Leaching of Heavy Metals Contaminants in Recycled Polyethylene Terephthalate Used for Food Packaging

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1 Leaching of Heavy Metals Contaminants in Recycled Polyethylene Terephthalate Used for Food Packaging Michael Whitt, Wyatt Brown and Keith Vorst California Polytechnic State University Summary Twenty-two recycled polyethylene terephthalate (RPET) packaging materials of known cadmium, chromium, lead, nickel and antimony content were stored with water or 5% citric acid solution for 1, 7 or 14 days at 45 or 72 F. This was done to determine leaching potential of the heavy metals onto food. In a separate test, the plastics were subjected to microwaving for 5 minutes in the presence of water or 5% citric acid solution. After storage or microwaving, the solutions were tested using an Inductively Coupled Plasma Atomic Emission Spectrometer (ICP- AES). Whether subjected to microwaving or storage, leaching from the plastics was minimal and well below the maximum allowable dose level (MADL) for each metal. Previous work indicated the heavy metal content within the plastics to be in the parts-per-million range. With respect to leaching, all samples tested below 1 ppb regardless of treatment or storage time. Significantly more heavy metal leached from plastics exposed to a 5% citric acid solution compared to water. Leaching varied with heavy metal antimony leached the least and lead the most but, again, leaching was very minor and of no health concern. Microwave Treatment Methodology: Twenty-two RPET packaging materials of known heavy metal concentration (Table 1) were tested for the leaching as affected contact with either water or 5% citric acid solution. The experiment was a completely randomized design with 3 replicates. The data was non-repeated as discrete samples were used for each measurement. Twenty ml scintillation vials with Teflon-coated lids were used to hold the treatment solution. The RPET samples were prepared by cutting circles of plastic to fit snugly inside each vial lid. The vials were then filled with 5.55 ml of either 5% citric acid solution or water. For accuracy, volume was determined using an analytical scale, based on the assumption that 1 ml water = 1 gram. The Teflon-coated lids containing the recycled plastic samples were screwed on tightly and the vials were placed in a microwave oven, upside down, so that the solutions were in direct contact with the plastics. the microwave oven was 1700 watts and the power level was set 70%. At 70% power, the vials did not leak though the solutions boiled within the vials. The samples were immediately removed and the treatment solutions analyzed using an Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES). Baseline heavy metal content was determined for both the citric acid and water used in the tests. Results. Prior research determined that the concentration of heavy metals in 22 plastics occurred at a concentration of parts-per-million (Table 1). In contrast, leaching of these same metals from the 22 plastics occurred only at the parts-per-billion level, regardless of treatment solution. All leaching was well below the maximum allowable dose level for each heavy metal contaminant.

2 Table 1. Concentrations of five heavy metals in 22 samples of RPET. Cd Cr Ni Pb Sb Total Heavy Sample ID (ppm) (ppm) (ppm) (ppm) (ppm) Metals FP-31P RP200-H BK B C D Average Std. Dev Overall, the heavy metals had significantly differently leaching characteristics (P-value <0.0001) with antimony leaching the least from the plastics and lead leaching the most. Plastics exposed to 5% citric acid solution leached significantly more heavy metal than when exposed to water (Fig. 1). Regardless of test solution, leaching from the samples was well below 1 part per billion. Microwaving did not have a significant effect on the leaching of heavy metal contaminants (Table 2) indicating that heavy metals are fixed in plastics, allowing RPET to be safely used with foods.

3 Fig.1 Overall effect of treatment solution on the leaching of heavy metal from recycled plastics. Within a treatment solution, i.e., for water, only or 5% citrate, only, heavy metal values with the same letter are not significantly different at the 95% confidence level according to Tukey s Studentized Mean Separation Test.

4 Table 2. Effect of 5-minute microwaving on the loss of heavy metals from 22 plastics of known heavy-metal content. Heavy Metal (ppb) Cadmium Chromium Lead Nickel Antimony Plastic Water 5% Citrate Water 5% Citrate Water 5% Citrate Water 5% Citrate Water 5% Citrate a z 0.22 ab 0.01 b 0.01 b 0.03 a 0.36 a 0.02 b 0.05 ab 0.00 b 0.00 b BK 0.06 a 0.15 a 0.01 a 0.01 a 0.02 a 0.31 a 0.02 a 0.01 a 0.00 a 0.00 a 1B 0.00 c 0.18 a 0.01 a 0.01 b 0.00 c 0.06 b 0.01 ab 0.02 b 0.00 bc 0.00 b a 0.10 ab 0.01 a 0.02 b 0.07 a 0.18 a 0.00 a 0.00 b 0.04 a 0.00 b a 0.06 a 0.01 a 0.02 a 0.04 a 0.04 a 0.00 a 0.00 a 0.00 a 0.00 a a 0.05 a 0.01 a 0.02 a 0.04 a 0.11 a 0.02 a 0.03 a 0.01 a 0.00 a ab 0.16 ab 0.01 b 0.37 a 0.18 a 0.31 a 0.01 b 0.00 b 0.02 b 0.00 b a 0.12 b 0.01 a 0.01 bc 0.09 a 0.30 a 0.00 a 0.02 bc 0.00 a 0.00 c 1D 0.00 a 0.06 a 0.01 a 0.01 a 0.05 a 0.03 a 0.01 a 0.01 a 0.00 a 0.00 a a 0.11 a 0.03 a 0.00 a 0.04 a 0.08 a 0.00 a 0.04 a 0.02 a 0.00 a a 0.07 a 0.02 a 0.01 a 0.12 a 0.15 a 0.00 a 0.24 a 0.00 a 0.00 a a 0.15 a 0.03 a 0.02 b 0.01 a 0.07 ab 0.00 a 0.08 ab 0.00 a 0.00 b 1C 0.05 a 0.20 a 0.01 a 0.03 b 0.07 a 0.12 ab 0.00 a 0.02 b 0.00 a 0.01 b FP-31P 0.08 a 0.17 a 0.02 a 0.14 a 0.02 a 0.00 b 0.00 a 0.02 b 0.01 a 0.00 b a 0.03 a 0.03 a 0.03 a 0.11 a 0.23 a 0.01 a 0.03 a 0.00 a 0.00 a a 0.06 ab 0.13 a 0.00 b 0.13 a 0.22 a 0.00 a 0.02 b 0.00 a 0.00 b RP200-H a 0.10 b 0.20 a 0.10 b 0.25 a 0.38 a 0.04 a 0.07 b 0.01 a 0.00 b b 0.09 a 0.03 b 0.04 a 0.10 a 0.17 a 0.00 b 0.10 a 0.01 b 0.00 a a 0.14 b 0.03 a 0.00 c 0.05 a 0.19 a 0.03 a 0.02 c 0.00 a 0.00 c a 0.09 ab 0.02 a 0.01 b 0.10 a 0.21 a 0.00 a 0.05 ab 0.00 a 0.00 b a 0.22 b 0.06 a 0.01 c 0.03 a 0.44 a 0.00 a 0.05 bc 0.00 a 0.00 c a 0.22 ab 0.07 a 0.06 bc 0.16 a 0.37 a 0.00 a 0.02 c 0.01 a 0.00 c z Heavy metal values--within a solution treatment--that have the same letter are not significantly different at the 95% confidence level according to Tukey s Studentized Range Test. Therefore, comparisons should only be made between heavy metal leaching as affected by citrate or only between heavy metal leaching as affected by water, e.g., cadmium leaching with 5% citrate vs. chromium leaching with 5% citrate.

5 Temperature Treatment Methodology: Twenty-two RPET packaging materials of known heavy metal concentration were tested for the leaching as affected contact with either water or 5% citric acid solution. The experiment was a completely randomized design with 3 replicates. The data was non-repeated as discrete samples were used for each measurement. Twenty ml scintillation vials with Tefloncoated lids were used to hold the treatment solution. The RPET samples were prepared by cutting circles of plastic to fit snugly inside each vial lid. The vials were then filled with 5.55 ml of either 5% citric acid solution or water. For accuracy, volume was determined using an analytical scale, based on the assumption that 1 ml water = 1 gram. The Teflon-coated lids containing the recycled plastic samples were screwed on tightly and the vials were placed upside-down in controlled environment chambers set to either 45 or 72 F. Vials were stored for 1, 7 or 14 days. After storage, the samples were removed and the treatment solutions analyzed using an Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES). Baseline heavy metal content was determined for both the citric acid and water used in the tests. Results: Neither storage temperature (P-value = ) nor length of storage (P-value = ) had a significant effect on the amount of heavy metals leaching from the plastics. Heavy metals were lost more readily when plastics were stored with 5% citric acid solution than with water (P = ), but leaching was very minimal in either case, less than 1 ppb. As with microwaving, overall, the heavy metals had significantly differently leaching characteristics (P-value <0.0001) with antimony leaching the least from the plastics and lead leaching the most (Fig. 3). These results indicate that RPET plastics are safe to use with food, whether whole or pre-cut and during normal distribution and retail marketing.

6 Fig. 3. Heavy metal loss from plastics without regard to temperature, storage duration or treatment solution. Means with same letter are not significantly different at the 95% confidence level according to Tukey s Studentized Mean Separation Test.