0.012mg/l to 0.060mg/l from the internal surface, while 2 released cadmium from the drinking rim (including 1 model with cadmium released from the internal surface), and the highest levels of cadmium detected in these 2 models were 0.016mg and 0.023mg per article respectively. Overall, despite 1 model detected with lead and cadmium release from both the internal surface and the drinking rim, the levels of lead and cadmium released from all models complied with the requirements of the relevant standards[2].
All Microwavable Models Not Detected with Lead or Cadmium Release
Under Simulated High Temperature Conditions
Apart from room temperature, ceramic tableware is often used to heat beverages or food in microwave ovens. Of the 30 models, 13 were labelled as microwavable, including 4 ceramic cups and 9 ceramic bowls. A test simulating microwave heating at high temperature was conducted to examine any changes in the amount of lead and cadmium released. As the international standard ISO 6486-1 does not specify a test for microwaveable ceramic products, the test was conducted with reference to the Mainland’s National Food Safety Standard-Food contact materials and products GB 31604.34 and GB 31604.24. Acidic food simulant (4% acetic acid) was poured into the samples, then set aside for 15 minutes at 100°C. The levels of lead and cadmium in the acetic acid solution were then measured. All models labelled as microwavable were found to be satisfactory with no release of lead nor cadmium.
While the current test results showed that there was no exceeding of limits for lead and cadmium, the German Federal Institute for Risk Assessment (BfR) concluded that products for daily use, including ceramic tableware, should not increase consumers’ exposure to heavy metals. The Council recommends that manufacturers review their production processes and monitor product quality, to further reduce the risk of heavy metal release, and to minimise the possible exposure of consumers, especially children, to lead and cadmium from daily use of ceramic tableware.
Some tips for consumers when purchasing and using ceramic tableware:
- Before purchase, check labelling information on products to see if they comply with the relevant food safety standards, or whether they are labelled as suitable for food contact or for use in microwave ovens and dishwashers;
- With reference to the recommendations of the Mainland’s State General Administration of Quality Supervision, Inspection and Quarantine (AQSIQ) and the California Department of Public Health of the United States of America, avoid products with food contact surfaces such as the internal surface and rims that are brightly coloured (e.g. orange, red or yellow) or are decorated with patterns, as well as decoration on top of the glaze instead of beneath it (with rough or raised decorations);
- Do not use antique ceramics, decorative ceramics, or ceramics not for food use as tableware;
- Consumers may refer to the recommendation of the Mainland’s AQSIQ and soak tableware in cooking vinegar for a few hours before first use. Consumers should consider avoiding use if there is a noticeable change in the colour of the vinegar as the risk of lead or cadmium released from these products is generally higher;
- Corrosion on glazed surfaces or grey powdery residue on glazed surfaces after washing may mean possible release of lead or other harmful substances and consumers are advised to stop their use;
- Do not clean ceramic tableware with wire brushes or scrubbing scourers to avoid scratching the vessel surfaces. It is recommended to wipe gently with sponges and dishcloths with mild detergent, then rinse with water and air dry.
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[1] The international standard ISO 6486-2 sets a permissible limit of 0.5 milligrams per litre (mg/l) for lead release from (internal surfaces of) cups and mugs at room temperature; while for ceramic bowls, categorised as small hollowware, have a permissible limit of 2.0mg/l. For ceramic products, as set by the French Directorate-General for Competition, Consumption Affairs and Fraud Prevention (DGCCRF), the limit of lead release by oral contact at the rim is 2mg/article.
[2] The international standard ISO 6486-2 sets a permissible limit of 0.25mg/l cadmium leaching from the internal surfaces of cups and mugs when used at room temperature; while ceramic bowls, categorised as small hollowware, have a permissible limit of 0.5 mg/l. The upper limit of cadmium release by oral contact at the rim is 0.2 mg/article in accordance with the level set for ceramic products by the French Directorate-General for Competition, Consumption Affairs and Fraud Prevention (DGCCRF).