## 4 Discussion
For a bottle wall concentration of 0.263 mg/kg, the results of migration into 20% ethanol after storage for 10 days at 60 \({}^{\circ}\)C were 3.4 \(\pm\) 0.7 ug/L. Based on migration kinetics into 20% ethanol from this study, a migration of 5.85 ug/L is predicted, which is in good agreement with the experimental result of [PERSON] et al. Another bottle with 1.26 mg/kg BPA results in migration value of 3.5 \(\pm\) 0.5 ug/L and 4.2 \(\pm\) 0.6 ug/L for 3% acetic acid and 20% ethanol, respectively. Based on the kinetic results of this study, 12.2 ug/L (3% acetic acid) and 30.3 ug/L (20% ethanol) were predicted after 10 days at 60 \({}^{\circ}\)C. The experimental values measured by [PERSON] et al. and the predicted values based on the results of our migration kinetics are approximately one order of magnitude above the suggested migration limit of 0.012 ug/L. However, this is due to the fact that 10 days at 60 \({}^{\circ}\)C greatly overestimates the migration and is unsuitable for a migration assessment for room temperature storage of up to 1 year. Some studies in the literature determined the concentration of BPA in water packaged in PET bottles. In almost all cases, however, only the water is measured, not the PET bottle. This can lead to false conclusions. For example, [PERSON] et al. [41] detected BPA in PET-bottled water. However, BPA was not detected in the PET bottles cut in pieces but was detected in HDPE caps. These results show the migration of BPA is most likely from the caps. [PERSON] and [PERSON] [42] found 0.0046 ug/L of BPA in water bottled in PET. After exposure for 15 and 30 days at around 40 \({}^{\circ}\)C, BPA does not increase in concentration, which is an indication that BPA does not migrate from the bottle wall but has another source. It is therefore very important that the PET bottle wall concentration is always determined in such migration studies. The diffusion coefficients determined in this work can also be used to validate the migration of BPA from the bottle wall into the beverage. Some studies investigated the influence of temperature or sunlight on the amount of BPA released into water [7; 43; 44; 45]. The concentrations of BPA ranged from 0.001 ug/L to about 0.02 ug/L. Increasing the temperature and sunlight increased the concentration of BPA in the packaged water. Unfortunately, none of the studies determined the concentration of BPA in PET materials, so no diffusion coefficients can be derived. A comparison with these results is also difficult as the migration is directly related to the concentration of BPA in PET, which is not known. However, the magnitude of the migration is in a similar range as in our study. [PERSON] et al. [46] determined concentrations of BPA in packaged drinking water to be higher by a factor of approximately 10. However, the concentrations of BPA in the PET bottles were not measured here either, so the cause of the higher concentrations remains unclear. The experimentally determined diffusion coefficients of BPA in PET from this study can be compared with those from another published predictive diffusion model. Using the so-called \(\mathrm{A_{P}}\) model [34; 35] and the \(\mathrm{E_{A}}\)-based model [36; 37], diffusion coefficients for BPA in PET at different temperatures can be calculated, as shown in Tables 4 and 5. The \(\mathrm{A_{P}}\) model works with a fixed activation energy of diffusion (\(\mathrm{E_{A}}\)) of 100 kJ/mol applicable to any molecule in PET. This value is significantly lower than the experimentally determined \(\mathrm{E_{A}}\) values of 131.2 kJ/mol (3% acetic acid), 140.9 kJ/mol (10% ethanol), and 153.6 kJ/mol (20% ethanol). The \(\mathrm{E_{A}}\)-based model predicts an \(\mathrm{E_{A}}\) value of 165.8 kJ/mol. Together with the pre-exponential factor (\(\mathrm{D_{0}}\)), the \(\mathrm{E_{A}}\) is important for correctly including the influence of temperature on migration.