Experimental And Theoretical Study On Migration Of Heavy Metals From Ceramic Food Packaging Material

Food safety, a global public security issue, which is closely related to the consumer’s health, has been one of the key international technical barriers in food trade. As an important food contact material, domestic ceramics, has been widely implied in the food packaging industry; however, the release of heavy metals from which, has a direct negative impact on hygiene and safety of food. The obvious disparity of standard permissible limits of release of heavy metals from ceramic materials in contact with food between our country and the developed country, has become the major bottleneck for both export of ceramic products and development of ceramic industry in our country. At the same time, research in our country on safety of ceramic food contact material is at the starting stage, and its foundation is weak. And the lack of systematic research on migration law, migration mechanism, influencing mechanism and migration model of heavy metals from ceramics into foods makes effective prediction and control of migration of heavy metals from ceramic food packaging material and hence implementation of safety evaluation and setting safety regulations lack theoretical basis.Aiming at the migration of typical heavy metals from ceramic food packaging, the author carried out some systematic research and exploration in this thesis. The author analyzed the influence factors of migration of heavy metals, obtained the migration law of heavy metal from ceramic packages into various kinds of food simulants and typical foods through the analysis of the migration experiments, and discussed the migration mechanism of heavy metals. Meanwhile, the author established a prediction model of migration of heavy metals from ceramic material into food. The main research contents and conclusions are as follows:(1) Establishment of migration test method of heavy metals from ceramic food packaging materialHarmful substances-lead, cadmium, cobalt, nickel and zinc were chosen according to their toxicity, frequency and amount of use.4% and 10% acetic acid,1% citric acid,1% lactic acid, Chinese liquor, yellow rice wine, mature vinegar and juice of cowpea pickled were selected on the basis of a short-term (24h) migration test and market survey in ceramic food packaging. Moreover, migration test conditions were determined according to a guide to test methods for the specific migration of substances from plastics to foods. Meanwhile, simultaneous determination methods of heavy metals by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES) from ceramic food contact material were established by means of matching standard solution with sample solution to eliminate matrix interferences.(2) Influence of production process on migration of heavy metals from ceramic glaze into foodThree main factors influencing migration of heavy metals into food simulant-the initial concentration of heavy metals in glaze, glaze layer thickness and firing temperature (temperature and time)-were analyzed through experiments. The results show that, the migration amounts of heavy metals into food simulant increase with the initial concentration of heavy metals in glaze only at the initial stage, and it was affected more obviously by the glaze composition as time goes by. Therefore, when preparing ceramic glaze, reducing both the initial concentration of heavy metals and the proportion of feldspar in glaze could reduce the release of heavy metals to a great degree. Moreover, the amounts of heavy metals migrated increase with glaze layer thickness and decrease with firing temperature, and the migration of heavy metals is more susceptible to firing temperature compared with glaze layer thickness.(3) The migration law of heavy metals from ceramic glaze into foodThe migration of heavy metals from ceramic glaze into 4% and 10% acetic acid,1% citric acid,1% lactic acid, Chinese liquor, yellow rice wine, mature vinegar and juice of cowpea pickled under 20,40 and 60℃ was studied by a series of migration tests. Factors on influencing migration of heavy metals including storage time and temperature, food characteristics such as pH value, and alcoholicity of food were analyzed. In addition, comparison of migration amount of lead and cadmium between food simulant and real food was also analyzed. Meanwhile, the author also made safety assessment of ceramic glaze prepared by experiment. The results of the investigation indicate that, the amounts of heavy metals released into food simulant and food increase with temperature, similarly, the rates of release of these heavy metals increase with temperature, too. The amounts of heavy metals migrated decrease with pH value of the food simulant and food under acidic environment. In alcohol food, with an exception of a positive correlation between cadmium migration amount and alcoholicity, the amounts of lead, cobalt, nickel and zinc migrated from ceramics are inversely proportional to alcoholicity of food. Moreover, according to the comparison between the migration amount of heavy metals into real food and 4% acetic acid, we can see that the migration amount of lead and cadmium into real foods are 1.9%-50.7% of which migrated into 4% acetic acid under the same condition. Meanwhile, the amounts of lead and cadmium release into 4% acetic acid are 7.6% and 50.7% of the most rigorous standard permissible limits of lead and cadmium.(4) The discussion of migration mechanism of heavy metals into foodThe migration mechanism of heavy metals from ceramic glaze into food were discussed in view of comparison between M:Si (M means heavy metals) ratio in food simulant and in glaze combining with kinetic analysis of migration test of heavy metals, referring to corrosion mechanism of silicate and the characteristic of lead migration from glass. The results indicate that the migration mechanism of heavy metals from ceramic glaze is a diffusion controlled ion exchange process.(5) Establishment of the prediction model of migration of heavy metals from ceramic glazeA migration prediction model of heavy metals from ceramic food contact material was established and characterized uniformly taking into account storage temperature. Then, the diffusion coefficients of heavy metals migrated were obtained by fitting the short-term (24 h) migration data to the model solution. Moreover, verification of the proposed model was carried out by comparisons of model predictions with experimental data obtained from the long-term (130d) tests. The prediction results show that the proposed model can effectively predict the long term migration behavior of heavy metals from ceramics into real foods based on short-term migration test.