Determination And Migration Of Heavy Metals In Food Paper-plastic Composite Packaging Materials

In recent years, food paper-plastic composite packaging materials are widely used in the food packaging industry, and its safety is an integral part of the food safety. Food paper-plastic composite packaging materials combine the advantages of plastic and paper, but paper and plastic will be adding a number of functional additives in production, so there is over the issue of migration of heavy metals, free monomers and degradation products. Heavy metals may migrate to food, once feeding by the body, easy to accumulate in the body, causing potentially harmful, even toxic reactions, which would be a threat to human health.In this paper food paper-plastic composite packaging materials being study object, detection methods of toxic heavy metals (lead, cadmium, hexavalent chromium and mercury), migration experiment and theoretical migration prediction modeling of migration of heavy metals from food paper-plastic composite packaging materials into food were discussed. The contents are as followings.1. The wet digestion-flame atomic absorption spectrometry detection methods of lead and cadmium were optimizedThe study identified pretreatment methods of lead and cadmium in the food paper-plastic composite packaging materials:the 0.5000g sample with 12mL of nitric acid digestion were the best results. The best optimized detection conditions of lead were as followings:analysis wavelength of 283.3nm, the lamp current of 8mA, a slit width of 0.7nm, the burner height of 7mm, the air flow of 14.5L·min-1, the acetylene flow rate was 2.2L·min-1. The best optimized detection conditions of cadmium were as followings:analysis wavelength of 228.8nm, the lamp current of 6mA, a slit width of 0.7nm, the burner height of 5mm, the air flow of 15.5 L·min-1, the acetylene flow rate was 2.2L·min-1.Lead and cadmium showed a good linear relationship respectively in the range of 0.10 to 1.00 and 0.02 to 0.10μg·mL-1. The respective detection limits were 0.0689μg·mL-1 and 0.0028μg·mL-1, the recoveries of lead ranged from 93.86% to 100.04%, and the relative standard deviations of lead ranged from 1.61% to 4.07%. The recoveries of cadmium ranged from 93.43% to 96.29%, and the relative standard deviations of lead ranged from 2.29% to 4.78%.2. The wet digestion-flame atomic absorption spectrometry detection method of hexavalent chromium was optimizedThe study identified pretreatment methods of hexavalent chromium in the food paper-plastic composite packaging materials:the 1.0000g sample with 14mL of mixed acid (nitric acid:perchloric acid=3:1) digestion were the best results. The best optimized spectrophotometric detection conditions of hexavalent chromium was as followings:when the optimum amount of (1+1) sulfuric acid was 0.5mL, the optimum dosage of (1+1) phosphate acid was 0.5mL, and the amount of color reagent was 2mL, measured the highest concentration of hexavalent chromium. Hexavalent chromium showed a good linear relationship in the range of 0.00 to 0.28μg·mL-1 with a correlation coefficient of 0.9999, and the detection limit was 0.0075μg·mL-1. The recoveries of hexavalent chromium ranged from 93.81% to 96.83%, and the relative standard deviations of hexavalent chromium ranged from 1.83% to 3.07%.3. The wet digestion-atomic fluorescence spectrometry detection method of mercury was optimizedThe study identified pretreatment methods of mercury in the food paper-plastic composite packaging materials:the 0.5000g sample with 10mL of concentrated nitric acid and 2mL of hydrogen peroxide digestion 4h were the best results. The best optimized atomic fluorescence spectrometer detection conditions of mercury was as followings:a negative high voltage of 210v, the atomizer height of 10mm, the Hg lamp current of 10mA, the carrier gas flow rate of 500mL·min-1, the shielding gas flow rate of 900 mL·min-1, reading mode of peak area, carrier medium for the 5% hydrochloric acid, potassium borohydride solution and the concentration of the potassium hydroxide solution were 5g·L-1. Mercury showed a good linear relationship in the range of 0.00 to 40.00ng·mL-1 with a correlation coefficient of 0.9992, and the detection limit was 0.0025μg·mL-1. The recoveries of mercury ranged from 95.93% to 97.38%, and the relative standard deviations of mercury ranged from 3.02% to 3.85%.4. Study on migration experiment of lead, cadmium, hexavalent chromium and mercury from food paper-plastic composite materialsMigration of lead, cadmium, hexavalent chromium and mercury from food paper-plastic composite packaging materials with different materials and different thickness into 3% acetic acid,10% ethanol,20% ethanol and 50% ethanol at 20℃,40℃ and 60℃ were studied. Migration were studied through two methods:one method was a direct migration test on two kinds of selected samples and another was a migration test after highly concentrated pollution treatment on four kinds of selected samples. Rules were identical by these two methods in the same migration conditions, and laws were identical by four heavy metals in the same migration conditions. The results showed that the maximum amount of the same element migration of different samples in the same food stimulants was proportional to the initial migration concentration of the sample element, while the real mobility was independent of the initial migration concentration at the same temperature. The maximum migration amount of the same element of different samples in the same kinds of food stimulants increased as the temperature rise, and the real mobility also increased. Migration laws of four elements to the four food stimulants at 20℃,40℃ and 60℃were identical. Migration rate of the same element into 3% acetic acid was the fastest. However, migration rate into 50% ethanol was the lowest at the same temperature, and the migration rate was faster as the temperature rise. The same element migration of the same material in printed materials was larger than non-printed materials. The effect factors on migration of the four heavy metals elements were analyzed from a microcosmic viewpoint in this paper, and the factors included initial migration concentration, temperature, molecular structure, food simulants, thickness of the material and printing. In addition, the initial total amount of lead, cadmium, hexavalent chromium, mercury from food paper-plastic composite materials and the total amount of migration in four food simulants at 20℃,40℃and 60℃were analyzed from a macrocosmic viewpoint. Food paper-plastic composite packaging materials were not safe when used for storage of acidic foods. However, they were safe when used for storage of milk products, oil in water foods, food products containing more than 20% ethanol at low temperatures, so as to provide a theoretical basis for the evaluation of the safety of the food paper-plastic packaging materials.5. In this paper food paper-plastic composite packaging materials were used as objects to establish a "limited package-unlimited food" heavy metal migration prediction model, which based on Fick’s second law, considered the diffusion and distribution coefficients, combined with the initial and boundary conditions. Using numerical methods, the concentration had been given the approximate solution of heavy metal migration.In the migration model, diffusion coefficients of the four heavy metals at different temperatures were estimated by classical models, and partition coefficients of four heavy metals in four food simulants at 20℃,40℃ and 60℃ were calculated in accordance with the definition of partition coefficient. Through analysis, diffusion and distribution coefficients were in line with the migration test results, and were estimated reasonable.The comparison of the migration of the forecast trend and the actual migration data were analyzed by Matlab. The results showed that the trend of the experimental values were in accordance with prediction model. And the deviation of the migration was also in line with the actual situation, the model predicted accurately lead, cadmium, hexavalent chromium from the paper-plastic composite packaging materials in 3% acetic acid,10% ethanol,20% ethanol and 50% ethanol.